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[Brakes] Out of ideas

A

Akumachan

NAXJA Forum User
Location
Goleta, CA, USA
I've been trying to resurrect my XJ that has been sitting for 4 years. It's an 89 with a 96+ booster/MC. I did a lift while fixing it up, so I added new SS brake lines front and rear. After bleeding them thoroughly, the pedal still goes to the floor. I get a little bit of braking force right before the floor, but not much before. Nothing I've tried has brought any real firmness to the pedal. Clean fluid is coming out when I bleed it, and plenty of it, and there are no leaks anywhere. Any ideas would be very much appreciated. I'd like to have it ready by Friday to take into the mountains.
 
Starting with the wheel cylinder farthest from the MC? RR, LR, RF, LF?

Didn't replace any other brake components than the flexible lines?

You can sometimes damage the piston seals in the MC if there are contaminates in the reservoir/MC bore and you fully depress the pedal. When you SLOWLY pump the pedal 4-5 times, and then hold pressure, THEN slightly crack the bleeders does the fluid come out with a lot of force?
 
Are the bleeders on top? ( I know, Duh, right, but I have seen it).

Did you replace the MC?
Did you completely drain the system?
If so you may need to bleed the MC (Master Cylinder).

A lot of folks use a vacuum bleeder. The hand pump ones are cheap. Just be sure to refill the MC often.

If you use the bottle/peddal method, make sure the hose is submerged in fluid so it doesn't suck air back in on the upstroke.

I usually start with the longest line first.
 
Correct, I bled them in the right order and quite thoroughly (put nearly a whole new bottle of brake fluid through it)

I did replace the hard lines the run from the MC to the proportioning valve, but I know for sure they are not leaking, and must be flowing freely or I wouldn't get fluid at the bleeders.

As for you last test, I'm not sure that would work, since there really is no pressure build up felt at the pedal. I could try it out and report back though.
 
TBH, I haven't bled the MC... when I had it all apart pure fluid was flowing from the 2 holes, but I could messed it up perhaps. How do I bleed the MC? Can I do it without removing it from the jeep?

Also, I've never used a vacuum bleeder, just use have someone push down the pedal repeatedly for me while I open and close the bleeders.
 
Is this the first time you have had to bleed your brakes? If yes, then check the front to make sure the bleeders are on top.Yes you can have the calipers mounted upside down.I have a friend who had his this way when he got a jeep an didn't even know till they changed his brake lines
 
Haha, I appreciate that nothing at this point is a bad idea, but I've been around and under cars long enough to know which way the brakes go. Bleeders and on top on all 4 corners.
 
Start with the basics.

1. Start engine and check the vacuum system to the booster, listen for any leaks.

2. Engine OFF--pump the pedal SLOWLY 4-5 times to dump the booster vacuum. IF THE PEDAL DOES NOT BECOME HARD then you likely have a bad MC possibly bypassing the piston seals.
 
Akumachan said:
Haha, I appreciate that nothing at this point is a bad idea, but I've been around and under cars long enough to know which way the brakes go. Bleeders and on top on all 4 corners.
Click to expand...
Hey i have seen people over look the easy stuff so many times.I know i have in my 40 years of working on cars.LOL.It happens:cheers:
 
joe_peters said:
Start with the basics.

1. Start engine and check the vacuum system to the booster, listen for any leaks.

2. Engine OFF--pump the pedal SLOWLY 4-5 times to dump the booster vacuum. IF THE PEDAL DOES NOT BECOME HARD then you likely have a bad MC possibly bypassing the piston seals.
Click to expand...

Pedal has never become hard in all my trials. I'm going to agree with you about the MC at this point. I'm not sure how sitting for 4 years killed it, but that really is the only thing that makes sense.
 
Akumachan said:
Pedal has never become hard in all my trials. I'm going to agree with you about the MC at this point. I'm not sure how sitting for 4 years killed it, but that really is the only thing that makes sense.
Click to expand...

Well, brake fluid is hygroscopic--it "pulls" moisture from the atmosphere--and that causes contamination in the system. Brake system should be FLUSHED and new fluid put in every THREE YEARS OR 30,000 MILES. And no, most people never service their brake systems other than replacing pads/shoes, turning or replacing rotors/drums as a last resort, or replacing leaking cylinders/calipers.
 
Sounds like a bad MC. Be sure to bench bleed it first!!! Then bleed the Combo Valve second, then bleed the slaves cycl/calipers.
 
You can isolate the back brakes by clamping the hose at the Tee on the rear axle.

Continue with the front left then the right.

The pedal should be solid at some point or you can bet the MC is shot.
 
I'll be getting a new MC in the mail tomorrow. I believe that the first stage piston is somehow damaged, and only the second stage is pushing fluid with any real pressure. I get a decent amount of braking power right at the very bottom of the stroke.
 
Well... I just replaced the MC and it's no different. Pedal still goes almost all the way to the floor before there is any resistance, and barely any braking power.
 
Akumachan said:
Well... I just replaced the MC and it's no different. Pedal still goes almost all the way to the floor before there is any resistance, and barely any braking power.
Click to expand...


Did you bench bleed the MC first? That is a must!!

Did you bleed the combination valve front fitting on the face/end fitting next?

And then bleed the rears, and then bleed the front brakes, longest line first, shortest line last?

Is the peddle hard after pumping with the engine off?

Was it a new MC, or rebuilt?
 
I fought with several of mine and finally got two of them fixed by bleeding the combination valve.

Did you replace the MC to combo valve brake lines or just the combo valve lines to the calipers and wheel cylinders? Could you have crisscrossed any of the brake lines?
 
Nealio is right. You need to make sure your pushrod on the pedal is the correct length.

I think if your new booster came out of a 96 it's correct but if it was any later, your pushrod is too short so you aren't getting a full throw. You can modify your brake pedal, there are various writeups on it. I'm looking for the link...
 
I just reread your earlier posts, looks like you need to bleed the Combo valve (Proportional valve) for sure, then rebleed the 4 wheels. BUT, if you did not bench bleed the MC, pull it and do that first!! Seems mounted bleeding does not stroke the piston far enough to get the last little bubbles of air out of the end, only bench bleeding seems too!!!
 
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