Rear end info

My '87 Silverado has a 350 and a 4 speed automatic transmission. All stock. I want a posi rear end.
A 373 seems to be the advice I am getting to enjoy it on the highway and get reasonable mileage.
What is the recommended set up for this type modification ?

What gearing do you have now?

I'm a big fan of the eaton truetrac differentials. They cost a bit more than some other options, but no clutches to wear out, no friction additive is needed. Perfectly quiet and just does its job without even knowing it is there.

http://www.eaton.com/Eaton/ProductsServices/Vehicle/Differentials/detroit-truetrac/index.htm

The gearing is currently the stock rear end.
Right rear tire spins but other does not.

The RPO sticker in the glove compartment should give you a clue as to what that stock gearing is (assuming no one's messed with it). The code should be GU*.

So you've likely got an open differential. That can be an advantage. If you're happy with the gear ratio, hopefully a 3.73 but even a 3.42 wouldn't be to bad for a 2wd and close to stock size tires, but if it's 3.42, 3.73 or 4.10 I'd go with that and keep that gear ratio. Then I'd go with a lunchbox locker. The lunchbox lockers are basically just a spider gear replacement system so you don't have to remove the carrier to install it which means you don't have to reset up your ring and pinion gears and it makes conversion to a locker very affordable and something you and/or someone with some basic mechanical skill can install yourself in your driveway. There's Lockright by Powertraxx parent company Richmond gear, there's a Spartan locker and I'm not sure what the Yukon calls their's but I think it's like a Grizzly locker or something of that nature, but there is like 3 different lockers that are just spider gear replacements sometimes called mini spools or lunchbox lockers.

http://www.rocky-road.com/lockright.html

https://www.amazon.com/USA-Standard...120475&sr=1-1&keywords=spartan+locker+10+bolt

Powertraxx also makes one that's not near as aggressive and is a bit more comfy on the corners. It's called a No Slip. @skysurfer runs one of these in his front axle of his 4x4 and doesn't have any rough issues with it or notice much torque steer with it. Being in the rear, torque steer isn't an issue with your.

http://www.rocky-road.com/noslip.html

Eric Sprouse said:

The gearing is currently the stock rear end.
Right rear tire spins but other does not.

Click to expand...

I like 3.42s for you.

Yeah me too, though with a 700r4, 3.73 or 4.10's won't be bad either but I'm leaning more toward the 3.42's being more common by 87.

1987 GMC Jimmy said:

The RPO sticker in the glove compartment should give you a clue as to what that stock gearing is (assuming no one's messed with it). The code should be GU*.

Click to expand...

1987 GMC Jimmy said:

The RPO sticker in the glove compartment should give you a clue as to what that stock gearing is (assuming no one's messed with it). The code should be GU*.

Click to expand...

thank you 1987 GMC Jimmy ! I took a picture of the glove box sticker. Appears to be GU2. I will try and upload. I should add that I have 20” tires on the rear.

That’s a 2.73 rear, I think. Yikes. My Caprice has a 2.56 rear, and I get around so don’t feel bad. It won’t matter if you change it.