Torque split on the TOD unit ranges from 0/100 to 50/50. You will always get at least 50% power to the rear axle. The rear has an LSD so the power can then be split 25%/25% if need be across the rear axle. I've been thinking of putting in an LSD in the front to split the torque across the front axle as well.
so if the rear wheels are slipping on ice and getting virtually zero torque sent to them, then the front is getting virtually zero torque as well even though it could handle more? Like an open diff then. If TOD could lock the front and rear axles together (like part-time system or TOD's low range does this), then torque split could be 99/1. I know this is a silly little question, but I guess what I'm asking is whether or not TOD can lock the front and rear together or is it always like an open diff?
If the rear is slipping, you are still getting at least 50% of the engine torque going to the rear axle. For instance:
lets say you are reving the engine to the peak torque of 230lbs and the rear wheels are on a frictionless surface, you would have 230/2 = 115lbs of torque going to the rear wheels or 57.5lbs to each rear wheel if the LSD activates.
In the front you would have 115lbs of torque going to the front axle, with 115lbs of torque to either the left or right side wheel in the front.
The TOD system works like an anti-open diffy, rather than put the power to the slipping wheel or the wheel with the least resistance, it puts it to the axle with the most resistance. There is no way to get TOD to act like a traditional Part-time 4wd in Hi-mode and lock it at 50/50. In Low range it locks the torque in at 50/50.
Yes the engine might make 230 ft/lbs, but what if the rear can only handle 2 ft/lbs (driving on slick ice) before it slips. Once the rears slip from a static friction (rolling) that allows 2 ft/lbs to a kinetic friction (spinning) which allows 1.5 ft/lbs then the front is only getting 1.5 ft/lbs if the rear were spinning on my theoretical low friction ice. When you rev the engine, the torque that the engine makes doesn't go to the ground, but goes into rotational momentum of the tires (spinning).
A part time system locks the speed of the front drive shaft and the rear drive shaft together. A part time system can have zero power delivered to the rear axles (spinning on ice) while the front is on pavement allowing 100% of the engine torque to go to it.
Don't get me wrong Paisan, I'm just curious as to the limitations of TOD, or if there are any. I know you still can lock it down into low range and all.
I know on paper TOD can split 50/50, but that would be bad if the rears were on ice and the front's weren't (yes an uncommon situation). The front tires wouldn't get any power. Are you up for a little testing??? Floor it and see if it will take off in the above mentioned situation, or whether it's spinning the rears on ice for a bit.
No the split doesn't know where the torque goes. It only knows that 50% of it is going to the rear axle. In your example of ice you are saying only 2ft/lbs are going to the ice and 2 ft/lbs are going to the front tires. In math/physics you can't have the other 226lbs dissappearing into thin air!
Basically the way the TOD works is that it uses speed sensors to compare the rear drive shaft speed to the front driveshaft speed. If the rear is spinning faster than the front it will change the clutch pack to allow more torque to go to the front driveshaft. If they are both spinning at the same speed, then 85% goes to the rear and 15% to the front. If the rears are on ice, it will put 115lbs of torque to the rear axle, and the rear wheels will spin away that 115lbs of torque and the front will get 115lbs of torque to apply to the ground or spin if the front axle is on ice as well.
The TOD doesn't work like a Viscous coupling that will always strive for a 50/50 split. In general vehicles with a center V/C cannot lock in 50/50 (although my '88 subaru XT6 does have a center air-locker) and generally don't have low range either.
A system that puts 100% front or rear when necessariry would be nice, but I'm sure there was a reason the B&W engineers set it up to only go 50/50. Essentially when you are spinning the rear wheels, you have a 50/50 torque split and thus have the same split as a center locking diffy.
I've actually done the tests at my place upstate in the snow. I drove up to a snow bank and had the rears on ice, fronts in snow. Once I got the rears spinning the front would pull up the snow bank, using the 50% torque to the front. The rears kept spinning though. I also tried all 4 on ice, that was cool 1 front and 2 rear spinning.
I only wish I had a front LSD so that it would be less likely to be stuck.
I agree with your thinking about the typical Trooper owner being more knowledgeable/detail-oriented about his/her vehicle than the typical Explorer owner. However, this could be just one of many reasons why Explorers are in the news for tread-separation-induced rollovers and Troopers aren't. Other reasons: fewer incidents because very few Troopers sold vs. high-volume Explorer sales, tires used on Troopers separate much less often than tires (Firestones) used on Explorers, etc.
My local Target store always had the lowest Mobil1 prices around. It was $3.04/qt for quite a while, then dropped to $2.94 for a few months in mid-2001. Then this particular Target location increased its price to $4.49/qt. All the other Targets in my area (southeast Michigan) were always $4+ per quart. Most other stores (Wal-Mart, Kmart, etc.) were $4+ as well. I'm not sure why the one Target store was so much cheaper than everyone else. Until now, I thought this phenomenon was unique to the store near me but fiveharpers has seen the same thing near him (Virginia). Strange.
I'm glad I loaded up @ $2.94/qt. My local Sam's Club also has Mobil1 cases for $21.98/qt.
St. Charles Isuzu is definitely the place to order them. Free UPS shipping. 800.727.8066. Mention ITOG or the St. Charles web site (www.stcharlesauto.com) and you'll get 15% off Isuzu list price. On top of that, the filters are frequently on sale below that price. You'll always be well below 5 bucks each, and under 4 bucks when they're on sale.
The Explorers roll over when tire tread separations occur. This seems to be made more likely when tire pressure is below a safe level. Ford specified 26psi (and Firestone 30psi - or was it the other way around?), which turns out to be too low to be safe, according to most folks.
My contention is that the Explorer is not defective. Their recommendation on tire pressure was too low, but the vehicle itself does not seem to be unusually tippy.
The problem is that they become tippy with 30psi in them. It was a catch 22 for them. If ford say put in 30psi, then they have a tendancy to roll. If they leave it at 26psi, they hope the tires don't heat up too much and the lower CG and more rubber help keep em from rolling, if there is tire separation, then they blame firstone. In this case it looks like their plan backfired though
Even with tread separation, and blow-out a vehicle should not roll over. There have been no cases of rollovers on the troopers in the real world attributable to the rollover-test that CU claimed. Funny how CU never rolled an explorer, yet there are tons of real world rollovers, in their test they roll a trooper but there are no real world cases of rollovers in that situation...
Let's say that the wheels can only handle 100 ft/lbs total. You have 130 ft/lbs left at wide open throttle (WOT). It goes somewhere, but not to the ground. It goes into the engine revving higher (rotational momentum +excess heat) It goes into the torque converter (fluid energy storage+heat) and the transmission (more rotational inertia). It goes into the axles and differntials and tires (rotational inertial again). The engine then hits redline where it's fuel is cutoff (not completley) so that the engine doesn't blow up. You are no longer at wide open throttle and have to be at part throttle not making 100% of your engines torque. So the moral of the story is the torque does go somewhere, just not to the ground
Yes I agree it is lost in the driveline, but X torque coming out of the tranny gets split 0/100 up to 50/50, it can't go anywhere else, so if the back is slipping it is still only going to get 50% of the torque and 50% of the X torque will be in the front. I wish the system could do a full range from 0/100->100/0 but it isn't in the cards, I guess because at 50/50 split it acts like a locked diffy, they figure no need to put more than that much power to the front?
I thought an open diffy delivered all to the wheel slipping, hence the situation where one rear wheel spins on ice while the other stays still.
In terms of the TOD vs 4WD Lo, I seem to recall last winter where 4WD Lo delivered a better low speed torque to all wheels in snow (especially while backing up a trailer through snow)than did the TOD. On a slippery surface the TOD tends to spin the wheels from a stop first, before splitting the torque.
An open diff is a 50/50 split. If one wheel starts spinning it provides 'virtually zero torque' to the ground. The same amount of 'virtually zero torque' is sent to the other wheel too. A spinning tire is worse than a rolling one due to static (rolling) and kinetic (spinning) friction.
I know it's all so confusing. That's why I wanted to know if TOD was truly 50/50 like an open diff or if it can actually lock them together like a part time system. I thought Isuzu might have said it can provide a 50/50 split because the public thought that was the best you can do. Oh well...
50/50 is not = to open center diff. There is no center diff on TOD. It is just a clutch mechanism the is engaged by a computer command based on variety of parameters. The clutch can be engaged fully (same as part time 4WD) and assuming that there is no wheel slip then front and back axles receive 50/50 torque but can quickly shift to 100/0 or 0/100 depending on which axle start to slip. However the degree of clutch engagement is not always full or 100% (clutch is mostly partially engaged in varying degrees). It is only fully engaged at all time when on 4low.
Can TOD go from 0/100 -> 100/0 or only from 0/100 -> 50/50. If the clutch packs can engage enough to lock the speeds of the front and rear drivelines together then it can go 0/100->100/0. If it can only go from 0/100->50/50 then it acts like an open differential at best (50/50). TOD is a differential. It may technically be a transfer case, but if it can allow the front and rear to run on pavement at different speeds it is then differentiating power between the two and hence is a differential. It is a very complex one though
Oh no I’ve gone cross-eyed and am now getting different answers
The TOD unit does not act like an open diffy. An open diffy provides the torque to the slipping wheel (path of least resistance) The TOD unit provides the torque up to 50% to the axles with the most resistance. There is no instance where the clutch can put 100% of the torque to the front axle, the most torque that can be sent to the front axle is 50% at any given time.
In 4wd Lo the clutch pack has nothing to do with the equation at all. In 4wd Lo, the front and rear are phyiscally locked together @ 50/50 torque split, and TOD clutch doesn't come into play.
I know it sounds conf00sing but it does make sense. I'm gonna try to explain it here:
Situation 1:
Rear wheels on frictionless surface, TOD will put 50% torque to the front axle, 50% torque to the rear axle. Rear wheels will spin and spin, front wheel will use that 50% torque applied to the wheel with the least traction in the front and pull the vehicle forward.
Situation 1a:
Non-TOD vehicle with part-time system engaged. 50% torque to the rear, rear wheels spinning, 50% torque to the front wheel with the least resistance.
Situation 2: Front and rear wheels on frictionless surface with some friction in spots. TOD will apply 80% powr to rear axle, 15% to front, rear wheels spin forcing 50/50 split, front spins, TOD shifts power back to rear 90% front 10%, front wheels stop spinning, and grab slightly, powr is then sent back to the front up to 50/50 thus pulling the truck out of the situation. I found this very useful in deep snow it "pulses" the front axle allowing the wheels to grip at times of near 0% torque to the front, and then jerk you forward out of the rut/snow/etc.
Situation2a: Traditional 50/50 split, you spin both axles unless you let off the gas allowing the wheels to grip the ground.
Hope this helps a bit, and feel free to correct me on this.
But the big key difference between and open diffy and the TOD system is that the TOD puts power to the axle with the *MOST* resistance, whereas an open diffy puts the power to the axle with the *LEAST* resistance. Another example I bring up here is the Automatic Tranny Subarus: They have a similar system to the TOD unit sans low range, and sans locking center. Their units are setup to be 80/20 as a normal torque split, ranging up to 40/60 torque split. Same concept is used on them weight and speed sensors are on each wheel/axle and tell the computer how much clutch to engage to shift the power back and forth based on inputs. If a wheel is spinning the put power to the opposite axle.
It seems if it's limited from 0/100 -> 50/50 it wouldn't be limited to the driveshaft with the *MOST* resistance, but would be limited by the rear driveshaft resistance. If the rear driveshaft could handle 100% then so be-it, no need for the front. If the rear driveshaft was on ice, then the front would be limited by that amount since it's set to recieve 50/50 and if the rear's 50 is almost zero then the front's 50 has the same zero.
Hmmmmmmm, maybe TOD can send, with the clutch packs, 115ft/lbs (50% of the 3.5L's power) to the front while sending 2.3ft/lbs (1% spinning on ice) to the back???
Ok, now I've really gone cross-eyed. Maybe I just need to: Stop thinking. Stop thinking. Stop thinking.
Now what you may mean to say is 50% to the front axle and wheel, and 50% to the rear axle and 1% reaching the ground via spinning wheel and 49% being lost to rear wheel spin. Then we would have conservation of 100% of the output torque (whatever that actual # is).
The reason that we see 15% going to the front is not due to the rear slipping, it is how the clutch computer is setup, it by default (above 5mph) sends 15% to the front axle. The reason for this is that it makes it a pro-active system rather than a reactive system (as is found in the CRV 100/0, Ford auto-4wd 0/100, GM auto-4wd 0/100, highlander 100/0) Other systems such as the TLC, Caddy, Denali, Mountaineer AWD, Manual subarus, Rav4 use a viscous center diffy, which puts 50/50 torque split and tries to maintain that.
Look what happens when you miss a night in town hall.
To add to Paisan's description. Not only are the front and rear physically locked in 4 low, but you are also getting a gear ratio of 2.48:1. Multiplying the amount of power applied to the front and rear. So at 15 MPH in 4 low, each axle is getting as much if not more power than rear does at 15 MPH in 2wd. Of course the engine has to work almost twice as hard to achieve this.
To start, in an open rear differential the torque is not sent to the wheel with the least resistance. It is split 50/50. Because the spinning wheel has less resistance it spins more for a given amount of torque. Therefore it may "look" like the spinning wheel is getting more torque.
Take an example when in 2wd with one side on ice the other on pavement. As the throttle is opened the 1/2 of the torque going to the icy side will easily spin that wheel. The other wheel with all the good traction (i.e. resistance) will not move with its 1/2 of this small amount of torque. It would move if a moderate amount of torque is applied. However in order for that wheel to get a moderate amount of torque the icy wheel must also get the exact same moderate amount of torque. The problem is that moderate amount of torque applied to a wheel on ice will over rev the engine.
A limited slip rear differential will, under some circumstances, lock the 2 axle halves so that they spin at the same speed. Now the pavement wheel can get 99+% of the torque if that is what it needs to move at the same speed as the wheel on ice.
I think the TOD confusion is more one of semantics/conditions. As the system senses rear wheel slip it shifts torque to the front to try and keep the 2 driveshafts at the same speed. Sometimes this up to 50% torque split is good enough to keep the front and rear driveshafts spinning at the same speed. Therefore the system acts like a locking center differential. However if the traction is really poor then it could take 95% of the torque going to the front to get unstuck. In these situations the TOD is then acting like an open differential as it is only splitting the torque 50/50 and not keeping the front and rear axles spinning at the same speed. In other words it is a locking differential up to a 50/50 torque split where it is then an open differential.
I am unclear on how a TOD system will ever exceed 50% to the front axle. The rear axle may have 100% of the torque (TOD not functioning) or it may have 50% of the torque (TOD fully "locked"). However, the transmission output is connected to the rear axle, through the transfer case/TOD unit, to the rear axle. Torque may vary to the front axle by the TOD unit. But, the TOD clutch fully engaging is the same as locking the two axles together--theoretically, there should be no TOD clutch slip. That gives a 50/50 split to each axle. Have an axle on ice does not change anything--50% of the torque still goes to that axle.
There is no way for an Explorer to direct 100% of the torque to the front axle unless the rear axle is somehow connected to the driveshaft by way of a viscous coupling or clutch. Which is probably not the case. If you think about how a transfer case is constructed, the axle that normally drives the vehicle can never have less than 50% torque.
If you lifted the rear end of a TOD Trooper off the ground, the front wouldn't get any power and you wouldn't go anywhere with a 50/50 split. In a part-time system if the rears were lifted, 100% of the engine's power would be directed to the front axle giving a 100/0 split
not that you're going anywhere anyway with the rear's in the air
That doesn't makes sense to me but everone seems to be conf00sed here and since I'm too busy to keep explaining it, I'll leave it alone today. I think the issue is semantics of the terminology in question, we are all on the same page though.
#3124 of 3127 I give up by dielectric7bb Feb 04, 2002 (09:11 pm)
I'll just assume it's a 50/50 split at best. I just wasn't sure if that's what Isuzu claimed because that's what the public would like to hear or what. Not too many people would understand it if Isuzu said hey it can go from 0/100 to 100/0...People would be like what the dill. Hmmmmmmmmm I understand what everyone's been saying, and I find the pulsing of TOD very interesting. And yes an open diff does provide a 50/50 split in torque. It doesn't seem like it would, but it does.
Part-time: Front and Rear driveshaft are locked together. If one rotates, the other rotates at the same speed. If one doesn't spin, then the other doesn't spin. They are locked together. If the rear is in the air then it has virtually zero torque going to it (except for a small small amount going to spin up the drivetrain). With the front's still on the ground, spinning at the same speed as the rears, which one is going to pull you out? The front's. Why...because they are getting virtually 100% of the power because the front and rear driveshaft's speed is locked together, not their torque.
If each driveshaft gets 50% of the torque, where does it all go? In all honesty it doesn't take very much to spin up the drivetrain.
a) TOD gives either 0% torque to the front driveshaft and 100% torque to the rear driveshaft.
b) TOD gives 50% torque to the front driveshaft and 50% torque to the rear driveshaft.
c) anywhere inbetween a & b. don't we like multiple multiple choice tests kids???
d) this one is theoretical since I haven't figured out if TOD can do this or not: TOD gives 100% torque to the front driveshaft and 0% torque to the rear driveshaft. (except in 4low)
If both rear wheels are off the ground and both front wheels are on the ground in a TOD equipped vehicle then:
a) the rear wheels spin since all the power is going to the rear wheels and the fronts get no power.
b) since the rear wheels are spinning the only torque going to them is to overcome friction, or is storing energy in the form of momentum, primarily in the tires spinning. If the rear's 50% is virtually zero torque, then the front's 50% has to be the same. 50% split is a 50% split and whatever goes to the rear has to go to the front as well. So the front's have virtually zero torque because the rear's have zero torque. In this way it acts like an open differential with a 50/50 split.
c) In-between a & b, I'll let ya figure it out on your own.
d) The rear driveshaft gets virtually zero torque, but the front gets all the torque it can muster. A part-time 'locked system' can do this, but it definiteley works in a different manner than TOD's auto 4WD system.
The answer is C. There is even a guage on the dash that tells you how much torque each axle is getting at any given time! It's infinitely variable. That is the difference between the ford and chevy "auto-4wd" systems. On the auto-4wd systems it is either 0/100 or 50/50 no variable in-between.
Folks, I 've been watching this board for nearly a year now, and I feel I should finally post, unfortunately a long post, please be patient. My personal experiences with my trooper: I have a 1999 S model, automatic with TOD (It was purchased as new in February of 2000 for $21,995 plus tax, no additional fees if anybody cares) This vehicle is the most bang for the buck based on features, initial quality, and reliability, although I am hesitant to carry the same attitude about the 2000 - 2002 models based on some of the posts that I have read.
1) In my opinion I can express the function of the transfer case as follows. The "high" range portion of the TOD transfer case functions like an electromagnetically controlled limited slip differential with one of the differential side gears welded to the rear drive shaft. Of course, there is no such welding within the transfer case.
Please envision a differential assembly such as the "open differential" comments mentioned in the posts above. However, please make these small adjustments in your imagination. 1)Imagine that the ring gear has been completely removed and that the face of the case that the ring gear was mounted to has been machined off(removed). 2) Imagine that the differential side gear that was previously simply within the differential case, now also has a larger surface external to the case that the transfer case chain is attached to. 3) Imagine that there are electromagnetically controlled clutches within the differential case.
How this works in the TOD transfer case: 1) Power/Torque is transmitted through the transfer case chain to the "TOD differential side gear". This gear is directly connected to the rear drive shaft. 2) Power/Torque will also be applied to the opposite side gear (which is connected to the front drive shaft) through the differential case and spider gears. 3) When the traction is the same between the front and the rear, power/ torque is still being applied to both the front and the rear because the TOD is acting like an open differential. However, when the rear slips, the clutches recognize this based on speed sensors and will begin to engage their clutches within this imaginary differential case. The rear axle will have power from the engine under all conditions because of the differential case design above. How do I know? because of two situations
1) I used two jack stands and raised the rear two wheels off of the ground. I then used a jack stand and raised the left front wheel off the ground. I started the vehicle, placed the transmission in drive and engaged TOD (auto button on the dash). I then released the brake pedal. I noticed that the rear tires and the one front tire (that was off the ground) began to rotate. None of the lights on my TOD instrument panel display indicated that power was going to the front axle. However, at that point in time, my friend began to apply resistance to the front tire (through a 2X6 acting as a lever) and noticed that the TOD instrument panel light lit up and tried to move the vehicle through the one front tire that was on the ground. 2) Us Georgia boys can get some serious ice in the Northeast Georgia area. I was kind of "stuck" on some ice that was on a slight incline. The Trooper was in drive, TOD engaged. The ice was so slick that all four tires were spinning. I did not have my foot on the gas pedal and none of the TOD indicator lights were on. As a matter of fact, this was so entertaining, my friend and I got out of the vehicle to see my vehicle spin it's wheels without anyone driving. Of course, I could depress the pedal(goose it), and the TOD instrument panel indicators would light up indicating that the clutches were trying to stop the shafts from spinning at different speeds.
At least this is my impression of how the TOD transfer case works based on my 4wd experience (my serious 4wd is a 1978 CJ-7, Chevy 400 cu in, Dana 300 transfer case, Dana 44 axles front and rear, 4-wheel disc brakes, 4.56:1 gears, Detroit lockers front and rear) and understanding.
Thanks for all the helpful info. I have installed Rancho 5000 shocks and the poly sway bar bushings and felt pleased with the results.
I have the 1999 Trooper S model. It did not come with the factory fog/driving lights. However, it does have the factory wiring(plug-ins) located where the factory lights would have been mounted. Does anybody with a wiring diagram know whether the wiring harness behind the instrument panel includes the plug-in for the switch as well? I have some driving lights that I would like to mount and use the factory wiring, including any wiring/plug-in that is already available under the dash. I could imagine that Isuzu designed one wiring harness for all automatic Troopers in 1999 independent of whether you had the luxury and performance packages. Please let me know when you have the opportunity.
Comments
-mike
lets say you are reving the engine to the peak torque of 230lbs and the rear wheels are on a frictionless surface, you would have 230/2 = 115lbs of torque going to the rear wheels or 57.5lbs to each rear wheel if the LSD activates.
In the front you would have 115lbs of torque going to the front axle, with 115lbs of torque to either the left or right side wheel in the front.
The TOD system works like an anti-open diffy, rather than put the power to the slipping wheel or the wheel with the least resistance, it puts it to the axle with the most resistance. There is no way to get TOD to act like a traditional Part-time 4wd in Hi-mode and lock it at 50/50. In Low range it locks the torque in at 50/50.
-mike
A part time system locks the speed of the front drive shaft and the rear drive shaft together. A part time system can have zero power delivered to the rear axles (spinning on ice) while the front is on pavement allowing 100% of the engine torque to go to it.
Don't get me wrong Paisan, I'm just curious as to the limitations of TOD, or if there are any. I know you still can lock it down into low range and all.
I know on paper TOD can split 50/50, but that would be bad if the rears were on ice and the front's weren't (yes an uncommon situation). The front tires wouldn't get any power. Are you up for a little testing??? Floor it and see if it will take off in the above mentioned situation, or whether it's spinning the rears on ice for a bit.
Basically the way the TOD works is that it uses speed sensors to compare the rear drive shaft speed to the front driveshaft speed. If the rear is spinning faster than the front it will change the clutch pack to allow more torque to go to the front driveshaft. If they are both spinning at the same speed, then 85% goes to the rear and 15% to the front. If the rears are on ice, it will put 115lbs of torque to the rear axle, and the rear wheels will spin away that 115lbs of torque and the front will get 115lbs of torque to apply to the ground or spin if the front axle is on ice as well.
The TOD doesn't work like a Viscous coupling that will always strive for a 50/50 split. In general vehicles with a center V/C cannot lock in 50/50 (although my '88 subaru XT6 does have a center air-locker) and generally don't have low range either.
A system that puts 100% front or rear when necessariry would be nice, but I'm sure there was a reason the B&W engineers set it up to only go 50/50. Essentially when you are spinning the rear wheels, you have a 50/50 torque split and thus have the same split as a center locking diffy.
-mike
I only wish I had a front LSD so that it would be less likely to be stuck.
-mike
I'm glad I loaded up @ $2.94/qt. My local Sam's Club also has Mobil1 cases for $21.98/qt.
My contention is that the Explorer is not defective. Their recommendation on tire pressure was too low, but the vehicle itself does not seem to be unusually tippy.
Even with tread separation, and blow-out a vehicle should not roll over. There have been no cases of rollovers on the troopers in the real world attributable to the rollover-test that CU claimed. Funny how CU never rolled an explorer, yet there are tons of real world rollovers, in their test they roll a trooper but there are no real world cases of rollovers in that situation...
-mike
TOD still is an awesome system
-mike
Torque and power are not the same thing! You can apply a torque but no work is done unless something moves. Power is work delivered per unit time.
tidester
Host
SUVs
0/100->100/0 acts as a locked
Good info.
In terms of the TOD vs 4WD Lo, I seem to recall last winter where 4WD Lo delivered a better low speed torque to all wheels in snow (especially while backing up a trailer through snow)than did the TOD. On a slippery surface the TOD tends to spin the wheels from a stop first, before splitting the torque.
I know it's all so confusing. That's why I wanted to know if TOD was truly 50/50 like an open diff or if it can actually lock them together like a part time system. I thought Isuzu might have said it can provide a 50/50 split because the public thought that was the best you can do. Oh well...
Oh no I’ve gone cross-eyed and am now getting different answers
In 4wd Lo the clutch pack has nothing to do with the equation at all. In 4wd Lo, the front and rear are phyiscally locked together @ 50/50 torque split, and TOD clutch doesn't come into play.
I know it sounds conf00sing but it does make sense. I'm gonna try to explain it here:
Situation 1:
Rear wheels on frictionless surface, TOD will put 50% torque to the front axle, 50% torque to the rear axle. Rear wheels will spin and spin, front wheel will use that 50% torque applied to the wheel with the least traction in the front and pull the vehicle forward.
Situation 1a:
Non-TOD vehicle with part-time system engaged. 50% torque to the rear, rear wheels spinning, 50% torque to the front wheel with the least resistance.
Situation 2:
Front and rear wheels on frictionless surface with some friction in spots. TOD will apply 80% powr to rear axle, 15% to front, rear wheels spin forcing 50/50 split, front spins, TOD shifts power back to rear 90% front 10%, front wheels stop spinning, and grab slightly, powr is then sent back to the front up to 50/50 thus pulling the truck out of the situation. I found this very useful in deep snow it "pulses" the front axle allowing the wheels to grip at times of near 0% torque to the front, and then jerk you forward out of the rut/snow/etc.
Situation2a:
Traditional 50/50 split, you spin both axles unless you let off the gas allowing the wheels to grip the ground.
Hope this helps a bit, and feel free to correct me on this.
-mike
-mike
Hmmmmmmm, maybe TOD can send, with the clutch packs, 115ft/lbs (50% of the 3.5L's power) to the front while sending 2.3ft/lbs (1% spinning on ice) to the back???
Ok, now I've really gone cross-eyed. Maybe I just need to:
Stop thinking.
Stop thinking.
Stop thinking.
Goodnite all 4 the moment
50% + 1% = 51%
The output torque from the tranny must = 100%
Now what you may mean to say is 50% to the front axle and wheel, and 50% to the rear axle and 1% reaching the ground via spinning wheel and 49% being lost to rear wheel spin. Then we would have conservation of 100% of the output torque (whatever that actual # is).
The reason that we see 15% going to the front is not due to the rear slipping, it is how the clutch computer is setup, it by default (above 5mph) sends 15% to the front axle. The reason for this is that it makes it a pro-active system rather than a reactive system (as is found in the CRV 100/0, Ford auto-4wd 0/100, GM auto-4wd 0/100, highlander 100/0) Other systems such as the TLC, Caddy, Denali, Mountaineer AWD, Manual subarus, Rav4 use a viscous center diffy, which puts 50/50 torque split and tries to maintain that.
-mike
To add to Paisan's description. Not only are the front and rear physically locked in 4 low, but you are also getting a gear ratio of 2.48:1. Multiplying the amount of power applied to the front and rear. So at 15 MPH in 4 low, each axle is getting as much if not more power than rear does at 15 MPH in 2wd. Of course the engine has to work almost twice as hard to achieve this.
Take an example when in 2wd with one side on ice the other on pavement. As the throttle is opened the 1/2 of the torque going to the icy side will easily spin that wheel. The other wheel with all the good traction (i.e. resistance) will not move with its 1/2 of this small amount of torque. It would move if a moderate amount of torque is applied. However in order for that wheel to get a moderate amount of torque the icy wheel must also get the exact same moderate amount of torque. The problem is that moderate amount of torque applied to a wheel on ice will over rev the engine.
A limited slip rear differential will, under some circumstances, lock the 2 axle halves so that they spin at the same speed. Now the pavement wheel can get 99+% of the torque if that is what it needs to move at the same speed as the wheel on ice.
I think the TOD confusion is more one of semantics/conditions. As the system senses rear wheel slip it shifts torque to the front to try and keep the 2 driveshafts at the same speed. Sometimes this up to 50% torque split is good enough to keep the front and rear driveshafts spinning at the same speed. Therefore the system acts like a locking center differential. However if the traction is really poor then it could take 95% of the torque going to the front to get unstuck. In these situations the TOD is then acting like an open differential as it is only splitting the torque 50/50 and not keeping the front and rear axles spinning at the same speed. In other words it is a locking differential up to a 50/50 torque split where it is then an open differential.
There is no way for an Explorer to direct 100% of the torque to the front axle unless the rear axle is somehow connected to the driveshaft by way of a viscous coupling or clutch. Which is probably not the case. If you think about how a transfer case is constructed, the axle that normally drives the vehicle can never have less than 50% torque.
Regards,
Tom
not that you're going anywhere anyway with the rear's in the air
-mike
I'll just assume it's a 50/50 split at best. I just wasn't sure if that's what Isuzu claimed because that's what the public would like to hear or what. Not too many people would understand it if Isuzu said hey it can go from 0/100 to 100/0...People would be like what the dill. Hmmmmmmmmm I understand what everyone's been saying, and I find the pulsing of TOD very interesting. And yes an open diff does provide a 50/50 split in torque. It doesn't seem like it would, but it does.
http://www.howstuffworks.com/differential5.htm
gives a good description of open differentials and how they work. Also discussed are LSD's on pages after the one above.
-mike
Of course the advantage of the Trooper is that by putting it in 4wd low the 2 drive shafts are locked.
If you lifted a TOD Trooper's rear axle into the air, The TOD computer would engage the TOD clutch up to a maximum of 50% torque to the front axle.
If you lifted the rear axle of a vehicle with a part-time system into the air, the front and rear axles each get 50%.
The surface that the tires are on is irrelevant.
You're just jerking our chains now, right?
Regards,
Tom
Jim
Part-time:
Front and Rear driveshaft are locked together. If one rotates, the other rotates at the same speed. If one doesn't spin, then the other doesn't spin. They are locked together. If the rear is in the air then it has virtually zero torque going to it (except for a small small amount going to spin up the drivetrain). With the front's still on the ground, spinning at the same speed as the rears, which one is going to pull you out? The front's. Why...because they are getting virtually 100% of the power because the front and rear driveshaft's speed is locked together, not their torque.
If each driveshaft gets 50% of the torque, where does it all go? In all honesty it doesn't take very much to spin up the drivetrain.
Let me think about it.
I actually have to get some work done today, but I'm enjoying this thread (even if I may have to retract my comments).
Please explain why a TOD-equipped Trooper with its rear axle in the air would just spin its rear tires.
Regards,
Tom
b) TOD gives 50% torque to the front driveshaft and 50% torque to the rear driveshaft.
c) anywhere inbetween a & b. don't we like multiple multiple choice tests kids???
d) this one is theoretical since I haven't figured out if TOD can do this or not: TOD gives 100% torque to the front driveshaft and 0% torque to the rear driveshaft. (except in 4low)
If both rear wheels are off the ground and both front wheels are on the ground in a TOD equipped vehicle then:
a) the rear wheels spin since all the power is going to the rear wheels and the fronts get no power.
b) since the rear wheels are spinning the only torque going to them is to overcome friction, or is storing energy in the form of momentum, primarily in the tires spinning. If the rear's 50% is virtually zero torque, then the front's 50% has to be the same. 50% split is a 50% split and whatever goes to the rear has to go to the front as well. So the front's have virtually zero torque because the rear's have zero torque. In this way it acts like an open differential with a 50/50 split.
c) In-between a & b, I'll let ya figure it out on your own.
d) The rear driveshaft gets virtually zero torque, but the front gets all the torque it can muster. A part-time 'locked system' can do this, but it definiteley works in a different manner than TOD's auto 4WD system.
-mike
pull the parking brake
Torque on Demand it varies the torque as you Demand it.
-mike
-mike
C varies torque from 0/100 to 50/50. It doesn't go to 100/0. Did you mean to say that TOD can do D???
-mike
-mike
1) In my opinion I can express the function of the transfer case as follows. The "high" range portion of the TOD transfer case functions like an electromagnetically controlled limited slip differential with one of the differential side gears welded to the rear drive shaft. Of course, there is no such welding within the transfer case.
Please envision a differential assembly such as the "open differential" comments mentioned in the posts above. However, please make these small adjustments in your imagination. 1)Imagine that the ring gear has been completely removed and that the face of the case that the ring gear was mounted to has been machined off(removed). 2) Imagine that the differential side gear that was previously simply within the differential case, now also has a larger surface external to the case that the transfer case chain is attached to. 3) Imagine that there are electromagnetically controlled clutches within the differential case.
How this works in the TOD transfer case:
1) Power/Torque is transmitted through the transfer case chain to the "TOD differential side gear". This gear is directly connected to the rear drive shaft.
2) Power/Torque will also be applied to the opposite side gear (which is connected to the front drive shaft) through the differential case and spider gears.
3) When the traction is the same between the front and the rear, power/ torque is still being applied to both the front and the rear because the TOD is acting like an open differential. However, when the rear slips, the clutches recognize this based on speed sensors and will begin to engage their clutches within this imaginary differential case. The rear axle will have power from the engine under all conditions because of the differential case design above.
How do I know? because of two situations
1) I used two jack stands and raised the rear two wheels off of the ground. I then used a jack stand and raised the left front wheel off the ground. I started the vehicle, placed the transmission in drive and engaged TOD (auto button on the dash). I then released the brake pedal. I noticed that the rear tires and the one front tire (that was off the ground) began to rotate. None of the lights on my TOD instrument panel display indicated that power was going to the front axle. However, at that point in time, my friend began to apply resistance to the front tire (through a 2X6 acting as a lever) and noticed that the TOD instrument panel light lit up and tried to move the vehicle through the one front tire that was on the ground.
2) Us Georgia boys can get some serious ice in the Northeast Georgia area. I was kind of "stuck" on some ice that was on a slight incline. The Trooper was in drive, TOD engaged. The ice was so slick that all four tires were spinning. I did not have my foot on the gas pedal and none of the TOD indicator lights were on. As a matter of fact, this was so entertaining, my friend and I got out of the vehicle to see my vehicle spin it's wheels without anyone driving. Of course, I could depress the pedal(goose it), and the TOD instrument panel indicators would light up indicating that the clutches were trying to stop the shafts from spinning at different speeds.
At least this is my impression of how the TOD transfer case works based on my 4wd experience (my serious 4wd is a 1978 CJ-7, Chevy 400 cu in, Dana 300 transfer case, Dana 44 axles front and rear, 4-wheel disc brakes, 4.56:1 gears, Detroit lockers front and rear) and understanding.
Thanks for all the helpful info. I have installed Rancho 5000 shocks and the poly sway bar bushings and felt pleased with the results.
Chad
Does anybody with a wiring diagram know whether the wiring harness behind the instrument panel includes the plug-in for the switch as well? I have some driving lights that I would like to mount and use the factory wiring, including any wiring/plug-in that is already available under the dash. I could imagine that Isuzu designed one wiring harness for all automatic Troopers in 1999 independent of whether you had the luxury and performance packages. Please let me know when you have the opportunity.