The Stovebolt Site Forums The Shop Area Engine Shop Combination vacuum pump / fuel pump question?

Rebuilt a combination vacuum pump/glass bowl fuel pump om my 1949 Chevrolet 3100 series 1/2 ton pickup with a 216 cu. in. 6 cyl. to assist with the vacuum wipers. Cycled the pump 5-6 times as per the Chevrolet truck shop manual before tightening the vacuum side of the pump. The pump I removed from the truck was a single stage pump that the plunger could be cycled with very light thumb pressure. The combination pump after fully assembled would only cycle if I pressed the plunger/lever to the top of my work bench. My question: Is it normal for the combination pump to be much harder to cycle than a single stage fuel pump, or is the single stahe pump I removed just very weak?

Found the answer in the truck shop manual. The dual action fuel pump cannot be cycled by hand due the the heavy pressure supplied by the spring in the vacuum side of the pump.

I found the same thing. Mine was new and it leaked fuel and oil. A replacement did the same thing. I finally gave up and went back to the single unit.

I learned TODAY that this can be an issue- in fact, that's why I'm on here tonight looking for a thread about what he describes.

A mechanic I trust very well told me in no uncertain terms that I should NOT use a mechanical fuel pump on my truck because those older style pumps have had problems with the diaphragm wearing out and allowing fuel to leak into the oil... often with catastrophic results. My first response was "they ran with mechanical pumps for a LONG time, why is it a problem now?" His pump was also a combo and it did that to him and so he was scared of using anything but an electric pump after that.

What is the opinion of the experts in this forum about those older designed pumps? I have a NOS combo that I would HATE to have to give up on. Should I just have it rebuilt w/ new diaphragms in case the others have dried out over 60 years (a possibility I expected from the start!)

Try this website.

This guy makes his own fuel pump

rebuild kits.

Check out his site:

http://www.classicpreservation.com/fuelpumpkits.html

GP

While we are on the subject, if any of you guys have the combo that has the hollow mounting bolt, please tell what it is plumbed to.
If you had not said you would hate to not use the combo, I would have said get a new quality single pump. They will not leak. Messing with rebuilding while worried about leaking into the engine is unnecessary behaviour. An electric is also just fine IF you get the right pressure and place it in the right place for your system.

I realize this is an old thread but I'm trying to find the purpose of the hollow mounting bolt as well. Right hand bold on the fuel pump is hollow - like an oil return line?? any idea what the purpose of this is and how it is plumbed?

As requested in your other post on this topic: can you post/attach a photo of the bolt?