What gear Ratio is best?

Tdean91491 · Mar 4, 2019

df2x4 said:
Depends on what you want the truck to do, and how you want it to behave. For occasional off roading but mostly street driving I'd look into an Eaton TrueTrac. The TrueTrac is a helical gear limited slip carrier that will transfer power between wheels smoothly on the fly as long as both drive wheels have at least some traction. If one wheel loses traction completely (like if it comes off the ground) that wheel will take all the power and spin freely unless you apply some brakes to simulate traction. If that bothers you or you're looking for a more constant 50/50 lock between the drive wheels then I'd go with an Eaton Detroit Locker. The Detroit is not nearly as smooth, you'll feel it engaging and disengaging on the street. Much more durable and better off the pavement, though.

If all you're trying to do is change the gearing there's no reason you can't just re-use the factory G80, though.

The truck sees pavement 99.99% of the time & I live in south Alabama so snow or ice isn’t a factor at all.
When I do the regearing I was planning on replacing the spider gears as well. The only thing I’m unsure about these.

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I’ve ready that you have to have a special tool to replace them & that no one offers them anymore. Any advice you could give me ?

Tdean91491 · Mar 4, 2019

David Barry said:
I concur with Randomguy - 4.56 ratio at a MINIMUM. The 4.88 ratio is probably the better fit, though. There is a formula to help with the numbers. (Those in the know - chime in!) I changed out the gears in my c1500, 5.7 from 3.42 to 4.10 to compensate for 31" tires. Truck runs great! I used the VSSB/DRAC calculation for my '93 to align the odometer and speedometer. [For '91 - '95s, not sure what year your truck is.]

My truck is a 96 K1500. Like I mentioned in a earlier post, I’m running 35’s at the moment. Plan on lifting and possibly running 37’s in the near future. Think the 4.88 would fit that situation?

PlayingWithTBI · Mar 5, 2019

Tdean91491 said:
Ahh I gotcha, I’m gunna save that list I’ll probably take that route plus doing the spider gears. Not like it’ll have my daily driver down. Probably replace everything that I can while I’m doing it. What brand dial indicator did you use for the backlash also what what brand dial torque wrench did you use for setting the preload on the pinion bearings? Or what brand would you guys recommend?

My son had the inch/LB beam torque wrench, you can probably pick one up at Harbor Freight. Note: I didn't have the adapters to go from 1/4" to 1/2" drive at the time of this picture (LOL) but, the next day I bought them for the final adjustment.

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This dial indicator and magnetic base came from Amazon.com, make sure you get the angle as close as you can to directly apposed to the tooth.
https://www.amazon.com/gp/product/B01K6KYHZW/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

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You also need to set the pinion depth as per instructions.

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Take your time, don't take any short cuts until it's within specs or your rear end will howl or dynamite!

PlayingWithTBI · Mar 5, 2019

BTW my 88 spiders look like this...

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Things you can do with old engine parts - I call him Chevy, LMAO!

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Tdean91491 · Mar 5, 2019

Thanks for the info! I’ve been doing a ton of research on how everything needs to be done. I’ll have plenty of time to do it seeing how it’s a spare rear end I plan on doing then once it’s complete I’ll stick it under my daily.

MarkZ28 · Mar 5, 2019

Find an open carrier and install a lunch box locker. They are cheap and easy to install. I used a Yukon brand in my Jeep Libertys diffs, have one for my 89 Silverado. They work similar to a Detroit Locker. Under power they lock solid. Around a corner they release and click/bang. Long wheel base vehicles tend to be quieter. Had a similar design locker in a 76 Landcruiser, 90 inch wheelbase. Thing would click bang and shudder on tight corners, sounded like a shotgun sometimes, but was fine. Could go anywhere in 2wd.

brutpwr · Mar 20, 2019

You will want 4.88's for the 35's and 5.13's for the 37's. I had 4.56's and they were great with 33's and not so great with 35's

upper_tanker · Mar 20, 2019

I don't know what trans you have, but this calculator is for 700r4 and 4l60e transmissions. http://chevellestuff.net/tools/rpm_calculator.htm

That's what I used when I was trying to decide what gears to swap my stock 3.42s for. I have 4.10s with my 265/75r16, and i'm about 2200 ish rpms @75ish mph. I get zero lugging up hills, and it barely ever downshifts unless I want it to. Acceleration is a world of a difference also. I'd assume you'd either want to go AT LEAST 4.56, if not 4.88.

That calculator that I posted, assuming you have one of those transmissions, lets you play with different gearing / tire sizes and lets you see what RPM you will be running at different speeds. If you don't have one of those transmissions, there are other calculators that you can use if you just type in " (transmission) gearing calculator" on google.

David Barry · Mar 23, 2019

Tdean91491 said:
My truck is a 96 K1500. Like I mentioned in a earlier post, I’m running 35’s at the moment. Plan on lifting and possibly running 37’s in the near future. Think the 4.88 would fit that situation?

I put you between the 4.88 & 5.13. You might want to also check out this site - http://tbichips.com/?page_id=517

What gear Ratio is best?

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