Brake Proportioning Valve Linkeage Adjustment - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-30-2006, 12:19 PM
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Brake Proportioning Valve Linkeage Adjustment

I recently noted the rusty mass of springs and once-movable parts between my 1993 Ford Taurus proportioning valve and the rear axle arm. I understand the general principle behind what the valve does, but have not seen an adjustment procedure in free literature so far for the operating linkeage.

I presume the car must be sitting on its wheels with no supports or jacks and then adjust the linkage to put some amount of pressure onto the valve actuator buttons on the proportioning valve to set the valve in the higher fluid flow condition.

Can anyone tell me the amount of pre-load to set on the linkage. I suspect another way would be to jack up the rear end a certain distance to resemble a front end dive during braking and then have the valve plungers just unloading.

Any help would be much appreciated. I don't think this thing has ever worked since I had the car since it put absolutely no pressure on the valve buttons at all when I discovered it. This could explain why the rear brake pads have virtually no wear!

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Old 02-01-2006, 07:03 PM
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I never really liked those load sensing type valves. I would just replace it with a normal adjustable one (like the one from Wilwood).
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Old 02-01-2006, 10:38 PM
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Doesn't that beast actually have two proportiioning valves back there working off the same lever? One for each back wheel, since it's a cross fed system?
They are known for failure, so if rust was present, they should probably be replaced.
When the rear is loaded, they're pretty much full open, or as full open as they get. In addition, they are set to not let the rear brakes lock up even on slippery surfaces.

I wish I knew the exact adjustment procedures, but you should probably start with a new valve assembly (or2 if required), and adjust it to your needs. As a guess, with the suspension hanging, you could adjust the arm to be just about to push the lever upwards, and that should be full restriction at full nose dive. Lengthening the arm from that point would allow more rear brake pressure, if I understand it correctly.
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Old 02-02-2006, 05:52 AM
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Thank you for the comments about the Taurus proportional valve. I did succeed in removing both valve spools from the valve without removing it from the car and probably destroying the associated brake lines.

The valve does have two plungers, one for the right rear caliper and one for the left rear caliper. The right rear wheel which would not bleed freely was apparently being restricted by the valve spool which came out of the bore of the valve body with a considerable amount of sediment coating the movable piston. Both valve spools cleaned up well and did not appear to be worn...just restricted by fine sediment coatings.

I found the linkage completely loose with the suspension loaded, so the rear brakes were in the "restricted mode" all the time. When I loaded the proportional valve, the left side of the valve went back to full flow but the right side stayed restricted and would not bleed freely. The reason why I got into this was the fact that the right rear wheel pads were ground down to the plate.

The fact that the proportional valve was stuck on that side must have limited the rate at which the pads moved back after brake application. I noted that when bleeding, that the left side released pretty fast but the right side stayed applied a considerable time longer when the pedal was released.

I reassembled the cleaned valve spools coated with brake fluid and set a moderate force on the adjuster linkage with the suspension loaded.

I like your suggestion about letting the suspension hang and let that represent the point where the valve is tripped to restrict the rear wheel fluid flow. I'll check with some Ford dealers and see what they say when I mention that. It sounds reasonable. I'd probably add on some load to the suspension prior to fully unloaded to get the force off the plungers.

I also just thought I could take a couple portable scales and lower the rear end until a certain fraction of the car weight registers on the scales and use that as a trip point for adjustment if I can get a load force from a dealer.
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Old 02-03-2006, 12:57 PM
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What happened wasn't that the piston wasn't retracting, but that the restricted caliper wasn't getting much force. The unrestricted side was doing all the work for the back brakes and quickly wore down.
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Old 02-03-2006, 03:08 PM
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Porportioning Valve...

Thank you for the comment on the probable reason for the worn pads.

The reason why I suspected the worn side to have been restricted by the valve was the fact that the opposite side bled with no hitch and the worn side hardly had any fluid flow during the bleeding process.

After cleaning the valve, the worn side began to bleed more like the other side. I put force on the valve linkage by lowering the rear suspension arms onto wood blocks with the wheels off for bleeding to simulate a loaded rear end condition.
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