Brake bleed not working?

[heyhar]

I've come home from the yard with various combo valves, one to be the dissection volunteer. For all the hoopla, all it seems to be is a chamber for the brake warning light switch. There's the piston in the middle, and if it moves off-center, as in a fluid leak, it actuates the switch to illuminate the dashboard display. It actually did its job once in my '92, after the hard line to the rear failed suddenly. Of course, my foot going quickly to the floor told me that something was wrong! Oddly enough, after we fixed the hard line, replacing the soft line with it, the pedal feel was the best it ever was. And that was without bleeding the combo block.

Another thing I've seen is that the combo is different form drum to disc rears, although the part #s for the M/C in the XJ and ZJ are the same (the later XJ M/C). If I get around to doing ZJ rears on my '96 this summer, I'll be sure to grab a ZJ combo valve with it.

Although, if I get good results by bleeding my current combo valve, maybe I'll get to do more this summer than work on the HEEP. Last summer was inner and outer rocker panels and major floor pan repairs...Thanks Pennsylvania!

 

[djgrayxj]

Note from DJ to heyhar

In your post #36 you stated Quote: “We have one of those pump-up Power Bleeders”.

Is this a homemade one out of a plastic garden sprayer?

Now hear is a note to Ecomike.

When you design the paint gun setup PM the plans to me so I can make on for my ’88 to use hear in the Los Angeles area. LOL!

 

[djgrayxj]

Note from DJ
If you want some good reading on the technical issues regarding brakes, take the time to look this over this.
The Brake Bible
By Bill "BillaVista" Ansell
From http://www.pirate4x4.com/tech/billavista/Brakes/
NOTE: Under the Maintenance Troubleshooting section I discoverer the following tips;

Under the Spongy Pedal section;
Air in hydraulic system
Hose swelling / Deteriorated flex hoses
Fluid boil
Badly worn pads
Uneven pad wear
Old or contaminated brake fluid
Faulty master cylinder
Calliper not square to rotor
Master Cylinder mounting loose
Clogged reservoir cap vent hole ( I would never thought of this)
Soft or swollen calliper seals

 

[heyhar]

Note from DJ to heyhar

In your post #36 you stated Quote: “We have one of those pump-up Power Bleeders”.
Is this a homemade one out of a plastic garden sprayer?

It's an item called Power Bleeder from MotiveProducts.com. Look in the back advertisement section of most auto magazines for the picture of the hot chick writhing on the floor, talking about she likes something hard...Oh, yeah, she's referring to a brake pedal. Duh, what was I thinking?

Anyway, back to reality. It's built on the same principle as a pump-up sprayer, but better quality, and specific parts. You've got to order it for a specific car, and it comes with a fitting that replaces the M/C cap. Pop it on, pump it up, and go one-man bleeding. It works pretty cool, but your arm will fall off pumping to 20 psi, which is still much lazier than someone's foot on the pedal. And, when you have to periodically top-off the M/C, you must remove the pressurized cap, losing all your painfully produced air pressure. I keep threatening to add a valve stem, but my son resists. 'Leave it alone, Dad'. I say 'OK, then get in the car and get ready'. Truth be told, it's handy if your alone, but I like the old school method better. Wives and kids have to earn their keep, don't they?

 

[N8N_99xj]

I had pathetic brakes after replacing front pads and rotors in my 99 apparently new pads not worn in were worse than old worn out pads... found that rears were out of adjustment and PO had been apparently driving w essentially only front brakes. They still take a hard shove to stop short. This is with performance friction carbon metallic pads. Maybe if they don't wear in better i will try EBC or black magic

 

[Ecomike]

Note from DJ
Master Cylinder mounting loose
Clogged reservoir cap vent hole ( I would never thought of this)
Soft or swollen calliper seals

The last two are knew to me (I did replace one caliper for that reason, loose-swollen like Caliper seal...too old, this week), the top is obvious, but you never see it listed, and the pusher rod length on the new BB needs to be checked when swapping the Brake booster.

 

[Ecomike]

I've come home from the yard with various combo valves, one to be the dissection volunteer. For all the hoopla, all it seems to be is a chamber for the brake warning light switch. There's the piston in the middle, and if it moves off-center, as in a fluid leak, it actuates the switch to illuminate the dashboard display. It actually did its job once in my '92, after the hard line to the rear failed suddenly. Of course, my foot going quickly to the floor told me that something was wrong! Oddly enough, after we fixed the hard line, replacing the soft line with it, the pedal feel was the best it ever was. And that was without bleeding the combo block.

Another thing I've seen is that the combo is different form drum to disc rears, although the part #s for the M/C in the XJ and ZJ are the same (the later XJ M/C). If I get around to doing ZJ rears on my '96 this summer, I'll be sure to grab a ZJ combo valve with it.

I am still scratching my head as to why AZ shows the MC on the 87 to be different than the 89, they look identical to me! Both with out Anti lock brakes.

From what I have read, the combo valve is a mild, low tech version of ABS, designed to "keep the rear wheels from locking up, by forcing more fluid to the front wheels if needed to avoid rear wheel lock up". It is a proportioning valve and also holds the brake light sensor, thus a combo valve.

 

[heyhar]

One thing I've run into thru the years is that as the soft lines age and deteriorate, the inside passage becomes constricted, to the point of either not passing fluid at all, or acting as check-valves. Your foot may be strong enough to push fluid in, but the return springs (or not, in the case of discs) don't push the fluid back to disengage. When the hard line on my '92 rusted through and leaked, I replaced everything from the first coupling back, including the soft line to the axle, and the lines on the axle to the cylinders. The rears worked like brand new!

How's the pad mounting surface on the front knuckle looking? I understand the earlier XJs have a different front brake than, say my '92, but I've had to fix the grooves cut into the mounting surfaces on our collection. My '96 was grooved to the point that an outer pad was jammed into the groove it had cut, and couldn't disengage, wearing itself down, giving a less-than desirable pedal feel. Just a thought...

 

[N8N_99xj]

yeah, what he said too. I haven't replaced the hoses yet on my '99 but probably ought to whenever I get around to lifting it. It was hard to bleed, 20 lbs. on the Motive didn't get good flow, had to pump bleed. Makes me think I probably should have replaced them, but I didn't want to because of ABS.

As an aside, if you can find a pedal jack, keeping the MC depressed slightly to close off the return port will keep all the fluid from draining out when you bleed (kind of like putting your thumb over the end of a straw.) However I have yet to find one in a store that I can buy (know about this trick from a job a long, long time ago)

 

[Ecomike]

One thing I've run into thru the years is that as the soft lines age and deteriorate, the inside passage becomes constricted, to the point of either not passing fluid at all, or acting as check-valves. Your foot may be strong enough to push fluid in, but the return springs (or not, in the case of discs) don't push the fluid back to disengage. When the hard line on my '92 rusted through and leaked, I replaced everything from the first coupling back, including the soft line to the axle, and the lines on the axle to the cylinders. The rears worked like brand new!

How's the pad mounting surface on the front knuckle looking? I understand the earlier XJs have a different front brake than, say my '92, but I've had to fix the grooves cut into the mounting surfaces on our collection. My '96 was grooved to the point that an outer pad was jammed into the groove it had cut, and couldn't disengage, wearing itself down, giving a less-than desirable pedal feel. Just a thought...

278,000 miles on the 87, and no groves, and plenty of flow through the hoses, even before I changed the hoses. The odd part, is that one would think that since the bleed is so easy, fast at each cylinder, that it can not be a restriction in flow (bad hoses, or collapsed tube), unless the restriction is only while sealed and under foot peddle pressure, i.e. the combo valve-air bubble?

Near as I can tell the 87 OEM hoses I replaced the last 6-7 years, were all still functioning properly, in spite of the serious external hose signs of extreme age when I retired them, LOL!

 

[Ecomike]

The more I think about, the more it seems logical that an air bubble trapped in the combo valve, could lead to just one set of brakes getting fluid under a real, sealed system load, and the bubble causing the mushy peddle.

The ability to easily bleed all four wheels, one wheel at a time with no air bubbles, is very deceptive,!!!!

 

[Ecomike]

Spent the last 2 days working on this AGAIN!!! To no avail.

Replaced one drum (one was nearly new, the other just past the wear limit), replaced one rotor (at the wear limit) and replaced one set of pads. The other pads and shoes were all nearly new still.

Bleed the combo valve, bleed all four wheels several times, and again on day two. Tried power bleeding (Jeep running, vacuum on), tried again with engine off (that worked better, got some air bubbles out finally), but when all was said and done, had no leaks, have no leaks, and brakes are no better.

The brakes feel like new brakes with the engine off. The vac booster works. But with the engine running (vacuum on) the brakes feel like mush!!!

Both the MC and booster were brand new (MC is new not rebuilt) and both are recently installed.

Has anyone ever had a bad MC where it held hydraulic pressure with no vacuum, but leaked internally (not externally), with vacuum applied?

This is the second brand new MC, Cast iron, from Azone in 2 years and 15,000 miles, that I have had this issue with. It either still has air I can't seem to get rid of, even after 20 hours of bleeding and a gallon of fluid, or the MC is junk?

Thinking of switch brands even though mine is a lifetime warranty?

Has any one ever tried bleed the MC while installed, right at the connections on the MC? I am wondering if there is a bubble trapped inside the MC that never got out?

 

[Ecomike]

Second question today!!!! I have heard rumors that MCs should bench bleed (like in a bench vise?) before mounting, but I have bleed mine while mounted on the vacuum booster the last 8 years or so with the little tubing kits and plastic holder that comes with the MC before I connected the brake lines. Bench bleeding and transport and mounting....a filled a bled MC seemed messier and more problematic than doing mounted on the VacBoster to me.

Has anyone else had a problem doing this on Renix jeep era MCs (or similar ones) and found air trapped in the MC by not bench bleeding first, versus bleeding while mounted on the VacBooster?

 

[old_man]

Personally, I use an electric vacuum bleeder. I've fixed a ton of "unbleedable" brakes on XJ's. The hand operated ones suck .

I put the wife on a stool so she can keep the MC full as I go around from wheel to wheel and vacuum bleed them I make sure to purge it to where clean fluid is coming through. That way you also get rid of old crappy fluid at the same time. It takes maybe 10 minutes and two bottles of brake fluid to do all four corners.

 

[Ecomike]

Personally, I use an electric vacuum bleeder. I've fixed a ton of "unbleedable" brakes on XJ's. The hand operated ones suck .

I put the wife on a stool so she can keep the MC full as I go around from wheel to wheel and vacuum bleed them I make sure to purge it to where clean fluid is coming through. That way you also get rid of old crappy fluid at the same time. It takes maybe 10 minutes and two bottles of brake fluid to do all four corners.

Well the problem is I think we got the air out (finally, unless it is stuck in the front end of the MC and trapped?), as the peddle is rock hard with just 1" of travel now, and like standing on concrete at about 1.5" of travel, but then with the vacuum on it goes down to about 1" from the floor before it bottoms rock hard, and takes almost 3" of travel to get good braking when driving. We bleed it with the engine running, and with out about 40 times the last 2 weeks. Even bleed the combo valve about 15 times. We even trtied pumping the peddle before cracking the bleeder. We used a 2 man system with the bleeder open about 1-2 seconds on each pump (pressing) of the peddle to make sure did not get back in through the bleeder threads.

When you vacuum bleed do you ever press the peddle or pump it or?? Or just suck it through period?

So I am thinking we got the air out, and still have the same problem. The last brand new auto zone MC leaked out the rear in just 2 years and maybe 15,000 miles of service and it was mushy just like this one.

 

[old_man]

Well the problem is I think we got the air out (finally, unless it is stuck in the front end of the MC and trapped?), as the peddle is rock hard with just 1" of travel now, and like standing on concrete at about 1.5" of travel, but then with the vacuum on it goes down to about 1" from the floor before it bottoms rock hard, and takes almost 3" of travel to get good braking when driving. We bleed it with the engine running, and with out about 40 times the last 2 weeks. Even bleed the combo valve about 15 times. We even trtied pumping the peddle before cracking the bleeder. We used a 2 man system with the bleeder open about 1-2 seconds on each pump (pressing) of the peddle to make sure did not get back in through the bleeder threads.

When you vacuum bleed do you ever press the peddle or pump it or?? Or just suck it through period?

So I am thinking we got the air out, and still have the same problem. The last brand new auto zone MC leaked out the rear in just 2 years and maybe 15,000 miles of service and it was mushy just like this one.

Just suck on it.

 

[cruiser54]

Got some modeling clay?

Remove the master cylinder. Put some clay in the pocket where the booster rod goes in. Bolt the two together. Unbolt them. Measure the thickness of the clay somehow. Toothpick or paperclip. Adjust the booster rod out about so that there is just a teeny bit of clearance between the rod and the pocket of the master cylinder.

 

[87manche]

Personally, I use an electric vacuum bleeder. I've fixed a ton of "unbleedable" brakes on XJ's. The hand operated ones suck .

this.

I hae a mightyvac that' suseful if I've just got to bleed one corner, and the system hasn't run dry.

anything else and I pull out a homemade vacuum bleeder arrangement that's a constant duty pump with a quart mason jar for a catch can.

it's the ONLY way to bleed an internal slave AX-15 and not have the pedal suck.

 

[Ecomike]

I just completed several test drives. The rear drums are staying cooler than the front rotors. I ran a series of severe repeated braking tests, then jumped out and measured the peak rotor and drum temps. ambient is 58 F here. PS rear peak 148 F, DS rear 110F, DS front 208 F and PS front 300F.

Then drove for a cool down to see if one of them might be stuck and dragging, got 110 and 100 F on the rear, 175 F and 260 F front (260 was the PSide again). Then a long drive barely using the brakes and got 98 F on both rears, and 148 F front DS and 225 F PS front. There is no pull to one side when braking soft or hard!!!!

The PS front is new pads, slightly used rotor, the cooler DS front is a new rotor with slightly used pads.

Not sure yet what to conclude from this test yet.

Thoughts???

I do have improved braking in forward and reverse, just still too much peddle travel before it bottoms 1" off the floor, and I do have good breaking at about 1.5 to 2" of brake peddle travel.

The higher PS front temp may just be new pads breaking in on a slightly worn rotor, or a slightly sticking caliper ( I feel no signs of brake dragging at idle coasting down from say 30 or 20 mph in Drive). Hard to say which yet, but neither would cause the mushy peddle. I was able for the first time to lock up a rear drum in reverse if I stood on the peddle a sign of better rear brake action I think.

 

[Ecomike]

Got some modeling clay?

Remove the master cylinder. Put some clay in the pocket where the booster rod goes in. Bolt the two together. Unbolt them. Measure the thickness of the clay somehow. Toothpick or paperclip. Adjust the booster rod out about so that there is just a teeny bit of clearance between the rod and the pocket of the master cylinder.

I think I have that covered already. Even if I close up a possible 1/4" gap, it would not solve 4" of brake travel mush IMHO?