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Having trouble with brakes.

Sounds like the MC is going bad. I went through three a few years ago, when replacing the original. A rebuild, a new (import), and a new from NAPA. Third time was the charm. Now my son is having the same problems.....

What it seems is that there is some confusion about booster vs. MC. A bad MC will allow the pedal to go to the floor. A bad MC with a good booster will go to the floor easier. A good MC (with the rest of the system up to snuff) will give a good pedal. A good MC and good booster will feel, well, good. A good MC and bad booster will give a high, but hard, pedal. If any of this makes any sense, it can help you narrow things down.

When I was playing the swapping game with my '96, I ended up replacing the hard line to the rears. Wow, what a difference! The line, rusty on the outside, was just as nasty on the inside. Considering the ages of our rigs, anything, and probably everything is possible.

A few years ago, the MC went on the Sable my daughter used to have. The brakes felt and worked great, as I always kept after them. Out of nowhere, down to the floor. But not always. Maybe one time in fifty. She finally told me when she almost wrapped it up. 'How long?' I asked. A few weeks. What? New MC, problem solved. They fail in different ways.
 
Heyhar, thanks for the info, I have been experiencing the high and hard pedal syndrome and was wondering if it was the MC or the booster. Glad to have narrowed it down with out much effort.
 
Grimm5577 said:
Heyhar, thanks for the info, I have been experiencing the high and hard pedal syndrome and was wondering if it was the MC or the booster. Glad to have narrowed it down with out much effort.
Click to expand...
If the pedal is high and hard with the engine off, and stays high and hard when you start the engine, that sounds like a bad booster. The pedal should sink a little bit when the engine starts and the vacuum-assist kicks in.
 
After reading all the posts and getting some help from a few friends I'm gonna try the MC first. Its also the cheaper of the two options.

Its there much difference in manufactures? And are there any companies that I sould just plain stay away from?
 
Menzenski said:
If the pedal is high and hard with the engine off, and stays high and hard when you start the engine, that sounds like a bad booster. The pedal should sink a little bit when the engine starts and the vacuum-assist kicks in.
Click to expand...

I'll have to hold my foot on the brake when I start her up to see if it drops. The other nail in the boosters coffin is that when I press the brakes, you need to press firmly to get it to stop. Pedal stays off the floor, just needs more than normal pressure.
 
Khary23 said:
Its there much difference in manufactures? And are there any companies that I sould just plain stay away from?
Click to expand...

Lately, I've had the best luck with NAPA stuff. Not to say there aren't other good pieces out there, but I'm on the third MC in my '96, and it was a new one from NAPA. I don't remember the brand, though. But don't forget all of the other components in the system. There is one company I will stay away from, though. They are now, I think, the largest 're-man' company, and they are based in Philly. I got burned with steering boxes back in the Seventies, and I tried one of their MCs this go-round. JUNK!!
 
Did you bench bleed the master cylinder?

I replaced the booster and the master cylinder in my DD civic last summer and didn't properly adjust the pushrod on the new booster at first. When I realized that, and adjusted the pushrod, the brake pedal went straight to the floor. I pulled the master cylinder and bench bled it again, and the brakes felt great after that.
 
I went out this morning to do some more trouble shooting. Two things I noticed. The first is no matter how many times I pump the brakes they do not get firm. The second is a whooshing sound while pumping the pedal that never noticed before.
 
Be sure and take a close look at that check valve, it is the fitting that the vacuum line attaches to at the booster.
Make sure that it didn’t get cracked some how during the replacement of your master cylinder.
Now when you insert the check valve back into the booster make sure that it is inserted all the way in and fits nice and flush with the edge of the booster.

Now start up your Jeep and check for the whooshing sound again and what do the brakes feel like this time.

That whooshing sound you heard could very well be a major vacuum leak that accurse when the brakes are applied.

Please keep us posted so we know weather or not the problem is resolved or not, and if resolved how resolved so the solution is available for the next XJ in trouble.

I also have more information that I can post if you need it.
 
djgrayxj said:
Be sure and take a close look at that check valve, it is the fitting that the vacuum line attaches to at the booster.
Make sure that it didn’t get cracked some how during the replacement of your master cylinder.
Now when you insert the check valve back into the booster make sure that it is inserted all the way in and fits nice and flush with the edge of the booster.

Now start up your Jeep and check for the whooshing sound again and what do the brakes feel like this time.

That whooshing sound you heard could very well be a major vacuum leak that accurse when the brakes are applied.

Please keep us posted so we know weather or not the problem is resolved or not, and if resolved how resolved so the solution is available for the next XJ in trouble.

I also have more information that I can post if you need it.
Click to expand...

I will take a look at the check valve when I get home from class this afternoon
 
Khary23 said:
I went out this morning to do some more trouble shooting. Two things I noticed. The first is no matter how many times I pump the brakes they do not get firm. The second is a whooshing sound while pumping the pedal that never noticed before.
Click to expand...


If the brakes do not get hard at all when pumping I would assume you have one of two things wrong.
1) You have a no good replacement master cylinder,
2) You have a massive air leak maybe at the master cylinder.

If at all possible, try to bleed the master cylinder again with a helper. Do not be pumping the master cylinder but instead use full single strokes ie:
Push the pedal as far as it would go and hold it there. Try to let the air out at the master cylinder line then close the line.
Release the pedal, wait a few seconds then push on it again using a single stroke and let the air out again at the master cylinder through the line.
Repeat this process until you are satisfied there is no more air in the master cylinder.
Repeat this process for the combination valve letting the air out at the connecting lines.
If you are satisfied with the results then move on to the wheels.

It is import to use only full single strokes then opening the bleeder and close it before the pedal is released.
Do not release the pedal with a line or bleeder open and do not pump the pedal repeatedly. Air could be drawn back into the system.
If you fail to get the breaks to firm up, replace the master cylinder "again".
 
[LEFT said:
djgrayxj[/LEFT];245331078]Be sure and take a close look at that check valve, it is the fitting that the vacuum line attaches to at the booster.
Make sure that it
didn’t​
get cracked some how during the replacement of your master cylinder.
Now when you insert the check valve back into the booster make sure that it is inserted all the way in and fits nice and flush with the edge of the booster.

Now start up your Jeep and check for the whooshing sound again and what do the brakes feel like this time.

That whooshing sound you heard could very well be a major vacuum leak that
accurse​
when the brakes are applied.

Please keep us posted so we know weather or not the problem is resolved or not, and if resolved how resolved so the solution is available for the next XJ in trouble.

I also have more information that I can post if you need it.
Click to expand...

Took a look at the check valve and its okay.
I had my uncle press the brakes while I had the hood open, and the whooshing seems to be coming from the area of the booster. I also pressed the pedal by hand with my head under the dash and the whoosh seemed to be coming from the fire wall.
 
Last edited:
This is just a guess, and I don't know if it will work, but what if you disconnected the vacuum line and plugged the port on the booster somehow? If you pumped the brakes with it plugged, wouldn't you be able to tell if the leak was in the booster itself rather than somewhere in the vacuum line or the check valve?
 
With or without the vacumn booster, the breaks should be functionable. Think of it this way,...you are driving down the road, the engine stalls, the breaks still functions and stops the vehicle. Yes, with a good vacumn booster, you get three +/- good strokes before the vacumn run out and the pedal stiffen up and get quite high but you still have enough breaks to stop the vehicle.

With or without the vacumn booster or the engine running the break pedal should be able to build pressure. If it do not then you have problem in the break hydrolic system.

I have bled many a vehicles equiped with vacumn booster,...I usually do not start/run the engine when doing so. The booster only help to make the pedal easier to push. That is it's only function.
 
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