It's been a while since I have posted anything here but I have started running in to problem after problem with my jeep. Last year, I picked up the 97 base model xj and I have been daily driving it since. Recently I had been having problems with the brakes and having a soft pedal so I decided to replace some components and started with the calipers in the front and most recently did the springs and wheel cylinders in the rear drums (Chrysler 8.25). Also replaced the master cylinder since replacing the rest didn't help. I correctly bench bled the master and properly bled the brakes so there is no air in the lines and it worked great for about 3 days. The pedal was nice and firm and I could stop on a dime. This morning I hop in to get ready to go and the brake pedal now practically goes to the floor. I don't see any leaking fluid from the calipers and the wheel cylinders are brand new (replaced 5 days ago). There is fluid in the mc reservoir and there didn't seems to be any leaking around there so as of right now, I am clueless. Could it possibly be a vacuum leak? My car idles and performs fine but these brake problems are starting to really get on my nerves. Any help is greatly appreciated. Also, if there is a lot of grammatical errors, I'm on my phone so dot blame me.

 

Someone correct me if this doesnt work with an XJ, I work on Hondas so sometimes the two worlds are pretty far apart lol

Before you start the car pump the brakes until they're hard. Keep pressure on the pedal and start the car. The pedal should go down to a normal braking position and stay there. If it does anything strange I would check the brake booster hose, sometimes they collapse.

Also check all the brake lines for swollen spots. If you find one I suggest steel braided lines. you can even get some vise grips and isolate each caliper, or front axle /rear axle by blocking the brake lines then go drive it until the pedal feels soft (which it will be a little stiffer anyways because of clamping lines). it should obvious at that point if there is a leak or swollen line .

hope any of that helps

 

Did you bench bleed the master cylinder?

If not, thats probably the cause. Most folks complain about having this issue if it wasn't bench bled.


If your sure it was bench bled fully, then there could be a leak somewhere. If no fluid is leaking, either there is still air in there, or your master is bad.

 

Let it sit awhile till it goes soft again.
DO NOT PUMP IT!
Try opening a blereder screw - there should still be a slight pressure. There is supposed to be a slight residual pressure held - less than 1 lb when parked. It keeps all the seals expanded, preventing air from getting in.

If not, try bleeding the brakes again to see which wheel has the bubbles. Start with the left front, then right front, left rear etc.

 

You want to start with the wheel furthest away from the master cylinder... rear right, then rear left, then front right, then front left. Not the other way around.

 

Yep....this

 

Yah, I know to start with the bleeder furthest away and then get closer. I think I will try bleeding the brakes again first, maybe the air from the mc has worked its way down to the corners. Hopefully that will solve the issue and thanks for all the help so far guys! It's greatly appreciated.

 

If bleeding doesn't help....is this a "rebuilt" master cylinder? What brand?
I've seen some rebuilts with residual bore damage from rust or pitting. The new seals hide it until you go to bleed the brakes and the seals reach down into the damaged section, which tears them up. It is fairly frightening what passes for "rebuilt" these days.

 

did you put the calipers on the correct sides? bleeder above the brake line...
happens all the time.

 

Good call.
Bleeder screws should be at the highest on the caliper.

 

please do not advise people in working on their brakes, when you dont know what you are talking about.
there is no presure in the brakelines when the pedal is released. if there is, something is wrong.

 

1. When I said CHECK to see which cylinder had air in it - i MEANT CHECK BY SLIGHTLY CRACKING IT. Not bleeding it!
READ WHAT I SAID!

2. There IS supposed to be a slight residual pressure held in the lines all the time. It's not enough to move the pistons, but it is enough to keep the cups expanded slightly to prevent air from getting in. Try cracking it on ANY car!

Google it if you don't understand basic hydraulics.

It's one of the many functions of the combination valve - often mistakenly called a proportioning valve.

When you don't have any experience or knowlege, it's best to keep your mouth shut instead of making a damn fool of yourself.

 

Says the guy that just informed someone how to bleed brakes the INCORRECT way.

 

Another yo yo that cannot read!

IT WAS NOT INSTRUCTIONS ON HOW TO BLEED THE BRAKES - it was to find WHICH wheel was letting the air in.

DUHH!

 

Does pedal ever feel correct or soft every time ?