Rear Disc Brakes

[Bunkerbuilder]

Are you aware of the combination valve that sits on the frame crossmember that is located under the radiator core support area.

There are after market valves to replace the factory valve.

The aftermarket valves are sold for the disc / drum and disc / disc configuration as well.

The brand and model I used was RPC WWW.RACINGPOWERCOMPANY.COM ITEM# R4510
http://www.usrpc.com/brass-pro-valve-only-disc-disc-894.html

This is just one example. And then there is the adjustable proportioning valve that would take the place of the one most truck owners of the cucv vintage remove unless a good replacement can be found. with the adjustable valve you can dial in the rear brakes depending on the weight in the bed

 

[rsh4364]

I have been looking at 1009 rear discs at 4WDFactory.Com for a while,seems pretty reasonable.

 

[Bunkerbuilder]

There is a GM bullitin on the web about how to go about removing this item when its found to be defective (which is usually most of the time with trucks this old)

http://www.steelsoldiers.com/showthread.php?32223-M1008-brake-cargo-load-valve-bracket

88-320-5: REAR BRAKE SENSITIVITY (HEIGHT SENSING VALVE REMOVAL) - (Aug 3, 198*

Model and Year: 1984-86 C/K 30 SERIES 1987-88 R/V 30 SERIES
1984-1986 C/K 30 and 1987-1988 R/V 30 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:
Parts listed below are currently available from GMSPO.
1. Detach rear brake hose 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 34897*and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (PIN 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 the rear brake hose.
9. Bleed and test brake system per Section 5 of the appropriate Light Duty Service Manual.


General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.

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I explained this in detail in post #75 of my rebuild thread. There are two things that you should pay attention to - 1.)- the little dot on the valve needs to be positioned at 12:00 with no weight in the truck, and 2.)- the angle of the two actuating arms needs to be at or close to 90 degrees with no load. The dot on the valve can be adjusted by simply removing the nut and pulling the short arm off, rotating the valve to the correct position, and then reinstalling the short arm and nut. A longer arm, if needed to accommodate a lift, can easily be fabricated by picking up a piece of 1/8" x 1" steel bar stock from the hardware store and cutting it to the appropriate length and drilling new holes.

Hope this helps.

 

[Sharecropper]

Bunkerbuilder - Thanks for your posts. I suppose I could remove my rear proportioning valve, however after fabricating the longer arm and clocking the valve with the dot at 12:00 with no load in the bed, my truck will stop on a dime, going forward or in reverse. I could not be more happy with my rear disc brake conversion or how it works. I will, however, retain the GM Bulletin 88-320-5 for future use in case I need to remove the valve.

Thanks again for your help.

 

[MilChevyguy]

This is a worthy mod for our trucks...Ive always been told by older mechanics that properly adjusted and maintained drums are just as good as discs, but it seems now with the fast pace everyone travels at, the discs are a necessary safety
requirement.....
For sure have to add this mod to the list!!

Thanks for everyone's input and real world results!
Best Site EVER

 

[Bunkerbuilder]

No problem, the thought of removing the valve was two fold, one to avoid having to extend the valve in the case of a lifted truck as an alternative to extending the valve and most of all since most cucv,s are 30 years old if this valve would need replacement we would mostly be SOL as im sure its obsolete from GM.

There is a GM bullitin on the web about how to go about removing this item when its found to be defective (which is usually most of the time with trucks this old)

http://www.steelsoldiers.com/showthread.php?32223-M1008-brake-cargo-load-valve-bracket

88-320-5: REAR BRAKE SENSITIVITY (HEIGHT SENSING VALVE REMOVAL) - (Aug 3, 198*

Model and Year: 1984-86 C/K 30 SERIES 1987-88 R/V 30 SERIES
1984-1986 C/K 30 and 1987-1988 R/V 30 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:
Parts listed below are currently available from GMSPO.
1. Detach rear brake hose 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 34897*and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (PIN 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 the rear brake hose.
9. Bleed and test brake system per Section 5 of the appropriate Light Duty Service Manual.


General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.