Posted: Fri Aug 09, 2024 10:44 am Post subject: M38 Vacuum and Fuel pump rebuild
Dear All,
I am restoring an M38 Vacuum and Fuel pump and when it comes to reassembly the fuel cover you need to place, according to the manuals, 3 pulsator diaphragms. In the NOS kit I located I found just 2 pulsator diaphragms... In the end I decided to use just the 2 I found in the NOS kit, but the thickness seems to become very high. I am now in doubt since when I disassembled the cover I found one, while the manuals say 3 and the kit had 2...
I think that the scope of these diaphragms is that of an expansion tank, that is to absorb and give back the pressure and to avoid excessive surge in fuel pressure.
There are only 2 diaphrams in the fuel pump and 1 rubber seal for the cap with the valves.Be sure to clean out all of the old valve gaskets before installing the new gaskets.
Manuals consulted: ORD 9 SNL G-759 SEPTEMBER 1956 (I know it's that of the M38A1... but my father liked the primer and went for that!)
TM 9-1828 B, TB 9-804-11.
The pump is installed an M38 S/N around 35.000.
The pump is P/N 8720570. The casting data indicate 1956.
I used many Kits: brought already opened and incomplete NOS Kits, NOS late unopened kits ex Greek Army P/N 2920 00 218 1276 / 5593325 and a new repro Kit Seal Tested WO 811396 (By far the most complete).
Just more info: the pump seemed to have been already modified according to TB 9-804-11: 1/8" hole drilled, rubber seal eliminated. The only incorrect thing is that the Vacuum exit fitting on body for the line to the bellhousing etc. has been closed with a Plug... A relief valve will be put instead...
Moreover, I bought this pump nearly 30 years ago in a surplus store in Vicenza northern Italy, for those not informed Northern Italy hosts 2 of the biggests US Bases in Europe: Aviano (USAF) and Vicenza (102nd Airborne). The pump was unboxed and in pristine condition, just one carboard box was attached which I did not bother to read or I forgot what was written on it. For sure the pump was professionally rebuilt and then surplussed.
That's all for now.
PS: I took away the 2nd pulsator diaphragm and left only one, definitely seems more correct!
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