Big Bird 88

About a week ago the brake pedal began to feel soft. Later that day, braking became very spongy and the Red brake light would come on in the Dash. The warning light would go out when I pressed the pedal.

I checked the fluid and the rear reservoir was about 1/3 way up from the minimum line and the front reservoir was at the max.

ABS is fine, it passes the self test on ignition and the ABS light does not come on.

I replaced the front pads, the car has 50k miles and they were the original and just over 50% used. Topped up he rear reservoir and it was good for a couple of days.

I went to check the fluid and I saw fluid on the top of the cap of the rear reservoir. This was odd as I had cleaned the caps. However it appeared the diaphragm had been compromised and fluid was getting into the space between it and the cap and then coming out the weep hole on the cap.

So I ordered a new diaphragm.

Well same soft spongy pedal happened last night along with warning light.

Front reservoir is at max, rear is about 1/8 inch below max and just a little bit of fluid on the cap.

No leaks in the brake lines that I saw when replacing the pads.

I'm thinking I have a bad master cylinder. Fix would be drain, replace and refill with dot3 ( entire brake system of course)

What do you think ?

Kevova

You could try to flush out old fluid first and see if it corrects problem if not then replace master cylinder.

Dt86

The rear seal of your master cylinder could be leaking. Unbolt the master from the brake booster and see if it's leaking there. Takes 5 minutes. If you need to replace it make sure you bench bleed it good to get all of the air out of it.

s carter

If your not loosing fluid, I would be looking at the Master it may be stroking though. pump up the brakes and and then hold pressure on the pedal it should go down the normal amount you are use to and hold, if the pedal pauses at that point then dives to the floor your master is probably going

HAD2HAV2

Big Bird, sounds like your master cylinder might be dying a slow death.
This is what I did for my brakes on my 88 to upgrade my braking. New master cylinder, new AC/Delco slotted rotors, and Hawk brake pads.

Big Bird 88

It is the master cylinder. Thanks for all the input guys, much help as always.

ddahlgren

If the seal leaks at the end of the MC it can kill the booster as well.