Kingbert06

I recently had a master cylinder that was leaking, from what I could tell all the fluid was gone before I replaced. before replacing the MC I bleed all the lines and made sure there is clean fluid throughout. after replacing the MC and bleeding again, I noticed that the brakes are very hard to push, I do hear the ABS go on but in guessing that there might be air in the ABS system. anyone know the procedure for bleeding the ABS? is there a test for the vacuum? thanks all!

c4cruiser

A hard brake pedal is usually indicative of the vacuum booster going or gone bad. Do you hear any sounds like air escaping when you press the brake pedal??

The ABS system does a self-test every time the car is started and moves forward thru 3-4 MPH. It's a buzzing sound that you should hear from behind you while sitting in the driver's seat.

Kingbert06

I don't hear any type of vacuum leak, I will check again. does the ABS need to be reset?

s carter

Now to go 1 step further, as above stated ABS will do a test 1 time, that's normal & expected. Next you say the pedal is hard, does it have any give (No travel) if you jump on the brakes does the car want to stop or roll on? If it stops on a dime your booster is good, you probably have a good bleed. you might have a different depth in the pocket hole in your master cylinder plunger and you will need to shorten up the adjuster screw. or possibly may not even be in the pocket.

Cliff Harris

The wheel sensors don't know if the car is moving forward or backwards. The ABS will also do the self test in Reverse.

Cliff Harris

The brake lines go straight through the ABS unit. There is no special bleeding procedure on '86 through '89 cars.

You have the symptoms of a ruptured brake booster diaphragm. You can test the brake booster by stepping on the brake with the engine off. Then start the engine. When the engine starts the brake pedal will drop slightly when the vacuum comes on.

Kingbert06

Thanks all, just got back to the forum. I will review all the suggestions tonight and get back. with an ABS system, does the car need to be running to bleed? when the car was put away for storage last fall, the brakes were perfect. I found that the MC did run dry bringing the car home. The car does not stop on a dime, but doesn't roll. any way to check the vacuum pump?

Kingbert06

So the vacuum test passed, pedal dropped about 2" after starting. does it need to be bled with vehicle running for the ABS?

Kingbert06

Checked the vacuum, it was great. checked to see if there was any fluid that leaked into the booster, that was dry. a buddy just received the latest VETTE mag., there is an article on this particular issue. now I'm wondering if I didn't bleed the MC correctly/enough. the article also says bleed closet to the MC first......I've always done furthest first.

c4cruiser

The master cylinder feeds the ABS unit and the lines to each caliper goes out from the ABS unit, not the master cylinder. So the "furthest" caliper is not necessarily the one you would think. In the FSM for my '87, it specifies this bleed sequence:
Right front
Right rear
Left rear
Left front

There is no need to have the engine running while bleeding the system. Just make sure that you watch the fluid level in the M/C reservoir so it doesn't go dry. If you did let the reservoir empty, you probably have an air pocket in a line somewhere. You may even have to "bench bleed" the master before doing any bleeding of the lines.

A pressure bleeder is a big help here.

Kingbert06

can I re-bleed the MC on the car?

Cliff Harris

Yes.

joendoodle

This post is quite timely (for me)..

Just got the '88 up and running...

However tons of pedal effort to stop and I hear "vacuum" noise when I apply the brakes... I was thinking "vacuum booster' from the symptoms, but just figuring (no real life experience with these symptoms)... read this thread... Now I'm confident I know what to do.. Now just to have the time and weather to do it...

THANX again forum folks

joendoodle

I picked up the powerbrake booster last night on the way back from de-masting / re-masting the "7 year itch" ( a friends sailboat).

Even though I was @ work past 6, when I got home it was cool with clear skies...Pulled the drivers seat and got the booster out and the new one in. For some reason it was ALOT harder to get the old one out than to put the new one in... And I only lost 1 nut (hex nut that is) (seat mounting).

Took her out for a spin (returning the $55 dollar core).

Sure is nice to have power brakes again....