I don't know a lot about automatics in our cars. Mostly because all my years owning an a body nothing ever went wrong with my transmissions. I have bought a 67 Barracuda with a 383 and a 727. It shifts fine manually, but in drive it shifts very early and very harsh, like maybe a lot of overlap. I know somebody has been in there because one of the pan bolts is oversized from re-tapping to the larger size. I did change the fluid and filter when I first got it. I have adjusted the kickdown with both the WOT method and the method in the FSM with no luck. I also have noticed that there is a big blob of something like JB weld around around one of the cooling lines. I assume from unbending it from shipping (wondering if a restricted line could cause any of this). I don't know if they did a shift kit or changed the valve body, but again it shifts strong when I manually shift it. It does kickdown properly too.
My question is - where do I start?
