I don't think my booster is working

[ksechler]

I drove my car for the first time since September tonight after rebuilding the front and rear suspension and redoing the entire brake system. The brakes are underwhelming. The pedal is heavy but with enough pressure will lock up the brakes. I don't think the booster is working at all. The pedal does not soften if you start the car while holding the brakes. So my questions are: How do you test the brake booster and what should the brakes feel like? I know feel is subjective but I'm wondering if stiff brakes are normal for an almost 40 year old car.

[black gold man]

If you have drum in back make sure they are adjusted properly.

With rear tires off the ground spin the tire hard by hand.

1/2 rotation would be good. This adjustment may need to be done by hand and not with e brake.

[olzed]

I drove my car for the first time since September tonight after rebuilding the front and rear suspension and redoing the entire brake system. The brakes are underwhelming..

If you had the vacuum line off, perhaps you have fitted the one way valve around the wrong way.

[Diseazd]

Did you remove the master cylinder for any reason?

[tlorber]

I recently replaced my booster. Before I did so, when I applied the brakes, I would hear a hissing sound and the idle would increase by a couple hundred rpm's.

[ksechler]

All:

Thanks for the replies. Here is what I have:

Stock Booster

15/16 Master from an '81 ZX (the right one with 2 reservoirs)

4-piston calipers with the proper, non-vented rotors

Rear disk conversion from MSA

Wilwood proportioning valve (to rear brakes)

New steel lines throughout

Braided lines to calipers

So to answer your questions:

I don't have rear drums

I did take the vacuum line off but not the check valve. Also there is no change in idle when pumping the brakes which I would expect with a bad check valve.

Yes, I removed the master cylinder. The current one is not stock for my car.

[Diseazd]

If it stops, but feels like you've got to stand on the pedal to lock it up, you've dropped the reaction disc in the booster. Take off the two nuts that hold the MC to the booster and pull it back a couple inches (no need to remove the brake lines ). Pull out the plunger from the booster.......neck down a vacuum hose to a small tube and suck the disc out of the booster. Super glue the disc to the back of the plunger and reinstall......night and day difference.

[Zed Head]

A super simple test that would at least tell you something would be to start the engine, turn it off without touching the brake pedal, then remove the vacuum line to the check valve on the booster side. If the booster has had engine vacuum properly applied you'll get a big hiss as the booster refills with outside air. This will tell you that the check valve is working correctly and that the booster chamber holds vacuum. If you don't get a hiss you might have the check valve in backward or the booster is leaking.

It's a simpler way to do the tests described in the FSM, Brake chapter, without a vacuum gauge. Basically, instead of measuring vacuum with a gauge you measure it with your hear.

[somecreep]

I have a related question: my aftermarket intake manifold isn't drilled for the check valve. Instead of drilling it could I get away with just using a small filter breather after the check valve, or does the booster need to be linked with the air in the intake manifold for some specific reason?

[240260280z]

I have a related question: my aftermarket intake manifold isn't drilled for the check valve. Instead of drilling it could I get away with just using a small filter breather after the check valve, or does the booster need to be linked with the air in the intake manifold for some specific reason?

The brake booster needs a vacuum source to function. The easy vacuum source in a typical car is the intake manifold. The only other vacuum source I have seen used in a car is an electric vacuum pump. This is typically used on electric cars and on some cars with racing manifolds and/or big cams.

FYI: SSBC Electric Brake Vacuum Pump Kit