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soft brakes

J

Jess

NAXJA Forum User
Location
Tennessee
It is a 94 non-abs.
I have replaced the mc about 4 months ago and bled all wheels in the proper order several times today and the problem persists. The issue that I have not seen before is the portion of the mc for the rear sprays fluid about 6 inches out of the resivoir when the brakes are pumped and the cap is off. I'm not sure if it is sucking air somewhere in the back or if this is normal. I have no signs of leakage anywhere, but am going to remove the rear wheels/drums tomorrow and examine the wheel cylinders more closely tomorrow. I hear no noise that would indicate a booster leak. I am running 31's and it will not even start to lock the wheels and the pedal will go almost all the way to the floor with moderate pressure.

Is the mc bad or is there other problems?

Thanks
 
Jess said:
It is a 94 non-abs.
I have replaced the mc about 4 months ago and bled all wheels in the proper order several times today and the problem persists. The issue that I have not seen before is the portion of the mc for the rear sprays fluid about 6 inches out of the resivoir when the brakes are pumped and the cap is off. I'm not sure if it is sucking air somewhere in the back or if this is normal. I have no signs of leakage anywhere, but am going to remove the rear wheels/drums tomorrow and examine the wheel cylinders more closely tomorrow. I hear no noise that would indicate a booster leak. I am running 31's and it will not even start to lock the wheels and the pedal will go almost all the way to the floor with moderate pressure.

Is the mc bad or is there other problems?

Thanks
Click to expand...

If you have pressure before you turn the ignition, then the pedal sinks to the floor after you start it, thats a bad booster.
 
That is one of the symptoms, but I thought a bad booster would make the pedal hard....with the lack of the power assist.
 
Make sure your rear brake's are adjusted properly.
 
Jess said:
That is one of the symptoms, but I thought a bad booster would make the pedal hard....with the lack of the power assist.
Click to expand...

I have a bad booster... It makes the pedal feel "softer" and it goes down really far before you get a lot of stopping power. but the farther you push it down even though it's soft, the more stopping force you get. It is really hard to lock them up! but I can get her to stop pretty quick when I mash it.
 
xj88superjeep said:
I have a bad booster... It makes the pedal feel "softer" and it goes down really far before you get a lot of stopping power. but the farther you push it down even though it's soft, the more stopping force you get. It is really hard to lock them up! but I can get her to stop pretty quick when I mash it.
Click to expand...

It does not gain much stopping power lower toward the floor. I get a very gradual stop. It seems that none of the wheels are getting full pressure.
Through my searching it appears as though my problem is somewhere in the rear. In the morning I am going to get a set of speed bleeders and new wheel cylinders and shoes. After rebuilding the rear (and properly adjusting) and installing the speed bleeders all the way around, bleed the entire system again.

Does this sound like the proper approach?
 
Seems right to me. It sounds like air in the rear system or a faulty proportioning valve. Have you adjusted the backs manually? In the rust belt where I'm located I adjust my rear brakes manually. P.S. The rears were done once by the dealer with all new hardware 4 1/2 years ago and by me 1 year ago with all new hardware including backing plates. They never seem to adjust fully.
 
Jeepm@n said:
Seems right to me. It sounds like air in the rear system or a faulty proportioning valve. Have you adjusted the backs manually? In the rust belt where I'm located I adjust my rear brakes manually. P.S. The rears were done once by the dealer with all new hardware 4 1/2 years ago and by me 1 year ago with all new hardware including backing plates. They never seem to adjust fully.
Click to expand...

I have bled the rear (and front) by several methods today to no avail. I have not manually adjusted the rear yet. This is the wife's DD and does not get as much attention as my trail rig, so unless it needs attention the wheels stay on and I have not checked under the drums in quite some time.
I am located in East TN, which is not in the rust belt, but things rust no matter where you are.


No one has said anything about fluid shooting out of the rear brake resivior when the pedal is pumped and the cap is not on. Is this normal, because I have never seen it before. It seems to me there is something wrong in the rear to cause this backpressure.
 
Jess said:
No one has said anything about fluid shooting out of the rear brake resivior when the pedal is pumped and the cap is not on. Is this normal, because I have never seen it before. It seems to me there is something wrong in the rear to cause this backpressure.
Click to expand...

Thats normal. There are "vents" iin each resevoir of the master cylinder. They help to equallize the brake pressure. Also, when you bench bleed a master (if you leave the cap off), you will get a squirt about three times that......
 
First of all, XJ brakes suck.

But the pedal going lower would most likely indicate unadjusted drums.

Even with new drum hardware mine become unadjusted after awhile, not sure why. Until I readjuist them I end up having to push the pedal further down to get the same amount of brakeing power.

If you have a bad booster the pressure on the pedal would bleed off.

As a test, turn the vehicle off and press the pedal until it becomes ultra firm. Come back the next morning and see if the pedal is firm, without starting it. If it is still firm, no pressure has bled off and the booster is fine. When you turn the vehicle on the pedal will sink, that is normal.
 
It is possible that yu have a bad rubber line somewhere. I am having a simmilar problem and that will be mynext step. when a rubber line gets weak it can balloon and not put as much presure to the wheel as it should. not likeley but a possability.
 
Well, so far, I have inspected the rear brakes. The pads were fine and the wheel cylinders were not leaking, however they were badly out of adjustment. I adjusted them and it still did not improve braking much. Since the mc was under warranty, I replaced it. After a bench bleed and another bleed at every wheel (in the proper order), the brakes are still not what they should be. I'm starting to suspect superjeep is correct with the booster.

Is there anything else I should try before spending the $100+ on the booster?
Is there any way to check a booster that is not on a vehicle to see if it is good? I have a spare that I removed from my trail rig when I installed WJ booster/mc combo. The brakes on it were poor, but I think its mc was leaking.
 
Jess said:
Well, so far, I have inspected the rear brakes. The pads were fine and the wheel cylinders were not leaking, however they were badly out of adjustment. I adjusted them and it still did not improve braking much. Since the mc was under warranty, I replaced it. After a bench bleed and another bleed at every wheel (in the proper order), the brakes are still not what they should be. I'm starting to suspect superjeep is correct with the booster.

Is there anything else I should try before spending the $100+ on the booster?
Is there any way to check a booster that is not on a vehicle to see if it is good? I have a spare that I removed from my trail rig when I installed WJ booster/mc combo. The brakes on it were poor, but I think its mc was leaking.
Click to expand...

That $100+ is the only reason I am still driving with a bad booster... Like I said, I can get 'er stopped fine when I want to, because the harder I mash the quicker it stops, but my booster is not completely dead, just leaking. I can't think of any way to test a booster other than bolting it up.
 
I found one of the hard lines to the mc didn't get tightened up all the way and had a small leak. I tightened the line and bled the brakes again all the way around. The pedal is now tighter and the braking power is adequate. The brakes are still not where I want them, but will do well enough for now.

I did also install the speed bleeders and they seemed to work great.
front= HELP part # 12701
rear = HELP part # 12704

I am going to start searching for a good used WJ booster/mc to upgrade the whole system. I don't think my booster is "bad"....its just not adequate for the job it needs to do.
 
glad to hear it's better now. You did a lot of work on those brakes man... good luck!
I don't think I need an upgrade myself, since mine are still working, I think a new booster will fix mine fine.
 
xj88superjeep said:
glad to hear it's better now. You did a lot of work on those brakes man... good luck!
I don't think I need an upgrade myself, since mine are still working, I think a new booster will fix mine fine.
Click to expand...

If you are going to replace the booster anyway, you might as well get the WJ one with the appropriate mc. All that is diffrent is you have to drill a bigger hole and cut the rod a little---then it bolts right up. You also have to flare and bend new lines.
If you knew the diffrence it made, like I do, you would upgrade. My trail rig, with stock drums, will lock up 35's. Before the upgrade it would just barely stop 215's.
 
Well, she is in a constant state of being upgraded, so when the time comes that I finally get to the booster way down there on the XJ to-do list, I will definitely consider it. Will probably depend on how much of a mood I am in to do a "project" LOL
 
A booster that is getting solid vacuum will engage high and firm. A booster that is getting low vacuum will engage low and soft. A booster that is leaking will engage high then sink. If you also hear a whoosh noise when you press the brakes, that's your booster leaking.
 
Yep, Mine's definitely the leaking whoosh. LOL There is a slight possibility I just need to replace the elbow, or it could be the line itself, but I have not had the time to investigate it.
 
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