Might take the hose loose from the intake manifold that supplies the air inlet to the compressor and ck for backflow out of it. Could be leaking back into the intake and may not be hear it.
Losing air pressure when braking hard or coming to a stop.
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by spindrift, Oct 27, 2021.
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Should have a one way ck valve that lets air flow to the compressor but not the other way.
spindrift Thanks this. -
I dont know on your truck if it has a dedicated ck valve or uses the reed valves in the compressor itself.
spindrift Thanks this. -
Funny story sorta related lol!
A friend of a friend used to set the air in his pickup tires with a hose and chuck off of an old dump truck he drove for a big construction outfit in San Antonio because he parked it next to the truck at their yard and would leave it for days or weeks sometimes. After a few years he got a severe vibration at 5mph and beyond. Since I was in the tire business He asked me if I could ride along to see if it was tire related. Along with the horrible shake I noticed when he came to the complete stop the little truck would surge forward a little. Long story short. The tires had a few gallons of water and oily crud in them from that old dump trucks compressor.N00bLaLoosh and spindrift Thank this. -
I ran into a similar problem years with a cement truck. The truck came
into the shop for its annual safety inspection. When I made a full
brake application with 120 PSI in the reservoir the low air warning came
on when the pressure dropped to 65 PSI. There was no air leak either.
When the outfitter installed the drum and hydraulics they moved the air
tanks to outside the frame to clear the drum drive and hydraulic pump
and lines. The pump was driven by a live PTO off the rear of the engine.
The truck had one compartmented air tank, a tank with approximately
25% wet tank 75% secondary reservoir with an internal check valve
feeding the secondary reservoir from the wet tank section.
When they reconnected the air lines to the tanks they connected the air
line that supplies air to the drive axle relay valve to the wet tank end of the
secondary tank and not to the primary tank so there was only 25% of the
reservoir volume to supply the rear brake chambers.
The cement truck was twenty years old and had this problem from the
day it went into service judging by the layers of cement built up on the tanks.
It had been through over twenty annual safety inspections as well and no
one ever addressed the problem.
Has any work been done on your truck recently that would have required
the removal of an air tank or disconnection of air lines from the air tanks?spindrift Thanks this. -
Glad you were able to find the problem. Hard to imagine it went that long.
No work of that kind done to my truck in the time I've owned it... -
Ever find the air leak???
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No sir. Still workin' the problem.
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Last edited: Nov 19, 2021
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