Yet Another Brake Problem

Hey everyone, so I replaced all my calipers, pads, rotors, and lines. I drive a 1985 200sx. I just took it for like a 15-30 min test drive today and noticed after a few minutes of driving the brake pedal would get stiff to the point where i barely need to push it down to stop. Also, I when it gets to that point, it'd probably to hard to push the pedal any farther than a centermeter. As the pedal gradually gets stiffer the brakes seem to be locking. By the end of the test drive the car was struggling to get through each gear and the pedal was almost impossible to push down. Also, when it gets to that points, I dont use the brakes to stop i just hit the clutch or put it in neutral and after about 3 to 5 seconds im at a complete stop without using the brakes.

So to summarize my problem:

THe longer i drive/use the brakes, the stiffer the brake pedal gets, and the slower the car glides in neutral indicating a brake locking problem.

The calipers arent frozen, they're new, all lines replaced.

This leads me to believe that the problem might be caused by a master cylinder or brake booster.

It'd be nice to figure out which ones causing the problem being that the parts arent cheap.

It seems like everything runs fine after i bleed all the calipers. Then once i drive for a while the pedal gets stiffer by a slight bit at every stop sign. Maybe my lines are getting filled with air everytime i release my pedal forcing the pads to the rotors without touching the brakes. Or maybe its a malfunction in something that releases pressure when i let go of the pedal.

I dunno, im stumpt, might bleed all my lines again, lets my brakes act up the way they do, then jack up my car to see if there are leaks. I'll probably give this post a week til i decide to just get a master cylinder.

the reason i dont think its a brake booster is b/c a brake booster is designed to help push the pedal down, in this case, its as if the pedal is pushed down while my foot is off of it.

Did you bleed it in correct order? Check if all lines were tight? If yes, then it might be your BMC. Rebuilding it yourself costs like 20 bucks.

When I changed my brake master and bled everything I got that same problem. All I did was adjust the brake slightly and it never locked up again. Maybe you should try that after making sure all the air is out of the lines and the master is good.

if there was air in your lines you would have a soft pedal, not hard.

gasses compress, liquids dont.

pull the vac line off of your booster, plug the vac line so you engine doesnt have a vacuum leak, and see what happens. you probably have a bad check valve, or your booster is bad/filled with brake fluid from a leaky master cylinder.

something along those lines.

or maybe you drifted to hard.

brewster240 @ Apr 10 2008, 12:40 AM

or maybe you drifted to hard.

actually, here, read this.

http://www.autoshop101.com/forms/brake05.pdf

sounds like the master cyclinder is leaking into the Brake Booster.

this is typical with hard pedal with little to no brake responce.

falkhen @ Apr 10 2008, 10:37 AM
sounds like the master cyclinder is leaking into the Brake Booster.

this is typical with hard pedal with little to no brake responce.

mod_mastaz @ Apr 10 2008, 03:13 AM
When I changed my brake master and bled everything I got that same problem. All I did was adjust the brake slightly and it never locked up again. Maybe you should try that after making sure all the air is out of the lines and the master is good.

brewster240 @ Apr 10 2008, 04:44 AM
actually, here, read this.

http://www.autoshop101.com/forms/brake05.pdf

Try adjusting your ebrake.

By adjusting the pedal, you go under the car and turn the rod. I've had this exact same problem. The brakes lock up and it's as if the pedal doesn't fully release when you let off it after the pads/rotors warm up(cuz metal expands when it's hot). If you want to imagine it, it's kind of like the brake pedal are always slightly engaged/pressed. In my case though, the car would stop itself. I just adjusted the rod and it never happened again. Took me days to figure it out.

Edit. I meant under the dash. It's the linkage that goes to the brake pedal.

This post has been edited by mod_mastaz: Apr 10 2008, 10:45 PM

mod_mastaz @ Apr 10 2008, 06:45 PM
By adjusting the pedal, you go under the car and turn the rod. I've had this exact same problem. The brakes lock up and it's as if the pedal doesn't fully release when you let off it after the pads/rotors warm up(cuz metal expands when it's hot). If you want to imagine it, it's kind of like the brake pedal are always slightly engaged/pressed. In my case though, the car would stop itself. I just adjusted the rod and it never happened again. Took me days to figure it out.

Edit. I meant under the dash. It's the linkage that goes to the brake pedal.

c3z @ Apr 10 2008, 02:39 PM

the way i see it in my head is when i hit the brakes, the booster pushes the master cylinder pistons down. When I let go of the pedal the booster SUPPOSED to suck the air out and release the master cylinder pistons. Which doesnt happen, it seems my calipers slowly after each use of my brakes get pushed more and more against my rotors. Gonna check all that today vacuum line and all.

anyway, NOPI Drift qualifying this saturday, you going?

Yep. Same symptoms. My pedal got really hard after a bit of driving, when everything heated up. It would be anywhere from 1 min to 10 mins. It happened AFTER I get a new master too. If you're going to adjust it, do it slowly and then once you heat up your brakes, go down a road and throw it in neutral, if you feel the brakes kind of still hold, adjust it some more until it's good.

mod_mastaz @ Apr 11 2008, 05:29 PM
Yep. Same symptoms. My pedal got really hard after a bit of driving, when everything heated up. It would be anywhere from 1 min to 10 mins. It happened AFTER I get a new master too. If you're going to adjust it, do it slowly and then once you heat up your brakes, go down a road and throw it in neutral, if you feel the brakes kind of still hold, adjust it some more until it's good.

mod_mastaz @ Apr 11 2008, 05:29 PM
Yep. Same symptoms. My pedal got really hard after a bit of driving, when everything heated up. It would be anywhere from 1 min to 10 mins. It happened AFTER I get a new master too. If you're going to adjust it, do it slowly and then once you heat up your brakes, go down a road and throw it in neutral, if you feel the brakes kind of still hold, adjust it some more until it's good.

I bought the car with a dead master. Replaced it and that's what happened. Everyone told me it was air so I bled it like 10 times haha. I was told it was a dead booster to seizing calipers. I even rebuilt one side(other was brand new). I drove it like that for a week or two til I looked through the FSM and saw the brake adjustment. It made a lot of sense afterwards though.

again for future reference if anyone finds this post while searching...

air in your lines will make the pedal soft/spongy, and will get worse the hotter it gets. worse as in softer/spongier.