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91 Brake problems

Guest Leroy Cook

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Guest Leroy Cook

:mad:I have a brake problem. The pedal travels quite a bit farther than it should. I have replaced the Master cyl, Bled the master cyl, Bled the wheel cyl. and the pedal still goes to far down. Is there an adjustment? What if the booster is bad? What happens?:confused:

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  • 2 weeks later...
Guest Mc_Reatta
I've got the same problem on a '90 Riviera. It appears it's the rear calipers that retract too much when they release. Not sure how to fix this.

Operate parking brake multiple times to adjust internal screw mechanism. If that doesn't work, replace calipers with rebuilt ones.

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It could be the rear pistons that are causing the problem but it would not have started suddenly.....there would have been a gradual change in the pedal position.

The design GM used on these rear disc cars was supposed to self adjust the rear caliper/piston for wear of the rear pads. However, if the self adjustment mechanism becomes contaminated with gunk within the piston cavity, the self adjustment does not work and the first noticable thing is the parking brake takes more than the 2 1/2 pumps to set the brake. This is a clue that the rear piston is out of adjustment and it may take more travel in the master cylinder to move the piston.

Since you have already replaced/done several things to help improve the operation and that did not work then you should check the rear calipers as noted above.

If you have the time and tools, there are a couple of thing you can try.

(1) move the parking brake lever one step on the hex stud.... on the back side of the caliper, the parking brake cable hooks to a lever. This lever is attached to the screw that moves the piston. By removing the nut, and moving the lever one step on the hex that is on the screw, you have manually adjusted the piston position. Unless the fitting are rusty, this is pretty easy to do once the rear tire is removed.

This also fixes the parking brake.

(2) the second option (aside from buying new/rebuilt calipers) is to put new pads on the rear. This will push the pistons back into the caliper and gets everything back into position.

Attached is a sketch of the rear piston assembly and a photo of the actual parts.



Edited by Barney Eaton (see edit history)
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Thanks Barney, you have explained exactly what I thought was (is) happening.

You also saved me from cutting open the piston to verify my thoughts that the inner piston was binding in the outer piston with your photo/drawing. Thanks.

I'm currently replacing both rear calipers in my '90 Riv after rebuilding the origional calipers (no new piston) and having no success.

Got a pair at Advance for $67/ea. with exchange. Core is $30!

Back in my Fiero days, I used to buy rebuild kits from GM that had a new piston in the kit.

Is there such a kit for the Reatta today?...and is it cost effective? I'm getting old with arthritis in the fingers and rebuilding these is become a PITA.

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