chrisl757

Hi all,
I just replaced the ball joints on my driver side (2001 xj) and when I went to go for a test drive after, the brake pedal was very spongy. I can get the pedal to travel all the way down to the floor with weak resistance. It feels like about 50 percent resistance of what it usually is.

Anyways, I drove around the block and can't come to a complete stop unless I use the emergency brake.

My rear brakes are solid, and the e-brake works great.

Obviously when I put the new ball joints in, I used a c-clamp to press the pads in so that I could remove the rotor. Normally when I do this, I don't have any trouble afterwards because I just push the pedal several times to the floor to reset the front brakes and that always worked.

This time it didn't.

Any thoughts on what to do? Thanks.

caged

check to see if you pushed any brake fluid out of the master. you may just need to top it off. hopefully you didn't get any air in the system, otherwise you will need to do a bleed.

Turbo X_J

Pistons seized in the calipers?

investinwaffles

I would bleed it anyways, at least the front end (factory rear brakes don't even do that much anyways).

If the brake is really spongy, you have air in the system or the master cylinder is somehow not holding pressure. I assume if the piston was seized it would at least still stop with the 3 other brakes?

PatHenry

If the calipers (and hence the seals) are original, it's possible that when you were compressing the caliper that you ripped the seal or something and the system is not able to maintain pressure. It's also possible that the rubber hose tore with the abnormal twisting that goes on when you're hanging the caliper off to the side.

I'd pull the tire on that side and take a look at the caliper and brake line. (Obviously after making sure it isn't something as simple as low fluid... )

fb97xj1

If you pushed the pedal all the way to the floor, you may have blown your master cylinder. Under normal driving/braking conditions, the o-rings only go so far within the bore. The space ahead of those o-rings stays full of brake fluid, which can corrode the bore surface, pitting it. Push the pedal all the way to the floor (just once is enough), and the o-rings are pushed past that point, ride the rough stuff, tearing them. This results in an internal leak. You might get a couple stops out of it if youre lucky, but the master cylinder is pretty much junk. Unless the o-rings are replaced.

This may not be what happened to you, but if you pushed the pedal all the way to the floor when bleeding, it is possible. I did this with the Mustang. Once. I got a couple stops out of it and the brakes went soft. The master cylinder was the culprit. I nicked an o-ring. Lesson learned.

PatHenry

That's interesting. I'd never heard that before about potentially damaging the O-rings in the master cylinder. I'm quite sure that I pushed the pedal on my TJ to the floor several times over the many years and various brake repairs and it had the original master cylinder the entire 305k/14y lifetime. Maybe I was just lucky??
So do you suggest sort of "half-pumping" the brakes when you bleed or compress the caliper to prevent damaging the master cylinder?