Losing air 5-6 psi per minute while driving

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

  1. Forever237

    Forever237 Light Load Member

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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!
     
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  3. 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...
     
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  4. 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.
     
  5. 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.
     
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  6. Forever237

    Forever237 Light Load Member

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    I did brake test with and without trailer hooked up. No difference
     
  7. 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.
     
  8. Forever237

    Forever237 Light Load Member

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    2018 VOLVO 780
     
  9. PE_T

    PE_T Road Train Member

    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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  10. ZVar

    ZVar Road Train Member

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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.
     
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  11. 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
     
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