My buddy has a 68 chevelle w/ a mild 350/th350 combo. The TH350 came out of my 72 chevelle that I’m doing the LQ9/4L80 swap on and I don‘t know its history or mileage but the fluid looked good when we did the filter/fluid change. The trans was shifting well and working normal until a couple of days ago it happened. The tranny started to have some slipping in 3rd gear. We had just replaced manifold intake gaskets and noticed that the trans vacuum modulator line came undone from the intake vacuum source. We hooked it back up and it seemed to be back to normal. Then the slipping came back and progressed to bad shaking when it shifts into 3rd and is now totally unusable. 1st and 2nd work fine and still shift nice and crisp. Any ideas on diagnosis? I don’t know much about trannys so bear with me. I think that if it sounds doable, I might try to rebuild it if it’s not too expensive. I don’t think we have much to lose at this point and it would be some good experience. Any thoughts on this? I have decent mechanical skills (supercharger installs, engine/trans swaps) but haven’t really got into the guts of an engine or trans yet. Is this something I should consider tackling on my own?

 

have you been letting it coast (no gas) and then floor it?

this causes damage to the sprag...... you might need to go ahead and replace the sprag and drum...

get the hardend drum and the 34 element sprag.... this is the first thing that usually goes in th350s

 

that's exactly what was going on before it first started. Does this affect 3rd gear only when it goes out? Thanks for the lead...anyone else?

 

does it slip in rev? third and rev. share the same clutch pack. if it does l'm afraid it's dead. good luck