Here's the deal. Two years ago I purchased a 1990 Dodge W250. Before putting it to work I did a complete brake job-turned front rotors; new pads and flex brake lines; rebuilt calipers; new (or could've been rebuilt?) master cylinder; turned rear drums; new rear brake shoes; new parking brake cables. Rear brake cylinders were fine. A few months ago two (related? I don't know) strange things started happening. 1) At a stop, applying enough brake pedal force to remain stopped, the pedal will slowly go to the floor and braking will diminish- if on an incline the truck will start to roll. A quick pump will restore braking, but the pedal will do the same thing. There is no obvious leakage of brake fluid (I do know what to look for) and the master cylinder is not losing fluid in either circuit. 2) When braking on gravel, or medium braking on asphalt, the right rear brake will lock up- only the right rear. This is most pronounced when the truck is unloaded. When pulling a loaded trailer (2000lb-8000lb), lock up does not occur. I have a fair amount of experience turning a wrench, but this is my first Dodge truck. I inspected the right rear brakes and they look innocent of any mischief. Any ideas?

 

did you replace all the steel brake lines? also did you make sure the rear brakes where adjusted properly. locking up rear brakes when there is no weight in the back is fairly easy to do. the old rwal system was not very great. you could make sure that the computer behind the glove box it still hooked up.

 

I agree with wolfie, the right rear is out of adjustment.
Your master cylinder is bad. Holding your foot on the pedal and it slowly goes to the floor indicates fluid is getting past the plunger and returning to the reservoir (hence the no fluid loss).

 

Thanks for reply. As of the time of the brake job the rear shoes were adjusted as I have done in the past- adjust until wheel is hard to spin, back off until wheel spins with very slight shoe contact, apply brakes and recheck. I did not replace the hard brake lines. I have experienced the flexible brake lines degrading and causing brake lock-up but not hard lines. As for master cylinder- that was my though, but I have never experienced this before so was not sure. What about the pesky ABS valve in the left rear on frame rail?

 

With the master cylinder, I dont know if it will be the same in your case, but on my '85 w350, the rebuild kit cost more than a new (reman) unit. I think mine was $26. Couldnt believe how cheap it was. Also, I would tend to agree with the rear brake being out of adjustment, however, it could also be that your drum on that side is slightly warped. After turning drums, they are more likely to warp being as the walls are thinner and heat up more quickly. You would probably be able to tell that it is warped if there is a vibration when braking that feels like its in your seat.

 

Another thing to look at on the right rear. See if you don't have an axle seal leaking. That will also cause a 'grab'.

 

I would simply bypass the ABS valve, and unplug the computer. No problems at all here after about 2 years with it bypassed.

 

This must be a strange one. The drums do not appear warped- no shimmy during braking but I have not mic'ed them. Also, when I did the brake job I also replaced all bearings and seal front and rear, so no oil/grease on the shoes. I will try the ABS idea.
On a separate note, I remember during the bearing replacement the repair manual noted that the rear bearings should be packed with grease. I thought that this was strange since the full floating axle allows diff fluid to enter the bearing cavity. I packed them anyway. Also. I changed out the diff fluid filling up to the fill hole (as I have done with every 100 or so diff's, gear boxes, mowers, tractors, transmissions etc.). Later I noted that the diff fluid should be 1/2" below the fill hole. Why? Is this so that the bearing grease does not get washed away? Long and short is that, indeed, while chasing this brake problem (removed drum) I discovered that the grease is completely gone. But the bearings seem happy swimming the the diff fluid accumulated in the bearing cavity. Think I'll leave the diff fluid filled up to the fill hole and not worry about grease.

 

you should always grease them even though they are lubed via the gear oil you don't want them run dry when right after a service. It takes a couple miles (and turns) for the oil to make it down the axle tubes then up into the hub assembly and through both bearings. After a service you should drive it then recheck the fluid as the level will go down as the hubs get filled. Some people will go to the extent of tilting the axle slightly from side to side and adding fluid to ensure the hubs are filled as well.

I know several people who thought the same thing and ended up needing not only new bearings, races, and hubs but spindles welded onto their rear axle housing.

Removing the RWAL ABS isn't going to help you with 1 rear wheel locking up. It is only a single circuit style abs.

As for you brake pedal "sinking" etc...you either have a leak or your master cylinder is going bad.

 

Maybe the rear slave cylinders were not as "fine" as you thought.