I am working on an 86 Iroc that I plan to put together as a daily driver and not do any high performance mods to. While servicing the rear axle, I found a boat load of metal shavings. Upon further investigation I found that the spider gears are worn along with the carrier housing. So in order to get this one back on the road it needs a bunch of parts and work. I do have access to 2 donor cars with better rear ends. One is an 87 Iroc and the other is a 91 RS. I was told that the 87 Iroc is a posi rear end, but have not checked yet. Both cars have over 100,000.

It appears to me that swapping will be more cost effective that rebuilding as long as my other choices are in better shape. Is there any advantage of one rear end over the other? Also, would you recommend bearings and seals while the rear end before swapping?

Thanks for your help.

 

One advantage, the 91 is a bit stronger with 28 spline axles and carrier vs. the 87 with 26... Check and confirm posi and gear ratio too.

 

And just because the 97 is a posi, doesnt mean that it is in good shape. The factory posi is an Auburn unit that cannot be rebuilt.

What ratios are they?

I would probably go with the 91, depending on the gears, since it will have 28 spline axles.

 

I'd go with the rear end out of the '87 if it is the same as what's under the car now. i.e. if you have a 9-bolt, I'd put another 9-bolt under it. Because if you aren't going to chop it up and make a race car out of it then it may be worth more down the line if it has 'period correct' parts on it. 9-bolts are expensive to get parts for (I know because I have one) but that's just something to think about.

 

First of all, do you have a 9 bolt or a 10 bolt? Are the donor rear ends 9 bolt or 10 bolt?

What is the gear ratio in the car now? If you want to keep it stock then go with a rear end that has the same gear ratio. Otherwise your speedometer will be off and you will have to go into the transmission to fix it.

If you want a better gear ratio then pick the rear end that has what you want. The 28 spline axles in the '91 would be an advantage, but chances are they are worn and need to be replaced anyway. This isn't a problem with the 9 bolt because it has press on axle bearings that don't run directly on the axle.

 

Go with the posi. When you go to sell it and the kid wants to mod it, hes gonna ask if it has a posi , not 28 spline axles.

 

first we need to hear what has been asked

is it a 9 or 10 bolt currently



my opinion would be to use the 91 rear, and but a posi unit with your choice of gears in

if the '87's posi unit is worn it's gonna peg leg any way, and like said can't be rebuilt

 

if one of the cars is a v6 it probably will have 3.42 gears which will make your car much faster off the line.

 

Guys I appreciate all the input.

To share some more info with everyone. The current rear end is a 10 bolt as is the 1991 rear end. Looks like my current ratio is 2.73 from other info I have seen on here. The number stamped on the ring gear is 15:41 7 5/8-10 at least. Guessing from production info on the 91 the ratio on that axle is most likely 2.73 as well but won't know for sure until I open it up.

As for the 87 Iroc rear end, since the vehicle is in storage about 10 miles away I have not checked that one yet. All of the vehicles had a 305 for an engine. My goal when I am done is to be able to have some fun driving it, but I also want something I can afford to drive 75 miles a day round trip to work and not break the bank. Otherwise it will sit more than it gets drove.

 

If I was still driving 80 miles per day I would go with 2.7x if it was mostly interstate (70 mph with little stop and go). If not interstate (some stop and go max at 55mph) then it would be 3.0x. This from experience driving it.

Driving that far I would avoid 3.2x. YMMV and IMHO

Are all the cars automatic?

I am lucky to now drive 16 miles round trip back roads 45 mph max and considering 3.45 but maybe 3.27. Mine too is a DD and used 99% for work.

 

All cars are automatic.

I am thinking my best choice will be to swap in the 91 axle. I plan to get the car pulled into the garage this weekend and pull the cover to see what it looks like inside.