Transmission modulator / vacuum pipe TH400
Thread Starter
Racer
Joined: Nov 2008
Posts: 491
Likes: 0
From: Myrtle Beach South Carolina
Transmission modulator / vacuum pipe TH400
'73 350, 400TH
A couple of questions:
1) what is the purpose of the vacuum modulator of the TH400 Transmission?
(I was thinking either it is the controller for downshifting or the controller for normal shifting?)
2) I bought a repro modulator-to-intake steel line. It is supposed to have a "restriction". It doesn't. How's about I make a restriction - fill one end with acid core solder and drill out 1/8 hole. Would that be close?
(I can't find a real pipe to see what the actual restriction is)
thanks!
A couple of questions:
1) what is the purpose of the vacuum modulator of the TH400 Transmission?
(I was thinking either it is the controller for downshifting or the controller for normal shifting?)
2) I bought a repro modulator-to-intake steel line. It is supposed to have a "restriction". It doesn't. How's about I make a restriction - fill one end with acid core solder and drill out 1/8 hole. Would that be close?
(I can't find a real pipe to see what the actual restriction is)
thanks!
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
I wouldn't worry 'bout constricting the tube; vacuum is vacuum. What the modulator does is tell the transmission how deep your foot is into the gas, so that it knows how long to delay the shift.
A turbo 400 has no detent cable, so the modulator is pretty important. At WOT, the downshift signal is sent electrically from a switch that closes when you mash the pedal. It signals the trans to downshift, as long as it's within RPM limits.
A turbo 400 has no detent cable, so the modulator is pretty important. At WOT, the downshift signal is sent electrically from a switch that closes when you mash the pedal. It signals the trans to downshift, as long as it's within RPM limits.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I do not know of any restriction but the tube is reduced in size on the end so it will fit into the end of the modulator. A short piece of hose then makes the seal. mike...
Just noticed my upper cooler line is leaking. Oh well, I needed something to do this weekend.
Just noticed my upper cooler line is leaking. Oh well, I needed something to do this weekend.
Last edited by mds3013; Nov 24, 2010 at 07:25 PM.
Thread Starter
Racer
Joined: Nov 2008
Posts: 491
Likes: 0
From: Myrtle Beach South Carolina
