Hi all,

I need some help with a brake problem. I am stuck.

My brake problem started when I started carrying my camper in the back of my truck (Lance 1040 weighs ~2,500 lbs). Now when the truck is loaded or unloaded, when I first starting off and hit the brakes and the rears will lock up with minimal front brakes being applied. When I put the vehicle in reverse and apply the brakes a couple times backing back into the driveway, the problem corrects its self and my brakes work great until the truck sits for a while.

My first guess was the height sensing proportional valve but the Manual says that the sensor is used on 4x4 2500/GVW 8,800. I have a 2wd auto so I shouldn’t have one.

I have been reading about the CAB but I haven’t thrown any codes.

I have inspected the breaks, bleed the system, adjusted both the shoes and emergency brakes.

Any suggestions?

Mods to the truck:
I installed 1 ton wheel cylinders a year ago. Haven’t had an issue, breaks are great. When I loaded up the camper, I installed firestone airbags, E rated tires, and stable rides.

 

how long is "a while"...we talking overnight or like a couple weeks between needing to tow your camper??

If its the latter of the two i would say its rust on the rotors making them stick right away and then once they get cleaned off they work fine, really nothing to worry about just facts of metal sitting...if it happens overnight i would think maybe something with the master cylinder, maybe??

 

I use my truck a couple weekends a month, so the truck sits for a while. Before towing I pulled forward into my driveway and backed out. This problem might have been there for while and did not start until I started parking differently.

 

I think it is just that little bit of rust on your rotors from it sitting and if it rains or is real humid it will probably amplify your problem the next time you go to use it take a look at your rotors before you move it and see how much surface rust is on them...parking it differently should not have any effect on your brakes, unless the parking brake isnt disengaging all the way, but being that your truck is an auto i doubt you are using the parking brake

 

but he has shoes and drums

 

same thing could happen to the drums though just you wont be able to see it

 

My '99 2WD has the proportioner valve, so check to make sure yours does/does not. I suspect that yours does too. The OEM setup with the proportioning valve and the 27mm wheel cylinders seem inadequate, which is why people install the 30mm wheel cylinders. However, when loaded down, with the 30mm wheel cylinders, it's really possible that the proportioner valve has too much authority. You can cut the rod that actuates the proportioner valve and install a turnbuckle arrangement there to allow you to manually 'tune' the proportioner (this has been done with good success by others here). You could also extend the arm bolted to the proportioner valve (and of course the attachment point for the rod) to decrease it's sensitivity to heavier loads. I like that approach, but it would require considerable experimentation to arrive at a lenght that offers the best compromise.
The puzzling aspect of your post is that it cures itself after braking while backing.

 

Grider Pirate,

The manual states that the 1500 use proportional valves. I am looking at my brake setup and it looks like a proportional valve but the manual calls it a combination valve.

Either way, your explaination sounds valid and would tend to agree but the brakes balancing out when I back up (or because it is an intermittent problem) makes it a....