Alistair

Ok. Quick background:

Just bought a 99 Cherokee Sport (see my pics in "introductions"). PO had driven the brakes almost through the rotors. I knew this going in, so was expecting to do the brakes right away.

So: Bought new brake pads and rotors. Upon disassembley, noticed the calipers looked pretty bad. Bought new calipers (right thing to do). Got it all on, and found the master cylinder was leaking........yep....bought a new master cylinder (well...a remanufactured one from Advance). Of course, one of the brake lines snapped when taking off the old master. Replaced that.

Try to bleed the brakes, and have a very soft pedal to the floor????

Ok....let's do the rear while we're at it.

All new drums, shoes, springs, hardware....etc.

Got everything together, and we still couldn't get a good pedal? Bleeding the master, then starting at right rear, we bled until there were NO air bubbles.

Still no hard pedal.....but now it's worse! Went to pull it out of the garage (needed it for something else) and the front left wheel was totally locked up? Still no pedal at all, and had to put it in 4L just to move it out!

I'm thinking we got a bad master cylinder from Advance, but I'm open to suggestions at this point.

Jamie57

might have to pressure bleed the system. There is a proportioning valve in the system so that the front brakes get more of the force being applied. Sometimes when you have a system empty like that the check ball in the valve moves out of alignment and will not allow the sysem to build pressure correctly. An old trick NOT guarenteed to work is to hammer on the brakes a couple of times.
Just easier to get them pressure bled. Shouldn't cost much, you've done all the hard work.

robertj

The problem lies with your attempt at bleeding the system. You gave us a lot of information but nothing relating to how you attempted to bleed the brakes. What method did you use? Did you bench bleed the new master cylinder per the manufacturer instructions?

Also, I agree with Jamie in that you're better off using some sort of pressure bleed system. I use a reverse bleed system that to me is absolutely a requirement when replacing brake components. It makes the job so much easier and takes all of the guess work out of it. The tool cost a little bit of money but makes everything from fluid flushes to overhauling the brakes so much easier.

PingPong

Buy a set of speed bleeders for all for corners, add a length of hose..and keep master cylinder full.

Cant tell you how many times with MJ's I have had to redo the whole brake system, and had issues with bleeding brakes.

Carl48

Make sure you have the calipers installed on their proper respective sides of the vehicle...bleeder should be at the top.

jblondie813

I experienced this when I changed my brake calipers. I'm not sure if all GC used the double piston calipers but they weren't labeled R or L sooo I just guessed... then I bled the brakes, they seemed to have been bled and NO air in lines but still soft pedal! So I troubleshooted and just switched the calipers, re-bled, and tadaaa the pedal finally got harder and 1 hr later I was finished!! ....Lesson learned!!!

Definitely make sure the bleeder is at the TOP lol

Bigclubs

Working in a shop part time, one night a customer came in with low brake pedal pressure after changing the brakes at home. We bleed the rear brakes and went to the front calipers and the master tech looked over the work the customer did at home and wal-la, he did just that. He installed the calipers on the wrong side.

The bleeder has to be on the top of the brake. It it's on the bottom, no amount of bleeding will bring the pressure up in the system. You will have a low pedal pressure no matter how much bleeding is done.

Also might be a good time to change the flex lines since you upgraded all those parts. Weak flex lines will give you low brake pressure.