Before my brakes used to work but when I shut off the engine while brake pedal pressed, the pedal would push my foot up to pedal not pressed position with great force.

Now the brakes don't work after 2nd or 3rd press on the pedal while driving. Pressing the pedal feels like I'm pressing a piece of wood.

Looks like the brake vacuum is low but we are not sure how much vacuum the RX7 system needs to work properly. It may also be the westinghouse not working properly.

We have bled the brakes properly, have new brake fluid, pads, lines etc.

Any ideas what to look at and how to troubleshoot?

 

Did you look at the brake booster line check valve? When mine was bad it did the exact same thing.

 

either that or the booster diaphragm itself.

One simple method to check the valve is by blowing through the booster hose. You shouldnt be able to. Remember its vacuum that it requires, so that should explain wwhat end to blow through. ie. disconnect from the engine. Try and suck it, and you should be able to.

You should be developing around 18" of vacuum.

 

1 think to note , When you are in boost and suddenly brake the pedal will be hard because hte motor is not producing any vacume . if in normal driving its hard the booster may be going

 

If the car is running, the brakes should be able to lock up. Period.

I agree about the check valve. Same thing happened to me when I swapped out my old calipers.

 

his problem isn't them not locking up its the pedal being to stiff atleast thats what I gathered from the "wooden pedal " description .

 

^^ Yes that is correct, I can't push the brake pedal in, it's stiff and the brakes won't stop the car as a result. I will check the booster and other things and report back. Thanks for the replies.

 

Tem120, the brake booster should have stored vacuum so it shouldn't matter if you jump on the anchors after boosting. If you try and apply the brakes repeatedly while still creating boost, then yes, the pedal will get hard as there is no more vacuum able to be created and stored.

Op, wooden pedal description points straight at the power assisted breaking system. Actually had a dodge Phoenix come in today with the exact same wording used by the owner. Found it quite amusing.

 

really ? mine doesnt haha mine gets stiff when i press the brakes hard and fast , but honestly I like it like that it keeps me from locking them up ( i know the car has abs but years of driving none abs cars sort of drilled the backing off the brake pedal a bit when tires lock into my brain )

 

So what do I check first, still the booster or something else?

 

Update: Brake booster line check valve is checked and works fine.

What is brake booster diaphram, how can I check if it works?

 

I could be wrong, but unless it's physically in rough shape (rusted, etc), the booster rarely fails on these cars.

The check valve requires very little resistance to open, if it takes too much pressure to open it still may be bad. I would remove that line and replace it with another line with no valve (large silicon line would work, or really just something from the department store - it's only a quick test). Drive it around with light load and certainly no boost and see if your brakes work. if you still have the problem, then you know it's not the valve.

Is there any evidence of an issue with the master cylinder (leaks, etc)?

 

If you keep pumping the pedal quickly, you will use up the stored vacuum, so yes it will go hard. it will go spongey again when the booster has had time to store engine vacuum aagain.

The power assisted breaking system IS the booster system.
The booster diaphragm is a couple big pieces of rubber inside the booster assembly in basic terms.
See if your car is developing enough vacuum first, then you can check the booster with a vacuum pump. The booster should be able to store the vac for a minute or so after switching the car off.

Your correct that boosters dont normally fail. In the whole time ive been working in the mechanical industry ive only ever replaced one booster. Booster failure ffrom what ive always been told is normally related to splits in th rubber from age/heat.

 

No leaks afaik. Booster seems to be fine. Will still do the test you've recommended.

My mechanic says it feels like there is not enough vacuum but as we do not have another rotary to compare he is not sure if the vacuum in my car is normal for a rotary or not. Vacuum is reached under max compression but having a hard pedal during idle makes us think there is not enough vacuum. Westinghouse is another parts he suspects.