Xnke Posted October 10, 2011 Share Posted October 10, 2011 Alright. So, RedZedTurbo bought the car ( a 1983 ZX turbo) with crummy brakes, and we've been trying to figure them out ever since. New front calipers, rotors, and pads New rear rotors and pads; calipers are fine. cleaned up sliders and pins and regreased. New 1983 ZX master cylinder. Bled all the brakes; no air in lines best we can tell. Pedal feels good. Brake Booster holds vacuum perfectly fine; check valve is working properly. Have ZERO power assist; and it's like doing leg presses to get the car to stop. BUT, if you get your foot into it, the car will stop fine, just really requires a scotsman's leg. Disconnecting the vacuum line to the booster and plugging the manifold (to prevent the vacuum leak) changes absolutely nothing. It feels exactly the same with and without the vacuum hooked up to the booster. BUT the booster will hold a solid vacuum for 10-15 minutes with no trouble. No hissing, no RPM changes, nothing to indicate a leaky booster. Also, when you DO get on it hard enough to lock a wheel, the rear wheels will lock first. The front brakes are NOT doing the job...after a series of hard stops to get the brakes hot, the front rotors are touchable, wheras you can't even get your hand past the wheel on the rears. If you sit down with the wheel off and have someone push on the pedal, you DO see the pistons in the calipers move up front, and there are wear marks on the rotors, but they are pretty light. You can still see the OEM finish on one of the rotors, as if the pads aren't even touching the rotor, on parts of the rotor. What do I look at next, guys? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 10, 2011 Share Posted October 10, 2011 Proportioning valve? Elementary question: Is the check valve in backward or blocked? If the check valve is ok, perhaps the internal parts in the booster are siezed and not allowing the boost function to operate despite the presence of vacuum. Quote Link to comment Share on other sites More sharing options...
Xnke Posted October 11, 2011 Author Share Posted October 11, 2011 Check valve checks out fine. Can NOT suck through the valve from the booster side, but can blow into the intake manifold no problem. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 11, 2011 Share Posted October 11, 2011 It sounds like the booster is bad. We have the same symptoms with our car. We had a bad proportioning valve, no rear brake pressure. Replace it with an adjustable type and now the rear brakes work but the pedal effort is very high and there is no feedback from the brakes. I can't tell when it locks a wheel unless the rear end tries to come around. I am going to open the booster and have a look in week or two and time permits. Your early rear brake lock-up is likely the proportioning valve. Depending on year, they are serviceable. Quote Link to comment Share on other sites More sharing options...
madkaw Posted October 11, 2011 Share Posted October 11, 2011 Sure it's the right MC and the pushrod is properly adjusted in the back of the MC. Kind of sound likes like what happened with my wildwood brakes on initial install. The pushrod was too short, but the brakes worked, but not very well and the pedal felt like no booster. Quote Link to comment Share on other sites More sharing options...
ModernS30 Posted October 13, 2011 Share Posted October 13, 2011 I was going to say your front brakes could have a bend or kink in the lines, or blockage. Causing the pedal to be firm like that, and for you to have no brakes on the front. Quote Link to comment Share on other sites More sharing options...
Xnke Posted October 13, 2011 Author Share Posted October 13, 2011 All the brake lines are fine, no kinks. I suspect a bad brake proportioning valve; it's a 1983 S130. The master is a 15/16" single reservoir unit for a 1983 turbo S130. Unhooking the booster from the engine entirely produces absolutely no change in the brake pedal; and the pushrod has been adjusted. Will update with a solution, assuming one is found. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 18, 2011 Share Posted October 18, 2011 Xnke, Sorry for the thread jacking. Since we are having a similar problem as you and we all seem to be stumped for the moment I thought it might help if I posted our activities here. We performed some diagnostics on out Z yesterday and the booster seems ok. It holds vacuum. When we started the car the brake pedal sinks a bit as the manifold vacuum is developed. When driving the car with and without the vacuum line connected we can detect a difference in pedal effort; lousy and worse. Our thoughts are now directed at the pressure differntial waring switch. In different, recent thread JohnC mentioned this part can cause a restricton if it gets into the "warning" mode. We have decided to remove to see if there is any improvement or change in the brake action. We will likely do this on Sunday. I will post the results. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted November 6, 2011 Share Posted November 6, 2011 We finally removed the pressure differential warning switch and replaced it with a tee. No improvment. So we decided the master cylinder might be the problem and replaced it. Still no good. Having eleminated the hydraulics from the list of possibilities we decided to go back to basics and look closer at the pads and shoes. All bad. Not worn out but badly overheated and glazed over. We replaced them and much to my chagrin the brakes work great now. I have never experienced bad linings cause such a change in pedal effort. It was as if the brakes were heat faded all the time even when cold. Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted November 6, 2011 Share Posted November 6, 2011 To the OP: Possible reaction disk issues? http://forums.hybridz.org/index.php/topic/69706-reaction-disk-pictures-and-walkthrough/ Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.