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willysmjeeps.com :: View topic - M38 fuel pump modification
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M38 fuel pump modification
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horse
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Posts: 187
Location: Yorkshire U.K.

PostPosted: Sat Jan 08, 2022 1:52 am    Post subject: M38 fuel pump modification Reply with quote

I understand that M38s before serial number 53262 had a plug in the body centre threaded hole. This is where a vent would normally be located used for various applications.

I have a rebuilt pump which I am getting checked out prior to fitting as I do not know who rebuilt it.

As I do not know the age of the pump which could be before or after serial number 53262 there is a modification you make to the pump as in TM 9-8012 Jan 1956. This modification is to minimise premature failures of the pumps caused by excessive pressures within the fuel pump.

Question is, mine does have the centre vent which is vented to the atmosphere,so do I need the additional modification or not?

Thanks Jonathan.
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RonD2
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PostPosted: Sat Jan 08, 2022 5:34 pm    Post subject: Reply with quote

Hi Jonathan,
I could be wrong, but don't think the two are related.
If you haven't seen it, here's a post that includes the Army bulletin modification order on drilling a hole in the pump body. http://willysmjeeps.com/v2/modules.php?name=Forums&file=viewtopic&t=10298&highlight=fuel+pump+mod

Whoever you have checking out your pump ought to be able to see if it's been done (or needs to be done)? I don't think having it done in any case would be a bad thing.

Good luck!
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1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

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horse
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PostPosted: Sun Jan 09, 2022 2:23 am    Post subject: Reply with quote

Hi Ron.
Thank you for the link.
The only numbers on my rebuilt pump are on the foot which fits onto the cam.
5592295. Nothing on the flange.
On the body 1538354.
As we know could have been made up from many past pumps.
I will have the mod done anyway as you suggested if no harm can be done.
Am I correct in thinking that the hand primer came in later so maybe these pumps do not need the modification?
Thanks.
Jonathan
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horse
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PostPosted: Sun Jan 09, 2022 4:52 am    Post subject: Reply with quote

Hi. Found a bit more from Wes posts on the G503 to which he calls the primer pump "manual operating lever" as the other is a Primer pump mounted on the dash which injects fuel directly into the intake manifold for sever cold weather starting.
The manual operating lever is to get the fuel from the tank to the carb bowl if the Jeep has been standing a while and the fuel has evaporated, which is why I am getting mine to work.
No other notes on which should have the modification other than the serial numbers which in my case are no help with my pump being made from the unknown.
Horse.
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horse
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PostPosted: Sat Mar 26, 2022 10:48 am    Post subject: Reply with quote

Hi. Just an update. The rebuilt pump I bought from Greece has finally returned.
The unit checked out fine and the modification hole had been done.
I also made sure the Manual operating lever would work as this is the bit on mine which I thought did not.

Talking to him I found out that the last quarter of an inch on the manual handle gives the action required to pump the fuel. In my ignorance I thought it was the full stroke which primed the carburettor but thought mine was damaged.

With this information I tried my old pump which is still on then Jeep, pulled on the lever got resistance at the top of the stroke then a little more and fuel ran into the see through filter.
So a good lesson learned. I have fitted the new pump and all is well even gives a bit more vacuum for the wipers. Keep the old as a good spare.
Horse.
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horse
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PostPosted: Sun Apr 10, 2022 5:20 am    Post subject: Reply with quote

Hi, not sure if this should be a new topic or not.
Anyway after fitting the fuel pump last weekend then driving about 15 miles she has sat all week.
This weekend she would not start, no fuel. I pumped it up to the carb with the hand leaver but she would soon stop.
I checked the fuel pressure on cranking and nothing.
So I have taken the rebuilt pump off to see the mistake .
All is well until you spot the foot which contacts the lobe in the engine to operate the pump, one foot is longer than the other.
Original pump part number on the foot is 5593764 and the rebuilt one is shorter in length and part number 5592295. Big difference in length. I am surprised she ran at all.
I have re fitted the original pump to keep a working Jeep ,but my question is if I took the spacer out in-between the pump and block could I use the pump with the shorter reach foot or just order the correct part?
Must learn to check the part carefully prior to fitting.
The parts manual lists as Arm. 7375382
Thanks.
Horse
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horse
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PostPosted: Sun Apr 10, 2022 11:52 am    Post subject: Reply with quote

I have found out that the spacing block has to be used with both arms.
I have found out Arm and Foot part number 5593764 are M38 and early A1 pumps. Part number 5592295 for later pumps.
Previous discussions say both are interchangeable however mine would only work with 5593764 Arm/Foot.
What is the way forward with my rebuilt pump with the 5592295 Arm/Foot which will not operate due to the foot not locating on the engine cam?
Thanks.
Horse
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wesk
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PostPosted: Sun Apr 10, 2022 11:25 pm    Post subject: Reply with quote

Horse,

In your last two posts you do a couple of things that can be confusing to anyone following this thread.

I - You are mixing ORD Part Nos with Manufacturer AC's part numbers. It is best to decide which series of numbers you wish to use in a topic and stay with that series. The ORD 9's have two different Federal Stock Number columns and two different part number columns (ORD # and Manufacturer's #).

2 - Don't try to group pumps and parts strictly as Early M38 and Late M38/early M38A1. There are pumps made for the M38 only after the AC 5592655 with hand pump handle which carries the G758 ORD Stock # that did not have the A1's pump handle.










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horse
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PostPosted: Mon Apr 11, 2022 7:00 am    Post subject: Reply with quote

Thank you for your comments which I will endeavour to keep to.
Not sure how to progress this problem as the parts list just shows one type of pump arm 7375382 but there are two different types. I have both.
One type of arm works on my M38 the other does not.
Can the arms be changed over or is each pump an individual to the arm?
Thanks.
Horse.
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wesk
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PostPosted: Mon Apr 11, 2022 8:07 am    Post subject: Reply with quote

Download and review our PDF copies of the M38A1 ORD manuals and the M38 ORD 8 Manual. The second PN arm only appears in the M38A1 ORD 9 along with the M38A1 hand pump style fuel pumps.
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Wes K
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horse
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PostPosted: Mon Apr 11, 2022 3:43 pm    Post subject: Reply with quote

Thank you for the pointers.
I could also see in the downloads how to rebuild the fuel pump which had a link to a conversation on the same topic many years back which you made the point " Arms are ment to be used on the pumps they are listed for"

As my rebuilt pump has no serial numbers on it and only the number on the arm and it will not pump when fitted, I can only conclude it has the incorrect arm fitted. Still very odd it ran approx 15 miles prior to stopping. Also if you put gas into it on the bench and move the cam arm it pumps gas.

Unless any other thoughts I will order the other arm and see how it works.
As far as I can tell it will not do any harm but open to advice.
Horse.
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PostPosted: Mon Apr 11, 2022 9:32 pm    Post subject: Reply with quote

What is the part number of your pump????

It is located on the mounting flange of the pump.


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Wes K
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horse
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PostPosted: Tue Apr 12, 2022 12:33 am    Post subject: Reply with quote

Unfortunatly it does not have the part number on the flange.
The one fitted now has 4260 on the flange and 5593764 on the arm. No help I know.
Can any damage be done to the cam lobe on the engine or pump side if I fit the other arm on the re built pump?
Thanks Horse.
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PostPosted: Tue Apr 12, 2022 10:14 am    Post subject: Reply with quote

I forgot to mention that the flange will carry only the last 4 digits of the pumps model #. So 4260 is pump model # 5594260 which came originally on the M38A1 and uses the late lever 5593764.
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horse
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PostPosted: Tue Apr 12, 2022 10:28 am    Post subject: Reply with quote

Thanks Wes, but as I said this is the pump which is fitted and working.
My other pump has no identification other than on the arm.
Would I cause any harm in fitting the different spec arm on my rebuilt pump which will not pump gas when fitted onto the Jeep?
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