No brakes after WJ booster/master cylinder.

Got a 93, and just swapped in a WJ brake booster and master cylinder from a 99 WJ. Still using my stock proportioning valve. Before the swap, I was using a 96 cherokee booster which worked awesome, but it took a dump.

So I swapped in the booster and master cylinder and bled the master cylinder with it on the Jeep by using some tube and pressing the brake pedal in and out. Like on this write-up: http://www.naxja.org/forum/showthread.php?t=924285&highlight=brake+booster Seemed to work some, but not awesome. The front port of the master cylinder didn't put out NEAR as much fluid while doing this as the rear did. Got it about the best I could and then went to bleed my brakes. Started at the passenger rear, and hardly any fluid came out. Did the other three and same situation.

Re-bleed them about three times and hardly no fluid comes out of the lines. Not sure what the problem is. Bad booster, bad master cylinder, still lots of air in the system (which there shouldn't be)?

Seems to build a little pressure if I pump the pedal with the Jeep off, but when I turn it on the pedal just goes to the floor...

northwestxj said:

Got a 93, and just swapped in a WJ brake booster and master cylinder from a 99 WJ. Still using my stock proportioning valve. Before the swap, I was using a 96 cherokee booster which worked awesome, but it took a dump.

So I swapped in the booster and master cylinder and bled the master cylinder with it on the Jeep by using some tube and pressing the brake pedal in and out. Like on this write-up: http://www.naxja.org/forum/showthread.php?t=924285&highlight=brake+booster Seemed to work some, but not awesome. The front port of the master cylinder didn't put out NEAR as much fluid while doing this as the rear did. Got it about the best I could and then went to bleed my brakes. Started at the passenger rear, and hardly any fluid came out. Did the other three and same situation.

Re-bleed them about three times and hardly no fluid comes out of the lines. Not sure what the problem is. Bad booster, bad master cylinder, still lots of air in the system (which there shouldn't be)?

Seems to build a little pressure if I pump the pedal with the Jeep off, but when I turn it on the pedal just goes to the floor...

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Did you install a spacer between the booster and firewall? Might not have enough travel on the rod.

joe_peters said:

Did you install a spacer between the booster and firewall? Might not have enough travel on the rod.

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No I didn't. I've heard mixed things about that. But in my case, I don't see how this would help. Putting a spacer there would pull the pedal closer to the firewall from the inside.

As it is now, when the pedal is just sitting there it goes all the way back against the brake light switch. Then when I push it in, it goes until the rod seems to bottom out. It's not like it hits the floor or anything and bottoms.

Seems to me like spacing the booster would actually make things worse by not letting the pedal push as far.

northwestxj said:

No I didn't. I've heard mixed things about that. But in my case, I don't see how this would help. Putting a spacer there would pull the pedal closer to the firewall from the inside.

As it is now, when the pedal is just sitting there it goes all the way back against the brake light switch. Then when I push it in, it goes until the rod seems to bottom out. It's not like it hits the floor or anything and bottoms.

Seems to me like spacing the booster would actually make things worse by not letting the pedal push as far.

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I was asking if you used a spacer, and if that spacer was preventing you from getting enough rod travel--in simpler terms, I was going to tell you to use a smaller spacer or remove it entirely.

Now, after all that, I'm on board for a bad MC.

joe_peters said:

I was asking if you used a spacer, and if that spacer was preventing you from getting enough rod travel--in simpler terms, I was going to tell you to use a smaller spacer or remove it entirely.

Now, after all that, I'm on board for a bad MC.

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I gotcha.

So, situation is completely different now. I finally gave up last night because I couldn't get any pedal pressure (pedal went completely to the floor and was extremely soft).

My plan today was to limp it down to Waltz or something and have them pressure bleed it to see if that might fix it. Threw the tires on and started it up, and there's brakes! All it did was sit over night and now it works. I don't feel like they stop quite as well as they did with the 96 XJ booster/master but they work pretty damn good.

Why would this be? Master cylinder wasn't opening/working last night and now it is?

Also, should you be able to hear a pretty loud whoosh sound when you press the pedal coming from the booster? I don't remember hearing it much on my old setup, but now it's much louder. Is the booster leaking air/vacuum?

Well, I have really bad hearing from a misspent youth with large caliber weapons and no hearing protection.

So, the only times I have ever heard a loud whooshing from a brake booster the booster was bad.

That said, give it a quick test: engine off, pump the brake pedal 3-4 times, then hold pressure. Start the engine, the pedal should drop about 1". That means the booster is working.

Here is a link to further testing: http://www.ehow.com/how-does_4829365_testing-procedure-brake-boosters.html

joe_peters said:

Well, I have really bad hearing from a misspent youth with large caliber weapons and no hearing protection.

So, the only times I have ever heard a loud whooshing from a brake booster the booster was bad.

That said, give it a quick test: engine off, pump the brake pedal 3-4 times, then hold pressure. Start the engine, the pedal should drop about 1". That means the booster is working.

Here is a link to further testing: http://www.ehow.com/how-does_4829365_testing-procedure-brake-boosters.html

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Ok, I'll check that out.

I just went out and re-bled them and now more problems. Back two went ok, although they seem like they should be pushing out a little more fluid then they do. But then went to do the front passenger, and the first time it pushed some fluid out but then the second time on the pedal went to the floor and no fluid is coming out at the caliper. I think it must either be air in the line still that we can't seem to get out by bleeding them regular (maybe a power bleed would work)? Or the master cylinder isn't working consistently.

I had a smaller problem when I did my conversion (no spacer used) that may help you. One of my lines had some crap in it that got moved around and clogged up the lines. A power flush and bleed cured it.

I'm so confused about this. When I posted yesterday I had just re-bled the brakes and it made my pedal go to the floor. Again, I left it alone and went to work on it today and tested it, and I have good brakes again. They can lock up all 4 tires. So I drove it today and was on the freeway after driving for 10 miles or so, and I started to feel like I was slowing down. The Jeep had to be in 3rd gear to maintain 50 mph and after driving for a minute or so I figured that something was wrong and pulled over. Brakes were smoking and it turns out my brakes were engaged and (without pressing the pedal). Jeep didn't even want to really go the brakes were grabbing so hard. The pedal was also very very hard.

I opened the back passenger side bleed valve and fluid shot out, and it released the pressure and they started working again. Would could be causing all this? I need to get this thing working, please help.

northwestxj said:

I'm so confused about this. When I posted yesterday I had just re-bled the brakes and it made my pedal go to the floor. Again, I left it alone and went to work on it today and tested it, and I have good brakes again. They can lock up all 4 tires. So I drove it today and was on the freeway after driving for 10 miles or so, and I started to feel like I was slowing down. The Jeep had to be in 3rd gear to maintain 50 mph and after driving for a minute or so I figured that something was wrong and pulled over. Brakes were smoking and it turns out my brakes were engaged and (without pressing the pedal). Jeep didn't even want to really go the brakes were grabbing so hard. The pedal was also very very hard.

I opened the back passenger side bleed valve and fluid shot out, and it released the pressure and they started working again. Would could be causing all this? I need to get this thing working, please help.

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I have seen that happen when the pedal rod is pushed too far into the master cylinder. That could cause constant pressure on the wheel cylinders/calipers. Opening a bleed screw will release the pressure. On the bleed problem, the piston in the master cylinder may not be returning properly thus not un-covering the hole in the master cylinder to allow a fresh charge of break fluid to enter from the resevor. That will make it difficult to bleed. However, a partial un-covering of the master cylinder re-charge port would it to refil over night resulting in good breaks in the morning. Ideally, the pedal rod should not be touching the piston when the break pedal is at rest. The other reason could be a bad master cylinder ie, the piston is sticking in the bore.

techno1154 said:

I have seen that happen when the pedal rod is pushed too far into the master cylinder. That could cause constant pressure on the wheel cylinders/calipers. Opening a bleed screw will release the pressure.

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Makes sense, but what would cause the pedal rod to be pushed too far into the master cylinder? The brakes hadn't been touched for over 5 minutes and the pedal was in its "rest" spot all the way out, where it touches the brake light switch.

The other part makes sense about the master cylinder. More than likely the master cylinder is bad, rather then there still being air in the system though?

The rod is pushed in too far into the MC because of the lack of spacers between the booster and firewall. I'm pretty sure that's why the spacers need to be used.

Did you get the MC/booster from a JY as a set, or did you buy them separately. And are they compatible? Meaning are they both '99 WJ units?
If the MC-to-booster rod is too long, the rear port inside the MC will be covered. Then, as you drive, the fluid in the lines will get hot and expand. With the port covered, there's no place for the fluid to vent, so the caliper pistons move out, applying the brakes. However, if I recall correctly, the WJ booster rod is not adjustable. So if the MC is not the correct part, you must insure the correct spacing. Did you install the "O" ring on the MC before it was installed? If not, then the necessary clearance between the MC and the booster rod may be lacking.
Also, I highly recommend you bench bleed the MC, unless the the MC sets perfectly level whine in the jeep. If the MC is slanted upwards toward the front, air can get trapped in front of the piston, and will be a bear to get out.

xjbubba said:

Did you get the MC/booster from a JY as a set, or did you buy them separately. And are they compatible? Meaning are they both '99 WJ units?
If the MC-to-booster rod is too long, the rear port inside the MC will be covered. Then, as you drive, the fluid in the lines will get hot and expand. With the port covered, there's no place for the fluid to vent, so the caliper pistons move out, applying the brakes. However, if I recall correctly, the WJ booster rod is not adjustable. So if the MC is not the correct part, you must insure the correct spacing. Did you install the "O" ring on the MC before it was installed? If not, then the necessary clearance between the MC and the booster rod may be lacking.
Also, I highly recommend you bench bleed the MC, unless the the MC sets perfectly level whine in the jeep. If the MC is slanted upwards toward the front, air can get trapped in front of the piston, and will be a bear to get out.

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Ya, both the MC/booster came from the same '99 from the JY.

I'm not sure what you mean about the "O" ring. I pulled the booster and master cylinder with them still connected, so if it's something when they're separate I didn't mess with it. The only thing I did was remove the reservoir to clean it.

Like I mentioned before, I did bleed the MC, but did it still on the Jeep. Maybe I should pull it off and bleed it. If I do that though, I may just replace the MC.

Does anybody else know about the spacers? I've heard so many mixed things about if you should use them or not. Some people do, and some people don't it seems. What's weird to me, is if the rod is pushed into the MC a little because I didn't use the spacer wouldn't the brakes be dragging some all the time? They haven't been at all, it only started yesterday after driving it for a little while...

You should hear a bit of a "woosh" that sound is the air going to the nonvaccum side of the booster. Its vent is around the rod on the booster that goes into the passenger compartment. Engine vaccum is on one side of the diaphram in the booster and atmosphere psi is on the other side of the diaphram.
Remove the master cylinder and bench blead it. Then install it and open all the bleeders and loosen the resivour cap and let the system gravity bleed for a bit. Then pressure bleed starting from the farthest from the M/C and moving closer.

Try spaceing the booster out a bit. The pedal will only go out so far toward the driver, so if the booster is partially depressed then the M/C is partially depressed which would cause the rear brakes to be depressed a bit.

The spacer between the booster and firewall is generally used to obtain firewall clearance. The WJ booster I had, had a booster to pedal rod length of 5&3/16"--my stock '88 booster was 5". The difference will not cause any pressure on the booster/MC; it will only change the position of the brake pedal.
I would pull the MC, and bench bleed it. This process will insure no air trapped, and should confirm good or bad MC. If it's a JY unit, who knows what the internal condition of the seals, etc are.

when i did the wj conversion on my 89, i bought the booster and master as a unit from the junk yard. the rod length was a non issue. as far as i know, the spacer is used to give you the proper pedal height. i clearenced the firewall opening with tin snips and a hammer.

with all that said, if this is true with your set up and your having problems, i say the issue is something else then the rod length and spacer. i also still have drum brakes so i did not do anything to the proportioning valve.

So I'm still having problems with this. I went ahead and pulled everything off and put a factory 96 booster spacer in between the WJ booster and the firewall (it was like a 1/4 inch). Then I put everything back on and bled the master cylinder with it on the Jeep again. It worked quite a bit better this time and more fluid came out. After this I bled the entire system. More fluid came out and it seemed to go pretty well, however after I got done and drove it the pedal is pretty soft and mushy but there seems to be no air in the system.

Since then I have bled it quite a few more times (including using a vacuum bleeder) and the issue I have is when I start it in the morning or after I haven't driven it for a while the pedal is pretty soft and the brakes don't work very well. However, after I drive for 5 minutes or so they get much much better. What would cause this? Also, when I bleed it, the back two usually go pretty well but when I get to the front passenger side the first or second time I open the bleed valve generally results with the pedal going to the floor for the person inside even though it was hard before. I keep bleeding and the pedal usually doesn't get better during the bleeding process (with the bleed valve(s) open) but after I close them it gets hard again.

I know that my booster is leaking pretty badly as it hisses almost all the time, and it's LOUD. But from my understanding this should make the pedal harder, not softer.

Bump. I really need to get this figured out and am not sure where to go with it next...

I am confused by this

I keep bleeding and the pedal usually doesn't get better during the bleeding process (with the bleed valve(s) open) but after I close them it gets hard again.

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Describe your bleeding process for us please. Step by step if you will... Thanks