Dieseldan77 Posted January 26, 2015 Share Posted January 26, 2015 Got an air pressure issue on 1980 r model. It will build pressure up to about 60 psi and hover there. It's not enough to turn off buzzer and light. I have found if i throttle it up, it will build slowly as long as I got my foot on it. When i let off it will start dropping right away. As long as I keep my foot on it and get the psi up over 90, it will start building pressure like its supposed to and I can let off the throttle. Any thoughts and ideas would be welcome. Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/ Share on other sites More sharing options...
Swishy Posted January 26, 2015 Share Posted January 26, 2015 Deezel DanGudday M8a few things I have found with air n up<1> the main pipe/hose from the compressor to the wet tank gets restrictedby a build up of crud - oil burnt like charcoal/tar in side the tube<2> a crack or leak from said hose th@ cant B detected with engine run n<3> compressor governor unload n.. if it is not lay n upright ovr time the inningz will wear with the help of gravitymy B replace compressor governor ..... they cheap n available @ all good cnr storesjist my 2 cents worth tax FREELOLcya§wishy Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276129 Share on other sites More sharing options...
j hancock Posted January 26, 2015 Share Posted January 26, 2015 LIke Swishy said, unloader is not doing it's job. Repair is pretty straight forward.If the problem has been getting worse over a period of time, compressor is just worn out. If it is original in a 1980, you got your moneys worth. Shop around, someone is bound to have your model on sale. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276137 Share on other sites More sharing options...
carlotpilot Posted January 26, 2015 Share Posted January 26, 2015 air the tanks up with a compressor- engine off- first then check all hoses lines etc repair all found leaks then if it still won`t air up start buying parts one common cause for what you describe is worn or stuck one way check valve where main line enters primary tank Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276140 Share on other sites More sharing options...
Dieseldan77 Posted January 27, 2015 Author Share Posted January 27, 2015 Thanks for the ideas. I'll check them out. If I drive it daily it's fine. Seems like if it sits a week or more, it's worse. Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276169 Share on other sites More sharing options...
turckster Posted January 27, 2015 Share Posted January 27, 2015 The rubber/steel braided line after the lead off line may be bad, especially if its old or never been changed. A spray bottle of soapy water should tell you right away. Soak the lines from the air compressor discharge to wet tank or dryer. If the line(s) bubble up there is your problem. Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276192 Share on other sites More sharing options...
Freightrain Posted January 27, 2015 Share Posted January 27, 2015 Unloader valve is cheap(like $15). If it is old just replace it. My b had same issues last summer. Put new unloader and all is good. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-276194 Share on other sites More sharing options...
HabelTrans Posted February 2, 2015 Share Posted February 2, 2015 I agree with the guys sayin unloader (that is if they are referring to what I call a governor). I drove a truck with a triple 4 cummins years ago that would eat them. I pulled MI gravel trains with it (so mostly summers) and would replace it about twice a season. Carried one in the toolbox at all times. It would work fine one day, then, the next the same problem as yours. With eight axles and three places to wiggle behind you, not to mention the 150,000 plus pounds, the last problem you want is an issue with air. I say replace it, it isn't expensive and is very easy to change. I used to do it in the dark with a flashlight in about ten minutes. Quote :chili:Take care of your ride and it will take care of you Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-277041 Share on other sites More sharing options...
eddeere Posted February 2, 2015 Share Posted February 2, 2015 I have read this post with interest for the past few days as my B model would only build about 80# but not hold. Found some leaking lines on removal of the cab. Thought I would replace the governor / unloader . Where is it located ( on firewall ? ) and where is a good source to get one. My air brake knowledge is limited. Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-277138 Share on other sites More sharing options...
Freightrain Posted February 2, 2015 Share Posted February 2, 2015 Here ya go: On the firewall, passenger side: The soft line goes to unloader on compressor.I originally pulled mine off and put a couple new o-rings on it. Seemed like it would be fine. Nope, a few weeks later the same issue. Just put a new one on it. Any big truck place will have one. I got mine at Cross truck parts. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/38608-trouble-building-pressure-on-1980-r-model/#findComment-277139 Share on other sites More sharing options...
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