willysmjeeps.com

Ok, on the servicing data plate that came off my 1951 US Air Force M38, the tyre pressures are noted as follows:

Highway 28 lbs
Cross-country 22 lbs
Mud, sand or snow 15lbs

Which ties in with what I see in Ryan Miller's excellent reference guide. However, most of the restored M38's I see have "TP25" stencilled on them, which ties in with the M38 maintenance manual I have (January 1956), namely:

Highway 25 lbs
Cross-country 25 lbs
Mud, sand or snow 10 lbs

This is also what I see in the M38A1 manual. Did the military change the TP's to make the M38's notation the same as the M38A1's, and if so does anyone know when this change came into use? Btw, the only remains of a TP stencil I found on my jeep was "TP28" next to the handbrake lever. Was the tyre presssure change only an Army thing, or would the Air Force have done the same? If I'm paying out for stencils, might as well have the right ones!

Thanks in advance,
Owen.

Owen,

The Army was primary contractor for the M38 and originally for the M38A1.During that time most of the services who obtained their jeeps thru the Army procurement system usually complied with the Army's TB's and MWO's.

TB-ORD-560 dated May 13, 1954 changed the tire pressures for both the M38 and the M38A1 in their original operator's manual TM 9-804 (M38 Nov 1950) and TM 9-804A (M38A1 Jul 1952) respectively.

The new pressures were:
Highway 25
Cross Country 25
Mud, Sand & Snow 10

The above pressures are reflected in both Tabulated data and Data Plates in TM 9-8012 ( M38 1956) and in Data Plates only in TM 9-8014 (M38A1/M170 1955 but original publication shows only one pressure (28 PSI) in tabulated data. This oversite by the tech writers was corrected initially in Chg 1JUN 1956 and then again in Chg 3 JUN 1958 where it became 25 Hwy, 25 CC, & 15 MSS.and changed again in Chg 5 MAR 1960 to the same pressures listed in Chg 3.

Thanks for this, Wes.

Like I said, I only found "TP28" stencilled on my jeep. But since my jeep was out of military service prior to March 1958, maybe the change didn't catch up with it in time? Would they have gone to the extreme of changing out the servicing data plate, or just stencilled the new tyre pressure on the jeep?

Wbr,
Owen.

The MWO directed the mechanic to remove the plate from the dash, black out the tire pressures and then etch the new pressures on the plate.