Brake Question

[Dadinator]

So, just replaced the front axle with a HP Dana 30 from a 97ish Cherokee.  Goodbye CAD!

 

Anyway, my brakes have been getting worse and worse even before I replaced the axle.  Once everything was back together, (and brakes bled), I took it for a test drive.

Brakes are weak as ever.  Maybe even weaker.  Cannot lock them up now matter how hard I slam.  Not spongy and no air in the lines.

 

I am thinking the master cylinder is just crapping out.

 

Thoughts?

[Jeep Driver]

Bleed and adjust the rears?

[Dadinator]

Not today...

[Dadinator]

Anyone else?  This has been an ongoing problem with this truck.

Brakes getting weaker and weaker.  Pads and shoes are OK.  Pedal is not soft.  Kind of stiff.

Booster?  Master Cylinder?

Or should I just do what he says and bleed the rears.

How do you adjust the rears?

 

Been working on other stuff on it right now.

Yesterday was the first time it has been off of jackstands since November.

 

Replaced shocks and front axle.  2" pucks in front and chevy drop shackles in rear.

 

Putting the rear shocks on tomorrow and then will focus on the brakes.

Hope to get it back on the road by next week.

 

Let me know your ideas oh brake gurus!

[Keyav8r]

Rears are theoretically self-adjusting. Pull forward, brake, reverse, brake, forward, brake reverse, brake, etc. the brakes are supposed to adjust one notch on the star wheel each time do the cycle. I usually manually adjust them with the drums off to the point that the drums will slide over the shoes with just a little drag.

There is a procedure for bleeding the brakes if you have the rear brake proportioning valve still in service (the valve mounted above the rear axle with the lever arm and link to the diff housing). Try searching MJ Tech section for brake adjustment or maybe someone will post a link to it.

If you don't have the rear proportioning valve, you bleed the brakes in the usual fashion. Right rear, left rear, right front, left front.

Also, you may have a booster problem. I think Hornbrod posted the booster testing procedure.

[cruiser54]

I'd be interested in seeing the brake bleeding procedure. I COULD go get my manual from the garage I guess.

 

Dadinator, have someone pump the pedal and you look for bubbles in the master cylinder. 

 

After the Jeep has run a bit, pull the plastic valve out of the booster. Is vacuum present? 

[Dadinator]

Thanks Keyav8r and Cruiser54.  I will try that stuff  :thumbsup:.  Not working on it tonight had to work late.  Going out with friends tomorrow, so it will be a weekend project.

[Jeep Driver]

Barring a bad MC or booster........

 

The brake system is just that, a system of fronts and rears.

 

As to the self adjusters theoretically self adjusting- wonderful theory until the adjuster wheel locks up and refuses to turn.

 

Rear get no attention, generally.

 

Remove drums, clean, replace shoes and cylinders if necessary.

 

Disassemble adjuster wheel and wire wheel the threads to clean, lube.

 

I adjust with the drum and wheel on, use a brake spoon to adjust while spinning tire with other hand until you sense the shoes begin to make contact with the drum, do both the same way.

 

Bleed all four- pass. rear- driver rear- pass. front- driver front.

 

 

 

I've got a whole bunch of brake on mine.

[Dadinator]

Bled them in order.  Test drive, No good.

Vacuum present in Booster.

Did the reverse, brake forward brake procedure to adjust rears.

When pulling off the drums, they seemed to be adjusted OK.  when I put them back on, there was slight drag.

No bubbles in master cylinder when pedal pressed. 

 

When pedal pressed, you can see it in the front of the master cylinder(like a little geyser), but the rear does nothing visible.

When pedal pressed, 1 side of each wheel cylinder pushes out the shoes, not both sides.

Is this normal when looking at them?

 

Also, the brake proportioning valve is in tact.  But now the rear sits approx. 2 inches higher.  Is there some adjustment to it that needs to be done?

 

Next steps?

[cruiser54]

Adjust the rear shoes. 

 

Possible bad master cylinder. 

[Dadinator]

I was thinking master cylinder.  but did not know how to tell for sure.

[cruiser54]

I was thinking master cylinder.  but did not know how to tell for sure.

Geyser in one part and not in the other? 

[Eagle]

Geyser?

 

I don't think I've ever looked into an uncovered master cylinder while someone else stepped on the brakes, but that doesn't sound right. The fluid is supposed to go through the line to the wheels, not geyser up in the reservoir.

[Jeep Driver]

Yes, the front of mine and others I have worked on will squirt out if  you don't put the cover on while bleeding manually.

[Jeep Driver]

Bled them in order.  Test drive, No good.

Vacuum present in Booster.

Did the reverse, brake forward brake procedure to adjust rears.

When pulling off the drums, they seemed to be adjusted OK.  when I put them back on, there was slight drag.

No bubbles in master cylinder when pedal pressed. 

 

When pedal pressed, you can see it in the front of the master cylinder(like a little geyser), but the rear does nothing visible.

When pedal pressed, 1 side of each wheel cylinder pushes out the shoes, not both sides.

Is this normal when looking at them?

 

Also, the brake proportioning valve is in tact.  But now the rear sits approx. 2 inches higher.  Is there some adjustment to it that needs to be done?

 

Next steps?

 

 

Cylinders are $10 each at  O'Really's (sarcasm)

[Dillithium]

In all seriousness, both pegs need to come out simultaneously on your rear cylinders. But that shouldn't cause THAT big of a brake performance issue. Try pushing in the stuck pegs, check for movement but you're probably due for replacing them.

[Dadinator]

I figured that both should come out the same.

Yep, I know they are cheap.  Just don't like buying parts I don't need.

 

What about that proportioning valve?

Anything I need to check there?

[Dillithium]

If I'm correct, but people who haven't eliminated it will know better, at max capacity the stock MJ prop valve lever will need to be vertical(for max brake power). Try tying it off in a vertical position with a zip tie, then do a test run. I don't know how to test the prop valve, tbh.

 

But again, most of your braking power comes from the front. I think you're putting too much effort in the rear. How are the front pads? Discs? Brake lines relatively new/good condition? If the lines are perished, they sometimes soak up a lot of braking force by expanding when you brake.

[Dadinator]

Pads rotors, shoes are all good shape.  Brake lines seem OK.

 

I am thinking the master cylinder may be the culprit, but I don't know.

[Dillithium]

Then I'm stumped. How clean is your reservoir? No sediment that could be clogging your MC lines?

[Jeep Driver]

If I'm correct, but people who haven't eliminated it will know better, at max capacity the stock MJ prop valve lever will need to be vertical(for max brake power). Try tying it off in a vertical position with a zip tie, then do a test run. I don't know how to test the prop valve, tbh.

 

But again, most of your braking power comes from the front. I think you're putting too much effort in the rear. How are the front pads? Discs? Brake lines relatively new/good condition? If the lines are perished, they sometimes soak up a lot of braking force by expanding when you brake.

 

 

Correct, about 70% of the braking is at the front.

 

That said, again, its a system, fronts are not independent of rears.

 

I made a proportioning rod mount that raised the rod up about 1 1/4" and that helped while running  empty.

 

When I'm loaded with about 600lbs I can feel a great difference in braking power, brakes come on as soon as I step on the petal, vs maybe 3/4" of an inch of travel when empty. That tells me the proportioning valve is still working.

 

You are also correct about the soft lines expanding, if they expand by 10% you may have a braking loss exponentially by x2 or x3 at the petal....IOWs a 30% loss of braking power.

 

 

My braking system has be completely replaced with exception of the proportioning valve.

Sometimes all that's left is to start throwing parts at it.

 

 

 

Keep screwing around with it.........rear-end someone at a stoplight........then you will no longer have to worry about throwing parts at it.

[cruiser54]

Still haven't checked booster rod to master cylinder dimension, have we? 

 

It's all the way at the end of this article.

 

http://www.autoshop101.com/forms/brake05.pdf

[Dadinator]

No rear ending anyone because I am not driving it until I fix it.

Not my driver. 

 

That's a hell of an article.

 

Master cylinders are fairly cheap.

I may just buy one and 2 wheel cylinders for the rear, replace all of them and flush with all new fluid and see what that does for me.

 

I appreciate all the input from everyone.

 

Thanks.

[cruiser54]

Make sure you check the pushrod dimension while you're at it. I like your approach.

[Dadinator]

Just replaced the wheel cylinders and took the rear adjusters apart and cleaned and lubed.  They were both locked in place.  No movement.  Move nice and free now.

Reassembled.

Took the master cylinder off and behold, the new one is WRONG! :fs1:

Crap!  This stuff happens to me all the time.  I must be cursed.

 

Took it back and am awaiting another new one.  Hopefully delivered to store this afternoon so I can finish this evening.  :???: