My father-in-law recently bought a 69 Camaro. It has a 502 crate motor backed by a TH400. I have driven the car several times and I swear for the life of me you can not feel this thing shift. I don't know if you have ever driven a CVT tranny car but that is what I would compare it to. Very linear. When you mash the throttle the RPM's come up and stay there and it just goes like a bat out of hell. Is this common for this tranny or is there a possible problem that can be corrected? I suspect low line pressure of some sort. The car definately moves but I think the tranny is holding it back in some regards.

What was done to the trans?

Sorry couldn't tell ya anything other than its a TH400. What kinds of things would you be looking for?

Norcal,About 15 years ago I built a real strong 400(34 element 2nd sprag,premium clutches,racing shift kit etc) for a guys 1970 chevelle with 454 LS 5. He got it installed and called me with almost same exact complaint. I had him bring the car by and test drove it,sure enough it felt like it was slipping constantly and you could barely tell when it shifted. Now I didn't install the trans or sell him the tq convertor he was running. We started looking at his overall combination,he had 3.31 rear end gears,fairly tall tires,cam that tq peaked motor at about 2800 rpm's,car with driver was over 3800 lbs and he had installed a 10 " B&M "3000" rpm stall convertor. Well, the convertor as installed actually stalled closer to 4000 rpm's behind his 500 plus ft lb tq motor and flashed to 4500 rpm's. Often convertors do this if they are intended for typical smallblock chevys with less tq and lighter applications with lower gear ratios. I sold him a factory ls-6 style convertor that was 13" in dia not 10" with a 1800 rpm stall rating. The car felt night and day different(as I expected it would)and instead of sliding thru the gears like it was burning up it would leave 20 ft rubber marks on pavement going from 1-2 gear. This may be the case with your 550 plus ft lb tq motor as well,first thing I would do is try to look at dia of tq convertor and its stall speed. I might be off base and your trans may very well be tired and/or damaged but I would almost bet you have similar problem,I have seen it quite a few times since the time I described above.If you do need a "tighter" convertor I have the BBC 1800-2000 stall 13 " dia convertors on the shelf for 150$ including core charge,Smitty
989-823-7319 between 3:30pm and 11:30 pm daily

Thanks Smitty,
I'm not all that up on trannies but verifying the specs of the torque converter would require dropping the transmission correct? I can tell you that it takes quite a bit of throttle/RPM to get the car moving from a dead stop. So I do have a feeling its got a pretty high stall rating in there.

Thanks Smitty,
I'm not all that up on trannies but verifying the specs of the torque converter would require dropping the transmission correct? I can tell you that it takes quite a bit of throttle/RPM to get the car moving from a dead stop. So I do have a feeling its got a pretty high stall rating in there.

High stall converter will soften shifts dramaticaly because you do not have complete lock from engine to trans. The converter is slipping and cushoning the shifts. At WOT and converter flashed, the shifts will firm up.

High stall converter will soften shifts dramaticaly because you do not have complete lock from engine to trans. The converter is slipping and cushoning the shifts. At WOT and converter flashed, the shifts will firm up.

But even at WOT you can't feel the shifts....

But even at WOT you can't feel the shifts....

You can hear the note of the engine change though, correct? Do you know rear gear ratio? If you hold brakes and "stall the convertor" how high will it go rpm wise?a 450 hp/550 ft lb tq gm 502 crate motor tq peaks around 3200,if your stall is substantially higher then I think we are looking in right direction.I have seen extreme examples of mismatched combinations of stall speed vs engine tq. Some of the cheap,junk convertors out there have windows milled in the stator fins to give them a higher stall rating and they are real inefiecent even on top end. Add a steep rear end gear and torqey motor and they end up stalling way higher than you'd expect. Add cheap construction and some abuse ( stalling convertor too long) and convertor can baloon(front and rear covers spread apart) which will give you even more slippage in convertor.
Norcal,if trans was actually slipping the clutches inside after completely shifting into say third gear,they would burn out in a very short time and fluid would also be burned. You might be able to figure out what convertor you have by pulling dust cover off trans and rotaiting convertor looking for a part # plus its obvious without measuring if your looking at a 10 inch convertor versus a stock 13",let us know,Smitty