Poor brakes

I did a search and didn't see anything, so sorry if this has been answered already.

I have a 95 Jimmy with ABS. It's my wife's truck and of coarse she hasn't said anything, but last weekend I noticed that the pedal seems really soft and will slowly drop farther down when breaking. Sitting at a light, the truck will sometimes start creeping forward and I have to push a little farther to stop it again. If I hit the breaks hard they will stop me fast and ABS seems to be working fine. I have no warning lights on the dash either.

I'm guessing it's the master cylinder, but looking here, it looks like it could also be the vacuum module.

Any thoughts as to the more likely candidate?

Fluid seem fine and the pads are good also.


Thanks for any help,

Delorian

Have you tried bleeding the breakes, cause you might just have air in the system that gets compressed when you sit on the brakes.

If there was air in the line, they would be smushy. (technical term)They're acting more like the fluid is leaking by in the master cylinder.

I haven't done anything that could introduce air into the system, but it's easy enough to do, I'll bleed them tonight.

i am sure u have checked but there isnt a wet spot under the master cylinder or around it is there????
i am more an older model shade tree myself so i aint really sure

Nope, fluid was still fine and no leaks that I've seen. Bleeding the brakes didn't help either, the pedal still drops slowly when pressure is aplied to the brakes. It's not real bad, slowing from 45 it will go down 3/4 and I give it a quick pump and can stop with just a little more but when stopped if I press a little harder, it will drop to the floor before the light changes.

Thoughts?

Thanks,

Took me a few days to think on this one. Inside the master cyclinder there is a cupped seal and when the brakes have been applied really hard or quick. It sometimes uncups or flattens out allowing the fluid to get by slowly. You would not see the fluid leaking anywhere. Had this happen to my 91 when my wife almost got into a wreck and had troubles with the brakes a week later. Master cost $30 with a lifetime warranty plus core. Might be worth the trouble to see and is easy to replace, (most of the time) did a 91 and 93 without problems.

Thought of one more thing to check. Noticed one time that the pedal went down when applied too. Turned out that the rear brakes where bleeding back into the mastercyclinder by the abs unit. You could see the fluid leaking back into the master when holding the brakes down.