Bearnecessities

Hi all new here,
Have a 1969 Cutlass S with 350 original motor with a few upgrades. Car had a big 750 cfm Holley on it when I got it, and it drove fine as far as the trans was concerned. I just installed a 4bbl Quadrajet which operates fine, but now the trans is shifting late and hard. Did a trans service last year and since then it has sat for a couple of months during the winter in my garage. Checked vacuum line to the trans and fluid level is good, any one have any thoughts on what may be going on?
Thanks for the input

BangScreech4-4-2

What is your definition of "late"?

oldcutlass

It could be that the vacuum line from the carb is on ported vacuum, a bad modulator, or low vacuum in the line. It could also be a mis adjustment of the kickdown switch due to changes in the linkage geometry from the carb change.

Bearnecessities

Late would be almost 3k rpm and not what I'm used to in this car

Bearnecessities

So the kick down is a switch by the gas pedal no linkage. It is on a ported vacuum line on the Quadrajet so I guess that's my issue I need full manifold vacuum.
Thanks all much appreciated.

joe_padavano

Ported vacuum is zero at idle and small throttle openings, then follows manifold vacuum as the throttle blades open enough to fully expose the ports. This will definitely cause problems with part throttle shifting.

Hammerdrop

Doesn't this car have a TV cable going to the transmission ?

oldcutlass

No, it's an electric kickdown switch.

Bearnecessities

Seems even the un-ported tube on the quadrajet did not have enough vacuum either, so I went right into the manifold works like a charm.

oldcutlass

Glad you got it fixed.