NinjaNife

I just bought a 1987 Trans Am GTA, and am having a few issues with the rear disc brakes not clamping (the front brakes work decently well; they hold the car in place (or lock and slide if not on pavement) if you give it gas, while the rear wheels just spin). I initially thought that the calipers were frozen/stuck, and since it is a used car, I decided to replace all of the calipers.

However, after replacing the calipers and bleeding them, the rear brakes still will not clamp. If I pump the pedal I get good pressure on the pedal, but the rear brakes quickly loosen after their initial squeeze. I tested it by pressing the pedal while a friend pulled out on the caliper, and he was able to move it away quickly after it clamped. When the engine is on and it is in gear, the rear tires (if the rear is jacked up) will spin, and applying the brakes only slows them for a second before they speed back up to the idle spinning speed.

I'm fairly new to older cars, and while I'm getting a lot of help from some people with a lot of experience with other cars, I thought I would post here and see if anyone had any ideas for this car specifically (I have read here/elsewhere that the '87 TA had a lot of rear brake issues). I haven't found any leaks, but it could be that I just missed something since there was some fluid residue from bleeding the brakes.

Any ideas/thoughts would be greatly appreciated. Thanks for the help.

Brendan "NinjaNife" West

Base91

iTrader: (1)

If there is no fluid leaking out of the system (level in reservoir not dropping) then it sounds like it's leaking back past the pistons in the master or slave cylinders. Probably one or both need rebuild/replacement.

NinjaNife

Thanks for your response. I am slightly confused though..does this car have a slave cylinder? I thought it only has a master cylinder and a booster; I haven't seen a slave anywhere (unless I misunderstood what you meant)

The master cylinder is what my friends and I had thought, but I wasn't sure if there might be something else going on since these cars apparently have so many rear brake problems.

Brendan "NinjaNife" West

mauijerky

"slave cylinder" is a term used for the hydraulic part in drum brakes. Technically a brake caliper is a "slave cylinder" but no one will ever call it that. You have 4 wheel disk, so don't worry about the "slave" thing.

I am some what new to the 3rd gen scene myself, but I also had damn near non-working rear brakes when I first got my car. Mine is a 91 but it has the '87 older rear calipers. Took me a while to figure that one out. First off, do your rear brakes grab the discs when you apply the parking brake? The pistons in the rear calipers have to be adjusted by using the parking brake a few times. I wrenched my parking brake lever a few times then I finally had some functional rear brakes. Although, the parking brake/adjustment mechanism that GM put in these calipers is a flawed design. GM recalled them on some models. Since you installed new calipers, then you might be OK. But, there is a kit you can buy that's "supposed" to fix the flaw.

Now if the rear calipers are properly adjusted and your e-brake works but still having the same problems, then you should look into a new Master. Also, a stiffer spring in the combo/prop valve will send more fluid to the rear calipers, thus helping them grab better.

NinjaNife

Oh alright, that's what I thought but I wasn't sure. Thanks for clearing that up.

Unfortunately the parking brake is also broken..it wasn't working when I got it, and I decided to put off fixing it until I worked on a few other things on the car, since I didn't feel a great need for it since it is an automatic and I wouldn't use the parking brake much (especially not in the next few months during winter).

I have read that the parking brake is used to adjust the calipers, but I thought that was just to tighten up the calipers and wasn't required to actually use the brakes. The strange thing is that it does still clamp, it just quickly looses the pressure. That's one reason I'm not sure adjusting the calipers using the parking brake will help (of course I will adjust them once my parking brake is fixed), although I'm definitely willing to listen if you have a different opinion. Do I need to fix my parking brake before trying to work on the brakes any more?

Thanks for the help.

Brendan "NinjaNife" West

mauijerky

I just wanted you to make sure the calipers are adjusted properly before buying more parts. (I went through my whole brake system before realizing that was my prob) You can actuate the the parking brake levers manually on each caliper if need be. Just ratchet the lever until the piston is applying light pressure to the discs. You should be able to hear the pads rubbing against the discs when rotating them. If the caliper pistons are where they are supposed to be but still losing pressure, then you might need a new master. Or just put in a new master to eliminate the possibility. Up to you...

NinjaNife

Thanks for the tip. I think I'm still going to replace the master cylinder (and probably the booster) just to be on the safe side; brakes are one thing that I want to be sure are 100% working. I'll definitely try to adjust the calipers by ratcheting the lever as well; that way I'll know that everything is functioning properly. Once I'm done, I think the only thing that will be original are the brake lines lol. They'll be replaced in due time as well I'm sure xD

Brendan "NinjaNife" West

NinjaNife

Well, after a long weekend of work, I have ended up with the same result..the rear brakes barely clamp, and won't stop the rear wheels if the car is idling in Drive when the rear end is lifted. On Friday I re-bled the brakes, and it seemed to clamp decently after that, but after replacing the booster and the master cylinder it went back to the previous state :/ The only thing that I haven't replaced is the proportioning valve, so I guess I'll try replacing that soon and see if that works.

Thanks for all of the help.

Brendan "NinjaNife" West

naf

iTrader: (7)

The Saginaw rear discs require the recall kit in order to operate effectively. There's no guarantee that store bought calipers will include the design changes that the kit adds. After rebuilding the calipers with the kit (which includes new pistons, etc. , the parking brake MUST be used consistently in order for the calipers to maintain adjustment.

The recall kit used to be available from GM Parts Direct. Part Number: 18019028 from GM Parts Direct, listed as "Actuator". That was in 2005 though.

NinjaNife

Ah..well that is disappointing to hear lol. I had hoped that the rebuilt ones always included the recall kit repairs

At any rate, when you say that the parking brake must be used consistently, does that mean with the original calipers or the ones fixed with the recall kit?

Thanks for the help.

Brendan "NinjaNife" West

naf

iTrader: (7)

The rear discs, whether original or with the kit, require the application of the parking brake to adjust them to the rotor as the brake pads wear. Best to get into the habit of cranking it up EVERY time you park it.

NinjaNife

Ah..so what exactly does the kit fix? Does it lessen the need for constant adjustment, or something else?

My parking brake is currently out of service (one or two lines are broken), but I'm planning on replacing it soon. I have all of the cables, I'm just waiting in the hopes that I can get it up on a lift instead of trying to crawl around under the car lol. I'll just try to bump up the priority on my list of things to do I'm also planning on doing the proportioning valve spring swap that I've read about, rather than just going and purchasing a new valve right away (which I will do eventually, but for now it saves me some $$).

Thanks for your help!

Brendan "NinjaNife" West

camaromike222

Before you go out and spend more money, do this. Take the brake light fitting off the prop valve, not just the connector. You should hear a slight pop or click or at least feel it. You essentially just released the plunger. Screw it back in. Now, bleed the brakes completely using vacuum and DO NOT BLEED WITH THE BRAKE PEDAL. It needs to be vacuum. Sometimes the piston or plunger gets stuck and by doing this you release it.

Did my LS1 rear brake swap and had no rear pressure at all. Just front. Replaced everything to fix it and the same problem lurked. Finally tried this after a friend suggested it and BOOM.

NinjaNife

How do I vacuum bleed the brakes? I've read about "power bleeders", but I don't own one (and they are somewhat expensive from what I have seen online)..is that what you mean by vacuum bleeding, or is there something else I'm not aware of?

Thanks for the help.

Brendan "NinjaNife" West

*EDIT*
Forgot to ask; when you say brake light fitting, do you mean the one that connects to the dash brake warning light? Or is there one connecting to the actual brake lights in the rear of the car? Sorry, you kinda confused me there lol xD

camaromike222

Yes, that very fitting. The one that connects to your dash. It has a hex type head on it below the connector.

You can buy a vacuum gun or rent it out from a parts store. They shouldn't be very expensive. I got one from Harbor Freight for like $15 for the kit. Came with hoses and couplers and what not. Bleeding with the pedal will just re-jam that little plunger in the valve.

camaromike222

But of course, you need to unscrew it from the prop valve and not the dash lol.

NinjaNife

Haha yeah I figured that lol.

Thanks for the suggestions! I'll give them a try this weekend if I can get my hands on a vacuum bleeder

Brendan "NinjaNife" West

camaromike222

no worries. Do keep us posted

NinjaNife

Well, after a LOT of pulling and yanking, I finally got the front parking brake cable through the rubber grommet/hole over the weekend..I have to admit, getting it through the hole took about the same amount of time as swapping all of the other cables installed. I'm not even going to say how long it took me to get the old cable off and the new one on...it's embarrassing lol . I also installed a stiffer spring in the proportioning valve, which should give more pressure to the rear calipers (following one of the other threads on these forums).

I haven't been able to road test the brakes yet due to the snow, but they appear to stop the tires with little difficulty when the rear is in the air and the wheels are spinning (which didn't work before).

One thing that I am wondering though; when the car is turned on, the parking brake seems to be easier to pull than when it is off..could this just be a weird thing that I am imagining, or is there a mechanical explanation for it? All I know is that when I first installed the cables, the handle was quite stiff (only pulling up like 1/2 of the way, since I set it to start engaging on the second click), but after I turned on the car and pumped the brakes a few times the handle was able to be pulled up nearly all the way. Do I need to readjust the cable after using the brakes for a while?

Thanks for all of the help!

Brendan "NinjaNife" West