First post.. I have an 87 F250 Diesel 4X4.. with a brake problem.
I have just replaced ALLthe brake lines- including flex lines, front pads, calipers, rear shoes (3"),rear cylinders, master cylinder etc.

The problem-- The rear brakes are dragging and not releasing. I went to move the truck and it moved great for about 5 foot (no drag). Then stepped on the pedal.. The Pedal dropped from a full pedal to about 1/4-1/8th pedal. With the next stroke the pedal returned to full pedal, and the rear brakes would not release. They still are not releasing. This was with the truck (brakes cold) so not a matter of air expanding. The brakes were adjusted to rotate freely.. Something is blocking the release of brake pressure... Any thoughts???

I am thinking possibly height sensing proportioning valve?? Maybe? Also I believe that in the event of a loss of brake fluid there is a valve that slides to cut off the offending wheel??? Maybe?? What else could restrict the release of brake pressure??? (new flex line in the rear also)


Thanks
antiqbob

 

did you rachet down the rear drum adjuster??? if you have rear drums like mine you need to take that adjuster all the way down or most of the way... if you don't the breaks will lock because you need to account for the extra pad that wasn't there before. I had the same problem... After driving and using the breaks for a while that adjuster at the bottom of the breaks will self adjust to the pads and drums...

 

My guess is you have the rear brake shoes installed incorrectly. Believe it or not there is a leading and a trailing shoe, the ones with less friction material are the lead which go on the front of each side, and those with more material go on the back.

 

My guess would be that the RABS module is bad. It is bolted to the inside of the left side frame rail about level with the drivers feet.
First unscrew the brake pipe nut for the rear brakes at the master cylinder a few turns. If the brakes then free up the RABS module is not the problem. If they do not free up then unscrew the pipe nut a few turns at the pipe going to the rear brakes at the RABS module. If the brakes then free up the RABS module is bad.

 

Paul,
Thanks, but they went back as removed.. Leading edge/trailing edge.. And in fact as I noted they were tightened via the ratchet untill the correct tightness (stop-then backed off 5 or so clicks untill wheel will move with only minor drag..).
The truck rolled forward (without brake bind) untill first stepping on the brakes so there was NO restriction as in shoes untill applying the brakes.
My thanks,

Bob

 

Lazy K,
thanks will try to check that out in an hour or so.. Temps now cool enought to go out there..
(RABS?? )
Thanks
Bob

 

RABS is Rear Anti-lock Brake System.

 

LOL I eventually got to the point of realizing that it was the rear ABS.. I didnt realize that there was an ABS system on the truck.. Especially when thinking in terms of an 87.. A brief computer search brought out the details..

Sounds like you got the answer to this puzzle.. I haven't tried it yet, but I will.. It makes sense..

My thanks,
Bob

 

Thanks Guys for the information..
I have found that the truck must be an early 87 as that is when they started the RABS program. Mine does not have them.

As to leading and trailing edge on the brake shoes I replaced as they were removed .. Paying attention to the leading and trailing edge.
The brakes were adjusted untill they stopped the wheel, then backed off about 5 notches untill the wheel would hand turn with "some" drag.

I have now come to the conclusion that the only thing remaining is the brake proportioning valve. I have one located and will try to replace mine tomorrow..

Currently the brakes still come on and lock on (cold). I have new flex line, ALL new brake lines, new master cylinder, new wheel cylinders, new calipers, new pads...
I have bleed the brakes about 5 times (RR/LR/RF/AND LF) IN THAT ORDER..
I just finished bleeding them again tonight and they are still release and untill I started to move forward they locked up.. I move around briefly and it was alright, but then I started to go for a drive and the first time I stepped on them they would not release..
Backed them up, drove forward and they were locked on.

So tomorrow MAY be the big day.. LOL
Thanks
Antiqbob