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Mod | | | Forums66 Topics128,113 Posts1,056,279 Members48,439 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Nov 2013 Posts: 56 'Bolter | | 'Bolter Joined: Nov 2013 Posts: 56 | I am referring to the 4138 AC unit for 261 truck motor. Does anyone know which vacuum port is intake and which is exhaust or does it matter? This is the fuel pump with the vacuum pump on the bottom of the fuel pump. When I move the pump lever I cannot tell which one is which. There is one port closer to the motor and one further away.
I know one is supposed to go to manifold and one to wipers. Thanks in advance.
1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
| | | | | Joined: Feb 2001 Posts: 4,095 'Bolter | | 'Bolter Joined: Feb 2001 Posts: 4,095 | I have a dual action fuel pump and A/C on my 54 and there is a hose coming off the bottom to the A/C but is to the right side of the pump as far as I can tell reaching under the pump.
Ron, The Computer Greek I love therefore I am.1954 3100 Chevy truckIn the Gallery 2017 Buick Encore See more pix1960 MGA Roadster Sold 7/18/2017
| | | | | Joined: Feb 2004 Posts: 29,805 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,805 | It's simple- - - -remove both hoses and attach a vacuum gauge to the pump nipples with the engine running. The one that pulls a vacuum goes to the wipers. Connect the hose from the intake manifold to the other one. You've got a 50/50 chance of being correct by simply attaching the hoses at random, but it's easy to do it right.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Nov 2013 Posts: 56 'Bolter | | 'Bolter Joined: Nov 2013 Posts: 56 | It's on the stand right now.
1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
| | | | | Joined: Feb 2004 Posts: 29,805 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,805 | Loosen the pump bolts a couple of turns and wobble the housing up and down- - - -that's plenty of movement to get a vacuum reading. It's too bad common sense isn't an off-the-shelf item at a parts store.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Nov 2013 Posts: 56 'Bolter | | 'Bolter Joined: Nov 2013 Posts: 56 | If you are implying I have no common sense that's not the case buddy. Hey thanks for the help.
1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
| | | | | Joined: Aug 2001 Posts: 3,599 Moderator | | Moderator Joined: Aug 2001 Posts: 3,599 | BigBlack
Jerry is a little rough around the edges, but a wealth of knowledge in that old noggin of his.
If you ever meet him in person, you will understand.
Please don't take any offence.
Hope you try his idea and it works out for you.
Don
1967 GMC 9500 Fire Ladder Truck"The Flag Pole"In the Stovebolt Gallery1946 2-Ton grain truck 1946 3/4-ton pickup, 1953 1-ton pickup 1957 1-ton flatbed dually, 1954 Pontiac Straight Eight Of all the things I've lost in my life, I miss my mind the most! | | | | | Joined: Feb 2004 Posts: 29,805 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,805 | No offense intended- - - -after 60-something years in the auto repair business and teaching the subject for 30+ of those years, some things that appear to be an obvious solution to me don't occur to others.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Mar 2010 Posts: 10,280 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,280 | I consider myself fairly knowledgeable with these old trucks and most things come easy to me.
Add a frustrating series of issues without any success in resolution, then the cuss words and tools start flying, and I find myself in need of someone like HRL to reel me back in.
Insults, manhood questioning, etc coming from him doesn't bother me. His background is High school automotive education. I think back 40 something years ago about my old shop teachers, and HRL seems like a cream puff in comparison. I met him in person a few times. He is indeed a cream puff, and his #1 goal is to selflessly help anybody who needs it.
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Apr 2005 Posts: 7,440 Bolter | | Bolter Joined: Apr 2005 Posts: 7,440 | Y’all are gonna make him blush! 
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
| | | | | Joined: Aug 2001 Posts: 3,599 Moderator | | Moderator Joined: Aug 2001 Posts: 3,599 | Jerry blush? Never!
Maybe a smile and a chuckle though!
Don
1967 GMC 9500 Fire Ladder Truck"The Flag Pole"In the Stovebolt Gallery1946 2-Ton grain truck 1946 3/4-ton pickup, 1953 1-ton pickup 1957 1-ton flatbed dually, 1954 Pontiac Straight Eight Of all the things I've lost in my life, I miss my mind the most! | | | | | Joined: Nov 2013 Posts: 56 'Bolter | | 'Bolter Joined: Nov 2013 Posts: 56 | The reason we could not determine which port was which, was the lower pump diaphragm was torn and not working. We ordered a new pump and down the road we go. Thanks.
1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
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