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Thread: 1985 suburban height sensor/ braking proportional valve

  1. #1
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    1985 suburban height sensor/ braking proportional valve

    Hey, I'm trying to replace the height sensor/ braking proportional valve. Part has leaking brake fluid. I cant find the part anywhere. I heard you can bypass this part. Whats the proper way of bypassing it?

  2. #2
    Senior Member scavanger's Avatar
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    the brake proportioning valve is a very important safety part of the brakes. I would not remove it. Never heard of one leaking before
    but then I don't work with it every day. should be able to find a used one for cheap at a salvage yard .

    You aren't saying the hight sensor is part of the proportioning valve? are you ?
    I assume you have air shocks and are looking at replacing the leveling switch?

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    I found out from the dealer today that its a height sensor and braking proportional control valve. It some how adjusts the braking as the truck takes more weight over the rear axle. Ive called all the places I know, looked over the net, can't find one any where. The dealer said they discontinued the part.

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    Have you talked to any brake shops, seems they would have dealt with this.
    They bound to have bypasses more than one of these, if unavailable.

    DS

  5. #5
    Senior Moderator chevychase's Avatar
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    Type this part# in google should be able to find it. 15538213 or install a regular valve .

    Gitter done have fun. Running on empty...running blind...running behind.....

  6. #6
    Senior Member chengny's Avatar
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    TSB on the "Load Compensator" issued August 1988:


    GMC NUMBER:88-T-151
    GROUP: 5 - Brakes
    DATE: August, 1988
    CORPORATE
    NUMBER: 865010R
    SUBJECT: REAR BRAKE SENSITIVITY - HEIGHT SENSING VALVE REMOVAL
    MODELS: 1984-86 C/K 3500 AND 1987-88 R/V 3500
    THIS BULLETIN IS A REVISION OF TRUCK SERVICE BULLETIN 85-B-79, DATED MAY, 1985, UPDATING FOR MODEL YEARS 1984-1988.
    1984-1986 C/K 3500 and 1987-1988 R/V 3500 series trucks are equipped with a rear suspension height sensing device that optimizes the brake proportioning valve setting for the load the vehicle is carrying. The height sensing system adjusts the brake balance in vehicles subjected to a range of loading conditions. Occasionally, vehicle modifications by body builders or owners influence the height sensing device. If a vehicle has had rear suspension modifications that affect its trim height or the spring rate, and the driver comments about the brake modulation characteristics of the vehicle, it is recommended that the height sensing system be removed and the brake system be revised as described below:

    1. Detach the rear brake line from lever and bracket assembly. Reference Figure No. 1.
    2. Remove lever assembly and bracket from axle.
    3. Install rear brake hose bracket (P/N 348978) and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (P/N 358000 - shorter bolt removed in Step No. 2) in the upper cover hole. Reference Figure No. 2. Use Loctite 75 or equivalent on the bolt threads.
    4. Attach brake hose to bracket with bolt from original installation.
    5. Install a 3/8-16 x 1-3/4 bolt (P/N 9439637 - longer bolt removed in Step No. 2) through spacer P/N 14055556 (removed in Step No. 2) in remaining axle cover attaching hole. Use Loctite 75 on bolt threads or equivalent.
    6. Disconnect brake pipes from height sensing valve and brake hose, and discard short brake pipe. Reference Figure No. 1.
    7. Remove and discard height sensing valve, bracket, and bolts.
    8. Carefully reposition the rear brake pipe, and connect it to tbe rear brake hose.
    9. Bleed and test brake system per Section 5 of the appropriate Light Duty Service Manual.



    There are associated images but the bottom line is - bypass the valve (or just disconnect the linkage arms).

    Apparently it was a bad idea.



    chevychase and hotrodpc like this.
    1986 Sierra Classic
    Lost it in a fire

    Replaced with 1986 Sierra K3500 single axle

  7. #7
    Senior Member scavanger's Avatar
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    I learned something here . Never knew they had something like that. I am going to
    have to check on that and see how they work.

    I assumed you were talking about the main proportioning valve on the frame near the firewall.
    Last edited by scavanger; 09-24-2012 at 07:57 PM.

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