Brake issues

[Joe94xj]

Missed that part.

 

[Frank Z]

Try pumping the pedal a lot ... all the way to the floor ... like 10 times, then check your fluid level in the MC. If it goes down, you have a leak somewhere, if not, you have a different problem. If your pedal gets firmer after a lot of pumping, then you need to bleed more.

Are your calipers seated properly ... is there anything that might be pulling your pads away from the rotors when you let up on the pedal? Too much travel would also cause the pedal to go to the floor.

Another question, has this combination of components worked in the past? Or did you just put them together and they aren't working?

I'm asking these questions to try to isolate the problem.

Pumped more than Arnold on a housekeeper.....

Never did get really firm and I did look for a drop in fluid level. Honestly can't say I saw a noticeable drop though.

The only recent change is the addition of the Chevy Calipers on my front D44. Everything was working Fine with my WJ brakes. That's why I'm gonna yank the front rubber and get cozy with the front end.

 

[Frank Z]

No worries Joe...happens all the time.

 

[Sidewinder CC]

Yes it's a stock M/C.

Fade: Peddle slowly goes to the floor.

This is a fault described in the FSM Master Cylinder/Brake Booster Diagnosis.

Here's an excerpt from the FSM:

"Start engine and note pedal action it should fall away slightly under light foot pressure then hold firm. If no pedal action is discernible, power booster, vacuum supply, or vacuum check valve is faulty."

Check for leaks at the brake booster to intake manifold hose, remove and inspect the check valve function. If no leaks are found and the check valve functions normally, I would suspect a bad brake booster.

 

[Joe94xj]

Not an ideal thing to do but if you can pinch off your brake hoses all at once and pump the pedal it will help you narrow down your issue.

 

[Frank Z]

This is a fault described in the FSM Master Cylinder/Brake Booster Diagnosis.

Here's an excerpt from the FSM:

"Start engine and note pedal action it should fall away slightly under light foot pressure then hold firm. If no pedal action is discernible, power booster, vacuum supply, or vacuum check valve is faulty."

Check for leaks at the brake booster to intake manifold hose, remove and inspect the check valve function. If no leaks are found and the check valve functions normally, I would suspect a bad brake booster.

No leaks at the hoses, no check valve either. Not a 100% stock motor.

It's the hold firm part that ain't happening.

Not an ideal thing to do but if you can pinch off your brake hoses all at once and pump the pedal it will help you narrow down your issue.

I'll be in touch.

 

[JJacobs]

You can always do the on-car m/c bleed.. same as at the wheels, just messier. Have someone turn the fittings loose while you run the pedal. I do like the idea of putting plugs in the m/c outlets and seeing if you have the same pedal feel.

Booster test, engine off pump multiple times until the pedal gets solid- if it doesn't don't bother continuing. Start the engine, pedal should drop some.

Once upon a time in a land not all that far away, I had a front wheel bearing go out. The Jeep would pull left until you got on the brakes, and it took a couple of pumps to get a good pedal. The rotor would tilt and push the pads back, a few pedal pumps would stand the wheel up straight. Any chance of some odd mechanical issue along similar lines?

 

[Frank Z]

You can always do the on-car m/c bleed.. same as at the wheels, just messier. Have someone turn the fittings loose while you run the pedal. I do like the idea of putting plugs in the m/c outlets and seeing if you have the same pedal feel. I'll see if I can find some plugs...

Booster test, engine off pump multiple times until the pedal gets solid- if it doesn't don't bother continuing. Start the engine, pedal should drop some. It doesn't get solid and will keep moving toward the floor

Once upon a time in a land not all that far away, I had a front wheel bearing go out. The Jeep would pull left until you got on the brakes, and it took a couple of pumps to get a good pedal. The rotor would tilt and push the pads back, a few pedal pumps would stand the wheel up straight. Any chance of some odd mechanical issue along similar lines?

No, not really. Unit bearing hubs have been replaced with Manual hubs and assorted parts from a variety of vehicles, but a common swap to get to 5 on 5.5.

 

[eflores]

Not an ideal thing to do but if you can pinch off your brake hoses all at once and pump the pedal it will help you narrow down your issue.

This was going to be my advice at least u can work your way back to other components that way

 

[montanaman]

Pumped more than Arnold on a housekeeper.....

Hillarious!

Never did get really firm and I did look for a drop in fluid level. Honestly can't say I saw a noticeable drop though.

No loss of fluid means no leak.

The only recent change is the addition of the Chevy Calipers on my front D44. Everything was working Fine with my WJ brakes. That's why I'm gonna yank the front rubber and get cozy with the front end.

So ... it could be:

- Problem with the vacuum booster as described in the previous post quoting the FSM
- A huge amount of air in the system
- Or the Chevy calipers are so big, they need more volume than the OEM MC can deliver. Do you know if anyone else has successfully matched those calipers with an XJ OEM MC?

Are you sure you didn't accidentally suck some air into the MC while bleeding? You sound like a tech-savy guy, so I mean no offense ... just another possibility. Did you bench bleed the MC before installing?

 

[NW-ZJ-SCOTT]

My money is on the booster... FWIW... Been there..

 

[JJacobs]

Just remembered something else. Got free play between the master and booster? Try shortening up the pushrod a hair.

 

[ClarkPeach]

Sounds like potential leak or possible swelling hose to me.

 

[xj-grin]

the XJ master will handle the Chevy calipers fine -- I ran it for years on my waggy front. sorry, Frank, I got nothing, I'm good at "breaking" things, but not so much at "braking"...

 

[montanaman]

I always thought a bad vacuum booster would make the pedal more firm ... like the pedal is rock hard but not doing much stopping. But I could be wrong ... never dealt with the boosters much. Can somebody explain how that works, and how it could make the pedal go to the floor?

 

[techno1154]

I always thought a bad vacuum booster would make the pedal more firm ... like the pedal is rock hard but not doing much stopping. But I could be wrong ... never dealt with the boosters much. Can somebody explain how that works, and how it could make the pedal go to the floor?

A break Vacuum Booster is also know as a 'Vacumn Assist Device' with the emphasis on the word Assist. In other words, all the vacumn booster does is make it easier too push the pedal to apply the breaks. The same goes for the power steering on our beloved XJ's. The XJ should be able steer and stop with or with out the engine running. If the break pedal goes to the floor with or without the engine running you have real problems.

Think for a moment about the many early Jeeps and other vehicles that were produced with no vacumn assist and are still on the road today. They require more foot presure, to stop them but they do stop. And the pedal remain firm.

 

[montanaman]

Yeah ... that's exactly what I was thinking ... I just can't picture how a bad vacuum boost would make the pedal go to the floor like Frank is experiencing. nw-xj-scott said he's experienced that problem before, and I'm willing to believe it, but I just can't picture it.

 

[old_man]

If the booster is a dual, make sure that it is sealed to the MC.

 

[Frank Z]

So Joe94 came by today and brought a fancy tool to force brake fluid into the reservoir. We bled the brakes by forcing fluid through the lines.....still had a crappy peddle.

Scratched our noggin's for a while and decided that i must have been the recipient of ye another crappy M/C. Get the "old" one off and grabbed another from the parts house.

Led calls and wants to come over and make fun of me....who am I to say no?

New m/C goes in.
Pump the system full of fluid again....


Peddle still goes to the floor.

We look.
We listen.
We bleed.
We look some more.

Nuttin' honey.

So Joe and led suggest crimping the brakelines and see if there's any change.

BINGO!!
Peddle goes stiff like a teenage boy on prom night.
caliper is new, still can't wrap my brain around what is wrong with it....but at least know we know.

All down hill from here...Right?

Led calls it a night, Joe and I head to the parts store only to find out they don't have the caliper. No worries, drive 5 miles to another branch and pick up another one under warranty.

Head back to the shack and get Joe's tools loaded up and sent him home.

Did I mention it's raining now?
Well .......it is.

I grab a quick bite for dinner and step out into the rain again.

Caliper goes on smoothly.
Banjo bolt goes in....and just keeps a spinning.
Funny....it fit the previous caliper just fine and the same bolt is the passenger side.

SIGH...

Back to the parts store.
Grab a banjo bolt from the HELP! section.

Back out in the rain,new banjo bolt in hand.
Test fit new banjo bolt into new caliper.
Fits beautifully.
Remove banjo bolt to install copper washer and insert through brake line.


Banjo bolt to fookin' big...won't fit into the banjo.

I'm going back out to apologize to the neighbors for my curse-laden outburst....and to get my tools out of the street.

 

[Joe94xj]

Its a never ending saga isnt it. I have a box full of banjo bolts. Might have one that works.