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Old 03-28-2004, 07:24 PM
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87 iroc rear disc brakes dont work

mt brother recently installed rear disc brakes in his 87 iroc 305 4 speed auto .He used new disc brake master proportioning valve new rotors calipers raybestos pads new cables all other components were in perfect shape from another 87 iroc the brakes barely work with car on stands at fast idle the wheels turn with brakes applied the system was bled numerous times quit certain theres no air in lines any advice would be greatly appreciated thanks a lot Sam

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Old 03-30-2004, 04:49 AM
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I am not sure if your problem is a result of the installation or a factory defect on Third Generation rear disc, but here is the factory fix for the design;

A technical service bulletin described this for early-mid '80s rear disk brakes. It seems that the rear disks in these cars would be adjusted by applying the emergency brake. When you pull the emergency brake lever up, the lever turns this little device called an actuator screw. This little screw type device is also on a ratchet, so that pulling the e-brake up, turns the screw. But letting go allows the ratchet part to function and set the pads at that time. So, using the emergency brake is mandatory for maintaining the rear disk setting on early model rear disk units.

But, here's the problem with them. There's a little spring on the actuator screw assembly that allows the pads to back-off from the disk a little bit before the ratchet mechanism is engaged. This must be done, otherwise full brake pressure would be left on the pads when the e-brake is released. Well, that little return spring K-factor was not correctly chosen from the factory, and the result is that the ratchet NEVER functions after the actuator screw gets a little dirty. Hence, the pads simply work their way out all the way when the e-brake is used. Using the e-brake all the time seems to keep the actuator free for a longer period of time, but even with the correct spring weight and screw, the e-brake is required to adjust the parking brake actuator.

The TSB states that cars with a manual tranny are eligible for a free fix as the e-brake is required to park the car, but the auto is not eligible. Why? Only GM knows. However, fixing it yourself should be relatively easy. The rear wheels are removed, and there is a nut on the back side of the brake caliper that holds the parking brake lever. Remove the nut, lever, and soft grommets. Put a large washer over the shaft to act as a spacer, and then put a wrench on the hex of the shaft, and tie it down with the nut. Turn the wrench to back the brakes off. After a while, this will over travel, as if there was a one way clutch. Tighten the shaft to see where the hex is when the pads are tight agains the rotor. If it is in a spot that the parking brake lever will fit, and turn about 1/3 of its travel to tighten apply the brake, then it is good. If not, try again.

This will remove some of the brake pedal slop also. It's supposed to be self-adjusting (apply parking brake thirty times), but it is common for it not to work.
-Sourced http://www.thirdgen.org/

Found this while searching swap info for son-in-law's IROC

So there is a factory GM TSB on this. I would try and find a copy of the TSB before trying the method above.
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Old 07-18-2005, 07:51 PM
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I was under the idea that the adjustment for the rear brakes via e-brake handle was only for drums?

I had a problem with my IROC where the brakes all seemed to suck real bad. The pedal was mushey and it didn't brake very well at all. Turns out there was a defect with the rear calipers. I bought a 30 dollar caliper rebuild kit from NAPA and it fixed my problem. It contained all new seals, pistons, clips, boot...everything to completely rebuild the calipers. apparently there was a fluid leak past the piston which hurt the entire braking system.

Just my .02
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Old 07-18-2005, 08:34 PM
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I work on those type of brakes on a reg basis and every so often I see one that is either locked up or not applying...? More often than not I find the caliper pin`s stuck or binding and of course repair them but if the calipers are sticking and overheating the rear brakes (either side) then I just R & R the caliper with a new or rebuilt unit... Most that are in this condition are old and I figured the same as the above service brief that there was a problem with either internal corrosion in ratchet mech. or something to that effect...? I hate to see a ratchet type caliper now because they just seem to give trouble even when you do a proper brake job...
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Old 07-18-2005, 10:10 PM
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Your new rear calipers need to have the pistons manually adjusted after install, or they wont work. If you can see that the piston/pads are too far from the disc, this might be your problem. The TSB write up is for the opposite problem... brakes locked up.
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