I'm having problems with my rear disc brakes on the 86 IROC. The fronts work great. I have a low pedal......no air, just a malfunction of sort with the rear brakes not grabbing the discs. It is apparent that both sides are not working by the formation of rust on both discs. I have a few things that come to mind.....

1. Calipers are frozen on both sides....(maybe a coincidence).

2. A problem with the master

3. A problem with the master causing the rear calipers to fail.

I haven't been able to pull the wheels yet to get a first hand look....but does anybody want to take a stab at this......maybe having a similar problem with the rear disc brakes? The car is going to have to sit for a few days before I can get to it. Any guesses???

I'd try and bleed just the rear. If no fluid squirts out after you step on the pedal a few times to pressurize the line, then chances are your MS is at fault. But do this 3-5 times to make sure there isn't any air in the line. The more times you do this, the harder the pedal should get, even if only air is coming out.

It sounds like you could have a leak in the rear, are you sure there is no air in the lines? Both calipers going at the same time is pretty rare unless you've had to hit the brakes hard enough that I'm sure you'd remember. Remember that the master cylinder is two separate chambers, front and rear; this is so that if one fails, at least you have the other and they operate more or less independently. I would follow the brake lines, and look for any wet spots. If you really can't trace it to a brake line, try taking the rear wheels off and cleaning the brakes and lubing the sliders, adjusting if necessary... sometimes rears tend to freeze up abit.

If neither of these help, check the master cylinder... or possibly the proportioning valve.

I'm not exactly sure about '86, however many GM rear calipers require constant use of the parking brake to maintain adjustment. You may simply need to adjust the brakes.

TTFN
Mat

Thanks guys for the replies.....I will check for leaks and try to bleed the system of air (if any). The master hasn't lost any fluid and nor did I add any. I think Mat might be right. The parking brake has to be applied constantly to adjust the rear brakes. The parking brake quit working about a year ago. I tried to ratchet the parking brake by putting my foot on the brake pedal and working the parking brake up and down to no avail. Something froze up and I have the feeling that I am going to have to replace both rear calipers anyway. I guess I am going to have to buy the wife some new calipers for Christmas!!! :D

Another thing you might want to check is that you're getting fluid to the calipers. I had a problem with a front caliper not working on my 85 T/A so I replaced it only to find out it was the brake hose, seems when they go bad they collaspe on the inside and don't let fluid go through even though they look fine on the outside. If this happened to the rear hose it would keep both rears from working

The '80s GM rear disc design was just plain bad. I had an '85 Pontiac STE with the same problem and we ended up replacing both rear calipers-when you try to retract the pistons for new pads they will not budge. Also if the pb wasn't regularly used the cables may seize and also require replacement.

Your call as to whether an '86 IROC is worth the expense.

Just an update..... I adjusted the equalizer for the parking brake and it did solve the problem. Both rear calipers are fine and the brake pedal is where it is suppose to be. The problem was just a simple adjustment. Thanks again for the replies. :thumbsup: