farmer52 Posted June 7, 2018 Share Posted June 7, 2018 On my trip last Tuesday from PA to Lexington, the air pressure held a constant 120-125psi. On Saturday when I got in to drive from Lexington to OH the air pressure dropped to 60psi (both red and green needles about the same pressure) and again held steady 120-125 during the trip. On Monday I drove from OH to PA and again the pressure was about 60psi after sitting on Sunday and as before the pressure held steady during the trip to PA. Wednesday afternoon when I needed to move it to mow grass around and under the truck, the pressure had dropped to about 30psi. As before both the red and green needles read about the same pressure. Now for the puzzling part. After about two (2) hours I went to move the truck back to its usual parking spot. The red needle read about 90psi and the green needle read about 20psi. What the fluff is happening to the air? I didn't hear any audible air leakage. I always let the pressure build to 135psi before moving. Previous years the air would drain to zero after sitting a few hours or over night. Also during trips it would cycle every 15-30 minutes. I was getting confident this past week that the air pressure drop had mysteriously healed itself. I will see what happens when I drive to Macungie next week. I just checked and both needles are at 70 (after sitting 24 hours). What the hay! Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/ Share on other sites More sharing options...
Lmackattack Posted June 8, 2018 Share Posted June 8, 2018 you will drive yourself nuts chasing a slow leak like that LOL....but I wish you luck 1 Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400213 Share on other sites More sharing options...
farmer52 Posted June 8, 2018 Author Share Posted June 8, 2018 7 minutes ago, Lmackattack said: you will drive yourself nuts chasing a slow leak like that LOL....but I wish you luck My concern (puzzlement) is why did the green pressure drop over 70psi in two (2) hours? I am pleased with the slow drop over a day or two when previously it would drop to zero within hours. And also pleased the pressure remains steady during driving rather than constantly cycling. It is the engineer in me...sorry! Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400214 Share on other sites More sharing options...
Lmackattack Posted June 8, 2018 Share Posted June 8, 2018 If I remember right the green needle is showing air pressure on the service side of the air brake system. if the orange needle stays up that tells me the check valve is working keeping the parking side of the air system charged. but Im not real savy on the air braking systems. Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400218 Share on other sites More sharing options...
carlotpilot Posted June 8, 2018 Share Posted June 8, 2018 if you blew the air horn at anyone on your recent round trip check that` horn valves tend to leak especially after sitting a long time` not enough to make any noise 2 Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400221 Share on other sites More sharing options...
MHfred Posted June 8, 2018 Share Posted June 8, 2018 You can tape a rubber glove over the horn and see if inflates. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400236 Share on other sites More sharing options...
farmer52 Posted June 8, 2018 Author Share Posted June 8, 2018 Perhaps I am not clear in the explanation of the issue. The air pressure held great until Wednesday this week. The pressure (both needles) showed about 60psi. I started the truck, let the pressure build to 135, and the compressor cutout. I released the parking valve (yellow knob) and drove the truck about 50yards and stopped. I stopped, applied the parking valve, and shut the engine off. Two (2) hours later the green needle was 20psi and the red was 90psi. I did not blow the horn, disconnect the trailer air lines, drain the tanks, no nothing. After about two (2) hours I started the truck, let the air build to 135, and returned to the usual parking spot (applied brake and pulled yellow parking valve). 24 hours later both needles still showed 70psi. Again, why did the green needle drop to 20psi within two (2) hours and before/after it did not drop? Is the tread valve the issue? The yellow valve and the others were replaced about two (2) years ago. Perhaps I should just forget it and drive it fatter, dumber, and not happy! Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400243 Share on other sites More sharing options...
Lmackattack Posted June 8, 2018 Share Posted June 8, 2018 It still can be a mix of things. you pushed in the yellow valve (parking system), used the foot valve (service system) and then set the yellow again (parking system). the service and parking sides of the air system are all connected yet operate separate. the green needle is the service side so I would assume that the foot valve stuck a little and bleed off air thru a leaky treadle valve or quick release valve? what I would do is repete the same series of events and see if it leaks down again. or spray the treadle valve with lube and see if the issue does not come back. also make sure the trolly handle is not pulled a little Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400245 Share on other sites More sharing options...
farmer52 Posted June 8, 2018 Author Share Posted June 8, 2018 1 hour ago, Lmackattack said: what I would do is repete the same series of events and see if it leaks down again. or spray the treadle valve with lube and see if the issue does not come back. also make sure the trolly handle is not pulled a little It was replicated when I returned the truck to its normal parking spot. Trolley lever never touched. What spray lube to you suggest? Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400249 Share on other sites More sharing options...
Lmackattack Posted June 9, 2018 Share Posted June 9, 2018 I used PB blaster or WD40 on the treadle valve but we get a lot of salt on them every year so its a constant battle with them Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400262 Share on other sites More sharing options...
Hobert62 Posted June 9, 2018 Share Posted June 9, 2018 Was it windy? Working air ride cab around when parked? Quote Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400271 Share on other sites More sharing options...
Freightrain Posted June 9, 2018 Share Posted June 9, 2018 How about a leaky ride valve on rearend? I know mine was leaky and would drop in a few hours of sitting. Once replaced the bags stay up all winter. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400276 Share on other sites More sharing options...
farmer52 Posted June 9, 2018 Author Share Posted June 9, 2018 7 hours ago, Lmackattack said: I used PB blaster or WD40 on the treadle valve but we get a lot of salt on them every year so its a constant battle with them I will try some PB Blaster 6 hours ago, Hobert62 said: Was it windy? Working air ride cab around when parked? NO 1 minute ago, Freightrain said: How about a leaky ride valve on rearend? I know mine was leaky and would drop in a few hours of sitting. Once replaced the bags stay up all winter. Spring Suspension - no ride valve Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/53523-mysterious-air-leak/#findComment-400277 Share on other sites More sharing options...
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