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88 K/W Air builds to 125# primary immediately starts to drop,

My 88 K/W builds air to 125#, then primary starts to drop. Secondary holds press. New A/Comp,new governor/brake pods changed/A/Bags changed, no audible leaks.Not sure were to look next.

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Do you have a air dryer? If so get under the truck and listen to the exhaust port for leakage. You might have a bad purge valve. I would also suggest that you take a a 3 gallon one you can buy at Lowe's and fill it with water and dish washing liquid and spray all your air lines down and look for bubbles. Strato-flex air lines with the fabric cover are real bad about silencing air leaks and can only be found by spraying soapy water on them and looking for bubbles......... ''italic text''

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the oneway check valve maybe weeping air back in to the compressor if this is only happening when engine is turned off too.


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yes go with the one way check valve first- then the air will be feeding back through bottom of air dryer or through possibly intake on compressor- which u have a hard time hearing because the ports are so big. air shouldn't be going anywhere backward to compressor when compressor shuts down. On an older truck like this check valves usually get oil and contamination on them- they are just a magnetic disk inside I believe- at that vintage I would just put a new one on - cheap fix.

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keith keown will be eternally grateful.
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