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post #1 of (permalink) Old 12-20-1999, 10:34 AM
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Brake bleedinq question

My brake system has the proportioning valve (attached to the frame). The manual says to use a special Jeep tool to open it when bleeding the brakes, but mechanics I've talked to say to ignore it. Anyone have experience with this?

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post #2 of (permalink) Old 12-20-1999, 11:54 AM
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Re: Brake bleedinq question

I have heard the same thing. It depends on the year but on one type there is a nipple on the forward end (I think) that needs to be held in and some years it needs to be held out. My '77 CJ-7 needs to be held in while bleeding the brakes. I just used a large C-clamp, you may also be able to use a block of wood wedged against the valve. Some people have told me that they didn't bother with it and had no probs bleeding their brakes. I used the C-clamp thing and it worked out fine. I am not sure if it would make a difference if I didn't. I know this is confusing but I had a late night in the French Quarter in New Orleans and am not thinking all that straight. But hopefully it'll make some sense when you check your out. HTH.
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post #3 of (permalink) Old 12-20-1999, 02:32 PM
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Re: Brake bleedinq question

also since we dont read instructions,least very often,i happened to once and with the double GM master cyl.it specified raising rear
of vehicle till top of master cyl was level before bleeding,reason being that air gets trapped in the front of the master because of way it
sits nose up.Thats what the instructions said anyway.I also one year ago flushed system and put in 2 new rear wheel cylinders,about
a week ago i was putting on new rear brakes,both of those "new" cylinders were leaking..They came from Advance Auto Parts.Now thats quality


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post #4 of (permalink) Old 12-20-1999, 04:41 PM
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Re: Brake bleedinq question

Help me out with this here............

Why would a proportioning valve inhibit brake bleeding?......other than a load compensating one (you know one of those that attaches to the axle and has a lever that senses the riding height of the rear - hence the load). With those you must "simulate" load by detaching the spring or lever to allow the fluid to reach the rear brakes. What I mean is .......you put your foot on the brake to stop and it reaches the threshold of the proportioning/metering valve ......why should bleeding be any different?
Just curious ......this is a first for me.

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post #5 of (permalink) Old 12-20-1999, 11:02 PM
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Re: Brake bleedinq question

The proportioning valve directs pressure to the front brakes first. At a set point determined
by the back pressure from the front brakes the valve opens a port to allow pressure to the rear brakes.
There is more back pressure from the front brakes when the vehicle is moving than when static, so
while bleeding you won't get full flow to the rear. Moving the pin in or out depending on the valve model,
opens a by-pass to allow equal flow through out the system.


post #6 of (permalink) Old 12-21-1999, 09:41 AM
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Re: Brake bleedinq question

I'm well versed on metering valves and proportioning valves......they've been in most cars since dual master cylinders were put in production cars.........the only time that I've EVER had to do anything "special" with them is either when it was a "load compensating" valve ...........or if one of the fluid circuits had a failure and the light came on in the dash..........I seem to remember.....I think it was AMC....that when one system failed.....a plunger inside the valve biased itself to turn on the light on the dash.......after it happened .....the thing was servicable only by replacement.......there was no way to "re-seat" the plunger.
I'll buy the stuff about the pin thing......but the caliper doesn't know if I'm going 95mph or at a stand still.......if I'm put X amount of pressure on the pedal..........there is X amount of pressure on the caliper.........so if I'm standing on the brake pedal (beyond a certain pressure) the proportioning valve shouldn't even come into the picture to inhibit the flow to the rear brakes. Maybe it's a "workers comp" feature so that petite 100lb. female (or male for that matter) mechanics don't develop vericous veins by straining to put enough pressure on the brake pedals.
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post #7 of (permalink) Old 12-21-1999, 11:53 AM
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Re: Brake bleedinq question

Forget the valve. I've replaced the master cylinder and every part except one caliper in the front. Then I switched to D44 axles and did it all again. You don't need to do anything with it, just bleed as usual. If you mess with it and it breaks, it's big $$$.

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post #8 of (permalink) Old 12-21-1999, 12:50 PM
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Re: Brake bleedinq question

Ditto what JEEPN said. I've had both my axles apart in the past month or so, just bled at the individual brakes as usual, no problem.

Brad (from the 4 Wheeling center of the universe, 4 corners USA)
post #9 of (permalink) Old 12-21-1999, 03:48 PM
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Re: Brake bleedinq question

a vacuum bleeder makes it much nicer to bleed them too.

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post #10 of (permalink) Old 12-21-1999, 05:30 PM
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Re: Brake bleedinq question

When I rebuilt my Jeep (' 84 CJ7) last winter, I replaced all the brake lines and the master cylinder. When the Jeep was back together I just bled the brakes as usual starting with the shortest run (from the master cyl) and didn't have to do anything with the proportioning valve.

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