Need help with Brakes! (front discs)

[ShinyXJ]

I was having problems keeping my Jeep from sliding off of steep rocks a couple of weeks ago on the Rubicon, so last weekend I pulled the wheels off and took a look at my brakes. The front rotors and pads looked pretty bad so I replaced all that. Ilso had to replace the driver side hard line which comes out of the proportioning valve as it got damaged on the trail.

So I got it all back together, and yesterday my brother came over and helped me bleed the brakes. I flushed all the old fluid out and got to the point where the fluid coming out the bleeder valve hose was clear and bubble-free.

Problem is, the brakes SUCK now. When the car is not running the pedal seems really stiff, perfect. As soon as I start it and the vacuum kicks in for the booster, the pedal goes pretty much right to the floor with little resistance. Before the brake job the Jeep was stopping pretty well on the street, it just wouldn't hold on really steep stuff. Now, I'd say the brakes are barely safe to drive on the street. Takes a long time to stop with all my weight on the pedal. Scary.

There's no air in the lines that I can tell. The padsa and rotors are brands new and the calipers appear to be seated properly. Anyone have an idea where to look next?

Thanks in advance, as always!

Scott

[AZ Jeff]

Pedal drop to the floor when the engine starts (and your foot is on the brake) can only mean one of two things:

1. air in the brake lines (still!)
2. a master cylinder that is leaking back on itself

Time to do some more digging. If you have bleed the ENTIRE system (front and rear), and are CERTAIN that you have no air in the system, then it's time to look at the master very carefully.

[ShinyXJ]

I didn't bleed the back brakes...could that be the problem?

Also, my manual has a thing about messing with the nut on the front of the proportioning valve. Says to unscrew the nut, attach a tool that somehow resets the thing, then you bleed the brakes, remove the tool and re-tighten the thing. It was so hard to break loose it seemed unlikely that that had anything to do with it. Any idea about that thing?

I will bleed the rear discs and see if that helps...I suppose there could still be air in the lines somewhere (back probably) though the brake fluid was always full enough to keep it from sucking air through the master cylinder...

Thanks for the help!

SCOTT

[mdwatkins]

Oh yeah...when you bleed your brakes you have to do all four...

not sure what you're referring to on the proportioning valve, but things should be like the front...loosen the screw, bleed till it runs clear (new fluid) without any bubbles. This should clear up all your problems.

Matt

[ShinyXJ]

Thanks Matt, I figured it was probably something simple like bleeding the rear too. My manual actually says you have to screw witht he proportioning valve, which I've never done. We cracked open that big nut on the front to try to open the valve inside, but that probably only induced air into the whole system. I'm going to bleede the back cyclinders tomorrow and see if that helps...if not, maybe the master cyclinder.

Thanks for the help,

Scott

[gw204]

Not trying to be a smart ass, but you did put the cap back on the master cylinder, right?!!??!

[ShinyXJ]

Well, I bled all four cylinders last night. Checked all the fittings and bleeder valves to see that they were tight. No leaks that I can discern, but my brakes still suck. They stop the Jeep, but barely. To recap:

New front rotors
New front pads
New front driver side hard line

=

crappy brakes!

Yes, the cap is on the master cylinder reservoir
What do I look at next? Any way to test the proportioning valve or the master cylinder? Could this problem be related to the booster? MaN I love wrenching!

Thanks,

Scott