What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Proportioning Valve Problems

pierce88K5

pierce88K5

1/2 ton status
Joined
Jan 11, 2005
Posts
134
Reaction score
2
Location
Alexandria, VA
Okay, so here is my problem. I just finished my 14 bolt swap on my 1988 K5 Blazer with the TSM Cadillac disc brakes and converted my 6 lug front end to the 8 lug rotors. I installed the rear disc brakes in on the opposite sides to make the emergency brakes work. After bleeding the brakes and getting all the air out of the line, my brake light came on would not go off. This happened once before when I was bleeding the brakes about 4 years ago when I installed the extended stainless steel brake lines and it was the proportioning valve tripped. So I took it to the local Midas shop and they stated that the proportioning valve was not tripped and force bled the brakes but the light was still on. Then I had the Master Cylinder replaced and still the light was on. They proceeded to tell me that there was evidence of brake fluid leaking into my power booster and they wanted $300 to replace it. I said no thanks and proceeded to Autozone and picked up one for $90. When I got home from work today, I crawled under the truck and looked at the proportioning valve and it appeared tripped again (button sticking out on the valve). I used a pry bar just to see if it would reset and it pushed right in. I checked the light and it was out. I stepped on the brakes and heard a pop under the truck and the light came back on. I checked the proportioning valve and it had tripped again. So I thought I needed to bleed the brakes again in the rear. A very small amount of air came out. Tried the brakes again and the proportioning valve tripped again.
Anyone know what would cause the proportioning valve to trip in this case? Would I still need to replace the power booster or do I need to get a new proportioning valve?
 
Did you change the prop valve from disc-drum to a disc-disc? Not sure it is necessary, but might help.
 
I did not change the proportioning valve to the disc to disc type. Every thread I read said it was not necessary. However, now I think it might be. Not sure what the difference would be. Hydraulic pressure is transmitted throughout the line when it is full of brake fluid. The only difference would be the amount of pressure applied due to the increase in surface area of the new rear disc brakes vice the old drum brake pistons. Sorry if I am nuking it out. But the proportioning valve is the only thing I have not changed out at this point. I just installed the new power booster and the light is still on. I will look into a new proportioning valve.
 
You said you swapped side with the rear calipers so the e-brake would work. Are the bleeder screws pointing up or down? The bleeder screws MUST point up in order to bleed the brakes and get all the air out. You could mount the caliper upside down but then you MUST remove the caliper and put a block of wood between the pads and then hold the caliper upright in order to bleed then reinstall upside down.
 
The brake light will come on for two reasons: the switch on the parking brake lever, or the slider in the combo (proportioning) valve. The slider is meant to detect a major pressure difference between front and rear, i.e. a leak. You should be able to reset it with your thumb; worst case a medium flat head should do it.

The booster is vacuum and rarely goes bad. You can test them; I've gone through it before...

http://coloradok5.com/forums/showthread.php?t=256008

http://coloradok5.com/forums/showthread.php?t=250090

Sounds to me like you've got hydraulic problems. Did you bench bleed the new master? Worst case, bleed the thing again. And again. Trust me. Bleed it more :D Any and I mean *any* air in the system will make it fail.

After that, I'd check the brake lines, hoses, and calipers for leaks. If the slider is popping, it's because the front circuit has a lot more pressure than the rear, or vice versa, and replacing the combo valve won't fix that.

-- A
 
Midas changed the master cylinder and I did not watch them bench bleed the thing. I assumed they knew what they were doing, but you know what assumptions lead to :)
As far as the bleeder brake screws, they are upside down. But I installed custom stainless steel flex lines so I can remove them and hang them right side up and bleed them. I believe my problem is I still have air in the line somewhere and I suspect it is in the master cyinder. The pedal is still mushy somewhat and I can't get the tires to lock up no matter how hard I press the brakes. I am going to pick some more bottles of brake fluid and bleed the heck out of it tomorrow. I have looked high and low for any leaks and have not seen any so I am ruling out leaks at the moment. I even pressure washed the frame to see if there were any leaks. Looks like I am going to be bleeding some brake lines tomorrow.
 
Yep, keep bleeding. Search any of my posts about garden sprayer pressure bleeding ... it's the shiznit. :deal:

-- A
 
Just make sure you hold that caliper so the bleeder screw is the highest point when bleeding and it also sometimes help to have a friend who can lightly tap on the caliper with a small hammer to dislodge any trapped air bubbles/pockets within the caliper. Of course you also want to make sure that the master cylinder does not run low on fluid otherwise you are drawing air back into the system .
 
Thanks, guys. I really like all the help and I will keep in mind your tips. DREMU, where is the post about your garden sprayer pressure bleeders?
 
So. I am trying to bleed my brakes today and the proportioning valve keeps tripping. Can you still bleed the rear brakes if the proportioning valve is tripped? I get some brake fluid out, but not a big squirt like I am used to seeing.
 
I used a power bleeder at my shop, opened all four bleeder screws so the pressure loss would be equal, with the key on, I pumped the brakes with the power bleeder on the master 3-4 times and it re-centered itself and the light went out right then and there. Hope this helps.
 
JMS what proportioning valve did you use? I just pulled mine out after reading that you need to change proportioning valves to one designed for 4 wheel disc brakes. I am heading to the parts store shortly and will be looking at buying a new one. I also bled the dickens out of my brakes until no air came out and the proportioning valve still tripped after applying the brakes. I am going to buy a new one and replace it. It is pretty corroded and looks in bad shape.
 
I agree. The parts store did not carry the proportioning valve (autozone, parks). They suggested the junk yard. I did find one on ebay that the hot rodders use (camaros, chevelles, el caminos,). It was a universal one specifically for a disc - disc brake conversion (pvc-pv4 part number? for $44). Anyway, I am beat up on this brake problem and will give it a rest for today. I may just order a stock one and be done with it.
 
Inline tube wants $99 for their PR101 valve. I picked one up on ebay for $70. It is a GM hotrodders 5 port disc-disc proportioning valve. Pics looked like my old with the same mounting hole locations. Just have to wait for the part to show up now.
 
New proportioning valve came in last week and it was one without the trip button and was plumbed for disc-to-disc with 50% pressure to the rear and front brakes. I built a pressure bleeder with the blueprints the DREMU gave me (thanks!) bled it twice to get the brake light to go out. Now the brakes work but the pedal is really slow to come back up when I let off the brakes. Anybody have that problem or know what would cause the pedal to slowly come back up?
 
You must log in or register to reply here.

Latest Posts

Top Bottom