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Losing air 5-6 psi per minute while driving

Discussion in 'Ask An Owner Operator' started by Forever237, May 18, 2019.

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  1. May 18, 2019 #1
    Forever237

    Forever237 Light Load Member

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    May 29, 2016
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    hello fellow drivers. Like headline says, i’m losing Air pressure while driving. Did static, applied test no leak. I don’t lose any air in 10 hrs while truck is off. What can be the reason? What should i look for? I hope its not transmission.

    Primary air tank goes up to 125 psi and drops to 100 in 5 mins.

    Thank you!
     
    Forever237, May 18, 2019
    Forever237, May 18, 2019
    #1
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  3. May 18, 2019 #2
    flood

    flood Road Train Member

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    because it's not leaking when your on your break it is something that only has air when the key is on...

    lift the hood then turn the truck on (don't start it) and start checking....the fan hub would be the 1st thing to check.... look LISTEN and feel for the leak...
     
    flood, May 18, 2019
    flood, May 18, 2019
    #2
    Flat Earth Trucker, Hulld and rank Thank this.
  4. May 18, 2019 #3
    Forever237

    Forever237 Light Load Member

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    Thank you for replying

    I’ll definitely do that. The thing is I left it on for 30 min and it didn’t lose air (don’t know exact numbers but definitely not 5 psi per min). It seems to be losing while rolling.
     
    Forever237, May 18, 2019
    Forever237, May 18, 2019
    #3
  5. May 18, 2019 #4
    062

    062 Road Train Member

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    Probably a leak in the brake system. Apply air to trailer and see if you have a leak. If no leak,set trailer brakes and apply air to tractor.
     
    062, May 18, 2019
    062, May 18, 2019
    #4
    Forever237 Thanks this.
  7. May 18, 2019 #5
    Forever237

    Forever237 Light Load Member

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    I did brake test with and without trailer hooked up. No difference
     
    Forever237, May 18, 2019
    Forever237, May 18, 2019
    #5
  8. May 18, 2019 #6
    062

    062 Road Train Member

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    What year and model truck?
    My next guess would be fan clutch or line going to it.
     
    062, May 18, 2019
    062, May 18, 2019
    #6
  9. May 18, 2019 #7
    Forever237

    Forever237 Light Load Member

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    May 29, 2016
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    2018 VOLVO 780
     
    Forever237, May 18, 2019
    Forever237, May 18, 2019
    #7
  10. May 18, 2019 #8
    PE_T

    PE_T Road Train Member

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    Texas (trucking since 02/2013)
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    Two possibilities are the air dryer purge valve or the fan clutch. Put your hand over the purge valve. To check the fan clutch, turn on the key (engine off) and listen for the air leak under the hood.

    Another possibility is the air brake system. Set your trailer brakes (or use a chock), then release your truck brakes (only). Get some soap and water and spray the airlines out of the brake chamber. Then you can switch this procedure by setting the brakes on the truck (or use a chock), then release the trailer brakes.
     

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    PE_T, May 18, 2019
    PE_T, May 18, 2019
    #8
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  11. May 18, 2019 #9
    ZVar

    ZVar Road Train Member

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    Flint, MI
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    Could be as simple as a sensitive leveling valve. Had a truck one time that was that way.
    Driving down these nice smooth Michigan roads (yes, that's sarcasm) it would vary between 100 and 125 psi. I figure as long as it doesn't drop below 100 it's all good.
     
    ZVar, May 18, 2019
    ZVar, May 18, 2019
    #9
    skallagrime, m16ty and Cam Roberts Thank this.
  12. May 18, 2019 #10
    062

    062 Road Train Member

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    I’m clueless on the new trucks. Is it a automatic?
    Try putting it in Drive and see if it leaks
     
    062, May 18, 2019
    062, May 18, 2019
    #10
    Forever237 Thanks this.
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