Need some help. I've run through the threads and can't find an answer (probably just posing the question wrong on my part).

Issue is with a 1998 F150 5.4l RWD, with ABS and rear drums. I replaced the HCU about 6 weeks ago due to brake pedal "fade" while stopped (the vehicle would always remain stopped, just the pedal would slowly go towards the floor as you kept pressure on the pedal). The proper ports indicated movement when removing the plug and checking with a small length of ground wire. I replaced the HCU and vacuum bled the brakes until clear fluid was running from all lines (bled in order as dictated from my Hayes manual).

Everything is good.

Flash forward to yesterday (6 weeks later), after a short drive of 10 miles or so, I feel a shutter, kind of like you are running on a pothole filled road. Stop the truck, and it smells like brake, the smell is coming from the left front wheel. No visible fluids from anywhere. Let the truck sit for 30 minutes and start the drive home. Truck seems to drive normal. At the end of the drive, it is beginning to deteriorate and the shutter is starting to return. When I stop in the driveway, the left front is smoking and there is definitely a smell of brakes.

Let the truck sit overnight. Pull the left front and pads are still good, there is some brake wear but the rotor is still good. Pulled the caliper and I can push the pistons back into the caliper. The rubber brake line appears good from visual inspection and there is no rust anywhere on it. The metal line back to the HCU appears good with no crimps or crushes on it. Fluid levels all good, no visible fluids anywhere.

I'm stumped.

Stuck caliper? Rubber brake line collapsing? Right front actually the issue, causing pressure transfer to left front (HCU)? Not properly bleeding the HCU when I replaced it? New HCU causing "downstream" issues?

Ideas/thoughts?

Thanks, in advance.

 

You should not be able to easily push the piston back into the caliper The only time I have seen where you could do this is where you have a fluid leak in either the brake line or caliper. Since you have no evidence of leaking fluid, I would first try bleeding the brakes again since this is low cost and could be your problem. If that doesn't work, I would be looking at the caliper.

 

My 98 had the same issue, first front left then front right 6 months later. Others on this site have had it as well and it appears to be a problem with the flexible brake line separating layers and acting as a check valve and not allowing the pressure to be relieved from the caliper. I suspected as much but chose to replace both the hose and the caliper when it happened to my truck. Problem solved.

 

If your smelling brakes, then for some reason the caliper is not releasing.

I am with re54drider, probably the hose deteoriating, but could be a caliper issue. As Frank Ford said, try a re-bleed. It costs nothing and could be the problem (not likely, but still, it is free).
A new set of calipers and some new brake hoses (both sides) would probably be the fix for it (and upgrading to SS brake houses would be a bonus).

 

Same here.

 

I'm probably going to switch out the rubber lines and the calipers on both fronts and use metal piston calipers. The pads and rotors still have lots of life in them, so I'll reuse them (making sure they go back in the same position they were in) until I verify the braking problem is fixed (that way I hopefully only go through one set of pads and rotors).
One side will probably fix it, but I've owned the truck for a couple of years and who knows what the PO did.