Keith27

I have a 91 Formula with rear drum and an open rear-end, Im going to switch the whole rear-end out of my 88 GTA with rear dics posi.

What all parts do I need to take off the the car and will it all bolt right up? (cables,brake hose)

I checked the parts catologs today and 88 and 91 have different brakes in the rear (pads, calipers,master cylinder).

Any help would be thankful

Peace

ANDYZ28

You might be better off to leave the '88 rear in the '88. Then get a posi drum rear in the ratio you desire, and convert it to the '90-'92 (PBR) rear disc brakes. They are much better than the pre '89 type rear disc brakes.

Thanx,ANDYZ28

Keith27

It does have the High Performance option RDB ( aluminum calipers) not sure if that is better but it is different in the parts catalog and alot more expensive $$$$.

Later

ANDYZ28

An '88 should have Delco-Moraine cast iron calipers. Do you have a picture of the rear brakes? Or should I post one of a late model ('90-'92) rear disc brake setup for you to compare it to?

Thanx,ANDYZ28

Keith27

There're aluminum with the fins on them, the parts catolog shows an option in 88 for aluminum calipers.
If you can post a pic on the 90-92 that would help.... thanks

Peace

LT1guy

iTrader: (1)

Will that work? I know the older (up to 87 at least) drum brake rears have a different housing end than a disc brake car.

ANDYZ28

Here is an image of the popular '90-'92 rear disc brake setup. The calipers are very distinctive.

Thanx,ANDYZ28

LT1guy

iTrader: (1)

Can you give us some info on your conversion kit? Price, whats included, etc.

ANDYZ28

Here is what is included in the drum to disc rear axle conversion kit;

1) New PBR loaded calipers.
2) New rotors.
3) New stainless steel prebent hardlines.
4) New "Earls" stainless steel flex lines.
5) New parking brake cables for your application.
6) New axle seals (you might as well replace them while you are in there) so I include them too
7) Special axle housing adapters to duplicate the original disc brake housings.
8) Shim templates to precisely locate the new mounting holes in the axle housing flange. They are also used to adjust the backing plate out from the axle housing. These have been discontinued by GM for a long time, so I have developed my own improved design.
9) New brake line/hose mounting brakets. These are also unavailable from GM.
10) New drill bits to modify the axle flange to the disc brake type.
11) Parking brake cable guides to keep the parking brake cables from rubbing against the axle housing.
12) Posi gear oil.
13) Tube of silicone to reseal the rear cover.
14) All of the various clips, bolts, and other fasteners to complete the job.
15) And best of all, I even include the correct GM combination (proporioning) valve for your application.
16) I also include the "ANDYZ28 1LE Plus CD ROM" Free!

All for $731.00 plus shipping.

Thanx,ANDYZ28

Keith27

Andy, those are the calipers I have. My wagner catolag at work list those calipers on the 88's also, its listed as an high performace option.

So I shouldnt have any problems doing the swap??
Thanks for the pic..

Peace

BretD 88GTA

As far as I know, the only '88 models that got those rear brakes were the few 1LE equipped Firebirds. I'm curious to know, what are your front brakes like on your GTA?

iroc22

In parts catalogues, the "High Performance Option" means 1LE.

Crisis

I did the same conversion.. The easyest way of doing it is leaving all the brake hoses on the rear and opening the joint thats in the front end of the well on the drivers side. eazy to find. the just swap the new rear in. take the brake balancer from the parted car if possible. if not you'll have to mod your old one. otherwise you won't have enough brake force at the rear of the car. drum braked cars use a 70/30 brake balace whilst the 4 disc cars use a 50/50 balance. the brake master cylindar is also 0.05" bigger on a disc car but i didn't get any problems with that. only the brake balace.

Crisis

and yes it will bolt up. take the brake master cylindar and brake balancer if you can. don't take anything off the rear(brakes). just open to joint to the car and you'll be fine. at least i was.

John Millican

iTrader: (1)

Can I get the "special housing adapters" by themselfs?

Spdfrk1990

If ur 88 has the rear pbr's i would just drop it in all you should need is the p valve.Im going to convert my pre 89 rear disc to the pbr's im waiting on my parts from andy . If ne1 knows where i can get a new rear cover for a 9bolt that would help and the rubber plug.

samdog1232000

My dad is a Heavyline Mechanic for GM and I asked him about doing this to my car. He told me I was better off finding a rear end off a 91 or 92 and bolting it up to my car. He said I would save alot of time and it is much easier to do! Plus you will have a posi!!!!!!!!! I have not started looking for one but I was planning to hit some junk yards. Finding a junked 91 or 92 Z is not easy. Does anyone know were I could find one in California!

Z28guy83

anyone have any idea where i can get the e brake spring bracket for the rear caliper i have the counter weight and spring i just need the bracket that mounts to the caliper any info would be appreciated

DaGoat

Anyone know where I could locate a proportioning valve for this swap?

Any model years that they came on from the factory or would I be better off hitting the junkyard?

jmnjn

So if i have an 86 Iroc with 3.23 gears and drums, can i swap my drum to disk? Or do i have to go out and buy a rearend that originally had disks on it. I wanted to just remove the drums and bolt up the disk. My intentions are to remove the carrier and put a SLP posi and change out the axles with 28 spline and bolt up the disk brake harware and call it done. Will that be possible or is there more to it than that?

BretD 88GTA

Yes, you just need to get the disc brake backing plates along with the calipers, carriers and correct prop. valve. The 10 bolt disc backing plates are still available thru GM I believe. You could also pick them up at a wrecking yard. From 90-92 all f-bodies with rear disc brakes used the 1LE set-up and 10 bolt rearends.

It us 9 bolt owners that are slightly challenged in doing this upgrade. The 9 bolt 1LE backing plates are long gone. The only option for us is Baer or custom work. Based on that, I'm considering going with the LS1 rear disc upgrade.

Zepher

iTrader: (1)

I just put a new complete LS1 rear on my 86 Trans Am so now I have a complete LT1 rear with disc brakes sitting around. I want to put those brakes on my 88 Formula and get rid of the drums.
I can't put that rear on the car since the 4.10's are shattered.

Will this be a plug and play conversion. I don't want to have the car down too long since it is my daily driver.

DJP87Z28

Picture of stock 1989 9-bolt rear with PBR caliper & 11.655 rotors.

DJP87Z28

88 350 tpi formula

iTrader: (9)

the 88 firebirds did too have pbrs I have said this on so many posts it is sick that no one listens! the ones on my car are from an 88 gta. it was not a 1le and it cam that way new. some 88s even that car had the vats key system if people would look these things up instead of just guessing there would be alot less missinformation on these boards

Spdfrk1990

yeh i would want the pbrs zepher the ta rear wouldnt be right for the 88 they use a different master cylinder and i dont like them neway that what i did on my rs and im goin to the pbr's now its a pain. All you would have to change is ur prop valve to a 88 with the 4-wheel disc.

samdog1232000

A buddy of mine wants to sell me a 89 Rear end with posi and the brake setup that is on a 91 and 92 Z! This rear end was of a Formula and I want to put it in my 92 RS which does not have posi and has drums on it! WHAT WILL I NEED AND WHAT WILL I NEED TO DO? I got the jist of it by reading threw the thread but I want to make sure it will work on my application............

My dad will help me do it but he is not sure what the exact differences are between the 2 setups..................

AaronIROCZ

iTrader: (5)

A friend of mine did to have a 88 GTA with the performance disc brake option and it WAS NOT a 1LE. It was the aluminim PBR calipers. It too had the vats. FYI

samdog1232000

What does VATS have to do with the rear end?