The rear brakes started locking up on my truck a few weeks ago. I took some time to rule out stuck parking brake cables, leaks and miss adjusted shoes.
I m thinking it is a bad Proportion valve. Can I do a rebuild on this with out replacing the whole master cyl?? any other thoughts?
I would really appreciate the help before I go and through a bunch of money in parts at this hopping some thing works!

Thanks a ton J

 

So here is a little more back story.
The shoes are a few years old. So I dont think they were incorrectly installed,

This just happened out of the blue. We had had a snow storm. with some melt and re-freeze cycles. We took the truck to town to pick up some lumber. had to make a sudden stop at a light and the rear wheels locked up hard and left two big black streaks! Now we have been driving. We were due for new tiers any way so we took it in. The mechanic at the tire store said the 75% of the time when he sees rear wheels lock up itis the Proportioning valve. As far as I can tell the Prop valve on our trucks in built in to the master cyl. .

I had some one else suggest RABS modual? that was my other thought.. are there any ways to test it?.. I don't have any warning light but will pull codes in about an hr.

thanks again!
J

 

Proportioning valve is inline on the master cylinder it threads into the master cylinder and the back brake line threads into that it can be changed.