Inliners International Forums General Discussion Engines 46 Chevy vacuum assist shift

Hi. My 46 coupe has the vacuum assist shifting & it worked just fine with the original 216 engine. Smooth as could be.

But I just completed an engine swap with a 1957 235 engine that I had a complete rebuild with 0.060 bore & flat top pistons, new valves with hard seats etc, dual Clifford heated intake with 2 two barrell Webber 34-36 carbs, Langdon HEI, new 264 grind cam, lifters, springs & other assorted goodies & although I have enough manifold vacuum for the vacuum advance to work & the engine runs great the vacuum shift barely allows me to shift. It is very sluggish.

Cannot find my vacuum guage but from memory that hotter grind cam should be what is the culprid on a loss of vacuum???

I don't think adding a canister will help because that will not increase the inches of vacuum, only the avalible volume of that lower vacuum??

If so I think my options are to either use a dual diaphram fuel pump (I have one) and run a line from it to the shift assist OR to order the shift link that bypasses the vacuum shift assembly entirely. I will be ordering some other items from Chevs of the 40's this week anyway.

So my question is from your experience which of these options would be in my best interest? Or other options? I have the 3 on the tree & this coupe will never be raced. Building it as my daily driver & for cruises, tours & shows.

Any advice appreiated. Thanks, Jimmie

Back in the '60s I took the Vacuum Assist trans out of my '48 with a 235 because it shifted too slow. I put a '53 trans in it. I had to cut 2 1/2" out of the drive line with help from my dad. I heard later was an easier way but this way was free.

I don't know how vacuum shift works but when you let off the gas to shift,doesn't the vacuum go up high bigger cam or not? I wonder if there is a vacuum leak, maybe a hose got damaged during the engine change? I have seen leaks do strange things. Jay 6155

Hi Jimmie . . . sounds like you're well on your way to a great cruiser. I agree with your assessment of the two options. One is a dual action fuel pump that will provide a constant vacuum source. The other is a kit to eliminate the vacuum assist. Chevs of the Forties has both:
Fuel+Vacuum Pump
Vacuum Assist Conversion

If your vacuum assisted shifter is working well the vacuum pump is likely the path of least resistance (it maintains originality and will help the Wipers too if you plumb them in). But they are ugly compared to the glass sediment bowl device usually found in this spot. I don't think the vacuum canister would be necessary with the dual action pump.

I don't have any experience with the mechanical conversion kit.

In '49 Chevy went back to an all mechanical linkage. It works well so long as it is kept lubricated. If allowed to wear the shifting rods sag and then bind. The geometry is maintained only by flat washers and cotter pins . . . hardly a precision piece of engineering . . . but effective if lubed to prevent wear.

regards,
stock49