Brake issue--booster?

#1

Just got this car put together with parts that worked on the old car.

On track, the brake work fine until I really go aggressive, then the pedal effort gets real high and I don’t seem to be getting any assist as the car doesn’t brake well.

Around the paddock, again no problems until I turn the car off. If I have the pedal depressed, it pushes back against me hard and I’m guessing I lose braking force because the car will roll alittle with the same amount of pressure on the pedal that I had when I turned off the ignition.

Booster?

#2

If you have no vacuum leaks and the check valve is good, replace the booster.

#3

Thanks. Uh, how do I check for leaks and the check valve?

#4

Lots of ways to check for a vac leak but a bad one would cause your engine to run poorly so that problem is less likely. But to check for a vac leak you can spray a flammable gas around your hoses and see if the engine surges as it sucks in butane, or whatever. Don’t blow yourself up. Or you can make a smoke generator and do a smoke test. This is where you put smoke into the intake at 2psi or so and look for smoke to come out somewhere. Google DIY smoke generator.

The check valve is the little plastic doohicky between booster and throttle body. You have high vac at idle and low vac at WOT. The check valve keeps the booster’s vac high so that you always get about the same amount of vac for boost, instead of losing some boost as the throttle gets pressed. Mine is suspect also.

I’ve not read the test yet, but it can’t be to hard to put a vac gauge on the brake booster line and see if boost is fluctuating. Or just replace the checkvalve from a junkyard car.

#5

Actually you can give it the suck/blow test. Take it off…you should be able to blow through it one way and suck it closed the other.

#6

I think I’ll just replace all the hoses and the valve (they are looking tired), and if that doesn’t do it, then the booster itself.

Thanks guys.

#7

If the pedal only gets hard under hard braking, I’d first suspect that the ABS is going into ice mode, perhaps prematurely.

#8

No I’ve experienced that. This feels like a lack of assist.

#9

I tried to take my checkvalve off this weekend. Hacked up a lot of hose than ran out of time. Is a tough bugger to get off.

My booster has same symptoms. I put this booster on because some folks were singing the praises of Girling boosters. I think I’ll put the ate booster back on.

#10

I ordered all the hoses and the valve and well see what happens. 60 bucks us woryh it to replace all this original stuff. Bringing a spare booster for the weekend.

#11

Newbie here. Joined as soon as I saw this thread. I have been tracking down the same exact problem on my e30 for 2 months now. New booster, new check valve, new pads, new fluid, new MC o-ring. A nasaaz e30 owner gave me the same advice as jlevie. So I pulled my abs relays and low and behold my brakes work. http://www.r3vlimited.com/board/showthread.php?t=310644

Before you spend more time and money just give it a shot. I pulled the 2 relays from the abs box in the engine bay but I think you can pull out one under the driver side dash too. 10 minutes just to be sure.

#12

If rear brakes are going into ice-mode, something else is going on. Might be better to go after the cause then kill ABS in order to stop the symptom.

#13

I agree. But disabling abs at least let me know it’s not my booster or a vacuum leak. I’m thinking my rear calipers may be sticking. I will Google ice mode.