Vacuum loss after warmed up?

Brake lights - jump the switch and see what you get. That being said, I will always remember one very long night troubleshooting before I realized every single bulb in the entire car was burnt out (on 852 S/C Phaeton)

So after a couple of shifts the contacts warm up due to the dirt and the resistance goes up.
Something to remember.
Thanks for sharing the solution.
Frank

Thank you to everyone with suggestions on my 810 shifting problem. After talking with Stan G., I removed the shifter switch from it's home by the master cylinder, opened it up and sure enough, there was some oily residue inside and the contacts were dirty. I cleaned and shined them up, reinstalled the switch and then adjusted the pin out about 1/8 inch. Now my Westchester shifts like a dream! Now if I can only figure out why I don't have brake lights, even after replacing the brake line switch....

I suspect a bad contact in the cross shifter switch. I use a modern switch made by Stan. I could not get 2nd or 3rd. Opened up the switch, and a small spring for the 2nd/3rd contact was bent.
If the selector is moving in the proper H pattern on top of the trans, then your vacuum should be good.
I would not open the can of worms called the shifter on the steering column. You can still check electrical signals coming out of the shifter by opening the wiring coming out of the firewall. Push a voltage tester sharp end into whatever color wire you want to check at that spot with the other end on the contact at the cross shifter. If the light comes on, you've got good voltage down to the cross shifter switch.
Tim.

You can check for vacuum by switching on the wipers.Try the wipers before the engine has warmed up. When you suspect a vacuum leak later on, try the wipers again. If they work as before, look elsewhere for your problem.
That is, if your wipers work at all.

I know less than you do about this, but I am starting to have a similar problem. Here's what a member suggested to me: Clean the contact points in the shift assembly coming off the steering column. I won't be able to get to this very soon, but I will give it a try later. Let us know what works for you.

Sorry you are having issues. Best I can tell you is vacuum will make the trans shift in or out of gear plus it causes the action of pulling or pushing the shift lever across the "H" pattern. I do not feel you are loosing a vacuum signal from the running engine. You could have many issues causing what you have posted. It could be a simple loose connection to one of the switches or a seal in the cross shift housing. The main shift vacuum chamber that pushes the shift lever in and out of gear could have bad seals or the switch that tells everything what is going on could be failing when things warm up. There is a lot of possible repairs. I hope someone with much more help chimes in with what it will take to fix this. Do you hear any gear grinding when this happens?

Hello all, something recently came up with my 810 that baffles me. I'm wondering if anyone has had this problem and what the solution is. After driving my 810 Westchester for short distances, the transmission will not shift from first to reverse or visa versa. If I turn the car off and back on, the proper gear is engaged but still will not shift into the other gear until the car cools. This has happened twice when returning home from a drive so I don't know if the other gears are affected. I've had the car for over a year and try to drive it regularly and this just popped up. Any ideas?