b0140765

Bought my son a 92. Over the last couple weeks the brakes have gone downhill. Pedal goes to floor and car barely stops. Took front wheels off, thought we would bleed them. Put new pads on, no leaks, but when the car is running and he pushes pedal to floor, I can still rotate disk by hand with little resistance. Plenty of fluid, no leaks, no air from bleed port just fluid--- very little with full pedal push. Some times abs light comes on when pedal at floor, sometimes no. Master cylinder? How to disconnect abs to check that? Those are some big plugs on that abs unit and I can't tell which are which...

jv9999

If there are no leaks, it's pretty much guaranteed to be the master. It's not the ABS (unless it's leaking).

hooked073

dont forget you have rear brakes that can cause this also. Were the brakes good when you got the car or were they so so? Sense you have no history on the car I do not take much into account that the fluid was full. In fact if it was complety full it would be my quess someone toped it off before you got it. I would pull the rear wheels and see what the rears look like also check for signs of leakage. Before I got jumped to far I would gravedy bleed the complete brake system starting with the rears. To gravedy bleed you open one bleeder and let the fluid run untill at least half the resivor has been gone threw. then top off fluid and go to the next bleeder and do this untill you have done all 4 wheels

Cliff Harris

This can be caused by an ABS unit that has debris in it. See this thread for the full story:

http://forums.corvetteforum.com/c4-t...e-failure.html

b0140765

We did replace the rear pads as well. Did not crack open any lines, just used a c clamp to press the pistons back so the caliper would fit back onto disk. Brakes when we got car about 3 months ago were so so. I will give the linked thread above... Master cylinder doesn't look hard to replace, or ???

Annoyed

First bleed ALL 4 corners properly, then worry about changing your brake master cylinder.

I thought my master cylinder went on me too when my brakes went soft, could push pedal to floor, brakes wouldn't pull-up car...
I bled 3 out of 4 corners (because I couldn't get the R/R side nipple off) and they were still crap.
Then I tried again, sprayed a tonne of CRC around the nipple, used a different socket/spanner, got it off, re-bled the brakes again.. and now it's all good (thank f*ck).

hooked073

still if it were my car I would bleed everything first

b0140765

All right all right.... I will bleed every brake before I change the master. You guys are relentless. Might take a while tho, I think the front right took about 10 pedal presses to fill up the 2 feet of hose I had and the fluid never touched the bucket. Very little flo. Clean as a whistle fluid tho.

jv9999

That's a sign of a bad ABS pump, especially if the other side flowed a lot better. Before you bleed everything again, unbolt the master and pull it forward half an inch. Shine a light into the back of it. If it's wet, it's bad.

b0140765

Bled all 4 and no difference. The volume from the rear was much more like I would expect, 10 times the volume of the front. It is obvious the fronts are doing nothing, and the rears are pretty normal. The new master is at the parts house....... Should I do it?

hooked073

In my opinion a abs pump cannot cause a low pedel that would be my next step

hooked073

Make suure you get the rod adjusted correctly when you replace the master

jv9999

I agree. My comment about the ABS pump was related to the low flow. It's possible to have more than one problem, especially on a 22 year old car.

b0140765

Ok. So we are a big soccer family. The master will have to wait until after the USA Germany game. But we will replace the master tomorrow afternoon/evening.

b0140765

Oh and I forgot, it's my sons birthday too. May not get to the job today...

b0140765

Well it took about 2 minutes to pull. 1 1/2 minutes was because the 2 nuts were different sizes. Unit says its a PBR. Vacuum booster says made in Australia. With the 2 size nuts I am sure someone has been in here before. The back of the master was dry, but it was a bit wet behind it, and around the plunger sticking out of the booster. Still suspect master???

b0140765

Put the new master in, bled it good. Stops like it did for the Road & Track test back in 92! Now, new water pump, alternator, belt, radiator, fuel injectors,................