Low Air Pressure Troubleshooting

[kymike]

When I started my M35A3 last week after sitting all winter, the air pressure didn't come up like it should. It's just below 60PSI. I checked for leaks by listening and the soapy water test with no leaks found. I drove the truck a couple of miles and the air pressure comes up to normal after a short drive, but drops back below 60 at idle. I followed the trouble shooing tests in TM9-2320-386-24-1-1. The compressor outlet line is hot to touch; I could not find any leakage or blockages; an air pressure reading at the horn matches the dash gage. I adjusted the governor twice (1/4 turn each time) with no affect. The TM indicates a bad compressor. I just wanted to check to see if anyone had any other thoughts before I go through the $$ getting a new compressor. Thanks in advance.

 

[Floridianson]

Sticky Governor maybe try some of my fav, air tool or replace Gov. would be my first.

 

[Jeepsinker]

Take a look at the blowoff valve on the bottom of the air dryer. They have a habit of sticking partly open and bleeding air quietly, or sticking open all the way and not allowing air to build at all.

 

[gimpyrobb]

Check the gladhands too.

 

[Jeepsinker]

Second gimp's suggestion as well. Did you get it figured out?

 

[welldigger]

Shut off your air assist steering and see if that makes any difference. Another thought is a sticky air priority valve on top of the outboard air tank. It is very common for these to stick shut on the a3's.

 

[kymike]

Since my original post I had a suggestion to check the compressor air intake for a clog or restriction, but that turned out to be OK. I'm going to try each of the suggestions in the above posts today. BTW, I'm not familiar with "gladhands"; what are they? Thanks all,any and all ideas greatly welcomed and appreciated.

 

[M35A2-AZ]

The gladhands are the air hookup at the back of the truck for towing a trailer.

 

[kymike]

I've made some progress. I closed the shutoff valve on the firewall for the steering assist system and the pressure came right up. Obviously I have a leak somewhere downstream from the shutoff valve. Tomorrow I'll check the lines with soapy water. Is it possible the leak could be within the steering assist cylinder itself?

 

[welldigger]

Unlikely the cylinder would have an internal leak. A hose or connection to the cylinder would be more likely. If it's not a hose or fitting leaking then the next thing to check will be the torque valve on the drag link. I would disconnect the supply line to it and squirt some air tool oil in. Then reconnect the hose and cycle it back and forth. That may free up the valves inside it.

 

[m109a2]

gimpyrodd and jeepsinker were right on in my case.The leak was in the in the gladhands.Thanks guys. Al

 

[Jeepsinker]

If it is in the cylinder I have a spare used cylinder I don't need.

 

[welldigger]

If it is in the cylinder I have a spare used cylinder I don't need.

I'll take the broke one if it comes to that.

 

[Floridianson]

Guess you do have an air leak.! So now we know you have an air leak and you know it's in the air assist half my answer I will still stand by. I have an A3 and she was loosing air on right hand turns. I ran air tool oil through and what ever valve was stuck cleared. If you get lucky maybe yours will to and if not there are threads where a member has taken apart the stearing system and cleaned and rebuilt. There is the exhaust line that runs from the system and maybe thats why you did not hear the leak.

 

[kymike]

I'd like to thank everyone for their help and advice. You guys are great. Interesting that the TM did not address turning off the air valve to the steering assist system; when the air pressure came up, it was clear where the problem was. Thanks welldigger! It turns out the air input hose that goes from the fitting on the fender well wall to the steering assist drag link was leaking. Interesting that it was leaking across the whole length with no obvious air leakage noise and the only way I found it was to spray soapy water on it.

 

[welldigger]

I'd like to thank everyone for their help and advice. You guys are great. Interesting that the TM did not address turning off the air valve to the steering assist system; when the air pressure came up, it was clear where the problem was. Thanks welldigger! It turns out the air input hose that goes from the fitting on the fender well wall to the steering assist drag link was leaking. Interesting that it was leaking across the whole length with no obvious air leakage noise and the only way I found it was to spray soapy water on it.

I'm glad you got it fixed!

 

[kymike]

Yesterday I took my A3 out for about a 20 mile ride and the purge valve starting venting continuously. The TM troubleshooting section said to disconnect the air line from the purge valve and see if air stops coming out from the purge valve. There are 3 lines connected to the air dryer purge valve. I disconnected the small line coming from the governor. Is this right? If I did this right, the TM says if air continues to vent from the purge valve replace the air dryer. Does anyone now if I need to replace the air dryer assy or rebuild it? I see in Sticky's parts list shows a NAPA PN for an air dryer repair kit.

 

[welldigger]

Just rebuild it. It should take you about 30 min to do and it is way cheaper to rebuild one than buy a new one. Once you rebuild it everything but the housing is new. Just be sure to get the serial # off of the air dryer. There are different kits that correspond to different serial #'s.

 

[kymike]

Would NAPA know the different it for serial numbers? Do you know a different source for a rebuild kit?

 

[welldigger]

Napa is as good as any place. There is a data plate on the air dryer. It will give you the model # and serial #. Just give that information to the parts guy.