Soft Brakes
 

Diesel Jeep has extra play in the brake pedal. It makes contact, then feels soft and depresses more than usual. But if I pump it up it gets rid of the extra play.

Sound like air in the system or a bad booster? (MC is full).

Bleed the brakes to eliminate the chance of air in them. A spongy brake is usually air in the system. However, I can tell you that on my Suburban (1999 with front disk rear drum) it started to feel spongy when the front pads got low. It might have been the semi metallic pads getting soft or something but I bleed the brakes and it didn't have any air in the system. I replaced the pads with some ceramic pads, adjusted the rears and the pedal is firm again and it stops great.

Yep, if the pads are low it will feel spongy

Weird. New pads going in tomorrow. Will bleed too. Thanks guys. No pun intended :p

Had this on the Vette not long ago. It was just a bit of air in the system. Bled and refilled MC, poof, brakes again!

Attachment 989

Ive put 70k miles on these brakes. Plus whatever mileage the first owner put on them, and they were at like 70%. Insane. Im not very hard on brakes apparently.

Brakes made it feel a bit better. Bled the lines and tried to move the old fluid out, felt a bit better.

Now they feel decent again, but still a bit spongy. Imagine making light contact with your foot at low speed, just sufficient to stop the car, but after the car stops your foot compresses the pedal an additional 3 inches.


Now I dont know if Im just paranoid and it was always like that, or if something else is wrong? Ug

Booster or MC may be sub-optimal.

Brakes still stuck. Is the booster supposed to hold vacuum? Is that the best way to test it?

Any test for the MC? How does it fail?

When the master cylinder goes bad it bleeds off pressure so the peddle will go to the floor. When the booster goes bad it leaks vacuum so the brakes peddle is hard to push. Like when you try to press the brakes when the engine isn't running.

You also have ABS so the ABS system may be causing issues. Do you have any codes?

Sure it's a vacuum system and not a hydroboost system?

Ya.

"The most common problems that occur in the master cylinder is wear in the piston bore and piston seal failure. The classic symptom of a failing master cylinder is a brake pedal that slowly sinks while pressure is held against the pedal. The cure is to replace the master cylinder."

http://www.import-car.com/basic-brak...ster-cylinder/

Pretty sure that's what I said.

I've had that happen on a few cars with the Chevelle being one of them.

Pedal doesn't go to the floor, it goes down a few inches more than usual then feels normal. That's why I didn't relate your description. Thank you though. I'm assuming the discrepancy is that there are two pistons in the MC, and probably only one is leaking?

Im surprised that you have a vacuum booster on a diesel being they do not create vacuum. I know it has a vacuum pump but it seems like a silly setup.

Makes marketing sense, not engineering sense.

Its primarily a gas engine vehicle, with mass produced vacuum boosters. Not cost effective to screw with all that.

Oh, and in case you were wondering:


Attachment 990

So fucking strange. Brake demons.

I changed out the MC today. Got in the car after bench and pedal bleeding, brakes felt the same, spongy. Drove down the street, slammed on the brakes and locked the tires out of frustration, then the brakes felt good again. Brakes felt solid for 35 miles out of my 45 mile trip to Pasadena... and now they're spongy again. Mother fucker. Im ready to sell this bitch.

Also, vacuum escaped when I took the MC off. So I know the booster is holding vacuum.

A little off topic, but is the diesel swap legal?

Pretty sure since Jeep is the one that crammed that thing in there. :sm_laughing:

Did you bleed the ABS module?

What Jeep does he have then? The only Jeeps I know of that are diesel are the new Grand Cherokees.

Diesel swap is never legal in an original gas engine vehicle. But Guy is right, mine is bone stock, and as American as German Apple Pie.

Mercedes 3.0 turbo diesels came in the 07/08 GCs, just not in CA.

Nooo... que?

Any time the MC is replaced there is a good chance that air has made it to the ABS module. Since it does not get bled with the rest of the system since fluid only goes through it when an ABS action is enacted, which might be why when you jammed on it, the brakes were ok until the new air bubble reached it. Typically you need a Tech 2 style scanner to get the ABS port to open, but sometimes you can go out and drive it, hammer down on it a few times and continue to bleed the brakes. Or, crack the fittings on the ABS module it self to try and bleed off the air, but again, since it only sees pressure during an ABS event, it won't always work.

Damn, ok Thanks Guy. Hopefully thats it.

No bleeders on the abs module.

I know, that's why you can sometimes cheat and crack the fittings on the brake lines