M38A1 Gas Gage Troubleshooting

Tarfu43 · Post by **Tarfu43** » Tue Oct 26, 2010 12:23 pm

I haven't even looked in the book yet, but I thought I would throw this out there. My M38A1 gas gage will not move off half-full, no matter how much gas is in the tank. It was working properly before, however. Is there a simple explanation for this that I could check before ripping things apart?

Thanks!

Post by **wesk** » Tue Oct 26, 2010 5:52 pm

It's not in the TM 9-8014. It is in TB 9-2300-228-20 Tactical Transport and Combat Vehicles: Troubleshooting for Instrument Cluster Gages, Switches, Circuit Breakers, Sending Units and Related Wiring dated 8 July 1960.

Go here, download the TB and go by step by step.
http://www.cj3a.info/sibling/milgauge/milgage.htm

For those of you that are new to this hobby Bob Westerman has done our homework for us and loaded all the answers on the CJ3A page where he is one of the key players. He has a completed a new book on the CJ3A which is the new ICON for "What is a CJ3A". He has been a CJ3A, M38 and CJV35 afficiondo for many years. He has even done our homework for the M38 fording and vent system: http://www.cj3a.info/sibling/m38vent/vent.htm
and the CJV35 Fording and vent system: http://www.cj3a.info/sibling/cjv35u/v35vent.html

He also put up a very good Fuel Pump rebuild page there as well.
http://www.cj-3a.com/Fuel%20Pumps.htm

Tarfu43 · Post by **Tarfu43** » Wed Oct 27, 2010 8:07 am

Wes,

As usual, another bullseye with information.

Thanks!

Post by **wesk** » Wed Oct 27, 2010 8:31 am

One important point is grounds. The sender must be grounded to the tank, the tank must be grounded to the tub, the tub must be grounded to the frame. Likewise the gauge must be grounded to the cluster assembly, the cluster assembly must be grounded to the dash and the dash must be grounded to the frame.

This all sounds foolish but when we restore, make pretty and paint our jeeps we take away all the quality factory grounds. The paint isolates the cluster from the dash since we usually manage to cover the wire type receptacles and the 1/4 turn studs with paint. The tub is well painted so the only bare metal to metal connection between it and the tank is the fuel lines. If you have rubber hoses interrupting this path to ground you have problems.

The two most overlooked grounds are the gauge case to the cluster and the cluster to the dash. One other is the sender to the tank, The sender gasket can isolate the sender from it's necessary ground with the tank.

We don't often see these problems with the oil pressure and water temp because they are very well grounded to the engine block.

Beacher425 · Post by **Beacher425** » Thu Oct 28, 2010 9:45 am

I anticipate I will be in the same boat as I went hog wild with the POR-15 thinking "My jeep will never rust again!" Would running short ground wires to a common ground be a viable option or do I need to start sanding and scraping at the appropriate contact points.

Post by **wesk** » Thu Oct 28, 2010 10:35 am

That would be a little over kill. I would add a ground strap from the passenger toeboard to the frame and from the right front fender to the frame. A good location on the frame is the voltage regulator mount. Then be sure for each electrical device to scrape the paint away under one bolt and use the internal/external star type washer. The gas tank should have a ground wire from the sender to the tank and from the tank to the tub. The instrument cluster should have a ground wire from the cluster panel to the dash.

BobW · Post by **BobW** » Sat Oct 30, 2010 6:46 pm

wesk wrote: For those of you that are new to this hobby Bob Westerman has done our homework for us and loaded all the answers on the CJ3A page where he is one of the key players. He has a completed a new book on the CJ3A which is the new ICON for "What is a CJ3A".

Thanks Wes!!