Brake System and Combination/Proportioning Valve Diagnosis

[coachdtierney54]

A trailer brake controller. If the larger is for the front, then why did I fill that one when bleeding the rear brakes?

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[87V30]

@coachdtierney54 Is that a tee fitting coming out of your forward most port on your MC? On my hydroboost setup the front (smaller) MC reservoir is for the rear brake system like Blue Ox said.

 

[coachdtierney54]

Yes that leads into the cab and connects to trailer brake controller.

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[coachdtierney54]

I have no clue what is going on with it

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[Blue Ox]

Okay, so a brake controller should be a switch. I don't think it has any bearing on the truck brakes unless it is leaking.

On my truck the larger reservoir is in the front, but the smaller one is still for the rear brakes. Calipers have much larger displacement and need a bigger reservoir.

 

[coachdtierney54]

Found the leak. What is this?

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[Blue Ox]

Load sensing proportioning valve. Good luck finding a replacement. Most folks, and apparently GM say to eliminate it. But I had severe rear lockup problems on my 'burb without that valve. YMMV. Although I would replace that rotten lower pipe before I condemned the valve.

 

[coachdtierney54]

Lot of rust for a southern truck... How did you bypass yours? I thought about getting an adjustable valve from Jegs.

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[Wes P]

Posting in all LSPV-related threads for reference:

LSPV delete on '85 C20 increased braking performance.

Basic procedure:
- Remove valve, post-LSPV hard line, hose, axle bracket
- Measure, measure again, cut, drill, tap, weld stop nut on bracket (or add a screw)
- Release axle hard line from clips
- Install bracket, brake hose (180 flip), zip ties
- Bleed brakes

Parts: 2 zip ties.
Materials: brake fluid
Time: 4 hours, leisurely, without experience, being careful.
Note: Be gentle with hard lines. Plug the hard line after disconnecting. Don't empty the master cylinder.

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