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Brakes, Brakes, give me a break.

Fred

NAXJA Member
NAXJA Member
:rattle:
I've done more than a few searches, and haven't found an answer to my problem.

Here's the summary.

90 XJ, brakes were fine until axles were swapped. Swapped in a non disconnect HP D-30 of the pre-90 era, just like the axle it replaced. Disks and calipers went right on. Also swapped in a D-44. After bleeding, the brakes would lock if really stomped on, but barely.

I got it home and bled it some more, but really didn't get more peddle. I put on new drums, and new cylinders in the D-44 so every brake part was new. Better but still not enough pedal. Fixed the YJ e-brake cables so they would work, and adjusted the e-brake to 4 clicks, better but still not enough pedal. Replaced a caliper that had the bleeder screw broken off, and put speed bleeders on all four corners. The caliper was used and had been sitting around, but it was full of fluid. Bled some more, still not enough pedal. Replaced the brake booster. Nada. Replaced the master cylinder, better but still not right. I've bled close to 3 quarts of fluid through the system.

Today, I tried replacing the front brake pads at the suggestion of my neighborhood mechanic. No better, actually seems worse. I'm thinking that the used caliper I put on isn't working as well as the other caliper, but it does work, it holds the wheel when the brakes are pushed. All of the flex brake lines are braided stainless steel, nothing is leaking significantly that I can see, brake fluid does not decrease noticably when I use it, but I don't really drive it much. It stops, but not as quick as it should.

Don't bother bemoaning the poor brake system in the XJ, mine when it was working right would lock up all four wheels without trying real hard. It should work just fine for 31's.

I'll probably replace the one caliper, but I can't see how that would magically make the peddle correct.

I'm open for suggestions. I'd like to get the brake stuff over with so I can move on to all the other crap I need to get done for Colorado Fest. It would be nice to actually try out the NP 241J and the TeraLockers and the MTR's on a trail. :laugh3:

Fred
 
Oh fun - another hydraulic problem!

Seriously, what ALL did you change? Sounds like nearly everything after the master cylinder, with the exception of the hardlines?

If you changed the hoses, you should have checked the hoses for "flappers' before you put them on - sometimes (rarely, I grant you!) you can get one slipping through quality control.

I'd also be tempted to check fluid delivery at the wheels - but I'd like to know what all parts you have replaced to help find the fault.

I'd not see why brake pads should cause the problem you're talking about - but I may or may not be missing something, so I'll reserve judgement.

Also not that handbrake adjustments should not effect the brake pedal - unless you overdo the handbrake adjustment and the brakes are "constantly partway applied." Separate actuation systems, that only converge at the brake shoes.

So, it looks like you changed both axles, right? What about hydraulic and friction parts? Detailed list, please - and why you'd have done them work (if not due to "I'm changing axles, and I'm down there anyhow...")

5-90
 
True - but two points there -

1) The bleed screws will be inverted. If you can't spot that, I'd like to know what you're doing working on brakes!

2) Even if you can't get ALL the air out, you should still have a working pedal - even though it might be soft or spongy. It sounds like he's getting NO pedal - or close to it.

The problem with doing major repairs to anything hydraulic is that it takes longer to find the fault. Changing a single part makes it a LOT easier to isolate - but when you change a lot of stuff at once, it's a good idea to check each part BEFORE you install it - especially since it's usually pretty easy to check them.

5-90
 
Calipers are on correctly, bleed valve pointed up.

To repeat: Rear brakes on D-44, every single stinking part is new. The brakes work. I put the axle on stands and had the kid step on the brakes. The wheels won't turn. You can lock the rears when stepped on hard when driving.

Power booster, master cylinder, and front brake shoes are new. Stainless steel flex lines.

The front brakes work, also tested on axle stands. There is plenty of fluid flow to all corners, easy to see when they are being bled.

The only hydraulic parts, aside from the hard lines, left to replace are the front calipers and the proportioning valve.
I have another used proportioning valve, but I can't see how that could be causing the problem. I also don't see how a slightly hanging caliper could cause the pedal I have.

It's a strange pedal. It feels soft, but will catch near the end of the travel. Pumping doesn't really bring it up, like it would there were air in the system. I'm pretty familiar with that symptom, and it doesn't feel like that. Wierdest thing is that replacing the front shoes made the pedal feel softer. Clamping the caliper piston pushed the fluid out of the reservoir as expected, and I refilled it after each caliper was mounted.

The axles were swapped into a working brake system. The only difference was the rear 44, and when working should help the braking. The 10 by 1.75 on the D-35 worked great when new, and I'd expect the 10 by 2.5 on the D-44 to be better.

I'm not exactly a newb when it comes to wrenching, but I've never had great luck with brakes. :laugh3:

Fred
 
I´ve got no silver bullet for you, but a couple of tips.
Sand the front pads to remove the glaze, makes breakin a whole lot quicker. Also sand the discs and drums, with 100 grit coated (blue) sand paper. First one direction at a 45 degree angle then, reverse at a 45 degree angle, so you end up with a bunch of X's. When sanding the pads and shoes, sand also at a 45 degree angle against the rotation. Just enough to rough them a bit.
When you get done, back up a few times and use the parking brake to stop, this really helps the self adjusters do there job.
Do a test, stop fairly quickly from about 20 MPH or so, with your hands off the wheel. This will tell you if the fronts are pulling together. Your probably gonna need a wet street, to test the rears for offside lockup, unless you have access to a brake machine.
Bleed the brakes from the shortest run, to the longest run of brake line.
Try not to get the brakes really hot, for a few hundred miles.
This isn´t stuff I dreamed up, this is they way Raybestos used to teach it.
If you sand the disc´s and drums at every shoe and pad change, they wear much more evenly.
It sometimes takes some break in, to get the shoes to fit the drums just right. Afer a week or so of driving, you can pull a drum and see right quick exactly how much of the shoe is making contact.
 
Fred, I had a similiar problem on my 89, with a low pedal after brake work. The solution was to simply adjust the shoes outward a little. The self-adjusters do not work well unless the shoes are in adjustment to start with, so try cranking them a little closer to the drums.

If that dosen't work, then your master cylinder pushrod must be too short, and should be adjusted outward. The best way to do this is to take measurements, and adjust the pushrod to give about 1/8" clearance in the master cylinder bore.
 
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Appears problem ocurred after swapping in D44 rear axel, with drum brakes. Are the D44 wheel cyliders larger than the D35 wheel cylinders? Could it be your stock master cylinder has insufficient capacity; ie, too small piston size for the new rear wheel cylinders? Could there be a problem with the matching of the combination valve and rear wheel cylinder capacity? I'm experiencing the same symptoms with my '88 after swapping in a D44 with disc brakes.
I've replaced my master cylinder with one having a larger piston; I've gutted my combo valve; and in desperation, changed the position of the the master cylinder push rod-to-brake pedal attachement to get more pedal. Then I made things worse by adding 33" tires! I'm still not happy with the brakes, and am looking forward to someone helping you find the solution to your problem. I think increasing fluid volume requirements by adding larger wheel cylinders, or caliper pistons as in my case, requires larger master cylinder piston. How much larger is the question. Adding a larger master cylinder, in turn, will cause the peddle to rise but increse pressure required to "lock them up". So, to offset that, you need to upgrade the power brake booster.
Upshod is, when you change ONE thing affecting brake efficiency, you NEED to address all other affected items.
 
D44 cylinders are larger than D35 cylinders, but not that much.

Did you replace your combination valve? That's most likely the problem.
 
I learned about adjusting the rear brakes the hard way, they are adjusted correctly. :laugh3:

I have never seen a different part number for brake cylinders for the D-44 or the D-35 of the same year, they are both 7/8". Nor have I seen any different part numbers for a master cylinder for a jeep with the D-44. Hard to tell about the proportioning valve, but I've never seen anyone post that a proportioning valve from a D-44 equipped XJ is any different from one without it.

Eagle, would you please explain to me how the proportioning valve could cause this effect?? I had a spare apart, and I just don't understand how it could. I'd go ahead and replace it with the spare, but the fittings are really tight, and I'm a little worried about messing it up worse than it is. :)

Keep the suggestions coming. I'd hate to take it to a brake place, only to tell me something I should have thought of. I hate that "Doh" feeling, especially when I'm paying for it. :)

Fred
 
Hey Ralph,

You need to come out for a visit!

I think the calipers are my next step.

Fred
 
Fred said:
Eagle, would you please explain to me how the proportioning valve could cause this effect?? I had a spare apart, and I just don't understand how it could. I'd go ahead and replace it with the spare, but the fittings are really tight, and I'm a little worried about messing it up worse than it is. :)
It's not a design issue, it's an equipment failure issue.

CHW, my predecessor as Pres of the North Atlantic Chapter, had the exact same problem with his '89 and a Dana 44 rear axle. No matter how many times he adjusted and bled, and bled and adjusted the brakes -- he never had any rear brakes, and he always had a really low, soft peddle.

After much consultation with wise men, soothsayers, mystics, mechanics, and other ill-assorted types, he finally determined that the only thing left that he had not changed at least once (and probably two or three times) was the combination valve. So he ripped it out along with all the existing hard lines, replumbed the system with all new hard lines, NO combo valve, and a Wilwood adjustable proportioning valve serving the rear circuit only.

He immediately had a rock hard peddle, and even with the proportioning valve turned way down he said he had better rear brakes than he had ever imagined an XJ could provide.
 
Rock Hard pedal, that is a pretty exciting thought for an old guy. :laugh3:

I'll keep that in mind, but if I end up doing that, it'll be another year before I get it fixed.

I did replace the caliper that was hanging up slightly, there was some improvement, but still not right.

FWIW, I don't think speed bleeders work very well, I get much better results having the kid pump the pedal, hold, open and close the valve. This after weeks of using them. They might be fine for normal everyday type maintenance, but if the system is problematic like mine, they don't get the air out well.

Fred
 
Did you bench bleed the master cycl.? Did a whole brake system upgrade on my XJ and had the same problem, ended up bench bleeding a second time and re-bled the brakes and 10times, and taking the rear drum brakes apart and re-installing everything, adjusted the shoes out to where my wheel would spin 1 full rotation or a little more and solved my issue. Hope that helps you some. Good luck!
 
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