Ive got an 89 xj pioneer 4x4. Ever since I bought the vehicle Ive had brake issues. I bled it multiple times when I first bought it because the pedal was super spongy and finally got some good brake firmness when I gravity bled it all around. Problem after that was that the rear tires would lock up at low speeds and the fronts would hardly grab?

So... onto my next question. I recently just did a brake job up front "rotors & pads" along with new u-joints and after putting everything back together I bled the brakes in order "from farthest to closest to the master" and all had great pressure and from what it looked like no air in the lines. I started it up and the brakes were very squishy. So I did it the manual way and had my friend pump up the brakes and hold the pedal while I bleed all 4 corners.

The brakes still are not any firmer? Heres the odd part. The brakes are firm when its not running but as soon as vacuum hit the booster the pedal sinks 3/4 of the way to the floor.

IDEAS?????

 

Bump. Any help is much appreciated guys!

 

Calipers on the correct side with the bleeder screw on top? Your brake booster could be bad. Does it make a hissing sound when you depress the pedal when turned on?

 

Calipers were not changed. No hissing from the booster and pedal doesn't sink when held with the vehicle running.

 

Are the rear shoes adjusted correctly?

 

Just check the calipers, pervious owner could have had them on wrong. Also make sure to have the rear brakes adjusted correctly as that could cause it also. Otherwise you may have a small leak somewhere in the lines.

 

Rear brakes are adjusted perfectly. Made double sure of it! And the front calipers are setup how they're suppose to be.

 

Do you lose fluid over time?

 

Nope! No fluid loss what so ever.

 

How is the fluid condition and color? When was the last time it got new fluid throughout the system? Fluid could be old and broken down and just wants to compress instead of providing hydraulic power

 

The fluid is crystal clear. I'm thinking that possibly the front rubber lines are expanding when under pressure. Ill have to take a look at them.

 

Could be the master cylinder...

 

Or maybe there is a tiny leak I had a truck with the same issue it was leaking from the partitioning valve a tiny bit if I would press the brakes the rear would lock very easily. Until I replaced it and no more.

 

My Comanche does pretty much the same but I know it has a leak and where, but I'm redoing all the lines since they are old and crusty

 

Whats perfectly to you ?