Vacuum Tanks and In Line Fuel Filters

When I purchased my 31 Cadillac 355A, it had an electric fuel pump installed, as well as an in line filter between the fuel tank and this electric pump. The pump was connected to a momentary push button switch ( the pump only ran when you held the button in) The vacuum tank was still installed and connected, but was not functioning properly. The car would run for 5 miles or so, and then start to cut out. Holding the button in for a few seconds refilled the vacuum tank with fuel, and the cycle was repeated. Besides being a pain in the neck, it was also dangerous of course, because if you happened to hold the button too long, it would be possible to overfill the vacuum tank. At that point, fuel would vent onto a hot manifold. Scratch one old caddy ( and maybe it's old driver).

After some difficulty, I was able to eliminate the electric pump (also removed the in line filter) and get the car to run perfectly on the vacuum tank - you guys who have fooled with these systems know what to check, so I won't go into that here. The fuel system is now as it left the factory in 1931, including the Johnson carburetor. The filtration consists of a screen at the fuel inlet to the vacuum tank, and the gascolater screen and glass bowl at the bottom of the vacuum tank.

All of the above is to set up my question: Is anybody running a vacuum tank system with an in line fuel filter between the fuel tank and the vacuum tank? My sense is that it would be too much of a restriction even when the filter was brand new. I know the simple answer: "Try it and see what happens." Trust me, when you finally get one of these things running right, you are reluctant to change anything. Part of me says "You've got the filtration now that it came from the factory with, and their fuel and storage tanks were probably way worse than what we have today." The other side is " If you get some trash in that Johnson carb, it ain't gonna be a pleasant day for you." Anybody who knows about the location of this carb down in the valley of this old V8, below the intake manifold understands.

Anyhow, if anybody out there is currently running a vacuum tank system with a modern in line filter, I'd sure like to hear your experiences.

When I purchased my 31 Cadillac 355A, it had an electric fuel pump installed, as well as an in line filter between the fuel tank and this electric pump. The pump was connected to a momentary push button switch ( the pump only ran when you held the button in) The vacuum tank was still installed and connected, but was not functioning properly. The car would run for 5 miles or so, and then start to cut out. Holding the button in for a few seconds refilled the vacuum tank with fuel, and the cycle was repeated. Besides being a pain in the neck, it was also dangerous of course, because if you happened to hold the button too long, it would be possible to overfill the vacuum tank. At that point, fuel would vent onto a hot manifold. Scratch one old caddy ( and maybe it's old driver).

After some difficulty, I was able to eliminate the electric pump (also removed the in line filter) and get the car to run perfectly on the vacuum tank - you guys who have fooled with these systems know what to check, so I won't go into that here. The fuel system is now as it left the factory in 1931, including the Johnson carburetor. The filtration consists of a screen at the fuel inlet to the vacuum tank, and the gascolater screen and glass bowl at the bottom of the vacuum tank.

All of the above is to set up my question: Is anybody running a vacuum tank system with an in line fuel filter between the fuel tank and the vacuum tank? My sense is that it would be too much of a restriction even when the filter was brand new. I know the simple answer: "Try it and see what happens." Trust me, when you finally get one of these things running right, you are reluctant to change anything. Part of me says "You've got the filtration now that it came from the factory with, and their fuel and storage tanks were probably way worse than what we have today." The other side is " If you get some trash in that Johnson carb, it ain't gonna be a pleasant day for you." Anybody who knows about the location of this carb down in the valley of this old V8, below the intake manifold understands.

Anyhow, if anybody out there is currently running a vacuum tank system with a modern in line filter, I'd sure like to hear your experiences.

I have a filter near the tank on my `31 Cadillac and have had no problem with the vacuum pump what so ever.

I have inline fuel filters in the supply line to the vacuum tank in my cars. I like a location that is accessible without being on my back. Often I'm able to locate the filter under a front floorboard along side the frame. Out of sight, but accessible.

I use clear plastic filters. I can lift up the floorboard and look at the filter quite easily. If there is crud in the filter, a new one is easy to replace with minimal fuss, and little gasoline spilled on my hands or car.

The original sediment bowl will do an excellent job keeping the carb's fuel supply clean, but the inlet screen in the vacuum tank doesn't do enough for my way of thinking. And get enough crud in the vacuum tank, and it will stop working.

GLong

I would say you have done everything you could do right. Stop worrying and go back to bed .

I would say you have done everything you could do right. Stop worrying and go back to bed .

don't worry, i think is not problem

Well there is the factory fuel filter, so why would you need another one. Also the bowl catches water and any rust particles that may come through the tank. There were two designs of fuel systems in 1931. Early and late, what's your cars engine number? Do you know what system you have? Was the recall performed when new? Are you running the pump? They should not be run if you have the upgraded system. My Caddy's ran more than 30 k miles on the tanks with no issues. LONG hill pulls could cause you to tun dry, I just pulled off to the side of the road to refill the tank. I only found three hills anywhere that made my tank run dry so it wasn't much of a bother.

Well there is the factory fuel filter, so why would you need another one. Also the bowl catches water and any rust particles that may come through the tank. There were two designs of fuel systems in 1931. Early and late, what's your cars engine number? Do you know what system you have? Was the recall performed when new? Are you running the pump? They should not be run if you have the upgraded system. My Caddy's ran more than 30 k miles on the tanks with no issues. LONG hill pulls could cause you to tun dry, I just pulled off to the side of the road to refill the tank. I only found three hills anywhere that made my tank run dry so it wasn't much of a bother.

I will address your comments/questions in the order you made them.

1) Is the "factory fuel filter" you mentioned the screen in the fuel inlet to the vacuum tank or the gascolater screen & bowl that I talked about in my original post,

or something else?

2) My car has the "early system" wherein a check valve is utilized and both the vacuum pump AND the intake manifold vacuum are plumbed to both the vacuum

tank and the windshield wipers.

3) The later system came after 8-7522, and eliminated the check valve. On those cars, the vacuum pump is plumbed to the vacuum tank only and the intake vacuum goes to the wipers only. The manual says this was done "to eliminate the check valve as a source of noise." Is this the "recall" that you are referring to?

4) I'm not sure what you mean by "are you running the pump?" As stated, I totally eliminated the electric fuel pump installed by a previous owner. If you mean the vacuum pump, yes it is plumbed and working as factory designed for an "early" car.

The car is running perfectly now with what I believe to be the exact fuel system that it left the factory with. I am simply trying to get input on whether adding a modern in line filter would be helpful or detrimental to the operation of the car. Oh, well - guess I'll just put one in and try it for awhile. Thanks for your input.

I have inline fuel filters in the supply line to the vacuum tank in my cars. I like a location that is accessible without being on my back. Often I'm able to locate the filter under a front floorboard along side the frame. Out of sight, but accessible.

I use clear plastic filters. I can lift up the floorboard and look at the filter quite easily. If there is crud in the filter, a new one is easy to replace with minimal fuss, and little gasoline spilled on my hands or car.

The original sediment bowl will do an excellent job keeping the carb's fuel supply clean, but the inlet screen in the vacuum tank doesn't do enough for my way of thinking. And get enough crud in the vacuum tank, and it will stop working.

GLong

Great info, and interesting perspective on keeping the vacuum tank itself clean. Thanks for sharing your experience with this.

I have one of the larger clear filters in the line from fuel tank to vacuum tank (under rear floorboard) and it doesn't adversely affect vacuum tank operation. I used a larger filter on the assumption it would have less pressure loss than a smaller one. YMMV.

I have one of the larger clear filters in the line from fuel tank to vacuum tank (under rear floorboard) and it doesn't adversely affect vacuum tank operation. I used a larger filter on the assumption it would have less pressure loss than a smaller one. YMMV.

Appreciated.

Sorry for not replying sooner......yes you are running the way you should be. You wont need another filter unless you have a rusty gas tank. I would expect you will be fine. It's nice to see a early 30's Caddy set up correctly, and being driven. Once you figure them out and get them running right they are great cars. They can be a challenge, but that;s why I liked them. My Best, Ed

I will address your comments/questions in the order you made them.

1) Is the "factory fuel filter" you mentioned the screen in the fuel inlet to the vacuum tank or the gascolater screen & bowl that I talked about in my original post,

or something else?

2) My car has the "early system" wherein a check valve is utilized and both the vacuum pump AND the intake manifold vacuum are plumbed to both the vacuum

tank and the windshield wipers.

3) The later system came after 8-7522, and eliminated the check valve. On those cars, the vacuum pump is plumbed to the vacuum tank only and the intake vacuum goes to the wipers only. The manual says this was done "to eliminate the check valve as a source of noise." Is this the "recall" that you are referring to?

4) I'm not sure what you mean by "are you running the pump?" As stated, I totally eliminated the electric fuel pump installed by a previous owner. If you mean the vacuum pump, yes it is plumbed and working as factory designed for an "early" car.

The car is running perfectly now with what I believe to be the exact fuel system that it left the factory with. I am simply trying to get input on whether adding a modern in line filter would be helpful or detrimental to the operation of the car. Oh, well - guess I'll just put one in and try it for awhile. Thanks for your input.

Hello  you mention a vacuum pump in this topic where can I find this pump? I'm working on a 1927 Gardner with very low intake vacuum. this vehicle also has a Vacuum brake assist which will not operate with low vacuum.  thank you   can also be reached through my email dcdiefenderfer@aol.com

The 1931 Cadillac V8 that was the subject of my post has a factory installed mechanical vacuum pump driven by a journal on the rear of the camshaft. It is a small cylinder with a piston and rod inside about the size of those used in a weed eater engine.

There are electric vacuum pumps available, although I am not sure if there are six volt versions. I once installed an electric vacuum pump on a street rod that had such a radical camshaft that the power brake booster would not function properly. It solved the problem there, but perhaps you need an engine overhaul? A factory designed stock system should function properly if everything is up to snuff. Packards of the '30's and some other brands utilized vacuum assisted mechanical brakes.