Just a couple quick questions before I plan on swapping out my open diff 89 rear to an 87 disc unit. I was wondering what problems I should expect to run into with the disc brakes, do I need a new proportioning valve and e-brake cables? What do you recommend for oil and additive? Thanks a lot.

 

Welcome to TGO, thunder.

Since there's not much on TGO that hasn't been asked and answered, a search can often provide the info you require.

I assume the 87 is a nine-bolt. The following is a 10-FAQ, but the braking systems are the same between the two.

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

I've spent lots of time on the site and find it very informative and the best source of information someone with a third gen could ever need. The seller of the rear end says it's from an '87 car and it's been sitting in his garage since '94. He has no idea what posi unit is in it and told me to come have a look. He sent me a picture and it appears to be a 10 bolt.

From my research on this site it appears GM changed their prop valve after 88, I was just wondering if my stock 89 valve would be compatible with the older disc brake unit.

I got two bottles of regular 80-90 gear oil and a bottle of additive just in case it has an Auburn limited slip. I just didn't know if one brand of oil is better then the other.

I went into my local parts store to find brakes for the rear end and the guy at the parts counter said there are two different types of pads, one for a 'high performance' rear end and the regular set. I'm assuming that the rear end he is talking about is the 9-bolt Borg-Warner one? Can you tell from my pictures which pads I need?

Thanks for all the help, much appreciated.

 

The pictured rear has standard, 82-88, rear discs. 89+ cars are equipped with 1LE or performance rotors and calipers. These latter can be seen in my vbGarage (lower left next to my online status).

As for the combination valve, if your 89 is an early run, you can swap in the appropriate disc/disc valve from an 84-88 car. If your 89 is a late run, you'll have a fitment issue (the tube nut threads are different--M1.0 vs. M1.5). While the drum valve will work, you may not experience the best brake performance, as the bias won't be correct.

JamesC