TH400 not shifting when it should
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
TH400 not shifting when it should
This morning I went out and hooked up my tach (which has been disconnected for years) and fired it up with my new tach-drive distributor, set the timing, adjusted my idle, etc. and then found myself NEEDING to go for a drive (like ya do when you finish tasks on the 'vette) and noticed that even at WOT my transmission is shifting at about 3500.
I had a problem earlier with it not shifting up into gears at part throttle, which was due to a disconnected vacuum line to the transmission, so I think this might be related.
Could damaged vacuum lines cause symptoms like these?
TIA
I had a problem earlier with it not shifting up into gears at part throttle, which was due to a disconnected vacuum line to the transmission, so I think this might be related.
Could damaged vacuum lines cause symptoms like these?
TIA
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
The vacuum lines going to the tranny are pretty trashed, so I'll replace those and see how it works out. If there are any other suggestions I'll look into them.
Again, TIA.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The vacuum modulator on the right side of the tranny (the vacuum line hooks to it) may be faulty. If you pull the vacuum line off and you see fluid coming out of the line, chances are that the diaphragm in the V/M is bad. An exact replacement requires some research to determine the correct part number...then find one. You can buy aftermarket "replacements" (
) at local auto parts store, but they are approximations, at best. If you obtain the correct V/M, they are adjustable via the screw/locknut on the casing. Check the GM service manual for correct shift points at normal acceleration upshifts and at WOT.
) at local auto parts store, but they are approximations, at best. If you obtain the correct V/M, they are adjustable via the screw/locknut on the casing. Check the GM service manual for correct shift points at normal acceleration upshifts and at WOT.
