Im going to need to do this and I've been doing searches and I've decided that if I want to get these rear discs in there right, I need to put the right proportioning valve in it. I've got a valve from the same 89 GTA that my rear is from... So it's a matter of installing it. Hopefully it's not from the dreaded "Early 89".... (Since mine is a 92...)

My question is, what all is involved. Is it a huge PITA to get the new air in the lines to bleed down after that? Will I need to "bench bleed" the master cylinder to do this, or will it be okay?

There will at least be air in the prop valve, so is this a good case for letting it "Gravity bleed"? Im not exactly sure what all is involved with that, but it seems like it just means to loosen all the bleeder screws on all 4 wheels and pop the cap off the resevoir and keep it full... am I right? I've never bled anything that far through it, no idea how long it takes or how hard that is to do.

 

It's not as bad as swapping the master. Just make sure you don't completely drain the master in the process. Looking at the prop year and the year of your car I don't think it will bolt in, just don't force it to go. Should you need another prop valve let me know, I have many of the correct disc props in the shop.

Good luck.

Ed

 

What is the difference between disc brake porportioning valve from year to year?

89-92 used PBR aluminum calipers and I've removed a couple of Disc brake rear ends from 89-92 with PBR calipers and I saw no differences between the PV. I believe the PV would be different on the 88 and older steel calipers compared to the PBR PV.

 

When you buy a new MC it is completely dry when you get it, so why would it matter if a used MC was drained?

Just like installing new calipers you have to bleed them when you install them.

Why wouldn't you install a dry MC fill it with brake fluid and bleed the system?

Maybe I miss understood what you said about letting it go dry. Did you mean while you are bleeding the system?

 

What is the dreaded early 89 B&W 9 bolt PBR disc rear end?

 

I don't see why a MC would be any harder to change than a PV.
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It would be harder if you were to change the booster and MC at the same time.

 

Thread sizes of the inlet and outlet fittings, piston and plunger bores and spring rates. I'm looking into them ver hard right now since the disc props have been discontinued. I have 4 each of the early and late props in my shop.

Ed
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Exactly...the master is completely dry when new and you need to bench bleed it before you install it in the car to ensure you get all the air out of it. If not bleeding will be a hassle and take longer as the end toward the front of the car is pointing upward and it would be extremely difficult to get that trapped air out of it, so don't let it empty out on you.

Ed
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Refers to the different line threads on the prop in this changeover year, you can't tell which one you have until you get it apart.

Ed

 

I've read more than once on these forums that for 91/92 the prop valve for the disk/drum cars was exactly the same as the prop valve for the disk/disk cars.

I therefore didn't change my prop valve when I swapped from drums to 98-02 PBRs, and everything seems to be fine. They are generating dust and I've had more than a few panic stops that haven't resulted in the rears locking up early.

Anybody care to comment on this? I don't know 100%, just sharing what I've heard and my experiences.

 

Master cylinders are the same for '90-92 rear disc and drum cars, props are different. I posted the list on here somewhere. I'll look for it. I'm not saying they won't work if you keep the valve, it's just what the manuals call for. Baer says you either need to modify your stock prop valve, install the correct disc one, or install an adjustable valve.

Ed

 

I sold this rear end to InfernalVortex which included the brake booster, MC, PV and the 2 rigid lines from the MC to the PV all from the same 89 GTA. The 3 brake lines exiting the PV could be different but, I seriously doubt that the threads and size of the exiting lines would be different.

How many times have we all found the manuals, instruction guides and parts catalogs to be wrong?

99.9% of these cars are running with the original brake fluid so even if you do a swap and get air in the system you should do a complete flush of the system and get new brake fluid in it.

 

I have 2 PV's from 91 PBR disc rear end and I still have all the brake lines from the 89 GTA. I will check to see if the exit lines will mate up with the 91 PVs.

 

I checked the 91 Disc PV, and the exit lines from the 89 GTA screw right in. I will post the #s stamped on the 91 PVs I have.

 

Ed,

If you change from drums to discs on the rear 1989 RS and leave the prop valve intact, will rear discs be ineffective (no or poor braking) or will the rear lock up before the front? I would guess poor braking based on other posts in this forum.

How do you modify the prop valve?

 

I'm also wondering this...

 

Well I am about to put a 87 PV in my 89 and it looks the same to me. I did go ahead and bleed the rear with the old PV to see it it would work. I dont think the drum PV puts out as much presure as the disk does. At least that was what it looked like to me.

Oh, also changing out the booster is not all that hard. Done it got the T-shirt. Just have to bleed the lines as they come from the master into a rag with the lines on then do the rest all on the auto. Get the air past the PV then start at the farthest wheel and work back. Simple as a homemade pie, I should no I can do both.