I bought a rear which has disc brakes on it. Decoded it to an '89, 3.23:1 LSD.

The rear axle housing has normal dirt & rust. Does not look as if the cover plate has ever been off it.

The disc brake caliper bracket housings on the end of each housing tube look almost new, black, no rust, bolts holding them on have no rust. I see no indication on any GM markings or aftermarket brand on the caliper brackets. These look like they would need to have the axles removed to install the caliper brackets.

Since the housing cover looks like it has never been removed and the caliper brackets look new, I am confused as to whether or not the disc brakes on this rear are original on this housing or if the have been added (aftermarket).

Anyone know how I can identify these?

 

An 89 with rear discs should have 11.7" rotors along alum PBR calipers. You can see a pic in my vbGarage (next to my online status), if you wish.

Oh, a pic would be useful.

JamesC

 

Pics? If it is a 10-bolt, the rear end cover would have to be removed to pull the axles UNLESS a C-clip eliminator had been installed at some point in the past. But that would involve removing the cover, so if the axles were pulled for an aftermarket disc brake install. So if that happened at some point in its past, the bolts could have just gotten grime covered again, but that wouldn't really explain the clean brakes. Maybe the previous owner just cleaned up the brake setup real good? With a good pic, I bet somebody here can identify it as GM or aftermarket.

 

Thanks James!

Saw the pic's of your and will do a comparison this weekend.

 

so the 89 brakes have no backing plate?

 

Yes, there's a backing plate (seen in the following link, post #2 and elsewhere):

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

JamesC

 

James,

Here are 2 pictures of the discs on the rear I have. The calipers definitely look different than the ones in the first post you have a picture of, so I have to assume that the ones you have are GM? Therefore, mine are probably aftermarket?

Any idea who they are made by?

I did a quick rough measurement of the rotor and it is a just a bit under 12", so size seems to be the same.

As you can see from my pictures, the caliper brackets paint is much newer than the rear, so again this lends to the fact that these have been added to this rear post manufacture from GM.

Bruce

 

If you check further in the above link, you'll see that the alum PBR calipers/backing plates/rotors are the same. The set-up appears to be OE. The calipers with the vibration donut would be from a fourthgen (93-97, which are nearly identical to the 89-92 version). The backing plate and hardware appear newish, so suspecting that they're an addition to an older axle (88-) is realistic.

JamesC

 

Hi James,

Thanks for the reply, sorry for the delay in responding.

I think I have firgured out how to proceed with this. The rear in my '90 IROC is the 2.73 posi with drums, which has a small bearing noise, so needs to be addressed. The rear in the pictures is one I bought which is a 3.23 posi, discs, from an '89 IROC. I looked into swapping the rears but there is just so much more (i.e. ECM modifications for Torq Lockup, tranny synchronization, etc...), so I have decided to just get the rear rebuilt and when I do that, just swap out the drums for the disc setup here. Only thing I see is that the disc backing plates look like they will not bolt up to the drum brake rear.

Is there something I am missing here? Should these 4th gen disc backing plates bolt up to my '90 drum assembly?

 

Never heard of having to do any of the above.

The backing plates won't bolt up to the drum rear.

The easy fix is to purchase Ed Miller's kit:

http://www.flynbye.com/catalog/i30.html

JamesC

 

Or just swap out the speedo gear for the change in rear end ratios. Then the ECM will be looking at the correct speed for lock-up, etc. The trans will be fine with no mods to the small change in ratio.

 

James,

When you change out the rear to a different gear ratio, the ECM is setup so that it has settings in 4 specific tables so that the torq converter lockup (and when it releases) kicks in/out at a certain point, therefore when the change from 2.73 to 3.23, the ECM would lockup would be kicking in too early.

I had this issue with an '88 IROC TPI setup I put in my '87 el camino with an '87 Monte SS 200R4/3.73 gear setup. I used the original wiring harness, ECM and had to modify the chip so that the percentage of TPS changed thus the lockup points changed. I know the ECM in the '90 is different but the same basics still apply. In addition, the 700R4 is setup for 2.73 and shift points will be different as well as the speedo gear.

All of the above is just more than I want to change, don't need the 3.23 performance, just a Sunday driver car but would like the rear discs.

I looked that the Ed Miller kit. Looks interesting.

Thanks for the input.

Bruce

 

If you're just going with a Sunday driver, there's a good argument for keeping the lower rear end. Better mileage, lower cruise rpms and less noise at highway speeds.

2.73 to 3.23 is a really slight change compared to going to 3.73. Shift points, as commanded by the TV system (which doesn't care at all what speed you're actually going) wouldn't change much. The only difference would be the slightly different throttle openings that the TV cable sees. It's self-adjusting.

 

Most members who do a rear end swap change the drive and/or driven gears to make the speedo read correctly, and little else--though depending on rear brakes, there's always the combination valve and parking brake cables to consider.

JamesC

 

Just a quick FYI, My early 92 formula 305 5sp has the lil vibration dampners on the calipers (they are org to the car). I'm not 100% sure but I think they were added around 90-91?? (edit: I just checked a early 91 rearend and it doesnt have the dampeners, soo just 92 got them)
Somewhere in the early/middle of 89 they changed the backing plate from a thin 2 piece (gold cad an zink plated) to just a simple and thicker 1 piece that was gold cadium plated.
I have both types on my 2 89s and they are about 4,000 cars apart. The change had to do with the loud moan though the car during a reversing move with light pedal psi.. So I hear.. My 89 TTOP car has the 2 piece mount and the moan problem.

The hardware on the backing plate to axle in the pic above is not GM hardware.
you can put backing plates on a drum rear with the correct mods. drill 2 new holes, drill 2 others bigger and cut the top part of the mount off. I've done it 2 times.
The rearend in the pic is a 10bolt 4 sure. You can tell by where the axle flange is welded on. 10bolts are right in the edge of the tube /flange and 9bolts are about a inch away from the flat flange..

One other thing I forgot to add. the PBRs on 93-97 cars dont have cooling fins all the way across the top of them like the 3rdgen ones in the pic above.. Also the 4the gen rotors went to a thin steel hat and cast iron ring unlike the 3rdgens all cast iron rotor.

 

Interesting. I've never seen a thirdgen with the dampner, but, of course, I haven't seen all of them (and 92 could easily have been the transition year).

Since the OP's question was about a bolt-on, I didn't provide any info that required axle flange modification, though that is an option he might wish to explore.

JamesC

 

I also am wondering about the 89 10 bolt he has and what it really came out of??
I thought only 89 rear disc cars were 9bolts because they were the only rear put behind the 350 and 305 5speed (performance) cars??
rear disc weren't offered on 10bolts that year were they??
Or is it really a 90-92 rear?? I'm going to guess thats it??

 

No 10-bolts with discs in 89.

Because of the painted backing plates, new hardware, and PBR's with dampeners, I supposed that the system had been retrofitted, much as I did mine several years ago. Your guess is as good as mine.

JamesC

 

OK, getting back to this now that I have some time.

Been considering the 3.23 rear I have and not on the top of my list as an option. Too much to change out to get it setup correctly.

Guy locally on Craigslist has and '86 9 bolt posi dis brake rear with 2.77's?

He took the rear cover off and counter the teeh on the ring and pinion and that's what it comes out to.

He wants $350 for the rear and that be the easiest option here to fix my rear and get the dusc brakes.

Any opinions or comments? What's the difference between the 9 bolt and the 10 bolt I have in the car now.

Another option is to take the ring & pinion out of my rear and put it in the 10 bolt 3.23 disc brake rear. That would keep the ratio the same and get me the disc brakes.

 

OK, need some more input here! :-)

I took a chance and ordered rotors and pads for an '89 IROC. Had a feeling they would not be the same and they are not. The rotors are ~10.5" and the pads are definitely not the same.

Guess I should order rotors and pads for a '93 rear disc?

Bruce

 

sounds like they gave you the rotors and pads for the older, iron caliper setup. They should have got it correct when you specified IROC, unless you just specified 89 camaro. Possibly they entered 88 IROC, which still had iron calipers?

$350 for that rear seems steep, and you'll be getting the 10.5" rotor/ iron caliper setup, which is far less desirable than the aluminum pbr calipers. PBR calipers are the ones you posted in your pics. bigger rotors, better calipers. This rear (craigslist rear) has the rotors/pads they just sent you.

The 9 bolt is stronger than the ten bolt, but parts are more scarce. I'd stick with the 9 bolt, though if its a weekend crusier either will work just fine. Also, the gears won't swap over from the 9 bolt to the 10 bolt, different sizes all together.

 

The store should have ordered 1LE and/or performance package parts. Apparently, they ordered standard rear disc parts.

JamesC

 

FYI: I have a 92 PBR. It has the rubber dampeners.

Although, I didn't know what they were until I read this thread.

Thanks! lol

 

Put the rear in, bolted up just fine. Still waiting for the delivery of the correct rotors. The spec's on the '89 rotors are 11.64" diameter with .79" thickness.

The rear is an '89 and has the PBR calipers. I got it with good emergency brake cables but they seem to be short for the mounts. Not the length to go into the cable bracket that pulls them, but the outer cable.

Any ideas or comments?

Bruce

 

I'm uncertain what the "outer cable" is.

There are two different lengths, 89-92: the first design is 1434 mm, the second 1460 mm. Both available at RockAuto. Also, Ed Miller fabs a custom cable for your specific application:

http://www.flynbye.com/catalog/i199.html

JamesC

 

What I meant about the "outer cable" is the outer sheathing. There is the actual cable inside the outer sheathing, this is what is short on the cables that came with the rear.

I checjed Rock Auto and they list Bendix and Dorman, both look to be interchangeable with one another. No spec's on the length.

Any idea on part numbers for the 1460 mm length ones?

 

I entered 91 Camaro on a couple of auto parts store websites, such as Autozone, and the latter's part number for 1460 is C1647.

Interested, I used a conversion chart to find that 1434 mm is 56.5" and 1460 mm is 57.5".

JamesC

 

James, Thanks! :-)

Now I need to ask you for some additional guidance here.

Got the correct rotors earlier today so rear is in and works fine. Last thing to work out is the Parking Brake Cables.

I measured the ones that are on the '89 disc brake rear and they came out to just a little over 56", so I have to assume here that I have the shorter of the 2 options. Issues that I have trying to get them in place:

1. If I run the cables through the original guides that bolt to the rear cover, they are too short.
2. If I run the cables directly under the rear they will reach the mounting bracket but then the cable is too long.

See the attached pictures I took (could only attach 2 pics to this post, so see other posts for more pics). You can see that I did not push the cable fully into the holdong bracket and the cable is about 2" too long, with the amount if I did push the cable into the bracket, it would be about 2.5" too long (both sides).

Seems like the mounting bracket on the inside of the driveshaft tunnel is for the drum brakes, not the disc brake emergency cables.

Was there any difference in the mounting bracket for drum brakes versus disc brake emergency cables? What about any difference between an '89 rear and my '90 car?

Need your guidance and expertise here! :-)

HELP!

 

Here are 6 pictures I took of both sides of the emergency brake cables:

http://s308.photobucket.com/albums/k...e/1990%20IROC/

 

The guides on the differential cover are not necessary.
And while you point it out, I even doubt the stock e-brake cables are even long anough to be used with those guides.

 

There were no cable guides on thirdgen cars. The cables route over the axle. Perhaps removing the guides would resolve the issue.

As I understand it, the shorter cable (1434) was designed for cars with the tunnel-mounted adjuster (seen below), 89 down. The longer cable (1460) was designed for cars without an adjustment mechanism, 90 up (though I've read that some members still have the piece).

https://www.thirdgen.org/forums/atta...e-adjuster.jpg

There's no difference in the adjuster/mounting piece between drum and disc cars.

Ed Miller makes a custom cable for your application as I mention above.

JamesC

 

I use the fourthgen guides with the 1434 cable. Works fine, but they're unnecessary. Next time I change fluid, I'll probably dump them.

https://www.thirdgen.org/forums/atta...-89-guides.jpg

JamesC

 

Must be a tight fit then, thanks for sharing

 

Yep.

JamesC