Predivore Posted October 20, 2010 Share Posted October 20, 2010 I have a 1986 R688ST Tandem Axle Dump Truck. I am looking to figure out what the problem is with my brakes, but the air lines are the biggest jumble of a mess i have ever seen, and I don't know where to start on this one. There are two things I would like to address here...1. I don't know where to start on this one, but the brakes just aren't as good as they ought to be (haven't been since we purchased the truck 5 years ago). I put all new drums, cans, and shoes around the truck, and a new valve under the pedal, but it just doesn't stop like it should. Anything else to replace that would help?2. I believe this may be a road tractor conversion, but all the tow lines have been capped off in the frame rails. I would like to tie the hand brake into the brakes of the truck. How would I go about doing this? Is it best to tie into the front or rear?Any help to this would be great! Quote Link to comment https://www.bigmacktrucks.com/topic/16215-r688st-air-brake-problems/ Share on other sites More sharing options...
fjh Posted October 21, 2010 Share Posted October 21, 2010 I have a 1986 R688ST Tandem Axle Dump Truck. I am looking to figure out what the problem is with my brakes, but the air lines are the biggest jumble of a mess i have ever seen, and I don't know where to start on this one. There are two things I would like to address here...1. I don't know where to start on this one, but the brakes just aren't as good as they ought to be (haven't been since we purchased the truck 5 years ago). I put all new drums, cans, and shoes around the truck, and a new valve under the pedal, but it just doesn't stop like it should. Anything else to replace that would help?2. I believe this may be a road tractor conversion, but all the tow lines have been capped off in the frame rails. I would like to tie the hand brake into the brakes of the truck. How would I go about doing this? Is it best to tie into the front or rear?Any help to this would be great!I highly reccomend a place to start is Any Big line from an air tank to the bottom of any or all relay valves first.I have seen lines degrade over the years and cause your exsact symtoms! Quote Link to comment https://www.bigmacktrucks.com/topic/16215-r688st-air-brake-problems/#findComment-65615 Share on other sites More sharing options...
rhasler Posted October 21, 2010 Share Posted October 21, 2010 I highly reccomend a place to start is Any Big line from an air tank to the bottom of any or all relay valves first.I have seen lines degrade over the years and cause your exsact symtoms!Agreed. Start checking the supply system and make sure you have full pressure to the valves at the "supply" ports and continue on from there. Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment https://www.bigmacktrucks.com/topic/16215-r688st-air-brake-problems/#findComment-65617 Share on other sites More sharing options...
theakerstwo Posted October 21, 2010 Share Posted October 21, 2010 Did you bleed all of the air out of the system? Some times its hard to do. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/16215-r688st-air-brake-problems/#findComment-65624 Share on other sites More sharing options...
convoyduel Posted October 23, 2010 Share Posted October 23, 2010 I think you're starting in the wrong place. I suspect your slack adjusters and/or s-cam bushings are extremely worn and not allowing the s-cam to rotate and apply proper pressure to the rollers on the shoes. I had a '97 CL713 that had the exact same problem. I'm also not sure what you would be gaining on plumbing the hand valve to the tractor service brake line. You would have to tie in the the outbound air line from the handvalve into the tractor service brake line. The easiest place would be to plumb it to the service INPUT line on the tractor protection valve as in your case the TPV is no longer something that is used. Quote Link to comment https://www.bigmacktrucks.com/topic/16215-r688st-air-brake-problems/#findComment-65710 Share on other sites More sharing options...
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