sww943 Posted April 17, 2014 Share Posted April 17, 2014 hello,i have a 93 ch,the back axle chambers are very slow to release when applying the foot pedal, the front rear axle chambers work as they should, any ideas before i replace parts needlesslythankssww Quote Link to comment Share on other sites More sharing options...
Freightrain Posted April 17, 2014 Share Posted April 17, 2014 Welcome to the forums.First thing I think of is quick release valve. Do you hear it while standing in the rear and have someone push and release the brakes? 1 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
sww943 Posted April 17, 2014 Author Share Posted April 17, 2014 yes i hear a gush of air and the parking brakes work instantly, Quote Link to comment Share on other sites More sharing options...
Freightrain Posted April 17, 2014 Share Posted April 17, 2014 I guess I would start with seeing if the cams are free. Unhook or loosen slack adjuster and see if you can rotate by hand easily. If that is good, then I would start with air lines. Maybe one of the rubber lines has a flapper in it and slowing the release?Is there only one quick release for both axles? If two, check to see if both feel the same on the exhaust port. Is the one taking a touch longer to expel? Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
j hancock Posted April 17, 2014 Share Posted April 17, 2014 May also be a defective relay valve in the air line to the rear of the truck. Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
ws721 Posted April 17, 2014 Share Posted April 17, 2014 Just a thought. Check the pins in the clevis to make sure they are free. I've had that happen more than once. The pins cease then the brakes take a while to back off. 1 Quote Remember if it's got a hood it's no good! Link to comment Share on other sites More sharing options...
thomastractorsvc Posted April 17, 2014 Share Posted April 17, 2014 Easy way to see if it is the quick release is to loosen the air line and see if it is holding any air. On my R the rear was slow to release loosened the air line at the t split mounted on rear axle and it had some residual air took the quick release off and disassembled it and cleaned it because it is aluminum alloy it has a tendancy to corrode and can stick. Cleaned mine up then sprayed with wd 40 to slow the process again been a year- they are not expensive if you need to replace. Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
sww943 Posted April 17, 2014 Author Share Posted April 17, 2014 thanks for the advice men, i have replaced the quick release valves and the rear relay valve, the brake chambers are almost new with excellant linings, i even lubed the foot valve- not removed and same old prob, with back axle, when drain the air system then rebuild it with air, and release the in cab parking brake, the chambers retract, then after depressing the foot brake, the back chambers stay in the extended position. im not really sure what to try next????scott Quote Link to comment Share on other sites More sharing options...
thomastractorsvc Posted April 17, 2014 Share Posted April 17, 2014 Did you check to see if the rear brake line is holding air at the t split? Did you recently have the brake shoes replaced? If so did the replace the brake hardware and springs correctly?Post some pictures of the valves that you replaced so we can tell what you call a valve is the same as what we call it. 1 Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
Freightrain Posted April 17, 2014 Share Posted April 17, 2014 I'm still wondering if it is an air line issue? Time to install a pressure guage, like right at one of the chambers(service side) and watch pressure. After releasing pedal, does it drop quick? No, then try back at the q/r valve. Does it drop quick there? Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
sww943 Posted April 18, 2014 Author Share Posted April 18, 2014 (edited) evening, ended the day where we have started, both quick release valves are replaced, both of the relay valves are replaced( square boxes with 5-6 ports). removed the slack adjuster from the clevis and backed off, the s cam moves freely and is well greased, the rear chambers will retract once all air pressure is out of the system and you refill the system to normal pressure, release the parking brake and it retracts in, mash on the foot valve and it stays outward, im guessing now it is in the foot valve??thanks Edited April 18, 2014 by sww943 1 Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted April 18, 2014 Share Posted April 18, 2014 my advice is work backward, pull application line at air can is air present ? if so go to relay valve remove control line from relay valve is air present ? if so chase control line to treddle valve. if coming from treddle valve is brake pedal moving freely? is plunger free to travel? Quote Link to comment Share on other sites More sharing options...
MACKS Posted April 18, 2014 Share Posted April 18, 2014 Sounds like the foot valve to me,something is sticking in the valve, maybe spray some w-d40 or something in there to clean it out and free it up. Quote Link to comment Share on other sites More sharing options...
thomastractorsvc Posted April 18, 2014 Share Posted April 18, 2014 I would not think it would be the treadle valve as it only happens to the rear axle and not both rears with a slow release.I would still like to know if you release the air line at the t-splitter on the rear axle if it holds air. 1 Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
thomastractorsvc Posted April 18, 2014 Share Posted April 18, 2014 Air Brakes Troubleshooting 101Slow or No Release of BrakesPOSSIBLE CAUSES:1. Hinge Pin on Brake Pedal2. Air Delivery Lines restricted3. Control Line restricted (Delivery of Brake (Foot) Valve to Service Port of Relay restricted)4. Relay Valve not exhausting5. Quick Release Valve not exhausting6. Brake (Foot) Valve not exhausting7. Binding parts in the Foundation BrakeStep #1Check Hinge Pin in Brake Pedal. If free, go to Step #2.Step #2Have an assistant make a brake application and release.Listen for exhaust noise from the exhaust ports of: Relay ValveQuick Release ValveBrake (Foot) Valve If there are no exhaust noises, go to Step #3.If exhaust is normal, go to Step #4.Step #3Check for restrictions in all Delivery Lines from the Valve that is not exhausting. If a kink or dent is not found, remove and check internally.NOTES: Line could be plugged or may have been crimped with vice grips or pliers.If line is free of restrictions, replace or repair valve. Step #4Check S-Cam. It should rotate freely (Cam Brakes).Check Anchor-Pins (Cam Brakes).Check Wedge Assembly and Actuation Housing (Wedge Brakes).Check Clevis Pin in Slack Adjuster. It should rotate freely (Cam Brakes). Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
sww943 Posted April 18, 2014 Author Share Posted April 18, 2014 we have a solution to the problem, one of the relay valves was hanging, the replacement part was just as bad as the origional, i used a less costly overseas brand and the tolerences were to tight inside for proper travel. lesson learned, thanks for all the ideas Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.