If I buy a drum rear and replace the axels with disks axels (which I was going to buy stronger axels anyway) and modify the housing so I can mount up the disk brake mounting plates will I be able to bolt on my 89 rear disk brakes right up? Or am I still going to have to use spacers or something on the axels?

 

To my knowledge there is no diffrence in the actual axles. iT is just the mounting plates and the backing plates. You should not have to use any type of spacers or anything like that.

 

GM only made 2 axles for 3rdgen cars. A drum brake axle and a disc brake axle.

For them,"The masters of mass production" to have done this. Their has got to be a difference!

Thanx,ANDYZ28

 

So if I buy disk axels and modify the housing so I can mount up the disk brake mounting plates. I will be able to bolt the rear right into my 89 IROC with disk 4W disks right?

 

Well sort of. If you guys can be a litte bit patient I am working on sorting this whole thing out. Give me 10 days or so and I will have it all straight.

ThanxANDYZ28

 

Well I don't have a car right now because I blew up my rear. What do you mean by "sort of" can you tell me the problems you are having doing this? I guess I should just try it I have no other options.

 

acutally ..there is another difference in axles .. spline count after 1989 .. from 28 to 26 ????

 

Give me some time and I will make it all very clear.

Thanx,ANDYZ28

 

i have just finished converting my 89 RS to disc with a 88 9 bolt and 89-96 braking system and I have had to reason to change my axles what so ever? The axles themselves have nothing to do with the actual mounting of the braking system. why would it matter if they came off a drum or disc rear? The only possible diffrence is the spline count or the bolt pattern both of which were the same in my case.

 

The 1991 GF parts book lists two different axles for the same differential. One is for disc brakes, the other for drum brakes. Their has got to be a reason for this?

 

Ok well i can argue with that. But the only logical diffrence is the flange that the disc slips over, what else of a diffrence could there be? Other than bolt pattern(which is not diffrent, we all know this) or the spline count. What other diffrenceses could there be??

 

Spline count is the same for both axles. I will know the difference by Wed. of next week. I bought a 10 bolt 3.42 posi disc rear assy. I am having it shipped to me. I should have it by Wed. Then I will take it apart and compare the axles.

 

Okay so you are saying there is a diffrence in the 9 bolt to 10 bolt axles. That would make more sense.

 

I just completed two change overs from drum to disc. Everything fits perfect.

 

If you really want it, drop us an email houser@rearman.com . Sometimes the best solution is to hire a pro...

 

Ok, quick question. I've asked a few people and done a search and still don't have the answer. Are the backing plates for '88 disc 9 bolts and '89-up 9 bolts the same? From what I understand, the answer is yes. I just need confirmation.

Thanks all...:hail:

 

The disk brake axle flange has 4 bolts that the backing plates mount to. Drum flanges have 2 bolt backing plates.

 

I hate to be the one to say it, but not all axles match up. I know some people with 9-bolt rears which do not accept the same length! Who knows what happens to these vehicles from manufacture to last owner? I'm glad we have the parts to compare and match...

 

ebmiller88, you know me pretty well by now. So when I say that I will find the answer to this question. That is exactly what I will do. Isn't it?

 

Art is the one who would know all of the answers. If you're aching to know, please email me a complete request to present to The Rearman. houser@rearman.com

 

No, the 88 and earlier have staggered calipers, while the 89 and up have both calipers on the same side of the rotors, the rear.

Also, the 9-bolt axles are different length left and right.
10-bolts are both the same length.

 

We're talking about modifying the flange and drilling the holes to mount the disc brake backing plates. By cutting the flange down it makes the flange the same size as the disc brake flange. All that is needed is to enlarge the two bottom holes, mark the two top ones with the mounting plate, and drill them.

 

As I stated above, I just did two of them, its fresh in my mind. What more info do you need? There was a tech article on how to do it, but unfortunately the site it was on is now down.

 

True and true. I learned that some people do not know their left from their right or cannot tell which way to put in the rear... The hazards of long-distance service... Another reason I ask people to email directly and give phone number. I really rather not embarrass anyone or myself...

 

Yeah, I knew that the caliper locations were different, but I was hoping you could just "turn" the drivers side backing plate around 180 degrees, bolt on a set of PBR cradles and put a set of PBRs in there, change the lines over and bada-bing...good rear brakes.

Just seemed too easy...


Andy, you haven't steered me wrong yet, I just needed a quick answer. I was debating on picking up a set of 9 bolt caliper brackets on the cheap, maybe putting them on my 88 rear. Guess I should come back to reality now..

 

Andy, you haven't steered me wrong yet, I just needed a quick answer. I was debating on picking up a set of 9 bolt caliper brackets on the cheap, maybe putting them on my 88 rear. Guess I should come back to reality now..

Is the '88 rear a 9bolt disc brake rear? If so ,I believe that the 9bolt "PBR" type backing plates will bolt up directly to your 9 bolt disc brake rear without any problem. But of course the only "proof" would be for you to do it. As you may recall from previous technical questions/problems that I have used this "proof" technique very successfully. But I do have other ways to find this out.

Thanx,ANDYZ28

 

Yeah, both of my rears are 9 bolt 2.77 posis, one 88 and one 89. I'm sure the backing plates will swap. I just didn't know if the caliper cradles would interchange. If the backing plates are different, I guess they won't....

Which leads me to the original question...are the 88 and 89 9 bolt disc backing plates the same? Does anyone know for sure? I just haven't been able to compare mine yet. I'll try my best to get to that this week.

 

Sometimes quick answers will get you in trouble... I hope I learn at least a third of what Art knows! :hail:

 

You're talking about two different animals here, the bolt pattern where they mount is the same, that is all. the '88 uses cast iron calipers, the '89 uses alum. PBR calipers.

 

Revlimit just swapped in a new rear for me. I'm not sure what year its from but I went from drum brakes, 2.73's and crappy one wheel drive to a disc brake setup, 3.23's and posi for $300. It works great even with the stock brake master cylinder, but soon I will be switching to a dual resevour brake master cylinder out of a 90 iroc we found at the junkyard. So my total cost to switch from drums to discs was $375 and alot of help from good friends. Good luck with yours!!