Brake Problem?

Bob Tailing should be the worst braking. If bob tailing is ok, then the trucks systems must be ok. I'm guessing there is an air problem on the trailer. Since you said they are different trailers, could it be your airlines on the cab leading to the trailer? To give a more scientific analysis, try the pull test with no trailer, then try with just trailer parking brakes on and then just cab. If it fails on either of those you might be able to narrow it down. It might be bad airlines on the tractor but you only notice it when they are used when you supply air to trailer. Also could be a airline getting pinched, but only when the suspension is weighted down. Also your truck brakes might be fine, but they are not triggering the trailer brakes for one reason or another. Try a pull test with the trailer hand valve. If it passes try to pull forward (low gear hard) with service breaks lightly applied. With an empty trailer it should lock all the wheels except the drive wheels which over come the braking power. If your trailer wheels roll instead of drag half a foot your trailer brakes a'rnt working right.

My guess is your airline from the truck is not telling the trailer brakes to come on. Your experiencing poor braking because your trying to stop the load with no trailer brakes and are over working the tractor brakes. It could be something wrong with the actuator in the petal or something wrong with the air system going back to the trailer.

In any case, your brakes on the tractor must not be damaged or miss aligned that bad if you can stop bob tailing. I think its something else.

 

what does your air gauge read and what temp does this happen at , i be looking at the trl then the tractor, i moved alot of trls around by just hooking up one air line , might too try that and narrow the leak down by doing that , but dont go on the street that way, just a drive around yard will tell you if you got a problem, are the trl air tanks drained , if they got drain peacocks , mayby full , and not building air , mayby,

 

s-cam bushings

 

Gunites and Haldex will make that sound and will also be harder to back off than tighten up. If you have a pawl that you have to remove to adjust your brakes, than no, from my experience anyway, those won't be like the others. Have you pulled your blue gladhand and confirmed that air is coming out of there when brakes are applied ?

 

9/16" Wrench/socket = Manual Adjust
7/16" Socket = Auto adjust slack and it will click when you back off (if it does not then the slack is bad)
5/16" wrech or square socket = Auto adjust. You have a pin that you pull out with a flat screwdriver to back these brakes off and there is no sound. If you can turn the adjuster both ways without the pin pulled out the slack is bad.