intermittent proportioning/combination valve

[Alumapro]

hello truck world,
i have a 94 k2500 reg cab with a 5.7.
just did brakes due to leaking rear axle seals, which of course turned into fixing 10 othe things at the same time, replaced shoes, all brake lines and hoses and master cylinder as well. set and bled brakes, quite happy with the outcome other than one thing. rear brake pressure is a little less than desired. slow pressure under normal slowing down braking is great. however hard pressure on the pedal for emergency braking the rears are dont grab hard enough. ive noticed that the valve in the proportioning body pops out under hard pressure and then resets itself when the pedal is lifted again. this does not happen when normal force is used slowly pressing on the pedal unless you push extremely hard. there is no air in the system and just about all the components are new exept the front calipers and rear cylinders. but have been disassembled cleaned and re-installed. ive had valve issues back in the day when i had no idea how the system worked. ive seen popped and stuck valves but never ones that pop out then back in. im guessing its faulty. but looking to know more about why this is happening. im guessing that is why the rear brakes are lacking under hard pressure. also note that there is no soft pedal or any sponge here either. to hop in and go for a drive i dont think anyone would notice unless they got in a pickle, and that what bothers me.

 

[Schurkey]

94 k2500 reg cab with a 5.7.

What brake option code? JB6? JB7? Something else?

just did brakes due to leaking rear axle seals, which of course turned into fixing 10 othe things at the same time, replaced shoes, all brake lines and hoses and master cylinder as well. set and bled brakes, quite happy with the outcome other than one thing. rear brake pressure is a little less than desired. slow pressure under normal slowing down braking is great. however hard pressure on the pedal for emergency braking the rears are dont grab hard enough.

Are you SURE the rear brakes are adjusted properly? All four rear shoes are tight to the anchor pins on top?

Shoes/pads burnished after installation?

ABS unit bled using a scan tool?

ive noticed that the valve in the proportioning body pops out under hard pressure and then resets itself when the pedal is lifted again.

"The" valve in the COMBINATION valve is the metering/holdoff valve which affects the FRONT brakes only--not the rear. This valve has NOTHING to do with the proportioning valve which affects the rear brakes only--not the front. They are in the same big brass body, along with the safety switch.

Having the stem push out under pressure, and then pull back in when the pressure is released is exactly how the metering valve works. Nothing wrong there.