6/98 Ford F150 4.6lt 4wd. Right rear brake locks up and will not release drum is to hot to touch. This is what has been done 1) new master cylinder. 2) new right front caliper and front pad. 3) new rear rubber brake line. 4) new rear wheel cylinders both side. 5) new rear shoes. 6) drums turned.
From this point my right rear is locking up will not release.
So in a process of elimination this is what was done. Rear ebrake cable disconnected inside the rear drums.
Disconnected all electrical such as rear speed sensor and abs module to rule out electrical and yes my abs light is on.
So the only thing that I can see at this point would be brake hardware ( springs and such ) as an issue. Will pick those up this week.
Also have thought maybe the rear axle is bent or something to that effect.
I know this topic has been duscussed and thread may need moving. I apoligize for any inconvience.
Thank you for you help
R. Parvin

 

Wheels Lock Up
Possible source of problem may be:

Hydraulic outlet (dump) valve. Go to TEST K .

Leaky inlet (isolation) valve. Go to TEST K .

Rear brake adjustment, linings, wheel cylinders, parking brake rear axle seal. Eliminate base brake system
as cause of problem.

K, -

1. Visually inspect brakelines from EHCU to each wheel cylinder. Visually inspect calipers and brake
components. If any damage is found, replace and/or repair as necessary and go to SYSTEM
PRECHECK . If no damage is found, go to next step.
2. Remove rubber boots from EHCU Low Pressure Accumulators (LPA). Insert clean paper clip into each
LPA port. See Fig. 2 . Have an assistant press hard on brake pedal while observing paper clips. If any of
the paper clips move significantly, replace EHCU. If paper clips do not move significantly, remove paper
clips, reinstall rubber boots and go to next step.
Fig. 2: Checking Dump Valves For Leakage
Courtesy of FORD MOTOR CO.
3. Remove fuse No. 14 (60-amp) located in engine compartment power distribution box. Test drive vehicle
at about 20 MPH. Perform light to medium (normal) traffic stop. If any one wheel locks consistently, go
to SYMPTOM DIAGNOSIS . If any one wheel does not lock consistently, go to SYSTEM
NOTE: This test is not associated with any DTC.
NOTE: A leaky dump valve is similar to a master cylinder bypass condition. Press
brake pedal quickly and forcefully to rule out master cylinder bypass.

 

I will check the hcu later this week.
On the other hand though one would be led ro believe that if the dump vavle was not working correctly both rear drum brakes would be locked up. There is only one metal line coming off the hcu going to the rear that i have inspected and also changed the short rubber line between the metal lines
However the hcu is where i was thinking the problem was/is