After a scarry ride backward down a hill, I am committed to getting my rear brakes to work.

This is a 75 CJ-5, Original Drum all around.

Have a relatively new MC. Air has been bleed out ok. New turn on rear drum and new shoes and adjusters. Rebleed the rears. Good pedel pressure.

Still will drag the front on even a small hill going backward.

Pulled the combination valve back part out (spring and plunger ) and seems ok.

what else am I missing?

Thanks
Mark

If your brakes are otherwise working properly, you might be up against the laws of physics.

In normal braking while moving forward the front brakes do most of the work - 70% to 80% usually. That's because weight shifts to the front axel under braking, and the front is heavier than the back to begin with.

When you're going downhill backwards there is considerably more weight on the back axel, but the front brakes are still trying to do twice as much. That will cause them to lock long before the backs get with the program. I don't know of any practical cure; it's something that you have to learn to work with as a driver.

Another thing to keep in mind; drum brakes are self-boosting. The drag on the forward shoe pushes the aft shoe harder into the drum, increasing the braking effect. The same thing happens when braking backwards, but to a significantly lesser extent because shoe sizes, geometry and friction materials are picked to optomize the effect while going forward.

I agree with your post. I would think that with enough pedal pressure, I could at least slow down the rear wheels in reverse. Can't lock the wheels in forward after some more test yesterday evening on wet pavement. Can lock the front up going forward.

I pulled the combination valve apart to make sure that nothing was stopped up in there. Didn't find anything that I would think would cause a problem.

I don't dare try to stop on a city street pointed nose up or I will slide uncontrolled down the hill......backwards. I'm not talking about problems on a mountain. I almost rolled the thing on a paved street here in town so I am a motivated investagator to the problem....

Are we talking power brakes? Bad booster maybe?

If you can't hold on a hill, you've got a problem with ALL the brakes, not just the rear. When you bled the brakes, did the pedal go all the way to the floor? Does it stop higher when you brake than when you bled the brakes? Does your e-brake hold?

The front brakes will lock up and I am dragging the front down the hill. Did not let the pedal go to the floor when bleding. Seems to have good solid pedal. E-brake is stretched cable wise and have not gotten the rusted adjuster to move yet, so, no the e-brake is not holding but you can tell it is set if that makes any sense.

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New turn on rear drum and ...

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The drums were checked to make sure they were not turned out past the max. diameter?

Another thought about the shoes, hard compound shoes take a very long time to wear in and seat properly. I like the cheaper (softer compound) shoes, they do not last as long but work much better while they last.

Good Luck

Seems that brake shoe manufacturors have forgotten brakes are a friction device.
Stay clear of the super hard "lifetime" shoes.
Generally the cheapies are nice and soft and work the best.

The valve - you are calling it a combination valve, I believe it's more aptly called a differential valve. Many operate a light on the dash.

There's a piston inside that moves when one side has more pressure - it ties both front and rear systems together in an emergency. You've seen how it works.

What could be happening is the valve has moved to the side - so one portion of the MC is trying to operate both.
You might notice when bleeding that one side uses considerably more fluid than the other.
To center it simply open the line on the side that's doing the work, push the pedal down till you hear a faint "click."

Hopefully it's that simple.

The turn diameter is withing spec.

Manual Brakes and no booster, just my 240# standing on it.... [img]images/graemlins/smile.gif[/img]

Here's a couple sites that explains the different sort of brake valves.
They call the hold-off valve the metering valve - same thing.

http://www.infodotinc.com/basae/174.htm

http://lidrock.howstuffworks.com/rac...ter-brake2.htm