Brake Booster ???

[kakarot135]

Okay here is the story, I was driving to work last Tuesday, about 20 miles on the highway, when I got the exit ramp and hit the brakes the pedal hit the floor. As I was downshifting and pumping the brakes on the fourth pump I got back to "normal" pedal feel. I figured that it was a vacuum line to the brake booster, after all it is an 18 year old car. Babied it all the way home that night and got home safe.

Got it into the garage and checked the vacuum lines and all checked out OK, I even got a hiss noise when I removed the line from the booster. This to me means that there was a vacuum at that time. I did the standard test with the car off pushing the brake pedal five times each time it got stiffer until there was no vacuum left in the system. I then removed the vacuum line form the Booster again, no hiss. Then I held the brake pedal in and started the car, as the engine started the pedal started to fall a little to normal position. When vacuum line was removed there was a hiss noise again.

These are the only two ways that I know to check a brake booster and it passed both of them. Is there something that I am missing or another test that I should do. I would hate to spend the money to replace the brake booster and master cylinder when I was hoping to get my lowering springs soon and that would put me behind schedule for other upgrades as well.

Any and all help would be appreciated.

Car is a 93 4 cyl SOHC with a 5 spd.

Thanks,
Jason

[Ryan]

I'm not sure why you targeted your booster in the first place.

A very HARD pedal suggests a booster problem, a dead pedal suggest a hydraulic issue. Leaks? low on fluid?

pump the brakes at a stand still and stick your head out the door and under the car and look for drippies.

[cout]

I agree with Ryan. Check fluid level; if it's low, then you probably sucked in air and need a bleed. If it's fine, then you're losing pressure somewhere. If everything else checks out then you may need a new master cylinder.

[Sleeper6]

I agree with Ryan. Check fluid level; if it's low, then you probably sucked in air and need a bleed. If it's fine, then you're losing pressure somewhere. If everything else checks out then you may need a new master cylinder.

+1

[PATDIESEL]

Just to add to the post for searching purposes:
The air line going from the intake to the booster has a one way valve in it about midway. This valve can go out too and it will give the same stiff pedal feel as a bad booster. Also, if you have the air line to the booster backward it will give a stiff pedal and no booster as well. There is an arrow painted in the line IIRC that show which way to install it, but it is a simple fix if you get it backward

So +2 on the hydrolic resolution, GL

[Inodoro Pereyra]

I agree.

Also, your car has drum brakes in the rear. The brake cylinders have a tendency to leak, and the fact that they're inside the drum can make it somehow difficult to spot the leak. If in doubt, I'd recommend you to open the drums (which can be a PITA), and eventually replace them. They're about $10 each, anyways. And while you're at it, take a good look at the drum surface, and the shoes. And a little cleanup wouldn't be a bad idea either.

[kakarot135]

ok, first off, thank you for all the replies, they are all much appreciated.

checking the fluid, it is full. there is no leak at the front calipers, pulled the back wheels and no leak is visable, I did not remove the drums.
the reason that I originally suspected the booster was to me if it were a leak I would not expect to get pedal feel back by pumping the brakes, I would also be losing fluid. It is intermittent, driving to work on the highway it does it, but runing errands does not. is there a way to test the master cylinder or is it just a replace it to fix it.

Assuming I replace the master cylinder, if I head to the junkyard amd pick up a master cylinder and booster from a v6 so that I can swap to rear discs down the line will that be bad to rn with drms for the time being. also would I need the brake porpotioning valve as well.

Sorry so many questions.

Thanks
Jason

[300zxrb26dett]

If your not losing fluid, and you can get pedal feel back by pumping the brakes, then its either air in the system somehow, or there is an internal leak in the system, like for example the seals on the piston inside the M/C are shot and just allowing the fluid to go around the piston instead of building pressure. If you pump the pedal and hold it, does the pedal slowly return to the floor?

[kakarot135]

300zx: if I hold the brake after pumping it does not sink back to the floor, it stays stiff

[300zxrb26dett]

If thats the case then, its either your brake booster has a problem that is random, but I kind of doubt that, or the only other thing i can think of is maybe one of your brake calipers or wheel cylinders is not functioning properly, maybe sticking on occasion, or there is debris in one of your brakes lines causing a blockage somewhere. Both of these things could give you a stiff pedal. What is the condition of the fluid? if its black or brown, try bleeding the entire system out and see if that helps. If its really old fluid that has a lot of moisture in it, then it may have corroded the metal parts. Also if you bleed the system, take your brake calipers off and open the bleeder, then try to collapse the piston, and you will be surprised the nasty stuff that may come out of the caliper that will never get removed from your standard brake bleeding procedure

[kakarot135]

ok, i am headed to the JY on Monday to pick up some parts. I hope to find a V6 with a master cylinder, booster, and rear hubs to be able to swap the back from drum to disc. Is there anything else that I will need or will this list do it. I was planning on picking up the rear calipers and rebuilding them as well. Do I need anything for the ebrake or will the existing cables work.

Also if I cannot find the rear brakes can I get the v6 booster and master cylinder and use that until I find the hubs with my drums that i have now.

thanks and sorry for all the questions.


Jason

[MrMazda92]

I've had a weird brake issue too, and was wondering if you have noticed this too.

I drive a lot, highway and city both, sometimes even country roads just to open her up a bit.

The thing is, lately when I drive around town I've heard hissing when I break hard(short yellow lights, somebody cuts me off, etc.)

It doesn't happen often, but when it does it will continue to do it whenever I break, until the car sits for a while unused(I'd say an hour or more)

Sorry to hijack the thread, just thought it might be a similar issue and I'd rather not clutter this section.

[dallasdc1]

sorry to hijack the post as well but i have an automatic 92 mx3 4 cyl and i replaced the front brake pads a week ago and since then my brakes are unresponsive my e brake works but the pedal hits the floor i have replaced the master cylinder and bled the lines no sign of air in the line and idk what else to do :/

thanks for any help

[kakarot135]

Dallas, sounds like you have a leak, check the calipers out and see if one is leaking. If you have already replaced the master cylinder, did you get a new on or a JY one. if it was a jy one it may not be good anymore try a new one, they are only about $40

If the calipers are leaking you can rebuild them if the parts are still good, just get all the new gaskets...

Hope this helps,
Jason

MR mazda. Check all of you vaccum lines there is one to the booster that has a one way valve in it, it sounds like this may be your problem.

[wytbishop]

Holy...lots going on in this thread...

kakarot...think about this. hydraulic fluid is incompressible. Your brake pedal is connected directly to the piston in the Master Cylinder, which acts directly on the brake fluid in the system. This is independant of the booster. The booster just assists you in moving that piston. If you are able to push the brake pedal to the floor one of three things must be true. 1) fluid is bypassing the piston in the M/C which has been suggested, 2) fluid is leaving the system..meaning a leak or 3) fluid is being compressed...i.e. something other than brake fluid is int he brake lines...meaning air. The fact that you are able to build pressure by pumping tells me that it's not #1. You would never be able to build pressure if the M/C was bad. The fact that the fluid level is not going down tells me it's not #2. Air in the lines is virtually the only way that the symptoms you describe can be seen. If it's soft and you pump it up and it gets firm and stays firm...that's air. Keep bleeding.

If your pedal is hard and you can't depress it at all...that's different.

AS far as replacing the master at the J/Y...I wouldn't. Brakes are critical and junkyard cars often sit without use for long periods of time which is death to things like seals and o-rings. Swapping to rear disks you don't need to swap the booster or the proportioning valve. if you did take a booster and M/C from a V6 they would work fine with your rear drums in the meantime.