Strange problem with TH400 kickdown
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
Strange problem with TH400 kickdown
Recently acquired a 68 327/300 with a TH400 automatic. Functions well except no kickdown. I thought the problem would be with the sliding switch at the pedal, BUT, after messing around with timing and distributor issues it just started working out of the blue. 2 to 1, even 3 to 1 downshifts were happening!
Then, I finished the tune up, with new cap/rotor/points and set final timing and .... no downshifts again! Weird.
So can anyone make sense of this?
Can anyone explain how the kickdown functions and all the components? It seems there is a vacuum contribution as well as the electric pedal switch.
Then, I finished the tune up, with new cap/rotor/points and set final timing and .... no downshifts again! Weird.
So can anyone make sense of this?
Can anyone explain how the kickdown functions and all the components? It seems there is a vacuum contribution as well as the electric pedal switch.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The only vacuum to a 400 controls upshift feeland timing, all the kickdown function is electric.
At WOT, the kickdown switch opens the solenoid and dumps 2nd or 3rd oil, (depending on what gear it was in when it opened), As speed increases line pressure rises and when it overcomes governor pressure, it shifts to the next gear.
At WOT, the kickdown switch opens the solenoid and dumps 2nd or 3rd oil, (depending on what gear it was in when it opened), As speed increases line pressure rises and when it overcomes governor pressure, it shifts to the next gear.
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
The kickdown function is totally electric. There is a switch located on the gas pedal, that once depressed provides 12volts to the tranny. I just had to replace my kickdown solonoid - very simple, and had to adjust my gas pedal to activate the switch. Your solonoid is easy to check, just apply 12volts to the connector on the outside of the tranny and you should hear the solonoid operate. There are several threads on the forum that explain the gas pedal adjustment. Trace the wiring for your 12volt source - it may be a bad connection around the distributor.
Last edited by JimT; Mar 7, 2010 at 07:19 PM.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
The kickdown function is totally electric. There is a switch located on the gas pedal, that once depressed provides 12volts to the tranny. I just had to replace my kickdown solonoid - very simple, and had to adjust my gas pedal to activate the switch. Your solonoid is easy to check, just apply 12volts to the connector on the outside of the tranny and you should hear the solonoid operate. There are several threads on the forum that explain the gas pedal adjustment. Trace the wiring for your 12volt source - it may be a bad connection around the distributor.
Looking at that passenger side vacuum connection on my car shows a steel vacuum line that comes from the right side of the intake manifold down to the tranny. The steel line comes all the way even with the connector on the the tranny, and at that point a rubber hose makes the connection between the steel line and tranny, but that hose is on a tight bend. I thought maybe it could have been pinched.
