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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.