Gearing ?

[Daniel U]

I'm new to the 73-87 truck, more specifically 4X4 world. I recently bought my wife her dream truck. It's an 85 Silverado with a 5.7 TPI motor. I want to tune it better but would like to figure out the best gears for it before I do so. It has a 4" suspension lift and currently runs 33's. I'd lke to go to 35's. Anyone think this is a good or bad idea? I also want to swap the light wieght running gear to a 1 ton front/rear. What gears should I be looking for when I go to a salvage yard to find my donor front/rear? 4.10's or 4.56?

[GMC Trucker]

Unless you have an overdrive trans, 4.10's would be my choice. The RPM's will get pretty high with 4.56's at highway speeds. If that's not an issue, go for the 4.56's.

Cheers,
GMC Trucker

[Daniel U]

Yeah, it came with the 700R4, so it really bogs now with the 33's and 3.73's. 1st to 2nd gear feel fine, but 2nd to 3rd and into OD is real doggy. So 4.56 with 35's should be good then?

[GMC Trucker]

Originally Posted by Daniel U

Yeah, it came with the 700R4, so it really bogs now with the 33's and 3.73's. 1st to 2nd gear feel fine, but 2nd to 3rd and into OD is real doggy. So 4.56 with 35's should be good then?

You'll probably need a good shift kit for the 700R4, especially with larger tires, and more aggressive gears. The nice thing about the 700 is the deeper than average first gear.

Cheers,

Trucker

[Daniel U]

I neglected to mention the shift kit. It's the only truck I've had with a shift kit, and this is our 1st 4X4, so the ride took some getting used to. With very little wieght over the bed and a shift kit, the drive wheel let's loose in a right turn with any enthusiasm, lol. Will the 1 ton axle have "2 wheel peel"? My IROC and Tahoe lock up both wheels if I hit the gas hard. Maybe the Silverado would too with the proper gears or tire size?

[GMC Trucker]

I'm not sure about the posi. I think if you put the trans in neutral or disconnect the drive shaft, and have both wheels in the air, and turn one, if the other wheel turn in the same direction, it's posi, if it turns the opposite direction, the diff is open.

Isn't your Tahoe 4x4? I don't think I've seen a Tahoe or Yukon in Canada that isn't 4x4.

Cheers,

GMC Trucker

[Daniel U]

GMC Trucker,
I'm from the central Coast of California, USA, so I rarely "need" 4X4. The Tahoe is 2WD, but I did go to the trouble of having custom snow cables built for the 22" wheels, lol. When we put the Baer 13+ inch disc brakes on the back of the Tahoe, we had to machine the axles down. While the axles were out, we swapped the gears from 3.73's to 4.10's. We decided to add an Auburn posi before we buttoned up the rear with an aluminum finned diff cover. A small project grew into a complex one. Don't they always?

[Daniel U]

Here's a shot of our '99 2WD Tahoe playing in the snow on '07.

[spinem]

Originally Posted by Daniel U

I new to the 73-87 truck, more specifically 4X4 world. I recently bought my wife her dream truck. It's an 85 Silverado with a 5.7 TPI motor. I want to tune it better but would like to figure out the best gears for it before I do so. It has a 4" suspension lift and currently runs 33's. I'd lke to go to 35's. Anyone think this is a good or bad idea? I also want to swap the light wieght running gear to a 1 ton front/rear. What gears should I be looking for when I go to a salvage yard to find my donor front/rear? 4.10's or 4.56?

what rear end does it have? bigger tires and lift=worse mpg, people can fight and knock it all they want, the truth is, is air resistance and replicating mass is unable of being beat.

[GMC Trucker]

Nice Tahoe, Daniel. Did you take all of the badges off the truck? I did the same thing on my Yukon? It looks like a GMC grill as well. Clean look.

[Daniel U]

Originally Posted by spinem

what rear end does it have? bigger tires and lift=worse mpg, people can fight and knock it all they want, the truth is, is air resistance and replicating mass is unable of being beat.

This I know for sure. It's getting 10mpg, where my IROC gets 20mpg, lol! Wind resistance(drag), rotating mass(bigg wheels/tires), gearing, overall wieght/mass of viehicle. They all play a factor in mpg.

[Daniel U]

Originally Posted by GMC Trucker

Nice Tahoe, Daniel. Did you take all of the badges off the truck? I did the same thing on my Yukon? It looks like a GMC grill as well. Clean look.

Thanks, the wife prefered the GMC look. I debadged all our vehicles.

[powerdriver 1958]

I'm going to move this to 4X4,Think the guys over there can help your with a few more ideas

[dammitmitchell]

im running 4/56' in my 14bolt corp 10 combo..
be warned they eat gas!... alot worse the 4.10s did..
but i also drive like crap.. the small tires and 4.56's will get you over and through pretty much anything....

i'd stick with 4.10's for streetability with a 33 or 35in tire.... take the money you save and put a posi in the rear

[Daniel U]

Yeah, that's my biggest ? 4.56 or 4.10's with 35's? I'd like to tach about 2k @ 65 mph with the 700R4 on O.D.

[Daniel U]

Originally Posted by powerdriver 1958

I'm going to move this to 4X4,Think the guys over there can help your with a few more ideas

No problem!

[dammitmitchell]

no more the 4.10's in my opinion....

[Tony@AirRideTech]

I you are going to run 35/36's go with the 456.... if you are running the 33's .... 410. I am running 456 in my 90 burb... 35" BFG's, Lockers, stock 350TBI motor and 700R4. I Calculated the grear ratios out to come back in on the stock power band as close as i could and that is the correct combo... at 65MPH my speedo is barely off by about 4 MPH ( reading faster than actual traveling ).......

[dammitmitchell]

4.56's and 38's my speedo reading is dead on..
it's going to boil down to a matter of prefference

[72chevyk10]

4.56s with .7 overdrive will put you at about 2100rpm(+/-) at 65. EDIT: and thats with the 35's

http://www.jawsgear.com/calc_rpm.html
i used this to find it.^ im gonna do the same gearing and trans as you are.

[dammitmitchell]

that's a bad ass site!