1967 Other Plymouth Models

I need to know which type of transmission fluid to use when I am a pint low.

I was using ATF+4 which I think was the correct one.

But, the other day the auto store was out of ATF+4 and they sold me Chevron MD-3 which they said was OK and compatible with my car.

I added almost a quart of the MD-3 and for the past three days the car seems to be shifting OK with no problems I am aware of.

However, I am still a little skeptical that the MD-3 is the proper ATF to use and that it might be doing harm to my old transmission.

If anyone knows if the MD-3 is OK or not I would appreciate any info you can provide.