Hook n ladder 1 Posted October 6, 2013 Share Posted October 6, 2013 I have a problem with my 98 CH613 with real jerky brakes. Very little foot pressure makes them grab and almost throw me through the windshield. Even when I'm inching up at a traffic light when I touch the pedal lightly they grab.I run a 23 foot dump and a 52 foot drop deck. It does it with both trailers but not as bad with the 52 footer on.I had the brake pedal valve tested (it was bad) and rebuilt. No change. I had also changed the springbrake control/relay valve near the rear drives. No change. All brake positions are in adjustment.Any ideas?Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/ Share on other sites More sharing options...
General Ike Posted October 6, 2013 Share Posted October 6, 2013 I have a problem with my 98 CH613 with real jerky brakes. Very little foot pressure makes them grab and almost throw me through the windshield. Even when I'm inching up at a traffic light when I touch the pedal lightly they grab. I run a 23 foot dump and a 52 foot drop deck. It does it with both trailers but not as bad with the 52 footer on. I had the brake pedal valve tested (it was bad) and rebuilt. No change. I had also changed the springbrake control/relay valve near the rear drives. No change. All brake positions are in adjustment. Any ideas? Thanks Does it only happen when the trailers are hooked up? Quote Ed Smith1957 B85F 1242 "The General Ike" Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210290 Share on other sites More sharing options...
Hook n ladder 1 Posted October 7, 2013 Author Share Posted October 7, 2013 No. When im bobtailling too. Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210629 Share on other sites More sharing options...
b61mack Posted October 7, 2013 Share Posted October 7, 2013 When you find out let me know. I have a 72 R Model doing the same thing, you barely touch the brake pedal and brakes lock up bobtailing or with a trailer. id hate to drive it on wet pavement, Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210681 Share on other sites More sharing options...
rsb502 Posted October 8, 2013 Share Posted October 8, 2013 I was actually going to vote for the relay valve being bad, I've fixed this issue with one before. Do you have an application pressure gauge on the dash? If not get some fittings and a cheap air pressure gauge that goes to 120psi and plumb it into the activation line to the relay valve(one from the treddle). When applying foot pressure to the treddle you should be able to watch the guage and gradually build pressure from 0 up to about 90psi. If the gauge jumps up as soon as it starts to move the treddle is bad, if the treddle applys gradual easy to control pressure its the relay valve. Quote "Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin"If your gonna be STUPID, you gotta be TOUGH" "You cant always get what you want, but if you try sometimes you get what you need" Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210762 Share on other sites More sharing options...
gearhead204 Posted October 9, 2013 Share Posted October 9, 2013 the spring brake control relay valve wont help. you need to change the application relay control valve . and one wont interchange with the other because the application relay has a lower cracking pressure. if you put a spring brake relay in place of the application relay you will have very abrupt brakes because their cracking pressure is much higher. Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210856 Share on other sites More sharing options...
j hancock Posted October 9, 2013 Share Posted October 9, 2013 One thing that I have to remember to do is pull the pin on the brake pedal to remove it and make sure the roller is clean, moves freely and is lubricated every so often. It is hiding in plain site.Not saying it is causing your problem but more of a maintenance item for good operation over the long haul. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-210910 Share on other sites More sharing options...
Hook n ladder 1 Posted October 10, 2013 Author Share Posted October 10, 2013 Where can i find the application relay valve and what does it look like?Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-211017 Share on other sites More sharing options...
gearhead204 Posted October 10, 2013 Share Posted October 10, 2013 chase the air lines from the service port of the brake chambers [line closes to the slack adjuster] upward the first valve you hit will be the quick release valve the next valve you come to should be the application relay valve. should be frame mounted and close to the drive axles Quote Link to comment https://www.bigmacktrucks.com/topic/33048-jerky-brakes/#findComment-211020 Share on other sites More sharing options...
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