# Brake valve on rear of K30



## 86CrewcabK30 (Sep 9, 2003)

I have an 86 Chevy crewcab SRW K30 and am having some brake problems I think are related to either my Hydro Boost or a brake valve located over the rear axle. The valve over the rear axle resembles a height control valve on an air ride trailer, it has a linkage arm that goes from the differential housing up to the valve which is mounted to one of the frame crossmembers. It appears to proportion the brake fluid flow to the rear brakes when either loaded or empty. I pull a gooseneck horse trailer with the truck and experience alot of front end "hop/shudder" when coming to a stop. I am suspecting that the front brakes are doing more than their share of the braking. Everything in the front end is tight and seems to be ok and the trailer brakes work good (thank God!). Brake rotors are not warped either.I haven't been able to find anyone that can tell me the function of this valve and any help would be appreciated. First time post, so thanks in advance!


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## wyldman (Jan 18, 2001)

The rear height sensing proportioning valve reduces rear brake pressure when the vehicle is unloaded,and increases it as the vehicle is loaded.As the rear squats down,it will apply more force to the rear brakes.

It could be the valve,or it could be bad front,or rear shocks.The valve can be bypassed if you want,just find a brake hose,or pipe which will fit both ends of the brake valve fittings.It will apply full pressure to the rear brakes,so they may lock up when unloaded.

Have you actually checked the rear brakes ? Maybe the wheel cylinders are sticking,or you have an axle seal leak,which would kill the rear brake performance.

I'd also double check your trailer brakes,as if they aren't up to snuff,the trailer will push the truck when braking.Maybe you just need to adjust the controller some.


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## 86CrewcabK30 (Sep 9, 2003)

Thanks for the advice! Front shocks are already on the list, so will try that first. I haven't actually checked the rear brakes, but no sign of leaking wheel seals. Will pull the drums and look them over and check my wheel cylinders. The trailer brakes are in excellent shape, controller is cranked up higher than I usually have it to avoid the hop/shudder problem by braking more with the trailer.
The main reason I was suspecting this valve is that the linkage is shot and the pivot is loose (no leakage though). Can a replacement be obtained or am I better off bypassing it if I don't find anything else wrong? We have some pretty icy winter conditions here and would hate to have a lockup of the rear wheels on icy roads with the old whale! Thanks again for the quick advice.


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## wyldman (Jan 18, 2001)

It's easy to bypass with a steel line or hose.If your concerned about brake lockup,then just add a cheap adjustable brake proportioning valve available at most performance parts shops.I usually hook them up right under the dash,so you can reach down and adjust on the fly.


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