Brake Problem

[81CJ7]

Some times when I hit my brake petal it will go all the way to the floor. To get a petal back it will just take one pump. Most of the time they work great. Ive bled the crap out of them and upgraded the master cylinder and booster, dont see any leaks anywhere. Wheel cylinders look good. Ideas please.

[robertf03]

what does this upgrade consist of?

[DRAGOONRANCH]

Bench bleed the master?

[85cj7]

its either a very persistant air bubble, or, is your master cylinder new or did you get it used with the yj booster you got? if its used or even if its new for that matter, it could be an internal leak of the master cylinder seals, allowing it to not hold pressure, thats why you have to pump the pedal to get pressure back.

[81CJ7]

Its a used yj master cylinder and booster. I did bench bleed it before installing. I'll probably try a new master and see if it goes away, but what are the odds that I would have two master cylinders having such a rare problem?

[robertf03]

look at the front calipers and make sure the bleed screw is at the top and not the bottom. I can't remember what the calipers look like on an 81, but it is possible on a few models to put them on upside down and still hook up the lines.

[StevenAg03]

how old are the calipers? the seal around the piston could be worn out. is there any sign of break fluid around the calipers?


something to think about...

[81CJ7]

bleed screws are on top. I will have to take a close look at all the wheel cylinders, but I'm pretty sure they are dry.

[Seth]

two used master cylinders failing does not seems that rare to me.

[robertf03]

good point, rebuilt master cylinders are junk. Found out today that corvette master cylinder I had was spewing fluid out the back into the pocket of the hydroboost and thats the reason I had no rear brakes, and the reason the firewall has no paint. It was maybe a year old