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Old 06-22-2003, 12:49 PM
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Proportioning Valves

Can a combination proportioning valve have the centering metering device stuck in one end, keeping the light on? This happened when I installed a maverick rear end into my 49 Ford. I pressed the brake pedal too hard the first time I bled the rear brakes and the light came on and has stayed on despite repeated attempts to block off front system and recenter the valve. I now have no front brakes. This is a new power brake conversion I did last year. Disc front, drum rear. Can anyone help me out? Thanks

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Old 06-22-2003, 01:31 PM
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plain & simply put, YES. But you may be able to tap on it w/the lines loose on it(no pressure), to free it.....joe
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Old 06-23-2003, 01:08 PM
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brakes

Finally got light to go out , bled rear brakes again, now I have to stomp on the pedal hard to stop. This is opposite of the way it worked before I changed rear ends. The brakes were always too sensitive to pedal touch & caused nose to dive hard.The rear end uses same wheel cylinders as 49. This is a Master Brakes PA1200K kit with pwer assist ,8" booster. I think somethings wrong with proportioning valve! Can pressure diff. switch have light out yet still block fluid to front discs? Factory set up uses larger resevoir for rear drums & small res. for disc front? Everything I've read on subject says opposite. Factory said don't worry about it? This new problem started when I got a piece of teflon tape on bleeder screw stuck in bleeder port. I pushed on pedal & it spat right out along with good squirt of fluid. thats when light came on.I'm using mighty-vac one man process & have had no problems in past with this method. They recommended small amount of teflon tape on bleeder threads to keep out false air bubble signs. Any help out there?
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Old 06-24-2003, 05:05 AM
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Go to -Master Power Brakes Web Page- and click on Technical Information. There will be flow charts there to help you.

Quote:
Factory set up uses larger resevoir for rear drums & small res. for disc front? Everything I've read on subject says opposite
The larger reservoir will be for disc, the smaller for drum.

Quote:
They recommended small amount of teflon tape on bleeder threads to keep out false air bubble signs.
This is one problem of using a Mighty-Vac to bleed brakes, the drawing of air around the bleeder screw threads. A small amount of tape will help the situation but if any enters the hydraulic system, it can cause trouble as you found out.
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Old 06-25-2003, 12:13 PM
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brakes

master power brakes still says my kit with larger resevoir feeding rear brakes is o.k. I completly dissassembled prop. valve & alooked o.k. cleaned out & mechanically centered press. diff. piston ,put all back together, re- bench bled master, rebled all wheels -still have very firm brakes , like there was no booster assist. pumped pedal & held firm, started engine, pedal dropped slightly. dismounted master from booster & depressed pedal slowly. stem moved o.k. Still lost! Any other way of checking booster? It definetley works much worse if i unplug vacuum. Maybe I was just used to the touchy nose diving stop when the press . diff. piston was favoring the front discs?
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Old 06-25-2003, 02:40 PM
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Question

The booster test is correct...you have assist.

Quote:
...master power brakes still says my kit with larger resevoir feeding rear brakes is o.k.
I am not familiar with their kit no. you gave or how it is plumbed...but Brake 101 clearly states that the larger master cylinder reservoir is to operate disc, as the disc brake pistons are much larger than wheel cylinders and require much more volume to push the pistons outwards. Just reading what you have written so far, my guess is that the front calipers are not receiveing enough fluid volume to operate them properly and is giving you the hard peddle (as you are squeezing too much pressure-too little volume thru the plumbing) and it is therefore acting as if the front calipers are frozen, resulting in a hard pedal condition.

If it was mine...sigh...and I understand that you have spoken to their tech guy, I would change the master cylinder plumbing around. You did rebuild the rear wheel cylinders didn't you?

After this and with the reputaion of MPB, you are going to have to source a set of brake pressure gauges (pad pressure guages would be nice too) to completetly go through the system. It is definetely a disc/crum master cylinder rght? You don't think maybe they put something wrong in the kit?

Another thought...is the booster pushrod operating the MC correctly?
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Old 06-25-2003, 02:48 PM
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What kind of manifold vacuum do you have pulling the booster? At least 18"?
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Old 06-25-2003, 05:13 PM
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Kultluz, I have not had brakes 101, but have set up many disc/ drum combinations and every one have the small reservoir feeding to the disc front and large reservoir to the rear drums. Most have been components from Mustang II, Granadas, Mavericks, Pintos, Chrysler Sebring and Chevy Monte Carlo types. I carefully mark the distribution valves and the MC before removing from donner car and plumb them the same way.

Trees
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