Need a TH 400 guru...
 

Having trouble with kickdown on our 68 BB Nova with th400 and Gear Vendors OD....it will only downshift via gas pedal when the car is going less than 40mph...above that, nothing. Would love to discuss this situation with someone who really knows this stuff...any help would be appreciated.

wilma https://www.yenko.net/ubbthreads/imag...s/confused.gif https://www.yenko.net/ubbthreads/imag...lins/frown.gif

Re: Need a TH 400 guru...
 

Why do you feel this is abnormal?In overdrive the governor is spinning slower so the shift points will be at a higher MPH.

Re: Need a TH 400 guru...
 

I should have been clearer.....this condition is without the O/D engaged....

wilma

Re: Need a TH 400 guru...
 

Have you done any checking on the detent down-shift system?Check your switch for 12V supply with ign.on.Then activate switch and check for 12V output at the wire that runs to the drivers side of the trans.If you have 12V signal at the trans.you will need to check the solenoid inside pan.This can be done without removal of the pan.Disconnect the wire at the connector and check for continuity with an ohm meter.Hook one meter wire to the spade on trans connector and the other to ground (trans case).You should get a reading if solenoid is good.If it reads a zero resistance,suspect a shorted wire or solenoid.This detent should give you a full throttle down-shift up to about 70mph in 3rd gear.Or a second to first up to around 30mph.You may be able to hear a faint click at the pan when the detent switch is hand operated with ign.on if solenoid is functioning.

Re: Need a TH 400 guru...
 

I talked to a good friend that has worked on GM automatics for years about your problem. He asked a couple of questions about your car.
1. What rear gear are you running?
2. Does it short shift during normal acceleration?

I'll forward your answers to him as his computer just smoked it's hard drive last night. He did think if your running a 4:88 or so the transmission might be running just like it was designed to. He thought you may have to play with the govenor springs to make it shift differently, also didn't know if there were springs you could by from the aftermarket that would work or just trial and error to get your kick down points right. He said a governor from an old school bus with a TH 400 might work as they ran a pretty steep gear.

Mike

Re: Need a TH 400 guru...
 

Mike, thanks a lot for the help....car has a 4.10 rear..27" tire....I have a couple of hi-perf governors....got a date tomorrow morning with a local tranny guy to kind of look things over...and yes, I think it short shifts under normal circumstances....what I am looking for ideally is to duplicate function of CW/CX code trannys from back in the day....high shift point..firm response...tom

Re: Need a TH 400 guru...
 

Wilma, John Force just called, he said he has an old airshifted Lenco available that should bolt right, I would jump on it

Re: Need a TH 400 guru...
 

[ QUOTE ]
Wilma, John Force just called, he said he has an old airshifted Lenco available that should bolt right, I would jump on it

[/ QUOTE ]

<font color="blue">I could use a Lenco ... https://www.yenko.net/ubbthreads/imag...-I-Have-It.gif </font>

Re: Need a TH 400 guru...
 

Tom, Good luck, I can put you in touch with my friend if you don't get the results you are looking for. Sounds like your on the right track.
Mike

Re: Need a TH 400 guru...
 

Met with a local tranny guy today and he drove the car....he feels the governor is the main problem. I have a couple of vintage hi-perf govs from L78 cars...gonna change one this weekend and then we will see...more to follow.

wilma