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Chevytuff19
06-13-2004, 11:52 PM
First off, let me say hello as I am new to this forum. My question for yall is: I have a 2001 Chevy 2500HD with the 6.0L and 4.10 gears. It has 305x70x16 tires on it right now and is pretty sluggish when towing heavy loads. The 4.10 gears were factory and I was wondering if I should upgrade the gears to 4.56 or 4.88 to compensate for the increased tire size. By the way, original tire size was 245x70x16 (not sure about the 70 part).

Thanks in advance,
Wes

1BADHD
06-14-2004, 06:20 AM
Anything over a 4.10 will really raise your RPM on the highway. A 305/70 isnt that big of a jump in tire size. If you tow A LOT.....and done mind the higher RPMS on the hiway, go ahead and re-gear with 4.56's. But 4.88's are way to steep for that small of a tire.

snoman
06-14-2004, 09:52 AM
Originally posted by Chevytuff19
First off, let me say hello as I am new to this forum. My question for yall is: I have a 2001 Chevy 2500HD with the 6.0L and 4.10 gears. It has 305x70x16 tires on it right now and is pretty sluggish when towing heavy loads. The 4.10 gears were factory and I was wondering if I should upgrade the gears to 4.56 or 4.88 to compensate for the increased tire size. By the way, original tire size was 245x70x16 (not sure about the 70 part).

Thanks in advance,
Wes

Go ahead, slap in the 4.56's and you will not be sorry. Those big tires take their toll on gearing and 4.56 would put to back it line and with OD there well be no MPG issue as many claim. I would not generally recommand 4.88 in a high use truck that may se a lot of miles as that gear ratio set has less pinion to ring gear contact area than a 4.56 or 5.13 due to gear tooth counts for than combo.

Chevytuff19
06-14-2004, 02:12 PM
I thought 4.88 gears seemed excessive, but then again it seems like the overdrive drops more rpm's than in Z71s and other trucks. Also, the first gear in my 2500HD seems a little overgeared and will easily pull the truck all the way up to 45-50mph. That just seems like a lot longer pull than you would expect from a 3/4 ton pickup.

So the concensus would be go with 4.56 gears to improve towing?

Thanks,
Wes

snoman
06-14-2004, 03:21 PM
Originally posted by Chevytuff19
I thought 4.88 gears seemed excessive, but then again it seems like the overdrive drops more rpm's than in Z71s and other trucks. Also, the first gear in my 2500HD seems a little overgeared and will easily pull the truck all the way up to 45-50mph. That just seems like a lot longer pull than you would expect from a 3/4 ton pickup.

So the concensus would be go with 4.56 gears to improve towing?

Thanks,
Wes

Most definatly. It will also put truck engine back in power better at any given speed. You did not say how heavy your tow is but if it is around 8000lbs or more you might do 4.88's . I know it sounds deep but we used to run 4.10's and 4.56's in trucks with 30 to 32 inch tires 25 years ago without OD trannies. They would tow like crazy too! I could pull heavily loaded 4 horse trailers up the steep grades on the interstates that I encountered and hold speed with little trouble too with them gears back then.

Chevytuff19
06-14-2004, 05:47 PM
Ok, so that is what I am going to do. Also, I was never quite sure about one other thing: When you put the gear shifter in "D" and have the tow/haul button on, does it disengage overdrive?

Thanks again,
Wes

snoman
06-14-2004, 06:13 PM
Originally posted by Chevytuff19
Ok, so that is what I am going to do. Also, I was never quite sure about one other thing: When you put the gear shifter in "D" and have the tow/haul button on, does it disengage overdrive?

Thanks again,
Wes

Wes

As a rule of "thumb" it is best to leave tranny in drive when towing but you can use a little common sense here too and use OD some with 4.56's if load is not to big or ground is pretty flat. Just kinda feel it out a bit and find where it is happy. Never "lug" engine hard towing in OD though.

James B.
06-14-2004, 07:19 PM
Originally posted by Chevytuff19
I thought 4.88 gears seemed excessive, but then again it seems like the overdrive drops more rpm's than in Z71s and other trucks. Also, the first gear in my 2500HD seems a little overgeared and will easily pull the truck all the way up to 45-50mph. That just seems like a lot longer pull than you would expect from a 3/4 ton pickup.

The Z71 trucks you are referring to have a 4L60-E trans. The overdrive ratio in those is 0.70 to 1. The transmission in your truck is a 4L80-E which has an overdrive ratio of 0.75 to 1. So, your are correct - overdrive drops RPM more in Z71 trucks. The Hydramatic 4L80-E is a close-ratio heavy duty 4-Speed. Part of the reason it was designed that way is because it was intended for use on high-torque low-revving bigblocks and diesel engines that do not have the RPM range that your 6.0 is capable of. Your first gear is 2.48:1. The 4L60-E in the Z71 has a first gear ratio of 3.059:1 which is a lot deeper. The ratios in the 4L60-E are actually a better match for your engine but the 4L80-E handles much more power and is more appropriate for your class of truck.

Chevytuff19
06-14-2004, 07:29 PM
In light of James B.'s new info about the ratio of my transmission, I might opt to go with 4.88 gears. That would put the power curve about on par with a stock Z71, correct? I knew I should have coughed up the money for the diesel.......oh well though. My heaviest load will probably be about 9000 lbs. if that makes a difference.

Thanks once again,
Wes

snoman
06-14-2004, 09:02 PM
Originally posted by Chevytuff19
In light of James B.'s new info about the ratio of my transmission, I might opt to go with 4.88 gears. That would put the power curve about on par with a stock Z71, correct? I knew I should have coughed up the money for the diesel.......oh well though. My heaviest load will probably be about 9000 lbs. if that makes a difference.

Thanks once again,
Wes

It will put you a little better than stock in performance. If you are looking at up to 9000lbs with them tires, go with 4.88 then. I know they make them for the front (Precision and Yukon) and you will hav to check which pig you have it back (might be a 11.5) to check ratio availiblity. It should give you about 2200 RPM at 60 in OD which is about right for that big heavy truck and tire combo.

BTW GM could gear 4L80E lower in first (about 2.8 or 2.9 if they wanted too) but then nobody would need to buy Allison then with a gasser.

lunaticeh
06-14-2004, 09:20 PM
When you put the bigger tires on did you get the computer recalibrated for the bigger tires? If the stock computer is still thinking it has 245's instead of 305's the truck will definatly feel down on power..... When I was workin at one of the dealer's, I reprogramed a guy's truck for 285's. Just checkin.... :D

Chevytuff19
06-14-2004, 09:21 PM
Anyone know what kind of rear and front axle came on a 2001 Chevy 2500HD 4x4 w/ 6.0L V8?

Thanks,
Wes

James B.
06-14-2004, 09:25 PM
Originally posted by Chevytuff19
Anyone know what kind of rear and front axle came on a 2001 Chevy 2500HD 4x4 w/ 6.0L V8?

Should be a Semi-Float 9.5" 14-Bolt with 8-lug axles.

Looks like this:
http://www.drivetraindirect.com/html2/gm95.html

Chevytuff19
06-14-2004, 09:35 PM
They apparently don't even make 4.88 gears for my truck.......anyone know where to find some?

Wes

snoman
06-15-2004, 05:50 AM
Originally posted by James B.
Should be a Semi-Float 9.5" 14-Bolt with 8-lug axles.

Looks like this:
http://www.drivetraindirect.com/html2/gm95.html

It will be a 9.25 in the front and either a 14 bolt 10.5 or 11.5 AA rear axle.


Originally posted by Chevytuff19
They apparently don't even make 4.88 gears for my truck.......anyone know where to find some?

Wes
Where have you looked and you need to confirm which rear axle you have. The front is no problem.

96ImpSS
06-15-2004, 06:11 AM
I would guess your stock tires were 245/75/16. Changing to the 305/70/16 reduced your effective gearing from 4.10 to 3.80.
I'm not sure if I would go through the trouble for the mild ratio change from 4.10's to 4.56's. If you're towing that 9000 lbs on a regular basis, I don't think you'd be disappointed with a steeper gear like the 4.88's. Another point to consider is: how fast do you like to cruise when not towing? If it's 65, go with something like the 4.88's. If it's 75 or 80, then you'll probably like the 4.56's better.

snoman
06-15-2004, 06:34 AM
Never mind, I found them . Yukon makes them up to 5.38 for 11.5 (which you should have) and they make a 4.88 (Part # YG GM11.5-488) for the rear axle and for the front one too (part # YG GM9.25-488R)


Originally posted by 96ImpSS
I
I'm not sure if I would go through the trouble for the mild ratio change from 4.10's to 4.56's. If you're towing that 9000 lbs on a regular basis, I don't think you'd be disappointed with a steeper gear like the 4.88's. Another point to consider is: how fast do you like to cruise when not towing? If it's 65, go with something like the 4.88's. If it's 75 or 80, then you'll probably like the 4.56's better.

Yes but bare in mind that with 4.88's OD really becomes a lot more usable towing like another gear. 75 mph in od with those tires and 4.88's would yeild about 2800 RPM which would work nicely. BTW I see you have a 96 SS, I had a 69 SS many many years ago with a 396. I wish I had it today and restored too.

1BADHD
06-15-2004, 07:45 AM
If you have a 6.0 you have a 10.5" FF 14 bolt. You can get 4.88's everywhwere for that rear. But the fronts will be a problem.

4.88's are gonna be WAY to much gear. The lifted guys dont put bigger than 4.56 in for their 35's and 36's. Let alone 33's. But at any rat. Let us know how it goes.

96ImpSS
06-15-2004, 07:56 AM
Originally posted by 1BADHD
.....4.88's are gonna be WAY to much gear. The lifted guys dont put bigger than 4.56 in for their 35's and 36's. Let alone 33's. ...
And the lifted guys wouldn't be towing 9000 lbs with those gears and tires either:wink:

1BADHD
06-15-2004, 08:46 AM
I tow 5-7k on a regular basis. I am still running 4.10's. Sure the engine raps out at times on hills. But it does fine. Sounds like he needs to invest in a 8.1 or max. :D

James B.
06-15-2004, 09:10 AM
So... have you identified the rear in it yet? please share and post for all to see...

1BADHD
06-15-2004, 10:34 AM
Originally posted by James B.
So... have you identified the rear in it yet? please share and post for all to see...

If its a 2500HD and has the 6.0, it only came with a 10.5" FF 14 bolt. The 1500HD and 2500 gets the 9.5" SF. If it a 2500HD or 3500 and has the 8.1 or Max, it gets the massive 11.5" rear.

snoman
06-15-2004, 12:45 PM
Originally posted by 1BADHD
I tow 5-7k on a regular basis. I am still running 4.10's. Sure the engine raps out at times on hills. But it does fine. Sounds like he needs to invest in a 8.1 or max. :D

No just better gearing thats all (and a lot cheaper than a new truck too) Gear will make or break ANY tow vehical. If they do not match the load for the engine it will not do very well.


Originally posted by 1BADHD
If its a 2500HD and has the 6.0, it only came with a 10.5" FF 14 bolt. The 1500HD and 2500 gets the 9.5" SF. If it a 2500HD or 3500 and has the 8.1 or Max, it gets the massive 11.5" rear.

From what I have seen, it could be either rear end though what you say make sense. if he has a 14 bolt 10.5 is can get a little complicated as to if it is the old style or new. (Old style has removable pinion carrier, new style does not and the gears do not interchange). If it is a old style the part number is YG GM14T-488T

Chevytuff19
06-15-2004, 01:58 PM
Precision gear carries the front 9.25 IFS ring and pinion in 4.88. Anyone heard anything good or bad about this comapny? I was going to go with a Yukon gear rear.

Thanks,
Wes

snoman
06-15-2004, 02:03 PM
Originally posted by Chevytuff19
Precision gear carries the front 9.25 IFS ring and pinion in 4.88. Anyone heard anything good or bad about this comapny? I was going to go with a Yukon gear rear.

Thanks,
Wes

They are not bad either but Yukon seem to have a wider selection of ratio and precision only just recently added the 4.88 to 9.25 axle support.