Proportioning Valve Problem?

[gmtofd]

Having a braking problem with the '79 Malibu. Everything is stock except for S-10 manual brake rear wheel cylinders. It seems that the front brakes lock-up much too easily and thinking that it is a proportioning valve problem resulting in insufficient rear brake line pressure . Been checking out some threads on proportioning valves that discuss resetting the valve. yet the shop manual has the valve as non-repairable, nothing about any sort of reset procedure,

The question is, has anyone actually been able to reset the valve? One of threads on proportioning valves mention that there are two different valves used. This valve has a reset button or whatever it is for the front lines and one for the rear.

Thanks for any response.

 

[timo22]

Is your brake warning light on?

 

[pontiacgp]

how much travel on the brake pedal, if you have no rear brakes or rear brakes are no properly adjust the brake pedal would travel too far.

 

[gmtofd]

Thanks for responding, the brake light is not on, and the brakes can be properly adjusted and there is still the no or not a lot of rear brake action. Recall that awhile back, the Malibu was off the road for a winter and remember when waking it up, there was a section of rear brake line that rust out, which resulted in loosing all brake fluid in the mc for that side.

Got a acceptable hard pedal back, but wonder if that is somehow tied in? Suppose the correct way to go is to purchase a brake line pressure gage for verifying line pressure at the wheel cylinders, but
the intend of this thread is to find out if anyone out there were actually able to reset a A/G body factory proportioning valve. I think I'm not getting correct rear brake line pressure.

 

[timo22]

Did you rebleed the MC? Do you get a good stream of fluid when bleeding the rear wheel cylinders?

 

[Tomeal]

I'm not a 100% certain, but my understanding is that reset moves a plunger that blocks fluid flow. You get a leak in the back, lose back pressure and the fluid pushes the plunger to stop flow so you still have some brakes. The reseting merely pushes the plunger back to center allowing fluid flow.

If you fixed your rear line and got fluid at the rear, I'd think it is something else. Air maybe?

 

[gmtofd]

Thanks again for all the feedback, To answer the question, the brake light is not on . Really think that there is insufficient rear brake line pressure. What little I know of how brakes are suppose to operate, thought that in a panic stop the rear brakes hit first to try and settle the car. That is not happening, the fronts lock-up and the car wants to switch sides.

 

[pagrunt]

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

 

[timo22]

Ok, more than likely , the combination valve tripped as stated above. I would unplug the brake switch wire at the combo valve and ground it with the key on. See if your brake warning light comes on. Maybe the bulb is burned out. Does the brake warning light come on when the e-brake is applied?
I had the exact same issue when I redid my Bonneville. When I pulled the rear drums off, it was apparent that the wheel cylinders were froze and the rear brakes had been non existent . After replacing hard lines , rubber hoses, calipers and wheel cylinders, I couldn’t get the rear drums to work. The fronts worked fine. And my brake warning ligh5 was on.
I ended up just driving my car hard and stomping on the brakes. You know like a panic stop. I did this several times forward and also in reverse. No change... I went to turn around and did a three point turn and all of a sudden, I heard a click and looked to see the light went out. Now my brakes work great.
timo22

 

[gmtofd]

The light is not on, the bulb is not brunt out, it is as if the proportioning is not exacting in the correct location, but not to the point that the brake light is tripped, (if that is physically possible to happen?

Anyway, thanks for the suggestions, I have tried reverse panic stops, with no apparent change.