Possible bad brake booster?

[glacier985]

Ok, I searched and could not find an exact answer to my question. I think my brake booster needs replaced.

Car sat most of the winter until wednesday when I started it up again. I drove it around, brakes were fine. I go to drive it today and the first time I press the brakes are squishly. So I go back to my house thinking its air in the lines, but its not. Everything checks out okay and the resiviour is full. I get back in my car and pump the pedal and it gets hard again. Right now I thinking wtf is going on. So I start up the car and press the pedal and the car idles down, almost dies and the pedal just about hits the floor. So is the brake booster bad, or something else?

thanks in advance

btw car is a 90 240sx 5spd

[ricebike]

Quote »I get back in my car and pump the pedal and it gets hard again[/quote]sounds like the booster diaphram is ok...

mebbe check the booster vacuum lines/ & that one-way check valve mounted in series against the firewall... u can only suck/blow on it in 1 direction...

on a different car, i experienced " squishy pedal" & saw that one of the rubber hoses expanding like a throbbing pimple when my assistant was depressing the pedal... but that's just another scenario.

[sleepyRPS13]

bad secondary seal ?

[glacier985]

have to check those things out, also someone told me that the master cylinder could be wearing out.

[TanManS14]

Im absolutely certain its not the master cylinder. Im having the same problem. My dad replaced my master cylinder before he gave my car to me for christmas, and mine does the exact same thing. They worked perfect until about a week ago when then this lady in front of me slammed on her brakes because of an oncoming abulence, I also slammed on my brakes and then felt them depressurize just as you described. Just goes all the way to the floor, but like if you first start it up it will be fine for like a second when you brake right, then slowly depressurizes? thats what mine does. And I also bled my brakes, and Im not leaking fluid, resevoir is full.

[sleepyRPS13]

did you slam on the brake hard? i mean really hard.

i had the same situation when i had to super slammed kick at the brakes. later on, i found out i busted my primary seal, leaking between the mc & booster.if that was the secondary it wouldnt leak but grip then drops to the floor.

he already did the booster test, unless its a vacuum...

[glacier985]

update on my situation, had engine troubles so I got those sorted out before the brakes.

I noticed something today, I took her for a drive and is I pushed the brakes like normal the pedal went to the floor. If I pushed and started pumping the pedal slowly came up and the brakes grabbed better. Any ideas??

I also checked the check valve and hoses, both fine. Don't know how to check the second seal, but I'm not leaking any fluid at all.

[sleepyRPS13]

if you had a line lock it would be easier to diagnose.

just get a new m/c

[gizzerd]

Sounds kinda like the brake master cylinder to me. I had to replace mine when I first got my 240. It had been also been sitting before I bought it. When I drove it, I had to pump the brakes a few times to really get any pressure. I ended up bleeding them all, and when that didn't work, I bought a new master cylinder, and that did the trick. If you decide to replace yours, just make sure you bench bleed the master cylinder really really well, then bleed at each caliper. Hope you figure out the problem!