Brakes lock

[grk nickafis]

I put in my new booster. I had someone bleed my brakes because its been really cold here lately. i figured ill pay the 50 bucks. They just called me and said that the brakes lock up (only the fronts) wen the brake is applied. Is there anything that i could have done wrong, they said the pin in the center of the booster can not move and if it does its broken

[robomatic12]

I'm going to take a guess that the brakes are locking up under unusually light pedal application? Obviously if they slam on the brakes they are going to lock up.

Are they saying that the pin is or is not moving?

[marty1mc]

Go back and look at the booster with the link below. Make sure it's moving in and out. Also, check your check valve and make sure it's directionally correct.

http://www.300zx.co.uk/cgi-bin/manual.c ... t&total=56

[grk nickafis]

see i didnt check that pin because i thought "oh its just a pin" but it was all the way in the way i had it when i took it out.

they said when the brakes are applied, the car stops fine and when he tried to go the front brakes were still locked. then he put the clutch in and reved it and the brakes lost pressure and came loose. he explained to me this elaborate thing but idk.

i also gave him my FSM to use incase he gets stuck. he said theres nothing about the pin adjustment in the book but obviously there is because that link has it right there. i'm going to print it out for them.


What seems to be the problem officer? did they not bleed them correctly or is it really the booster and i have to get a new one? or can i just adjust the old one

[Main Man]

go to UTI... learn how brakes work... then try again

[grk nickafis]

go to UTI... learn how brakes work... then try again

really? thanks, let me wait a year and then work on my daily driver. ill just walk everywhere

[grk nickafis]

could it be from not bleeding the right way?

[marty1mc]

go to UTI... learn how brakes work... then try again

This comment was totally unnecessary. I would rather see someone do "something" and screw it all up than not do anything at all. Being a smartass doesn't make you smarter.

[marty1mc]

could it be from not bleeding the right way?

No, bleeding would most likely cause a soft pedal, not a lock. Something is binding. Is your pedal returning and do you have good pedal? It is also possible you have a stuck caliper.

[grk nickafis]

i havent picked it up from the shop yet. they couldnt figure it out and refuse to work on it because they dont know the car. They said the brakes engage fine and disengage slowly in the front but the pedal goes to the floor. i thought it might be the ABS that they didnt bleed

[marty1mc]

Could also be the master. That thing can take a while to bleed. I usually bench bleed them, then install, then bleed the brakes.

[robomatic12]

Definetely bleed the abs pump, I tried not bleeding it after removing my front calipers and could not get a proper pedal feel. Bleed it for sure, but this wouldn't normally cause brakes locking up, only pedal falling to floor.

[grk nickafis]

I got the car back today, the pedal goes to the floor. I dont know why they said that the brakes lock up, they dont. the pedal goes right to the floor tho, no resistance. the brakes work tho. they dont lock up or anything.

[marty1mc]

Sounds like you still have air in the system.

[grk nickafis]

i dont think they bled the abs bc to take that panel off u have to grab it and pull and there were no finger marks (that panel is really dusty, cars been sitting for 3 weeks)

[grk nickafis]

Turns out, theres SO much air in my lines that I'm surprised the brakes work at all.

When I pump it the brakes are firmer, meaning theres air in there... So i bled One tire and There was way to much air, i couldn't finish it.

Any suggestions on How to bleed these? I heard a "reverse bleeder" would be better

[robomatic12]

Attach a clear line to the bleed screw, then grab a friend, pump the pedal a few times to build pressure, hold the pedal down and tell your helper to open the bleed screw. Then after the fluid has come out, close the screw and you can lift the pedal again. Repeat until you see clear fluid come out of the bleed screw. Do it in the correct order including the ABS pump in the service manual available online.

[grk nickafis]

I know how to bleed it, theres too much air in the lines that it never comes out without bubbles, i was sitting there for like 20 minutes on One tire.

[robomatic12]

Errr.. you have other problems then. There must be a hole/leak in the system somewhere that's causing air to get in. Or the master cylinder seals were ruined and it's pulling air into the system. Perhaps a brake line was pinched and has a pin hole in it? When you bleed an old master cylinder you should never pump all the way to the floor, it can cause the piston inside it to go further than it normally has and encounter rust which will kill the seals.

PS: You could try gravity bleed for a while, fill up the M/C and open all the bleed screws.

[grk nickafis]

Figured it out in case someone else has this problem. Its the master cylinder. They say interchangable between the years but in 1991 they changed it to a 1" bore from the 1 1/16" bore on the pre 1/91 models. Buying a new cylinder and putting it on. Thanks for the help guys, btw anyone in the area, north jersey, this shop is great PM for info.