Lloyd,
Many thanks for the info on your DIY vacuum actuator.
I'm sure if I were looking at your unit your description would match
perfectly.
BUT not having one in my hand, I must confess the description leaves me a
bit confused : - (
Any chance you could e-mail a drawing or equivalent???
This is clearly a case of needing to see the 'picture' before I can see the
'light' : - )

And thanks to all the others who offered great suggestions for obtaining a
commercial substitute!
I'll keep them on file in case my DIY version fails to perform...

Chet


YES! I built my own cruise-control in the 1980s. I built a "sock"
type actuator. It's really simple.

Get an inner tube of the un-inflated diameter about what you want.
Find a piece of metal or plastic tubing into which it will fit
closely.
Find or fabricate a disk that will fit inside the inner tube when it
is doubled over inside itself.
Cement/fasten/clamp the inner tube to the disk. Then turn the whole
assembly inside-out, so the disk pulls the "inner" portion down inside
the "outer" portion.

Now slide the whole tube/disk affair inside your metal tubing, and
fold the free end of the inner tube over and around the butt-end of
the tube.

Seal it with a little adhesive between the outer surface of the metal
tube and the inner tube fold-over. Add over that a cap that fits
tight. Apply vacuum to the cap end.

You may also install a return spring inside, or rely upon an external
return spring.

Mine lasted eight years of daily interstate driving without a leak.

LLoyd