EdmontonCanada

So I've got bigger tires on my truck and I'd like to change the gear size in the differential to bring back the original RPM-to-vehicle-speed ratio.

Does anyone know what parts I would need and some ideas of where I should get them? I'd take the parts into a transmisison shop and have them do the work.

Nate-03 D

Im guessing you have 3.73's? You're not really going to notice any ill effects if you don't change gears. Do you have the option to adjust tire sizes w/ a programmer?

EdmontonCanada

Not sure about that. It seems to have most power at 120 km/h and struggles too much when towing up hill. Transmission doesn't change at quite the right RPM anymore either.

I'd just like to put it where it was engineered to be. I do have a programmer but I understand that has nothing to do with shift points, just speedometer and line pressure?

Nate-03 D

Yes it will help get the speedo back where it should be. But I don't think it'll help the line pressure, that's all internal of the trans.

What gearing would you like to switch to 4.10's? Thats just going to make the truck rev even higher at highway speeds.

EdmontonCanada

I want to switch to whatever gearing will get my truck back to where it was. When in towing my 7000 lb utility trailer, the truck is either happy at 90km/hr (too slow and too high RPM) or 120km/hr (10km/h too fast).

I found the website differentials.con and I'm going to give them a call to see what I need.

AH64ID

It won't have any effect on the speed as the truck uses wheel speed sensors, not a gear in the trans anymore.

If the truck has 3.73's then 4.10's are what you want.

Be sure your speedo is correct as that has an effect on shift points.

BR1

WOW. wouldn't have thought a 7000 lb trailer would really matter. must be that much difference between the 6 speed and auto. i've got 35's on and the 3:73's and i can pretty much tow my 7000lb loaded in 6th all day long

EdmontonCanada

No, of course the gear change won't affect speedometer. I think he meant the programmer, which electronically makes the change.

My truck tows the 7000 lbs just fine...but if I want to drive 65 mph it seems to be right on the verge of being in or out of overdrive. Not good for fuel economy. I want it to be comfortably in overdrive.

Guy from differential shop told me 4.10 would only make a 150 RPM difference (costly for a small change he said). 4.56 would put me at 2000 RPM at 65 mph - a little too high for my liking.

I think the 4:10 would be good enough.

AH64ID

4.10's will run 10% higher at a given speed/gear across the board. So if your doing 1800 now it will be 180 more rpms.

At your current setup you should be at 1690 rpms at 65, 4.10's will put you at 1857, and 4.56's at 2066. Stock tires/3.73's is 1835, so 4.10's are 1.2% lower than stock with 35's.

OD gear ratios are quite different, especially if you have a 05.5-07.5 G56.

BPoulsen

I have 3:73's and 35's and I do wish I had 4:10's instead. There are several 7% hills on the way to our camping spot, and 4:10's would sure make towing our 10k camper a little easier.

But, instead of changing my gearing, I'm going to compensate for the loss by adding power after I get my transmission built up a bit.

Danderson

Agreed. I've got the g-56 with the 0.79 final drive ratio which mimics 4.10's. I'm running 34" tires and with the camper couldn't imagine higher gearing.

Grit Dog

I'd look for someone who has 4.10's in their truck and is sick of the high revs and do a swap. Bet there's someone close to you that would like to drop rpms as much as you want to raise them.