limited slip rear for 87 truck/91 suburban - donor vehicles and ratios?

[Chuck78]

My daily driver is an 89 suburban (fyi through 1991 suburbans are the old body style like 73-87 trucks). Just got a bunch of 89 suburban parts in the junkyard to bolt to my 1962 GMC 1000 panel truck. I figured since I am going to have the entire front crossmember/suspension/brakes/steering/steering box/ps pump/booster & MC/etc off of an 89 suburban, I might as well be looking for an 89 suburban rear end as well, so that it would make future parts sourcing easier. The 63-ish and older rears are a weaker 12 spline I am told(newer are a 30 spline), and all the pre-71-ish are the harder to find 6 lug pattern. Since I'd have to buy special custom 6 lug aftermarket rotors in front for the 89 front end on the 62, and I already have back wheel spacing issues that need resolved, I might as well just do the rear end now and get a newer 5 lug axle...

Anyhow, I wondered how common limited slip rears were in these years of trucks? I have a coil rear, but coil suspension truck differentials are few and far between, so my sources are limited (1990's Caprices??? have the 5 on 5 bolt pattern). There are kits to convert any leaf rear to coils, made with my era of trucks in mind. I might just look for a Caprice 3.08-3.42-ish posi, maybe a 3.73, and just swap on suburban rear brakes if I can. Swapping the whole suburban rear is not out of the question though, hence the post.

Thanks!

Chuck

[LONGHAIR]

Man that's some confusing reading.
Can you clarify it some?
You are looking to put a 5-lug rear into your 62 GMC panel?
Matching a swapped in 'burb front crossmember?
A car coil rear end is not the same as your old truck.
Cars are essentially triangulated 4-link with short links and totally different mounts.
The truck-arm style rear end is more like ladder-bars, with a pan-hard bar. It has saddle mounts similar to leaf-spring mounts.
Finding a car axle is fine, but none of the bracketry is going to help you. There is going to be some fabrication work there.

The gearing question has to do with the transmission you are running, tire diameter and driving style.
Posi...You aren't going to get much there. Gov-locks aren't worth having, they are more of a problem than an advantage.

[Chuck78]

I just got an 89 suburban crossmember for the 62, so I will need to either go to 5 lug wheels, or get the 6 lug aftermarket rotors.
My 6 lug aluminum wheels are like 12" wide in the rear, with not enough backspacing. It has a 225/75/15 on it - the wheel is about 2-1/2" wider than the tire tread (looks bad)! The tire almost rubs the wheelwell lip as is! So basically, I have rear wheel tire clearance issues.
Almost thought about getting the wheels cut and rewelded to a narrower width, and retain the 6 lug. If I could get a newer rear, and swap to 5 lugs, I could have more readily available parts, and 5 lug, which would help out in the front a lot. It would also be nice to have a limited slip rear end if I could find one, or swap one into a later housing from a Camaro or something if it were compatible. I'm going out in a few to check out what ratio I have in the current stock rear, which might further motivate me to look for a donor.

[COMP]

Originally Posted by Chuck78

I just got an 89 suburban crossmember for the 62, so I will need to either go to 5 lug wheels, or get the 6 lug aftermarket rotors.
My 6 lug aluminum wheels are like 12" wide in the rear, with not enough backspacing. It has a 225/75/15 on it - the wheel is about 2-1/2" wider than the tire tread (looks bad)! The tire almost rubs the wheelwell lip as is! So basically, I have rear wheel tire clearance issues.
Almost thought about getting the wheels cut and rewelded to a narrower width, and retain the 6 lug. If I could get a newer rear, and swap to 5 lugs, I could have more readily available parts, and 5 lug, which would help out in the front a lot. It would also be nice to have a limited slip rear end if I could find one, or swap one into a later housing from a Camaro or something if it were compatible. I'm going out in a few to check out what ratio I have in the current stock rear, which might further motivate me to look for a donor.

a 225 on a 12" wide wheel ,,Noooooooooooo way

[Chuck78]

It's a shame, because they'd be decent alloy wheels if they fit better.... If I trimmed the wheelwell lip down some, they might do alright with some 255's in the rear. It's REAL close as is... they need about 1" more backspacing. Too bad, they're 6 lug wheels and all...

UPDATE, Just went out and double checked, 15X8 front, and 15X12 rear!!!!! Looking from the back at the bulging rear tires is scary! I stuck my tape measure into the wheelwell lip, and there's 1-1/8" overhang that could be trimmed out before hitting the vertical part of the outer wheelhouse. If I took out most of that out, a tire the width of the rim would work... Might go scrounging for a deal on a pair of 255's or 275's...

Also, this was the first time I really payed a whole lot of attention to how the rear suspension and the differential housing connected. Looks like it'd be a fairly easy fabrication job. The shocks attach to the rear of the trailing arms behind the axle, and at the tops to the frame; and the springs sit between the trailing arms and frame! My 89 truck rear end has the axle positioned below the leafs. My 71 Camaro has the axle sitting on top of the springs. I guess this has to do with stance, I suppose. Axle on top makes the body sit lower in relation to the axle (car), axle on bottom makes the vehicle sit higher in relation to the axle (truck). I suppose , if the leaf spring perches on the axle could work out at the same width as the truck arms' position, then a car leaf spring axle would work out almost perfect! Just have to fabricate a large bracket for the panhard bar to attach to the axle. Maybe I could get lucky and find another vehicle with something similar in the yards and sawzall it off?