Proportioning valve?

[72dartnotus]

Here's my symptom on my '72 Dart Custom S6: If I brake fairly hard (not slamming on the brakes, but just a quite fast stop) it locks one or both rear brakes. It feels like they are not proportioned properly. Is there a front-to-rear brake proportioning valve that's adjustable on the Dart?

 

[zkx14]

Stock valve/block was not adjustable.
What do you have? Disk/ drum? And what master cyl? Anything changed or stock system?

 

[72dartnotus]

Everything is totally stock time warp on my car. Rear brakes are SBP drums, front never even checked! I think they are discs in the front. I should know what I have on the front, embarrassing!

 

[zkx14]

If all stock, it won't be an issue... What I was questioning is if MC was mismatched . Must be correct for all drum (equal reservoirs) or disk drum ( diff size for front and back).

 

[mopardude62]

If everything is all stock, like you say it is, my suggestion would be that maybe sometime in the past someone put bigger wheel cylinders on the back brakes. If you do have disc brakes on the front there should be a proportioning valve integral with the distribution block. If you have drum brakes all the way around, there will be a distribution block only. Whatever you have, distribution block only or proportioning valve/distribution block it is usually mounted under the master cylinder to the side of the inner fender.

 

[BillGrissom]

Pull the rear drums and inspect. You usually have to back off on the self-adjusters (pry thru slots in backing plate). You could have leaking brake fluid or axle oil gumming up the shoes.