Please help with brake problem

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fionntan

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I am having trouble with my brakes. I did a rear disc swap and I am now having a problem that I cant figure out. I swap rear discs from a teg, replaced the booster with a new one, got a mc from a yard and ordered a 4040 valve from ebay. After I did the swap my rear calipers started sticking so I replaced them and now that is ok. Now my front calipers are rubbing. I replaced them thinking that would solve the problem. It got better but not fixed. When I drive around I can tell that they are rubbing because I get poor throttle response like i am ridding the brakes. The strange thing is that it is not constant. Sometimes it will get steadilly tighter as I drive, then when I turn the car off for a bit they release and I can drive around for a long time and they will be fine. Also when it does tighten up it seems to be tighter on the front passenger side, sometimes making the car pull right. I know it could be the mc but when ever I do the checks from the helms manual everything seems ok. Could it be the prop valve and if so how can I check that? I am really stumped and could use some help. Thanx in advance for any advice.
 
Sounds like a faulty booster. One with a leak from the low pressure to atmospheric pressure side. Maybe a bit of debris or a bad seal, could just be way the heck out of adjustment not allowing it to seal all the way.

Also could be moisture in the lines, expanding when it gets hot, but after replacing that many brake parts I'm sure the fluid has been changed 2 or 3 times in the process.

Judging pedal feel in a car with all new components would be a tough one. Does it get spongy? Do you notice the freeplay in the pedal becoming more significant when it starts dragging?
 
your pushrod could be adjusting itself to the vibrations of car which would mean you have to replace the booster.... or it could be the calipers what type of caliper do you have
.....or it could be something as simple as to much brake fluid in the master cylinder

More than likely its a booster problem though
 
When the brakes tighten up the pedal does too. The system has been bled in the last two months about 6 times the first one I did I let bleed until everything that came out was as clear as when it went in. Wouldnt a leak at the booster show up when I do the test described in the helms? The booster is new I didnt pull one from another car so it should be good.
 
you could have a faulty secondary seal on the primary piston on the master cylinder you would never see it if you have a vacuum booster if its a hydraulic booster then ill have to get back to you

what kind of calipers do you have
 
ok after reading your problem over again i have an idea....... when you got new rotors of off the car did you have them tuned on a lathe if not there probely out of round or have taper........if they have been turned but they were not sanded to a cross hatch pattern then that could be all your troubles
 
If the brake pedal drops when the brakes start dragging, its obvious that the booster is not opperating correctly.

Step one: Bring a ruler, and look at the stop above your brake pedal, its a button with two wires connected. It has a lock nut on it as well. Make sure the brake pedal is resting firmly against this button. Measure from a point on the pedal to the floor behind the pedal. Make sure you remember exactly where you measured from.

Now, disconnect the brake pedal return spring. Take another measurement. The freeplay in the pedal (It should drop) Should be 1mm-5mm. If it does not drop, you need to adjust the freeplay via the switch.. back off the lock nut and give the pedal more room to move out. Tighten it back down and repeat until you have 3mm "free play"

This should solve your problem.

Taken directly from the service manual:
WARNING:
If there is no free-play, the master cylinder pistons will not return to their stops. This can block the compensating ports, which prevents the brake pads and linings from returning fully when the pedal is released. This will result in rapid brake burn-up. Free-play provides a safety factor against normal rubber swell and expansion or deflection of body parts and pedal linkage.
Click to expand...

So, go do the measurement, remove the spring, measure again, and come back and post up the results.

If not this, then we'll dig further into it.
 
The front rotors are not new, and I havent had them checked lately. Are you talking about measuring the pedal hight Phyregod? If so I will check that tomorrow, I have to work all day today. Oh and the pedal does not drop when the brakes drag, it get stiffer with less travel before engaging.
 
the man has a point about your booster and pedal travel......... but about those front rotors your going to have problems soon enough if you dont fix those.
 
Ok so I went and messed around with the pedal hight, and I now when I brake it engages slower and more smoothly instead of the original press with instant braking. The wheels feel like they turn more freely with less drag. I dont know yet if that fixed the problem. It wasnt dragging when I messed with it, and it is not now, so I guess I will have to wait and see if that was the cure. I must add that in the helms it says that there should 160mm between the pedal and the floor (with floor mat removed) mine is at about 140 and so is the other eg that I have at my house. There is no physical way for me the get the pedal out to 160. The bracket that holds the brake light switch would stop it about 155 (guess).
 
Ok I drove around for a bit today and everything seems ok. I will give it a few more days to be sure since it wasnt a constant thing. It does seem a bit less responsive, is that normal?

I tried to throw some rep your way phyregod, but it says I have to spread it around. Anyway just know that I tried.
 
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