Proportioning valve issues.

[83swb]

Just redid the WHOLE brake system on my truck, with the exception of a booster.

I bought a CPP factory style combination valve to replace the factory one that was in rough shape. All the brakes are plumbed correctly and the master cylinder and booster are in working order. I'm only getting some fluid to the rear brakes and the drivers side front caliper, the passenger side caliper is bone dry. I have a little pedal with the truck not running and no pedal when the truck is running (after some bleeding obviously).

I know there's some crazy sliding valve in the combination block, but how do I get it to open up?

[MikeB]

I assume the new valve has 2 ports for the front brakes, as opposed to a single port with a line running down to a tee fitting? Any pictures?

[83swb]

Originally Posted by MikeB

I assume the new valve has 2 ports for the front brakes, as opposed to a single port with a line running down to a tee fitting? Any pictures?

Yes, one port for each side. Its identical to a factory valve, just machined from brass.

[775stepside]

Interested in what this might be because I plan on replacing all my lines too, what did you use and where did you buy the lines?

[geezer#99]

You need to push the button in on the front and hold it in while you bleed.

[83swb]

Originally Posted by geezer#99

You need to push the button in on the front and hold it in while you bleed.

Actually borrowing a GM tool to do that but the tool won't work with an aftermarket valve. Looks like that what I'll be trying next.

[83swb]

Originally Posted by 775stepside

Interested in what this might be because I plan on replacing all my lines too, what did you use and where did you buy the lines?

Used copper coated easy-bend line from a local parts store, I'll never use anything else.

[MikeB]

Originally Posted by 83swb

Yes, one port for each side. Its identical to a factory valve, just machined from brass.

Looking at this diagram of a generic combo valve, both front ports go to the same place, with initial pressure delayed by a metering valve. If you have pressure at one port, you should have pressure at both. I wonder if a Chinese worker forgot to drill a hole?

[83swb]

Thanks for the diagram. I was able to get some fluid to the passenger side but I'm waiting for a second pair of feet to bleed them out.

[mpierce9]

I ran into a similar issue a few weeks back. My solution was
1. Clamp down the Combo valve button.
2. Remove the MasterCylinder cap
3. open the rear bleeders (both sides)
4. monitor the MC fluid level
It took 48 hours to get good fluid out.

All this should be able to be resolved with a two person bleeding job much quicker. I was told that slow 1 pedal pump bleeding works best because the volume of air stuck in the line after making such major changes.

I was making the mistake of doing a two person bleed job allowing the person that pumped the pedal to pump it up multiple times to build pressure. This was causing my issue that filled the line with air and didn't allow fluid to the rear.

[mpierce9]

I ran into a similar issue a few weeks back. My solution was
1. Clamp down the Combo valve button.
2. Remove the MasterCylinder cap
3. open the rear bleeders (both sides)
4. monitor the MC fluid level
It took 48 hours to get good fluid out.

All this should be able to be resolved with a two person bleeding job much quicker. I was told that slow 1 pedal pump bleeding works best because the volume of air stuck in the line after making such major changes.

I was making the mistake of doing a two person bleed job allowing the person that pumped the pedal to pump it up multiple times to build pressure. This was causing my issue that filled the line with air and didn't allow fluid to the rear.

[MikeB]

The latter half of this video is a good demonstration of how the metering valve works. All it does is delay pressure to the front brakes. But you can see how both front ports should have the same pressure.

I still don't have a real handle on the inner workings of the prop valve, but I know that it limits maximum pressure to rear drum brakes in a disc/drum vehicle. Of course, you're stuck with the preset pressure determined by the spring.

https://www.youtube.com/watch?v=PlElcEGjfd8

[83swb]

Found a possible issue tonight. Somehow (dumbass me) didn't realize that I had the lines switch from the master cylinder to the valve, had the front reservoir feeding the back and back feeding the front brakes. BUT the bigger issue was the way the valve itself was machined. The valve is machined for a 3/16" line for the rear inlet (should be 1/4) and the front half is machined for a 1/4" (should be 3/16").
So this valve is getting sent back to summit and I have a line on a factory valve to put in its place.
So beware if buying a CPP combination valve for your truck, may have been mishap in the machining process.

[MikeB]

That's seems odd. Can you post pictures of this valve and its part number?

[nonstop]

CPP had a bad batch of valves a few years ago. I added discs to a 50 Chevy truck and the valve was leaking out the back with no miles on it. Googled it and found out there were many folks with this problem. I'm not too impressed with the quality control of some of CPP's stuff. Might be better off with a JY replacement.

[83swb]

I'll take a few pictures of the valve tonight, haven't been keeping track of responses.

[MikeB]

Originally Posted by nonstop

I'm not too impressed with the quality control of some of CPP's stuff. Might be better off with a JY replacement.

Yeah, their stuff is hit and miss. I bought a pair of their upper control arms (not the budget models) for a 55 Chevy car, and they were great. But both of the pre-installed ball joints had cracks in the grease boots. And my buddy had the exact same problem a few months later!



I think most of their their stuff comes from China, and their customers do the QA. I will say that Aaron at CPP sent us both new sets of ball joints, but I ended up using Moogs.

Buying CPP products from Summit Racing is the only way to go, because of their customer-friendly return policies.

[hatzie]

There are two tools that might help
I'm using nomenclature, in quotes, from the cutaway pic in post #8...

Kent Moore J-23709 is little more than a 90 degree bent piece of stiff metal with a slot that fits under the mounting bolt. The 90 degree tang depresses and holds the "bleeder rod" to center the "pressure differential valve" piston.
There's another slick little tool that temporarily replaces the warning lamp switch and locks said piston once it's centered. This tool from Brothers Truck Parts --->http://www.brotherstrucks.com/prodin...number=PVBT087 There are many other suppliers.

[83swb]

I did have a GM tool to compress the bleeder, but found my real issue before trying it.

[83swb]

Should have made them bigger, oh well.

[RichardJ]

>> holds the "bleeder rod" to center the "pressure differential valve" piston.<<

The pin sticking out of the metering Valve (bleeder rod), has nothing to do with the "pressure differential piston". Moving that pin in or out DOES NOT move the pressure differential piston.
I said "in or out" because on some combination valves, the pin must be held "out" when bleeding. This tool is a spring clip that holds the pin "out" for that type of combination valve.

[RichardJ]

Kent Moore J-23709 is shown below being used on a combination valve that requires the metering valve pin to be held "IN" while bleeding.

[Just call me Sean]

The proportioning valve with the pin you hold is used on single reservoir master cylinder systems.