Doesn't want to shift gears when cold

My 1970 chevy c10 pickup is a 350 with automatic transmission 2wd. It doesn’t get driven frequently and when I do the first time I put it into gear, fwd or reverse, it is slow to engage. Shortly after it has warmed up however, this problem goes away. Does anyone know what this sounds like?

Servicing the transmission every 12,000 miles under normal driving conditions was recommended by the factory. How many miles since the last service?

Hard to say, I bought it used. I have checked the fluid repeatedly and the level is fine. Perhaps it needs a flush?

Maybe someone put in the wrong tranny fluid, with the wrong low-temp viscosity?

The last thing your transmission needs is a flush. Just drop the pan, drain the fluid, install a new filter and fill it with the proper transmission fluid. Your problem will probably go away.

Your transmission is hydraulically operated. The transmission fluid is pressurized by the transmission’s front pump and sent throughout the transmission to engage the various components. Everywhere the fluid goes there are seals to ensure that there are no fluid/pressure leaks.

What you are describing is the classic problem with older / high mileage transmissions. Internal seals get hard after so many years of heating / cooling cycles and no longer seal effectively. The reason it takes longer for the transmission to engage is because it takes longer to build hydraulic pressure because of the leaks. As the transmission gets warmer the seals become more compliant and don’t leak as much, so the problem diminishes.

You can try a transmission seal reconditioner, which MAY restore some of the life to the seals, but eventually the seals will get so bad that they’ll need to be replaced. At that point an overhaul is the only solution.

When my early 70’s Ford truck transmission started to do that, it wasn’t very many months before it was in the shop for a transmission rebuild, which fixed the problem straight away. I agree w/the above posts, the first step is to do a proper service. Might well fix the problem.

I like the look of those early 70’s C10’s. Good on you for keeping a classic on the road.

I was a kid at around that same era, I’d go to church on Sunday, and one of the other families had a new C10 they’d park in the parking lot while attending the services. 4 of us teenage ner-do-wells, not much interested in the services, discovered one day that one of our own keys fit the C10 door lock. So instead of attending the services, we’d sit in the truck and play the radio and listen to Jimi Hendrix and The Who and goof off with the CB radio. “Breaker One Nine …” … lol … So C10’s bring back some fun times.