WHICH REAR END?

rfloyd

I'M READY TO BUY THE 99 SILVERADO 2500LS EXCAB LB
6.0L ATM . MY DILEMMA IS THE 3.73 OR 4.1O RE. I
WILL BE TOWING ABOUT 10K LBS 4-5 WEEKS OUT OF THE
YEAR, THE REST OF THE TIME WILL BE BACK AND FORTH
TO WORK. I WOULD LIKE THE BETTER GAS MILEAGE OF THE
3.73 BUT WILL I NEED THE EXTRA TORQUE I WOULD GET
WITH THE 4.10? I WILL BE GETTING ALL THE TOWING
PACKAGES OFFERED....CAN I LIVE WITH THE 3.73 AND
NOT JEOPARDIZE THE ENGINE AND TRANNY?

dave40

I think the 3.73 would suit your needs. That 6.0 with 300hp and the Tow-Haul Mode works wonders.

tnt2

I wouldn't even think of the 3.73 if you tow 10K. I tow 10-11k all summer with an F350 with 4.10 and with all the torque and hp of the PSD, the 3.73 just won't cut it.

FETZ

Definitely go with the 4.10.

First of all, towing 10,000 lbs. you will exceed the tow rating if you go with the 3.73.

Secondly, when you're pulling up long grades, you will certainly wish you had gotten the 4.10!

If you do go with the 3.73, be prepared to see a lot of middle fingers waved your direction from folks that have been stuck behind you on those long grades!

Rich

If you're going to tow 10K, you need an EFFECTIVE ratio in the rear end of 4.10 or 4.30. When you're not towing, you want the 3.73.

There are three solutions that come to mind.
1 - Order the 3.73 and manually shift the transmission to lower gears to keep both speed and RPMs up. To my way of thinking, this is the best option. Others may disagree.
2 - Order the 3.73 or 3.55 and then add a auxilliary transmission underdrive for an effective ratio of 4.10 or 4.30. Good but you're looking at an extra $2500 or so.
3 - Order the 4.10 and auxilliary overdrive transmission. This is kind of yucky as you may be shifting a lot commuting. Again you'll need some pocket change to the tune of $2500 or so.

I've been in the situation of towing with a 3.73 but not with as heavy a load. All that it took was to manually pull the transmission down to the appropriate gear. It wasn't a big deal. I was able to go up hills reasonably well. I never had to drop all the way down into low.

Rich

tnt2

Going with the 3.73 and downshifting would still be a mistake. If you travel at highway speeds, 65-70, where would your rpms be? It wouldn't take much of a grade with a 3.73 ,2%?, for the speed to start dropping off. That would mean you would spend most of your time in a lower gear with high rpms, which would make me nervous. I travel alot, and I can always tell a truck that is geared wrong, they're the ones creaping along with the motor wound out. The 4.10 is the way to go, even considering an auxillary transmission.

larry18

Need to remember that the 2500 maxes out at 10K even with the 4.10. You should definitely consider the type of driving and distances you will encounter while trailering. While the 3.73 may be fine for driving on reasonably flat highways, those steep grades tend to be the great equalizer for engines, transmissions, and axles. You might also want to check into the legal requirements of the states where you will be traveling.

Rich

tnt2,
For the purpose of this discussion lets assume that the difference between the ratios of top gears of the transmission are 10%. The difference between the ratios of 3.73 and 4.10 is also about 10%.

The question is that if I use the transmission to increase engine RPM, (for a given speed) how is that different from using the rear end ratio to always increase the engine RPM (for the same given speed)???

The engine RPM and speed are the same in either case. What you are describing a truck wound up and still going to slow is probably pure abuse of too small an engine and too large of an over load.

Rich

tnt2

rich .... You first have to get to cruising speed. This is where the biggest difference comes into play. If the motor, transmission, and gear ratio, can't move the load to highway speeds, downshifting won't mean a thing.

Rich

tnt2,
You have me confused. I think that we're saying the same thing but I'm not sure.
If I remember correctly, each of my F-250s and a 3.73 rear end will go 70 MPH and use 2100 RPM.

If I had a 4.11 rear end it would take 2310 RPM to go 70 MPH. A 4.30 rear end would require almost 2500 to achieve the same 70 MPH. With a heavy load you may never get into the highest gear of the transmission, but if you're huffing and pufffing while moving at 70 MPH, what's the difference?

To move any load by a truck there is a specific requirement for torque. To meet the requirement to perform the work of moving the load, a certain number of RPM are necessary. Does it really matter how those RPM are generated? What is the difference between running in OD with a 4.11 or locking OD out with a 3.73 IF BOTH produce the necessary RPM and torque?

There is probably one aspect that we haven't addressed, efficiency. An aux transmission probably would incur a slight efficiency loss due to the additional gears being turned. (Probably 1 or 2 percent, if that.)

quadrunner500

Rich, you are right in what you are saying. And I'm not trying to say which one is better, but just make a general statement that when you go from a 3.73 to a 4.10, the rpm drop on each up-shift is reduced on the 4.10 compared to the 3.73, effectively bringing your ratios closer together. It just means that for every gear situation except highway cruising in top gear, there is a selection available that's a little closer to optimum with the 4.10.

Rich

quadrunner500,
Hadn't thought of the closeness of the ratios. That could make the towing vehicle a bit more raodable.

I guess it breaks down to what are you going to do the most? If you're towing 90% then the 4.30; but if you're empty most then 3.73 and an auxillary transmision to give an effective 4.30. I know that when I'm ready for that 5th wheel, I'll be going the aux route!

Rich

tnt2

Rich .... I thought about the aux. route myself, but from reading the installation instructions and the reference to "pounding the floorboard with a sledge" to make room, this kind of scared me off (for the time). Of course this was for 4x4 CC. That, and the switch looks tacky.

Rich

tnt2,
"Pounding the floor with a sledge" sounds like an interesting installation technique to me. I can't imagine why it wouldn't be the same for a 4x2 SC. The end of the transmission is under the front seat. I've been told that the aux replaces the tail shaft and housing of the standard automatic transmission.

Rich

Robj

On thing to consider is if you have a 4.10 and you go from a 245 tire to a 265 tire you now have aprox. a 3.96 rear end. Might give you the best compromise. Tire is about an 1" taller and speedometer is only off about 2 miles. For a very good site with calculations for different ratios versus tire sizes check out- http://www.off-road.com/tools/gearcalc.html. Hope this is of some help.
Rob

pathomp

I am planning to buy a GMC 2500 4WD ext cab SB, and have the same question as RFLOYD regarding axle ratio. It makes sense to me that a 4.10 would be essential to tow the 10,000 lb he mentioned. I plan to tow 5000-6000 lb but I'll be in the mountains at least some of the time. How does this change the assessments that have been made? I also will be doing most of my driving without the load and would like to get decent mileage. Does anyone know how much gas mileage might change (unloaded) between 3.73 and 4.10 for city and highway driving?

quadrunner500

No worse than 5-10%. Maybe not at all worse when towing or hauling.

But then, if as you say you will be doing most of your driving without the load, you might consider the 1/2 ton truck, which can still tow your load.

Big difference in fuel mileage between 1500 and 2500, but not much difference between the 4.10 and 3.73 for either one.

1500 4x4 can tow 8000 pounds with 4.10 axle, and towing package.

markbuck

While the numbers look convincing on paper between the two tranny's, if the 3/4 ton has a higher stall speed (torque multiplication) then the effective ratio's might be much closer.

mgdvhman

I know...but it's nice to know what all the factors are..

mgdvhman

Now you got me wondering ...
I had thought about that..but not real hard..
I can't find that data anywhere

Oh well..

Still going 4:10's

"I'm trying to think, but nothin' happens."
-Curly

rcn

Needing some help on this question. At what point does a lower rear axle begin to limit acceleration speed? Obviously, everything being equal, a 3.08 would not be as quick as a 3.55. But, what about the difference between a 3.73 and say a 4.10 or 4.30. There has to be a breaking point somewhere or everyone looking for stop light quickness would want something geared like a dump truck.

markbuck

you reach that limit when you are in top gear at the max hp rpm.

A trick for the stoplight racers is to gear in the 5.xx to 6.xx range.

rcn

So assuming everything else is equal, a lower rear axel ratio will provide quicker 0 - 60 acceleration? Right?

My interest came about when someone on another board mentioned that Ford Superduty's with the 4.3 rear didn't respond quickly because gearing that low produced slower acceleration.

So, everything being equal, a F250 V10 with a 4.3 rear should be slightly quicker than an F250 V10 with a 3.73. Right?

I think that person was combining the effects of lower rear axles with the additional lower transmission gearing that comes with the heavier commercial trucks. Just guessing on that though.

markbuck

'bout the only negative is shifts happen quicker, possibly adding a shift right as you reach your ideal race top speed.

For instance, if you can run to 60 mph with just first gear, and by going to a higher numerical rear end, the thing needs a shift to 2nd at 55 mph, you might hurt acceleration....

Other than that one instance, bigger rear end numbers produce more rapid acceleration.

rcn

Thanks for the response Marbuck,

But your response makes me wonder if that is the limiting factor in the example with the Ford Superduty 250 that I mentioned previously. Especially since 3/4 ton trucks are designed to haul and tow heavy loads and not drag race unloaded at the stoplight.

I'm assuming that the transmission gearing is lower and the shift points come sooner in order to get those heavy loads moving. Therefore a 3.73 may not downshift quite as soon as a 4.3 and run a little quicker in a short sprint.

Am I on to something here?

cdean

rcn, I side with you and disagree with Markbuck. there is a point when the gear ratio is so low, that you hinder acceleration. Your engine can only "rev" so fast, that there is a point where the gearing is so low, you are not using the engines torque to its full potential. what i mean is, if the gearing gets so low you only need 80% of the actual max torque to get the to redline, then you are actually going to go slower than if you had a higher gear ratio.

did i make my point, or just confuse?

quadrunner500

I see both points. It's called the flywheel effect. Inertia is the tendency of an object at rest to remain at rest, or in motion to remain in motion. (Newton) The amount of rotating inertia reflected back to the transmission input shaft decreases as the square of the drive reduction ratio.

Put another way, there is a point at which you can have a ratio that is too high numerically, for the amount of engine flywheel present. To make the Mark Buck case, if you double the ratio, you need to reduce the inertia of the engine (flywheel) to 25%. Then, Mark wins every race to 50% of Cdean's top end.

quadrunner500

Of course, the reverse is true also. That is, going to a higher ratio, like from a 3.73 to a 4.10 is only about a 10% change, it results in about 21% more inertia being reflected from the engine flywheel into the load, giving a better towing feel.

quadrunner500

Oopps

mfreeman

I've driven sports cars for the last 15 years, and this will be my first truck. I've ordered a Sierra 5.3 extended cab, 4x4 Z71, with a 3.73 axle. The biggest thing I ever plan on towing is maybe a 30' boat some day when I find the money. Modifications planed are a better air cleaner, and some exhaust work, maybe headers. I ordered the 265 size tires, and may get a little bigger if needed, but not too much bigger. No scary off roading, but I bought this truck to go up into the hills, and I want the clearance to do that with the extended cab.

Okay, sorry for all the info, here is my question. Do you think I should stay with the 3.73 or try to change my order to the 4.10. 95% of all miles on this truck will be on the road with no load, and out of that 60-70% of those will be on the highway to and from work. I don't plan on racing cars at the stop light, but I would like to be able to keep up with other trucks.

Thanks,
Mike

quadrunner500

Mike, no one but you can ever know what it takes to be satisfied. Remember, there is only a 9% difference between the 3.73 and the 4.10.

And while I can't speak to what's right for you, I can tell you in my own case, I waited an extra month because 3.73's were everywhere, but I was stubborn enough to want the 4.10, and felt I could use it to maximum effect.

Emotions aside, since you want something for the hill country, like I did, AND are thinking about going to larger diameter tires, I still believe the 4.10 is the better choice for you. Whether it is worth it to change the order at this point, just depends on how relevant the extra wait is to you.

mfreeman

I really don't want to wait any longer then I have to for my truck. I know the 3.73 will probably be all I ever need, I just don't want to be in a situation where I am cursing myself for not getting the 4.10.

Thanks for the help, I'll have to think about it.

Mike

Rich

mfreeman,
Don't worry, there a lot of options.

First while you're towing, there's nothing wrong with using lower gears in the transmission to achieve adequate response. The whole thing is getting the proper engine RPMs for the driving situation.

If the 3.73 is really such a big pain while towing it can be replaced two ways. First, have the rear end gears replaced. My guess is that a grand and a half should cover it. The second option is to install an auxiliary transmission. I've seen quotes of 25-3500 installed by Camper World (Maybe that's not the name, but it's the one with the "Presidents Club" and a 10% discount.) If you're near Indiana, US Gear will do it for less. (www.usgear.com)

You're saying 95% is w/o the boat. So probably you have 2 or 3 hills with the boat that may require some transmission shifting on you part. That is probably less than 1% of your total driving.

Is the 1% where a 4.10 or 4.30 would be nice worth the lower gas mileage, higher engine revs for the other 99%? Or is the aux trans cost really, really worth the 1% convenience during the towing.

Good luck,
Rich

jonesst

I am about ready to order the 2000 Sierra SLE 2WD Ext. Cab, short box, w/ 5.3L V8. I plan to do little, if any, towing, and most miles will be commuter/around town, with some cross-country travel (no trailering) also. I see that most of the trucks w/o "trailering packages" on the local lots are set up with the 5.3's and 3.42 rear ends. My question: should I order a 3.73, or go with the "standard?" 3.42 rear end? What about the highway/cruise mileage and economy with these two rear ends, if trailering is not part of the equation?

mgdvhman

3:73 has got to be the all around perfect for everything rear end. It has power for pep..enough power for towing...and gets good mileage.

4:10 is for serious towing and gives that extra pep when empty as well. The MPG difference is hardly noticable.

3:42 is the best bet for MPG...but may lack some pep and will limit your towing...(maybe not much ..depending on what you are towing)

I'd go with 3:73 for an all around perfect gear.
4:10 if you want that extra pep for highway passing and take off's
3:42 for decent pick up..and the best economy

3:73 is the best choice perhaps?

Good luck

Tim

jonesst

Thanks Tim - that's about what I thought - I am leaning toward the 3.73 for a bit of better towing capability, but any idea if the lesser economy would be noticeable over the 3.42?

mgdvhman

3:42 and 3:73.....maybe enough to buy an extra burger at the arches next time.

3:42 and 4:10?....maybe enough for an entire mac combo?

get 3:73....you won't be dissapointed. If you really don't mind a tiny bit extra in gas....get 4:10 and have all the pep you will ever want.

let us know what you do.

Most Silverado's probably have 3:73 in 4WD....3:42 in 2WD...but don't quote me..

- Tim

mgdvhman

as farr as $1500 for new rear end gears go?....It's about 1/3 that installed here..or less.

If you are unsure...remember...it's all the same price when ordering.

mfreeman

I've heard some good points. I think I will stick with the 3.73 and drive it for a while. If I start running into problems, I'll change them. But it really sounds like the 3.73's will do everything I need them to.

mlfreeman

rfross

My '99 Sierra is a 5.3, extended cab, 4X4 with the 3.73 locking axle. The 3.73's are perfect for me and give me better than expected gas mileage. Exceptional over-all performance whether stop-light acceleration or towing our 2,500 pound pop-up camper.

With conservative driving and a tonneau for improved aerodynamics my best tank for combined city/freeway was 17.8 mpg. Way better than I expected. And that's with only 2,500 miles on it!

I've just added a Gibson low restriction cat-back exhaust and I will be checking mileage in the near future after the novelty of the improved acceleration and great sound wears off. This thing really kicks now. Can't wait for K&N to release the new FIPK for this engine.

doickle

I noticed postings about going with an auxiliary transmission. No where have I seen anyone say anything about a two speed rearend. I understand that there is a place in OK that has a after market two speed rearend, but I'll be darn I can't find out who it is. Does anyone know of this?
I think that a two speed rearend would be great, how about some feed back on that!

cdean

one thing to remember is that picking a rear ratio is not a linear process. because your engines torque curve is not linear. in the C/K series trucks, the 3.42 was really a useless rear end. Why? In relation to the torque curve, it actually kept you slightly out of the powerband. I thought the 3.42 in my truck was the best rear, until i drove one with a 3.73. The 3.73 had more pep AND got the same if not better gas mileage. Depending on your driving, the higher gears won't always give you better mileage.

For the new GM's it looks like the 3.73 and 4.10 are the best choices. I think the 3.42 is only a decent choice for these motors if you are doing LONG, cruise control trips all the time. The mileage reports that are being posted here show very little penalty for choosing the 3.73, or even the 4.10.

Brutus

mfreeman,

I agree that the 3.73s are the better choice for the type of driving you mentioned. mgdvh mentioned that the difference between the 3.73 and the 4.10 is about the cost of an extra mac combo next time. That's pretty close to what I calculate, as long as you go to McDonalds once a week. I have a Ford V-10 with the 4.30. The 4.30 cost me about 2mpg compared with the 3.73. If you drive 15,000 miles per year, that's about $5 extra per week, depending on the gas prices in your area.

wallifishrmn

Still not sure after reading all the great imfo on this topic. Right now I have a 1990 5.7L chevy with a 3.03 rear end. I pull a 18 foot bass boat (total weight approx. 2500lbs) once a month at best. Rest of time is mainly 65mph cruising. My truck has 168,000 miles and still does great on gas. With the smaller 5.3 and the above info would you go with the 3.42 or 3.73? Can you really tell that much difference in pickup and gas mileage?? With the 3.03 the engine doesn't even seem to pull at 65. Want the rear end that's easiest on the engine. Would like to get another 10 years and 170,000 out of the new truck. Thanks Paul

mgdvhman

3:73 is the best "all around" gear...hands down.

Brutus

I don't know that much about Chevy engines, but I will venture a guess that the 99 5.3 has more horsepower and torque than the 90 5.7. The liters don't necessarily tell the entire story.

Just as an example, the 99 Ford 6.8L V-10 had 275 horsepower and 410 lb-ft of torque. The 2000 Ford 6.8L V-10 will have over 300 horsepower and 430 lb-fts of torque. The liters didn't change, but the horsepower and torque did. The Ford 5.4L also gained horsepower and torque between model years.

arkie6

When selecting the proper axle ratio, you also need to consider the tire size. Larger wheel/tire combos result in a higher overall gearing ratio.

Many of todays trucks come standard with 16" wheels where previous models had 15" wheels. With 16" wheels you could get the next lower axle ratio and still end up with the same overall ratio that you had with the 15" wheels.

glenn2

go with the 4:10, I would rather have too much gear then not enough.

edwardj

Am looking at "99 Ford F-250 SD, SWB, SC w/ 5.4 V-8. Will be driving 20-30 miles per weekday locally (no trailer) and 1-200 miles on weekend w/ 2 or 3 horse trailer and horses. What rear end ratio would be optimal with manual transmission and/or automatic comparatively?

jerobbins

What is your total towed weight?

edwardj

Towing weight would be from 6-8,000 lbs...maybe on occasion, up to 9,000.