86TpiTransAm

I have a suspicion that my proportioning valve has gone out, if that's possible. Where exactly is it located and how hard/easy is it to change??

poncho9789

It is easy to change, the hardest thing to do is to blead the brakes.

The proportioning valve is right under the master cylinder follow the lines from the master cylinder and it leads directly to the proportioning valve.

86TpiTransAm

Cool thanks, I hope that's what the problem is. My back brakes are only working at about 5% of what they should right now. It's either the propotioning valve or they need to be adjusted and I don't know how to do that yet. As far as the bleeding goes, that won't be a problem, I plan on buying some speed bleeders to help with that.

TomP

Dude, ever work on your rear calipers before? No? Did you know about the recall on them? No? Search on this board for info about "rear disc recall", and read this message of mine: https://www.thirdgen.org/techbb2/sho...threadid=78725

PF Flyer

I've got one of the 'kits' that TomP talks about, if you need it.

Drop me an email if interested.

86TpiTransAm

You go here to the National Highway Traffic Safety Administration website and look for a recall on the disc brakes for an '86 TA ... IF you find it let me know because I sure at hell don't see it. Maybe GM themselves recalled them because they weren't happy with them but it's not a big safety issue or else it would be on the NHTSA website. I could care less anyhow. My back brakes barely work and they've been like this for 2 years. My car stops on a dime just fine. Brakes and wheels are a waste of money IMO. The money could be put to better use for something that's actually going to make the car go faster. Again, just one man's opinion.

http://www.nhtsa.dot.gov/cars/proble...call_links.cfm

TomP

Sure. Here's your number. 91V055000 .

The adjusters are why there's no parking brake; the worn pads dont' stay against the rotor. If you want to "waste money for brakes" and replace your prop valve, then at least "waste money for brakes" on the right piece. You yourself said your back brakes barely work.

The recall was for ALL 82-88 Rear Disc Brake (J65) equipped f-bodies with manual transmissions. These are the cars that GM fixed for free. 82-88 Rear Disc (J65) equipped f-bodies with automatic transmissions weren't covered under the recall, but the same problem applies, so GM issued a TSB (technical service bulletin). The TSB tells a mechanic how to fix the 82-88 rear discs, and also gives part #'s that total upwards of $200. The recall package is cheaper, and that's what GM doesn't want us to know. You can also look your car up at http://www.alldata.com/recalls/index.html ! Good luck with it, let us know how it goes.

And sorry if you "interpreted" my first message to you as being "snotty", it wasn't intended to sound like that. I was trying to help, but hey, whatever.

86TpiTransAm

Well it did indeed sound like a rude post but I apologize. Things are are often misconstrued on the internet.

I guess it just made me mad because I knew someone would post something about the recall on the brakes. I am aware of the problem and I too agree that it's probably the adjusters that are bad. However, the NHTSA website says that the parking brake adjust can quit working when the pads get worn. My pads aren't worn and actually look very new so that's where part of my confusion comes from. I really haven't been all that worried about my back brakes to be honest. I've had this problem for 2 years and I haven't felt the need to do anything about it so far. I've just been thinking about switching to an adjustable proportioning valve and was curious as to where it's located, that's all.

Don't get me wrong though, I appreciate your effort to help me out. It's more than certain others on this board will do.

TomP

Next time I'll throw a boatload of those damn smiley faces all over the place! I was going "No? No?" since I was hoping that you didn't touch the rear calipers yet, and that they're the problem, not the prop valve.

I swapped an '84 rear onto my car, with discs. I put new pads on, and rebuilt both calipers. Er, okay, I rebuilt one with new seals. The other was too rusted on the inside, and I traded it in for a shiny new Pep Boys one. The Pep Boys one never wore the pads down! The "original" caliper wore them down a bit, but at an angle. The one I rebuilt (which came with the axle) did. I bled the brakes numerous times; nothing. I found it interesting that a freshly rebuilt (and $65) rear caliper didn't have the updated pistons in it! I kept the original pistons, in case I ever have to bring a caliper back for a new one, I'll put the old suckers in; I'm not giving Pep Boys my recall parts!

Check to see if your rear pads are touching the rotor. They should almost be riding on top of the rotor, with no visible gap in between. This recall stuff deals with the adjuster. Forgive me if ya know all this stuff, but when you pull the parking brake handle, the cables pull on levers at the calipers. These levers are connected to an actuator screw, which goes inside the piston. The center of the piston is threaded to take this screw. When you pull on the lever, the screw turns, and "screws" the piston outward, which pushes the pads against the rotor. When you release the e-brake handle, everything snaps back to normal; and the pads retract a bit.

Normal brake operation- the fluid flows into the rear caliper, and pushes the piston out. The actuator screw, connected to the parking brake lever, does not move. Thus, to make the pad extend, the piston "freewheels" (actually ratchets one way) on that center screw, and this lets the piston move outward (to touch the pads against the rotor) while the actuator screw stays in place. When the pedal's released, fluid leaves the caliper, and the piston retracts just a bit- pulled backward by the brake fluid.

The recall involves actuators (pistons) whose ratchet mechanism is frozen. So instead of the piston extending independantly of the actuator screw, it rides the actuator screw the whole time. (Yeah, baby!) So when you release that brake pedal, the piston doesn't stay there- it "unscrews" along the actuator screw, and leaves a gap between your pad and the rotor.

At least, that's the usual problem. If you pull the rear wheels and look thru that brake-pad inspection hole on the top of the caliper, see if the rear pads are touching the rotor. If they're backed off, they're bad.

Supposedly you can pop the pistons free. This involves a big screwdriver! You unhook the e-brake cable from the parking brake lever at the caliper. Then, you bring the parking brake lever (at the caliper) to it's rest position... the return spring should help. You would then insert a large screwdriver thru the pad inspection hole, and wedge it against the tip of the piston. There's a groove in that piston that the inner pad's pad-to-piston clip sits on, put the screwdriver in that. Now, pry the piston (and pad) towards the rotor, as you work the caliper's parking brake lever back and forth. That's the "grunt" way of popping the pistons free... but eventually, they could lock up again. The theory is that GM used a spring inside the piston with the wrong coefficient of .. er.. i forget... "K"? Damn physics. Anyway the spring wasn't strong enough (or weak enough) to do what they wanted it to do.

I leaned like hell on the screwdriver with both calipers, and they didn't pop free. The recall kit was the solution for me. And man, it was great to have back brakes again! I actually had to double-pump the brakes to get those rears to kick in. I assume it was because my pads were retracted from the rotor. I figure that my initial pump was extending the pads halfway to the rotor. By doing a quick release and a quick 2nd pump, the pads never got a chance to retract, so they were near the rotor, and that 2nd pump got me some brakes.

Good thing I fixed 'em when I did, too. The guy I go to for inspection for the past 5 years hasn't ever driven my car down the road. This year, he did! Whew.

Also, if your prop valve was bad or stuck, you'd be seeing a "BRAKE" warning light on the dash (same light as for pulling up your parking brake). That light tells you when you have unequal pressure between the rear line and the front line. In fact, I've heard it said that the J65 (82-88) cars' prop valves don't do any proportioning, that each wheel gets 25% of the master cylinder's output- but I don't know if that's true or not. Supposedly there's only "proportioning" on a disc/drum car.

Try a double-pump on the brake pedal to see if your car's braking improves. Also, check to see if the rear pads are touching the rotor, or hovering away from it about a 1/2" or so. Let us know what you find!

86TpiTransAm

Thanks. I'll take a look this weekend. I know my brakes work somewhat because when I had the back brakes on jack stands this last summer I was inside adjusting my B&M shifter and I decided to play with the brakes. When I pushed the brake just one time th wheels stopped. When I pulled the Ebrake the wheels stopped. But when you put the weight of the car and forward momentum on the wheels, the brakes don't do squat for stopping. I found this out when I had my muffler hung. The shop that did it had a lift where the front two wheels sit on sliding mechanisms... so they would stay still while the back wheels drove the car onto the lift. When the guy did this he said that my back brakes just BARELY work and almost didn't stop the car in time.

george 88gta

iTrader: (1)

TomP, I had the same problem with NAPA calipers, they also did not have the recall pistons. I installed the recall kit and saved the old pistons as well. One thing I am noticing, when I apply the brake, the caliper seems to rotate slightly. I would have thought that it would be a straight line compression of the pads to the rotor. My pads were worn unevenly. Could this be a defective backing plate? The rebuilt calipers came with all new hardware, so I doubt that the bolts and sleeves are the cause.

86TpiTransAm

Well, I think I found a solution to my brake and rear end problem all in one. A friend of mine has an '89 Iroc and he just bought a rear end out of a corvette that he's going to modify and put in his Iroc. When he does the swap, he's going to sell me his 3.23 10 Bolt disc rear end and since the corvette rear has dual piston calipers, he's going to sell me the entire brake setup from his 10 bolt with it. He said his '89 brakes and ebrake works just fine.

Another interesting thing I found out... if you look at older disc brake systems like my '86, the back calipers are opposite. Drivers side caliper is located at the rear of the rotor and passenger side caliper is located at the front of the rotor. On newer disc brake setups like the one from my friend's '89 Iroc, the calipers are located in the same location on both sides.... both at the front of the rotor I believe. Anybody know why GM did this??

poncho9789

I came accross a thing on gtasourcepage.com awhile back that said to remove valve for the rear section of the proportioning valve. We tried it on a friend of mines car (scott88gta on this board) and he noticed a great improvement in braking and performance in his breaking system with no ill effects. Here is the link try it out and read it and I think you will be satisfied. He was doubt full but very pleased after we finished and it only took us about 30min.

http://discussions.gmforums.com/show...?threadid=7614

TomP

I never noticed if my calipers rotated or not. (I was going to suggest the bolts, slides, & bushings, too- but you got new stuff). Could the slides have twisted up in the caliper? Which way does the caliper rotate, sideways? I'd say I'd go check my car, but I blew up my posi in that axle, and I'm running on a $100 junkyard 3.42/open/drum axle for now. How'd you notice they were rotating?

george 88gta

iTrader: (1)

TomP, the right caliper rotates to the outside. The pads wear as follows: the outboard pad is worn at the edge that is close to the rotor hub and the inboard pad is worn at the edge that is close to the outer edge of the rotor. I noticed this as we were bleeding the brakes. Disassembled the caliper and pads and could not find anything unusual. Still rotated after assembly. Next thing I plan to try is to really go over the backing plate for damage,etc.

george 88gta

iTrader: (1)

TomP, rotating caliper mystery solved.As you know, the rear calipers are the same casting and are interchangeable. The calipers I purchased from NAPA, were the loaded variety, all new hardware and pads. They were packaged as a left and a right, this is due to the wear indicator on the pads. However, Raybestos ( who does the remanufacture), uses different size caliper bolts. The left side bolts are approximately 3/8" in diameter while the right side bolts are turned down to approximately 1/4" at the outside end. To make these reduced diameter bolts fit the casting, they use an oversized rubber grommet on the right side caliper. We called Raybestos, and they verified that the castings are the same, and they did not have an immediate answer as to why the right side caliper was fitted with the large rubber grommet and the turned down bolts. They checked stock, and all of the parts are configured this way. The local NAPA dealer warrantied the right caliper (it only had 2300 miles on it) and gave me a new left caliper for the right side. I added new pads so that the wear indicator would be in the right position and installed the caliper on the right side. No more caliper rotation when the brakes are applied. Car is not on the road so I cant seat the pads yet, but there is a noticeable difference in braking ( tried it out in the driveway).