Truck#1 Posted July 26, 2007 Share Posted July 26, 2007 Hey guys, My parkiing brake knob doesn't pop out until the pressure is down to 0 psi. Is the valve behind the knob bad??? Also, I've been driving a 95 CH613 for about 10 years...it has a big ass air dryer on it. I just bought a 98 CH and it needs a new air dryer....but the one on it now is tiny compared to the 95. Why the difference? Thanks in advance.Rob Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/ Share on other sites More sharing options...
theakerstwo Posted July 26, 2007 Share Posted July 26, 2007 Hey guys, My parkiing brake knob doesn't pop out until the pressure is down to 0 psi. Is the valve behind the knob bad??? Also, I've been driving a 95 CH613 for about 10 years...it has a big ass air dryer on it. I just bought a 98 CH and it needs a new air dryer....but the one on it now is tiny compared to the 95. Why the difference? Thanks in advance.RobSounds like the parking brake vavle is wrong so check when there is no air on system and see if the vavle is spring loaded out that would be the right vavle and there is another vavle that looks alike but is not sping loaded.Also the later trucks will not set the park brakes untill as low as 30psi and when I worked at freighliner we had many times when drivers though they should set at 65psi like old time systems and we was have trouble exsplainig to then so I pulled it out of the sevice manuel and made copies for all and that problem when away. glenn Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13138 Share on other sites More sharing options...
theakerstwo Posted July 26, 2007 Share Posted July 26, 2007 Sounds like the parking brake vavle is wrong so check when there is no air on system and see if the vavle is spring loaded out that would be the right vavle and there is another vavle that looks alike but is not sping loaded.Also the later trucks will not set the park brakes untill as low as 30psi and when I worked at freighliner we had many times when drivers though they should set at 65psi like old time systems and we was have trouble exsplainig to then so I pulled it out of the sevice manuel and made copies for all and that problem when away. glennAnd about theaair dryer the old one was a ad9 bendix and was good dier but all trucks use the the small light weight and it will work as good as old one but cost more be buy byt lighterin weight. glenn Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13139 Share on other sites More sharing options...
Truck#1 Posted July 27, 2007 Author Share Posted July 27, 2007 Thanks Glenn. Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13146 Share on other sites More sharing options...
ThaddeusW Posted July 28, 2007 Share Posted July 28, 2007 Rob, Some air dryers sometimes have a built in purge reservoir that holds dry air to purge the desiccant after the compressor cuts out. Thats why they are so big. Some dryers let dry air from the wet tank back through the dryer to purge so they are more compact. Some dryers even have a small external purge tank like the Bendix ADIS. I would replace that park knob before it gives you any more trouble. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13159 Share on other sites More sharing options...
Truck#1 Posted July 29, 2007 Author Share Posted July 29, 2007 I need to replace the whole valve/knob assembly right??? Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13183 Share on other sites More sharing options...
ThaddeusW Posted July 30, 2007 Share Posted July 30, 2007 I need to replace the whole valve/knob assembly right???There might be maintenance kit that includes a new valve slide and O rings. You would have to check with the manufacturer. If you have the individual valves I would replace the whole valve. They can be had pretty cheap, something like 20 bucks for a new PP-1 on eBay. If you have the compact all in one two valve unit like the Bendix MV-3 it might be more economical to rebuild it since they can cost around 200 bucks. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13210 Share on other sites More sharing options...
LeakyBoot Posted August 13, 2007 Share Posted August 13, 2007 You guys seem to know your brakes--so here is another on a GMC. 84 Brigideer and has some sort of dryer but not like on my Topkick. It's under the driver door and not much to see. What triggers the air to go off on the dryer? The Whoosh I mean--you get ever so often??After you stop it will hiss abit then go off then stop hissing after that? There is a little round cylinder about the size of a pop can. That's all I can see. Tube comes out and that's where the air comes from. Thanks, LB Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13386 Share on other sites More sharing options...
LeakyBoot Posted August 13, 2007 Share Posted August 13, 2007 You guys seem to know your brakes--so here is another on a GMC. 84 Brigideer and has some sort of dryer but not like on my Topkick. It's under the driver door and not much to see. What triggers the air to go off on the dryer? The Whoosh I mean--you get ever so often??After you stop it will hiss abit then go off then stop hissing after that? There is a little round cylinder about the size of a pop can. That's all I can see. Tube comes out and that's where the air comes from. Thanks, LB SORRY__MEANT UNDER THE PASSENGER DOOR Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13387 Share on other sites More sharing options...
theakerstwo Posted August 13, 2007 Share Posted August 13, 2007 I think you are looking at what i call a sluge vavle or purge vavle or spitter vavle and it sees water and spits but dont have a signal line and in my eyes ant too good. glenn Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13390 Share on other sites More sharing options...
MidniteMechanic Posted August 14, 2007 Share Posted August 14, 2007 The 'pop can' cylinder sound like a Stemco moisture ejector. It has an air line going to the air governor that causes the ejector to spit when the compressor unloads. There the biggest piece of junk waste of money there is. A simple pull type drain valve on the wet tank is much more effective.A Bendix MV-2 valve is rebuildable, the MV-3 is not. A new MV-3 only costs about $85. If it's a Midland valve then it'll cost $200-300. Quote Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13398 Share on other sites More sharing options...
ThaddeusW Posted August 15, 2007 Share Posted August 15, 2007 You guys seem to know your brakes--so here is another on a GMC. 84 Brigideer and has some sort of dryer but not like on my Topkick. It's under the driver door and not much to see. What triggers the air to go off on the dryer? The Whoosh I mean--you get ever so often??After you stop it will hiss abit then go off then stop hissing after that? There is a little round cylinder about the size of a pop can. That's all I can see. Tube comes out and that's where the air comes from. Thanks, LBThe governor controls the compressor, air dryer and even an alcohol injector. Its purpose is to cycle the compressor which keeps the air system charged. The governor has three air lines coming from it: one controls the compressor, one line comes from the tanks to monitor the system pressure and the third controls the air dryer and an alcohol injector. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/2692-yellow-knob-question-and-air-dryer-question/#findComment-13407 Share on other sites More sharing options...
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