Old car transmission problems

I have a 1979 Toyota SR5, small truck. I just bought it for 1300 dollars. it drives nicely but the transmission slips every now and then, sometimes worse than others. I know the car has not been used very much in the past several years. I heard sometimes you dont want to change the transmission fluid and filter if the vehicle is old. I guess im asking whether to try changing the filter and fluid or taking to a transmission place to get looked at? And how much should taking somewhere to get looked at cost?

There is absolutely no reason not to change the filter/fluid. If anything bad happens after that its just b/c it was going to happen anyway. In fact, the “don’t touch it” advice (which I’ve gotten before myself) is by far the worst thing to do.

In the long run you might be better off taking it to a local transmission shop (not a corporate chain) to have them drop the pan/filter. One of the important things about the process is inspecting the contents of the pan. An experienced tech can check out the pan and put it on a scanner and tell you what you’re likely to be looking at.

Do drop the pan, inspect the debris and magnet(s), clean the pan, install a new filter, refill, and test drive. Also check the setting of the throttle valve linkage – it will probably be a cable adjustment.

Don’t bother with scanning the PCM because this transmission isn’t computer controlled.

“Don’t bother with scanning the PCM because this transmission isn’t computer controlled.”

Good point. My bad.

At that age it’s possible the transmission could be on the way out. Rubber degrades with age and it’s at least possible that various seals, O-rings, etc. could be faulty.

Change the transmission fluid/filter and add a can of Berryman B-12 to it.
(B-12 is carburetor cleaner and can possibly help with this kind of problem.)

Yea a lot of transmissions go out shortly after having a fluid change. There is a cause and effect relationship, but it is the other way around. Those cars are already having problems because no one bothered to change the fluid before the problems were showing up. Then the blame the poor guy who changed the fluid.