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Old 09-16-2010, 12:49 PM   #1
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How do i modify the brake prop valve

Anyone know of a sight i can go to get pics of modifying the brake valve

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Old 09-16-2010, 12:56 PM   #2
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Why do you believe it should be modified? I imagine you are asking about removing the o-ring, right? The same brake prop valve is used whether you have drum or disk brakes in the rear so you don't really benefit by doing the mod that some have done.

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Old 09-16-2010, 01:18 PM   #3
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The rear brakes on my TJ are weak, I just installed new shoes and drums, bled the brakes countless times and when the back end is on jack stands I could put it in drive and the rear tires will not lock up even at low idle. there are no leaks in the wheel cyls, or lines.
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Old 09-16-2010, 01:34 PM   #4
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Rear brakes are NEVER EVER supposed to lock up, that would be extremely dangerous if they did. The rear brakes are only supposed to provide 20-25% max of the total braking force, the fronts are set up to provide the vast majority of your total braking.

When the rear brakes lock up, that is an instant skid/slide/out of control condition. All this is why there is a brake proportioning valve in the first place, to limit the amount of brake line pressure sent to the rear brakes.
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Old 09-16-2010, 01:51 PM   #5
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I have the same same problem jerry, the brake pads and drums are like brand new in the rear i bled the brakes. And while i was applying brake pressure at the pedal my dad was able to turn the rear wheels by hand. Is that a problem? or is it supposed to be weak to that extent.
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Old 09-16-2010, 02:00 PM   #6
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Your rear drum brakes have a problem, you shouldn't be even close to being able to rotate the rear wheels with the brakes on. They are either out of adjustment, and that adjustment is easily done, or the brake shoes etc. were installed incorrectly.
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Old 09-16-2010, 08:30 PM   #7
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My dad said it could be the brake cylinder, because the e-brake works like a charm whenever i need to use it on hills.

Does that narrow it down at all?
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Old 09-25-2010, 11:19 AM   #8
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bump?
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Old 09-25-2010, 12:17 PM   #9
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Two things:

1. The lining material used - if you are using the "lifetime" linings, usually touted as the best, they are too hard. They make them super hard so they will last a long time, but they don't stop very well. Remember - brakes are a friction device! Use the cheapie linings, they are softer and will still last a long time, but they will stop nicely.

2. The way you are adjusting them - the cylinders can only push the linings out so far. If you are at the end of their travel they can't push hard.
Try this - pull the E-brake on a little, then try to turn them. If the wheel is tight now, readjust them properly.

Jack up both rear wheels off the ground.
Properly - loosen the E-brake cable till it's slack.

Turn the adjuster wheel so the inside of the adjuster wheel goes UP (on both wheels the direction is UP to tighten.)
Tighten until it nearly stops the wheel from turning.
IMPORTANT -- Step on the brake pedal, then release - that centers the entire lining assembly - it'll probably turn easy again.
Tighten the adjuster again till the wheel barely turns, step on the pedal again.
Keep doing that - tightening, then stepping until it stays tight after stepping.

After it stays tight all the time -
Back the adjuster off 4 or 5 clicks - turn adjuster so the adjuster wheel goes DOWN - (you probably will have to poke a small screwdriver in through the adjuster hole to push the self adjuster lever away from the star wheel.)
After those 4 or 5 clicks, step on the pedal again!
It will be looser now. If it's still dragging back it off another 4 or 5 clicks.

Now readjust the E-brake cable so it's tight but not pulling.

The Bendix system pivots around only one point, the assembly gets off center slightly when you turn the adjuster's star wheel, giving you a false indication of how tight it is. When you step on the pedal it centers itself - reality check.

Unfortunately the term "proportioning valve" is a misnomer. It would be more aptly named "hold off valve." Disc pads ride right up against the rotors, so they react immediately. Drum linings are held back a little. If both front and rear got pressure at the same time the discs would apply braking force long before the drum brakes would. The effect would be weird braking.

The proportioning valve as they are called by some people (some mfgrs correctly call it "holdoff valve",) creates a slight delay to the front. Typically the system applies about 3 lbs pressure before the holdoff valve allows pressure to the discs, that's enough to let the drum linings get into position.
The "adjustable valves" simply allow you to change that "holdoff" pressure from 0 to 8 lbs. Once the "holdoff" pressure is obtained, front and rear should apply equally.
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Old 09-25-2010, 12:27 PM   #10
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Yes,by all means adjust your drum brakes-its very easy to do with proper tools and a cold beer.
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Old 09-28-2010, 08:26 PM   #11
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I know this thread is old but thats why I love this forum! Good job rrrich on explaining this crap. I've been struggaling adjusting mine and DIDN"T EVEN REALIZE there was an adjuster hole in the back of the drums.

I've been taking the wheels off and adjusting and anyway doing way to much work.

Work Smarter not Harder... Should have checked with you guys before I 'bout kill myself locking rear tires in the rain!

This should be a sticky in the common issues forum.

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