Yesterday I noticed the trolley valve on the truck wasn't stopping the trailer. I supplied air to the trailer and applied the trolley brakes and then the service brakes separately as well and I have air coming from the truck at the glad hands strongly. I followed the service line back to the valves on the trailer tank and cracked them and I have air there as well. I pulled off a service line coming from a relay valve on one of the tanks on the trailer where it goes to the air can and I have air coming through there, however it did not feel as strong as where it was at the glad hands. Am I on the right track to replace the air relay valve on the service side? Spring brakes work great on the trailer, it is a 2005 with ABS. Slack adjusters and pushrods are in good shape and they are properly adjusted and greased. Do these valves fail often or get sediment build up inside of them? A friend who runs OTR told me he had to replace one once because of a check valve failing inside of it. Also, could ABS have anything to do with the service brakes not functioning at all? I am very new to working on class 8 trucks so any help is appreciated. Thanks, Keith
Sounds as if the relay valve is not functioning correctly. It is probably an R-14 valve or newer style but is suspect as the more pressure you put to this relay valve, the more pressure it should put to the service side of the brake chamber(s) increasing braking force at the wheel end. Basically, that is where I would start.
Brakes are working now. It was the relay valve for the service side. $320 at fleetpride. Thanks.