Transmission snake oils

FWIW, a 1993 Cadillac Sedan DeVille appeared which was “stuck in 3rd.” If manually shifted all ranges were solid. It had been parked for more than a year, yet it ran well other wise. After adding a bottle of 'snake oil" and driven, manually shifting at proper speeds, the transmission’s problem went into remission after less than 20 miles. It has now been driven several hundred miles and all is well.

Go figure…

So, quick, tell us which “snake oil” you used. Inquiring minds need to know.

Trans-Medic was the elixir of choice.

I’ve “cured” (possibly a bad word) about half a dozen transmission shifting problems with Berryman B-12 carb cleaner also.
As long as it works.

Remission is probably not the correct word here. Resolved is more likely correct.

You have to understand how an automatic transmission shifts to get this. There are barrel shaped valves that slide within the valve body, and as they move from one position to the next they open some hydraulic circuits while closing others. These valves have very little clearance in their bores. It doesn’t take a lot to make a valve stick, and sitting unused for a year is an excellent way to accomplish just that. A stuck valve means that something isn’t going to shift. There isn’t a lot of pressure moving them around, so they need to move freely.

A little bit of a cleaning additive can go a very long way for this, freeing a stuck valve permanently. Do yourself a big favor and drive it a little while and then change the fluid and filter.