VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 1948 Chevrolet -Vacuum gears versus floor shift

Mine shifts effortlessly, like it's supposed to. It's just the popping out of gear that's the issue. Next week, a friend and I are removing the transmission to replace the bearings. When we install it, we'll pay attention to the vacuum cylinder and all the other adjustments and linkages and see if that solves the problem.

I have to be honest, that I put up with the thing dropping out of 2nd once in a while because I do not want to get the old body under there to adjust the cylinder.....After you've done it a few times you will find it is not as easy as it may seem when looking at the shop manual....The biggest issue is getting the linkage off the tranny...You may find you may not be able to get a wrench on the nut and bolt from underneath and may need to pull the inspection cover from inside the car...All was sweet when I had little to no interior...Not the case now...Once you think you have found success with proper adjustment, the rubber boot will throw you another curve, not to mention your rods could have got thrown out of wack.....My 48 shifts very well, so for now I will leave thing the way they are...I do have the conversion kit, but hope I never have to use it

One of the problems with the vacuum shift slipping out of gear is the vacuum hose from the vacuum unit to the "J" pipe extending down from the manifold. If this hose has become hardened it can pull the transmission out of gear. So check the hose and change if stiff.

Great advise Ray...Not my problem though, it's still pretty new and still flexible

Yes, all good advice - I'll have to check the hose when I get under there.

M. Holton

Lately I also had some troubles with my gear shifting.
In your case I should advice you to adjust your thinner rod lengthening it by turning the swivel 3 or 4 complete turns.



Whatever you do with adjusting try to note how many turns you did so in case it doesn't work you can set it back to its original position.
I should also advice that you have a look at the condition of your engine and transmission mounts, if they are too soft ( due to aging )that will have an effect on the position of the engine to the frame at different driving conditions and that will play havoc with your rods adjustments.In my case that was the problem.After installing new engine and transmission mounts all my shifting problems were solved.

Jianis

Jianis...Is your spring adjusted to 3/4"???

Chef

Yes that's right its 3/4 inch (according to the Manual) but what is very important is the positioning of the lower support bushing as the manual says at page 7-14 figure 25 at 19/64 inch.I myself turned a new bushing from ertalon and adjusted it even shorter to compensate for the linkage wear so it should have more freedom shifting to first and reverse.

Jianis