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Old 10-26-2017, 10:13 PM   #1
Registered User
Join Date: Oct 2017
Location: Grass Valley, CA
Posts: 1
Hydroboost and proportioning valve problem

Hey, all. I'm new in here. 1st post. I have a question regarding a conversion to hydroboost from my factory vacuum boost brakes. The kit I purchased was from Tallon Hydraulics, and came with a GM style master cylinder. Currently my truck has disc fronts and drum rears. The brakes work great, except for one thing. The brake light on my dash is constantly being activated by the brake switch on the factory differential/proportioning valve. I've been thru all the remedies, such as possible air still in the lines, shoes not adjusted properly to the drums, etc.

To date, I've bled my supystem at least 20 times, and gone thrust at least a gallon and a half of brake fluid. I have no air whatsoever. My shoes to drums are adjusted perfect, and I have new pads on my working calipers.

I've come to the conclusion that my new hydroboost is overpowering the differential valve, causing the metering device inside to shift off center and trigger the light. What's weird is, a second quick tap on the pedal re centers it and the light goes off. The problem with that is when it is centered, and I come to an emergency stop, it shifts off center and part of my braking works, and the other is not. I've had a few close calls, so for now I'm not driving it.

I came up with an idea, and this where I'm asking the advice- I had a machinist friend of mine machine out a copy of the plastic, delrin bleeder plug that one puts in place of the brake switch, to keep the metering valve centered while bleeding. This new plug, made of steel, is simulating the brake switch, but the inner pin won't move, forcing to keep that metering valve secure from shifting.

What gave me the idea, was I put in that delrin bleeder tool and took the truck for a spin, and the brakes worked flawlessly as they should've been the whole time, and the metering valve never shifted off center. What happened though, when I pulled out the delrin tool the plastic rod was messed up, from that metering valve trying to shift. So that's when I came up with the idea to have one machined out of steel. So let me know if you all think that's a good idea.

I do have two more back up plans, which is to try another differential valve from summit, a more modern one. The other is to rid of the valve altogether, and just pipe in an adjustable proportioning valve. These two plans require me to fab up completely new brake lines. Although I'm tooled up and ready to do that, I'd like to know your thoughts on the machined plug, to see if that can be a permanent set up to rid of that metering valve from moving.

Long post, yes, but I needed to pass on all the details, somyou all knew where I'm at with this thing.

Thank you very much!
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