I'm at a loss, does anyone out there really and truly know about the brake system on an F-600 with hydrovac booster. The right rear wheel is locking up and not releasing or releases slowly.<O></O>
I have replaced all the brake <NOBR style="FONT-FAMILY: Arial; COLOR: darkgreen; FONT-SIZE: 100%; FONT-WEIGHT: normal" id=itxt_nobr_3_0>lines</NOBR>, wheel cylinders sanded the ridge off of the backing plate, cleaned and lubed adjusters, replaced the hydrovac and master cylinder, brake linings are new, drums seem to be good ( no groves. There is good fluid flow to all the bleeders and I have pumped a gallon or more brake fluid through the system. <O></O>
Please can someone Help???????<O></O> <!-- / message -->

 

Wow you've replaced just about everything. The only thing that is left to try is a new brake hardware kit (brake shoe returns springs and hold down springs) maybe the old return spring is too weak to retract the brake shoes. try Napa or Job Lot automotive.

 

Check to see that your master cylinder is releasing.When the brakes are locked loosen the bleader with no pressure on the pedal and see if there is pressure on it
Only other thing I can think of now is the drum isn't centered with the hub,I've had that happen a couple times.but you should notce that while adjusting the brakes

 

Thanks for your input. I have already replaced the return springs I had the same thought. What happens is, when the brakes are applied the right rear brake locks up and after a short while it will release just a little but still drags. If I loosen the bleeder the brake will release. That’s how I came to replacing the brake lines. this didn't cure the problem so I thought that maybe there was something in the wheel cylinder (maybe from the collapsed rubber line) so I remove the wheel cylinders and found one of them to have some pitting so I replace it. anyway I've pumped well over a gallon of brake fluid through the brake system.
Could air cause this problem?? My thought is that air can compress so the springs should return the shoes. I'm just wondering what else I mite check?????????????????.
Thanks again for any thoughts you all mite have……

 

If the master cyl is not releasing it can hold pressure on the brakes.The tightest one would lock There is an eccentric bolt that attaches the MC push rod to the brake pedal turning it will give the MC more free travel
Air would only give a low or spungy pedal

 

I also had the same idea, so I backed off the brake that locks up almost all the way and it still locks up and the left rear releases fine (it makes no sense to me). After I posted this yesterday I looked at some photos that I had taken of the brakes just to make sure they were installed correctly. The shoes look to be the same, is there always a forward and rear shoe? I have the original service manual for the truck and this style of brake is not in the book (good thing I took pictures) anyway, it has two wheel cylinders centered top and bottom with unequal length springs. Something as simple as brakes should not be this much trouble. I sure do want to thank you for trying to help. I'm really lost at this point.

 

Did you replace the jumper lines from bottom to top WC?If not what shape are they in?

 

When you say jumper lines are you referring to the flexible line? I have replaced all three two up front and the one at the center to a tee fitting over the rear axle. I evan cleaned the tee fitting

 

Are you talking about the line from the bottom wheel cylinder to the top? this line I cleaned and blew out with air..................

 

I've pulled the right rear apart again. with everything off the backing plate except the wheel cylinders and the brake lines still hooked up with only minimal fluid pressure, I tried to move the wheel cylinders back and forth (that is to say side to side). The top cylinder seemed to be slightly stuck and hard to move at first and then it seemed to free up. The bottom one feels like it has some chatter or roughness and was hard to push back and forth.
The cylinders are new and one was bad and was already replaced. What if I was to run a hone through it? How far would you hone the cylinder?????????? Or is there some other reason they are acting like this or maybe this is normal??????????
Anyone have any thoughts

 

I would check the plungers and cyl bore for roughness or rust pits
if there are any rust pits inside it's pretty much junk
The plunger should slide easily inside the cyl lubed wth brake fluid
it won't hurt anything to hone the cylinder bore or to polish plunger with fine emory cloth