Help me understand the brake proportioning valve

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Illahe

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Hello all,

I'm troubleshooting a brake pulse in the right front of my sons d200. It pulses when coming to a stop on the right side only. We have swapped the rotor to a trued unit, added a new idler arm, caliper and a drag link. I'm stumped, and wondering if the pulse has something to do with the proportioning valve malfunctioning.
 

I don't think it would in any way it would cause pulsing.

When the pressure in the brake lines goes above 300 psi, the pressure to the rear brakes is proportionally reduced.

Master, Front Disk, Rear Drum
250 psi 250 psi 250 psi
300 psi 300 psi 300 psi
400 psi 400 psi 350 psi
500 psi 500 psi 400 psi

The drum brakes are self-energizing so they don't need as much hydraulic pressure as th calipers. In addition the harder the braking the more weight shifts off the rear to the front. The proportioning valve helps prevent the rear drum brakes from locking up under hard braking.

 
Frank Mopar said:
I would check the rotor runout with the rotor on the vehicle to start.
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We’ve been through that with an indicator. It acts like the pressure is bleeding off. Thanks for the response. I’m going to take a look at the upper control arm bushings next.
 
Is it possible you have a collapsed hose on either side on the front?

I had a dodge once that wore through rear brakes a lot. Thought it was something wrong with the rear brakes. Turns out the front rotors / pads were really glazed. The rear brakes were doing all the work. Replaced rotors and pads and problem went away. Car stopped better too.

The moral to the story is that if it is not what you think it is, it might be something else causing the problem indirectly.
 
Mike69cuda said:
Is it possible you have a collapsed hose on either side on the front?

I had a dodge once that wore through rear brakes a lot. Thought it was something wrong with the rear brakes. Turns out the front rotors / pads were really glazed. The rear brakes were doing all the work. Replaced rotors and pads and problem went away. Car stopped better too.

The moral to the story is that if it is not what you think it is, it might be something else causing the problem indirectly.
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Thanks, I will flush the system well. Could the front portion of the master cylinder be failing?
 
Seems like both front brakes would be affected if master cylinder was bad. Have you tried swapping tires from side to side or front to back?
 
I just replaced the rear drums on my 1993 D250 and had a “surge” when applying the brake.

Turns out the new Chinese drums were out of round and needed to be turned.
 
Illahe said:
It pulses when coming to a stop on the right side only.
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Any time I have felt a "pulsing" in a car, I felt it in the brake pedal. If that is what you mean by "pulsing", how do you know it was the right side? Just asking.
 
harrisonm said:
Any time I have felt a "pulsing" in a car, I felt it in the brake pedal. If that is what you mean by "pulsing", how do you know it was the right side? Just asking.
Click to expand...
Under braking there is a surge going thorough the chassis on the right side as if the brake caliper is loading and unloading during the rotation of the wheel assembly. Not a pulsing of the pedal are shake in the steering wheel.
 
Illahe said:
Under braking there is a surge going thorough the chassis on the right side as if the brake caliper is loading and unloading during the rotation of the wheel assembly. Not a pulsing of the pedal are shake in the steering wheel.
Click to expand...
If you don’t feel it in the steering wheel, it’s probably in the back brakes.
 
What kind of wheels?

Are the lug nuts torqued?

My 2000 Dakota R/T kept warping rotors until I started paying better attention to torque and sequence.
 
BTW- Mopar "proportioning" is done with the bore sizes of the caliper pistons and wheel cylinders.
 
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