Air pressure gauge sticking?

[DownRange762]

One week into the A3 adventure and after letting the truck sit for 6 days the air had of course bled down to zero. Fired up the engine, low air buzzer and light are on as expected, but noticed the air pressure gauge wasn't moving. After 45 to 60 seconds the gauge jumped from 0 to 60, the low air pressure buzzer and light turned off, and the air pressure continued to build to about 105-110 where it holds steady when idling or running down the road.

Long story short, I'm guessing this is just a sticky gauge problem, right? No odd air leak sounds (as if I could hear them anyway) coming from around the dash and surely the compressor didn't just move from zero to 60 in an instant.

I've looked at Saturn Surplus but they didn't have air pressure gauges. Any other military sources for a NOS/NEW gauge as I'm not eager to try an Ebay gauge of unknown parentage.

Thanks.

 

[Westech]

Most of the A3's do that. It is a electric gauge. I have driven about 10 of them and all but one did that. Not to worry

 

[187]

Mine works that way as well. Not to worry.

 

[Danl]

Danl M915A1

try putting air tool oil in your system it will help with all your seals and little things two table spoon works after a few days blow down you tanks and all will be good

 

[1 Patriot-of-many]

No worries, mine has always done the same thing.

 

[Rustygears]

It's a mechanical gauge. It is not sticking. There are a series of pressure sensitive valves that kick in at 40 to 60 psi to try and isolate the brake system. When everything is at 0 pressure, the inlet pressure from the compressor has to build above that threshold for the valve to open. That's why it holds off for a few seconds, then all of a sudden jumps up. Look at the diagrams in the tech manual!

The operation you describe is not only normal, it is indicating that all protection systems are functional.

 

[187]

Danl,

Where do you put the air tool oil in at?

 

[Rustygears]

Oil won't make any difference. If a gauge is sticking, it is the mechanical part. The gauges work on the flex of a curved brass tube that straightens with pressure. Putting oil in the air line has no effect on a sticky gauge.

As stated, the hold-off, then sudden uptick of the system pressure as indicated on the dash gauge is due to the protection valves doing what they are supposed to do. Read the TMs.

 

[187]

Rustygears, Thanks for the very informative posts I have read from you in recent days in regard to the A3.

I understand the air gauge and the delay. Makes perfect sense.

I have read quite a few threads that talk about people adding the airtool oil to the air system. Some reasons stated are that it helps with the seals and the air brake system. Any truth to that and if so, where would you add the oil?

Just curious. I have only owned my A3 for a little over a month and still in the tinkering/figuring everything out stage So far so good.

 

[AceHigh]

Rustygears, Thanks for the very informative posts I have read from you in recent days in regard to the A3.

I understand the air gauge and the delay. Makes perfect sense.

I have read quite a few threads that talk about people adding the airtool oil to the air system. Some reasons stated are that it helps with the seals and the air brake system. Any truth to that and if so, where would you add the oil?

Just curious. I have only owned my A3 for a little over a month and still in the tinkering/figuring everything out stage So far so good.

Oil will screw up the dryer and the CTIS manifold. You can add oil to the steering drag link and the steering cylinder. Also oil can go into the air pacs on the brakes. By the way, it is not an air brake system as such.

 

[Rustygears]

Ace high is right. Some of those threads on adding oil were for A2's. There are other threads about fixing the air assist steering by adding marvel mystery oil or air tool oil into the inlet line of the air assist drag link to unstick it. I've authored a few of those threads and others have too. That's very different from dumping oil into the main line. If the dryer is working correctly (many arent because of being gummed up with snot due to rapid cycling), it will just remove it and possibly be gummed up as a result. The other fact regarding that misconception is any oil added will get caught in the wet tank, unless you add so much you fill the tank. Then you get hydraulic lock and the fun really starts because everything is plugged up.

The only place I'd ever consider adding oil into an airline on an A3 is the inlet to the drag link on the air assist. It lubricates the oft-corroded drag link valve assembly and either frees and/or stops from leaking the stuck valve packing. It also lubricates the air assist ram for the steering. Then it vents overboard out the drag link exhaust. No chance of getting in the brake system and no chance of getting in the CTIS system.

Many of the claims of broken CTIS are in fact due to the CTIS manifold valve becoming gummed up with oily snot!

Have fun, but please don't try to lubricate the truck air supply gauge, a bourdon-tube type gauge by putting oil into the air system.

 

[187]

Thanks, completely understand now.