Proportioning Valve Problem?

[Tomeal]

Check and see if your valve has a reset. Maybe it's stuck and seated in one place not letting full fluid to the rear. Maybe a little flex in your rear flex hoses? Did you replace them when you did the cylinders?

 

[gmtofd]

Thanks for the suggestion about the rear flex hose. It never been changed and the Malibu will soon be 40 years young. Maybe it is partially collapsed, although when they internally collapse they won't allow a caliper or wheel cly to retract?

 

[Tomeal]

although when they internally collapse they won't allow a caliper or wheel cly to retract?

Or slowly.

Thought maybe soft hose ballooning slightly under braking pressure?

 

[gmtofd]

Checking back in to say that it was not a rear brake problem after all, but a seized right side caliper. It would brake straight during normal braking situations, but with panic stopping the Malibu would want to do a 180 clockwise, which really does not make sense as the left side caliper is working fine and logic would say that it would want to go ccw?

 

[69hurstolds]

Another fix! Glad you didn't have to troubleshoot for a long time on it.

 

[mikester]

Maybe try this tool when you rebleed the brakes. You have to take warning light switch out of the proportioning valve & put it in it's place.
https://www.summitracing.com/parts/clp-pv-tool

Do those tools work with a factory proportioning valve ? I know they fit the brass aftermarket valves but are the originals set up the same way ? Im just curious. Both of my cars have aftermarket valves. I used the tool on the coupe. Dont remember what the original looks like.

 

[69hurstolds]

The originals were cast iron mostly, and one company made them out of brass. Most got Bendix cast iron from the factory, but I believe there were 3 or 4 different companies making them. I have an NOS 25509419 valve in CAST IRON. It's an early one. Amazingly, they shared the same part number when they swapped them out to the blocky brass ones.

There was a reason for it. GM found out early on they had a problem with those cast iron combo valves (I think it was GN powerboost failures driving this) and they would rust and corrode and fail frequently. Thus, they went exclusively to brass. I've probably got the last NOS cast iron combination valve out there. I haven't seen a cast iron one in the box since. Unless you're into full factory resto work, go with the brass ones. They work the same, and likely will last longer without corrosion issues.

I've never had a problem bleeding the brakes and have never used that bleeder tool. I've considered it many times, but never needed it.

This is a picture of a brass one, but the box has both the GM and Delco p/n on it and both numbers did not change from original.

 

[pagrunt]

Do those tools work with a factory proportioning valve ? I know they fit the brass aftermarket valves but are the originals set up the same way ? Im just curious. Both of my cars have aftermarket valves. I used the tool on the coupe. Dont remember what the original looks like.

The pressure switch fits both types so there shouldn't be an issue unless the cast iron one is really rust damaged at the threads.

 

[mikester]

The pressure switch fits both types so there shouldn't be an issue unless the cast iron one is really rust damaged at the threads.

Good to know !

 

[69hurstolds]

Be careful and ensure it fits or at least ask. There are some of those tools that specifically state they fit only their brand of combination/proportioning valves and do not fit the factory ones. But some do. Like this one claims to:

https://westernchassisinc.com/Propo...v0DvBxaiZmcdON79ymiHshaQdvvx2H2hoCGakQAvD_BwE