904 transmission blows 2nd to 3rd shift under heavy power

[Bl1zzard]

My son said this happened to him the other day. I thought maybe the fluid level was low. He said it seemed like it slipped when shifting from 2nd to 3rd when he was hitting it hard.

It's a 1974 Dart Swinger with a newly rebuild 360 and a 904 bone stock transmission. Small rear end 7.25" I believe.

Anyway it did the same thig to me today. I checked the fluid levels, it's at full warmed up in neutral. I hit it to get on the highway, everything was going well till I hit about 70mph with the 4 barrels still wide open, then it bucked like it lost all power and then jumped back in it.

Thoughts? I've neve been inside the transmission. It was with the car when I bought it. Originally a slant 6 car, so I assume the whole drive train is from the slant 6 era.

 

[Dana67Dart]

Fuel starvation!???

Was it hot out?
Are you running stock pump gas with alcohol?

My bone stock 67 273 would do that but only when it was really hot out. First time it did it I thought I floated a valve. Scared the crap out of me.

Lately I have been buying alcohol free gas and I have not had the same issue since, and I have tried to get it really hot, ideling in gear, stock temp guage at 1/2 way mark (Normally it sits at 1/4 to 1/3) And no more problem

 

[lemondana]

Do you have a functioning kickdown setup? If not, your trans is probably toast.

 

[Bl1zzard]

It was hot, 88 degrees, but she runs cool 190 all day long. I run premium gas in it, which is supposed to be ethanol free. RPM were around 4000 so I don't think its floating the valves. The kickdown works fine, I have the Lokar kickdown kit. It's always kicked down when I need it to. Could be fuel starvation, but it only bucked for a half second. I hope its not the tranny.