Switching To A Double-Action Mechanical Fuel Pump

[CarlN-NDC]

I am in the process of cleaning, inspecting, and replacing the fuel system in my 1941 DeSoto DeLuxe 2-Door Sedan.  As part of the project, I was considering upgrading to a double-action mechanical fuel pump.  In 1941, DeSoto was starting to offer an electric wiper motor on the higher tier "Custom" cars, but the lower tier "DeLuxe" cars still had vacuum wipers that typically ran on engine vacuum.  However, customers with "DeLuxe" DeSotos had the option of upgrading to a double-action mechanical fuel pump which had a small vacuum chamber on the top of the fuel pump that would supply the vacuum wipers with consistent vacuum no matter the engine speed; which prevented the wipers from slowing down or coming to a halt while accelerating or climbing a steep hill.

 

While I try to avoid driving my DeSoto in the rain as much as possible, I do plan on taking it on some tours and to the national conventions, so I want to be prepared if I do encounter rain during my travels.

 

Currently, my 1941 DeSoto has the standard series "AT" AC 588X single-action fuel pump.  The "upgraded" double-action fuel pump for a 1941 DeSoto would be a series "AS" AC 506X.  However, in reviewing my vintage AC Fuel Pump catalog and comparing pictures online, it seems the AC 588X and the AC 506X pumps have noticeably different pump arms.

 

Here is a picture from my AC Fuel Pump catalog comparing the "AS" & "AT" series fuel pumps side-by-side, along with a close-up of their respective pump arms:

 

 

 

I have found a few AC 506X style pumps for sale online, but I have been hesitant to purchase one due to my concern with the pump arm.  (I am still pretty new to the hobby, so I don't have a ton of spare parts or fuel pumps to compare or test with.  So I apologize I cannot provide any real-world pictures of the pump arms.)

 

My question being, does anyone know of these pumps interchangeability in a standard 25" 228cui flathead 6?  Or maybe someone has even swapped between a single-action and double-action fuel pump in their own car?  The last thing I would want is to damage the camshaft lobe that actuates the fuel pump arm!

 

 

I am probably overthinking this, but I'm an engineer for my day job, so it's par for the course!  

 

 

Thanks!

 

Carl

[Sniper]

I don't have a Desoto parts catalog, but here's my thinking.  The fuel pump is driven off a lobe on the cam.  So if they use the same cam there should not be an issue?

[kencombs]

The arm shape and material is not important, as long as the cam contact area is in the same place relative to the mounting pad.   The pics seem to show them in the same area.

[CarlN-NDC]

21 hours ago, Sniper said:

I don't have a Desoto parts catalog, but here's my thinking.  The fuel pump is driven off a lobe on the cam.  So if they use the same cam there should not be an issue?

 

I checked for the camshaft part number in both my 1941 DeSoto parts book and 1936 to 1942 DeSoto condensed master parts list.  Each book only lists 1 part number for the camshaft and neither have an "*" to indicate a special use case.  Although, there are two different part numbers between the two books.  I am guessing the camshaft PN was superseded.  My copy of the 1936 to 1942 DeSoto master parts list doesn't have a superseded parts number section, so I cannot 100% confirm this to be the case.

 

1941 DeSoto parts book PN# 855471

1936 to 1942 DeSoto master parts list PN# 1067201

[Booger]

fuel pump got lazy on Booger. I added a electric inline fuel pump instead of messing with a replacement. Very happy with results

an option to consider

Edited March 24, 2024 by Booger
spel

[Sniper]

1 hour ago, CarlN-NDC said:

 

I checked for the camshaft part number in both my 1941 DeSoto parts book and 1936 to 1942 DeSoto condensed master parts list.  Each book only lists 1 part number for the camshaft and neither have an "*" to indicate a special use case.  Although, there are two different part numbers between the two books.  I am guessing the camshaft PN was superseded.  My copy of the 1936 to 1942 DeSoto master parts list doesn't have a superseded parts number section, so I cannot 100% confirm this to be the case.

 

1941 DeSoto parts book PN# 855471

1936 to 1942 DeSoto master parts list PN# 1067201

 

That tends to back up what Ken was saying.  I think you'll be ok, but a close comparison of the old vs new before installation would cinch it.  Use a square to measure the two, distance from mounting face and height from the same bolt hole?

[kencombs]

In addition to the pump, it will help to provide a vacuum 'storage' container.   Storage in quotes because it seems silly to store nothing!   Anyway , a vacuum storage can can be found on several older vehicles on the brake system, or make one from a piece of large PVC pipe, two caps and a couple of fittings.   Most PVC caps are thick enough to drill and tap for small pipe threads.  Add a one way check valve to the line.   This will even help a single pump equipped engine run vacuum wipers.

[Sniper]

Ford as used a can that looks a lot like something you'd find juice in.  Might be cheap to buy some juice and use that can to make a reservoir.

[CarlN-NDC]

1 hour ago, Booger said:

fuel pump got lazy on Booger. I added a electric inline fuel pump instead of messing with a replacement. Very happy with results

an option to consider

 

The previous owner of my DeSoto actually already installed a low pressure inline electric fuel pump.  I know the electric pump works, but I am not sure how old it is or it's overall condition.  He mainly used it for filling the carburetor bowl if it sat for an extended period, otherwise, he strictly used the mechanical pump.  I plan to replace the entire fuel line from the tank to the junction block that transitions into the soft line.  Currently, the fuel line is a mix of the original 83-year-old line, a straight section of steel that was done in the 1980s, and a small section of NiCopp that was done within the last 5 years.

 

I will inspect the electric fuel pump when I remove the hard line.  Depending on it's condition, I will either reuse it or install a new electric pump.  I definitely want to have a backup pump if one or the other fails.  I'm also partial to the idea of having an electric pump to push through vapor lock, should it occur during the Summer months or while on tours.

[Booger]

23 minutes ago, CarlN-NDC said:

 

The previous owner of my DeSoto actually already installed a low pressure inline electric fuel pump.  I know the electric pump works, but I am not sure how old it is or it's overall condition.  He mainly used it for filling the carburetor bowl if it sat for an extended period, otherwise, he strictly used the mechanical pump.  I plan to replace the entire fuel line from the tank to the junction block that transitions into the soft line.  Currently, the fuel line is a mix of the original 83-year-old line, a straight section of steel that was done in the 1980s, and a small section of NiCopp that was done within the last 5 years.

 

I will inspect the electric fuel pump when I remove the hard line.  Depending on it's condition, I will either reuse it or install a new electric pump.  I definitely want to have a backup pump if one or the other fails.  I'm also partial to the idea of having an electric pump to push through vapor lock, should it occur during the Summer months or while on tours.

the fuel line replacement is a great idea as well Your on top of it

[Doug&Deb]

Go with the Nicopp. It’s pricey but it’s easy to work and will last forever. The electric pump is nice to have for the reasons you mentioned. Be careful removing the line at the tank. There is a ferrule in there that tends to bounce and disappear into a black hole.