Automatic Downshift Question
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,712
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From: Shreveport LA
LA Events Coordinator
Automatic Downshift Question
My 75 has a Turbo 300 automatic connected to a GMPP crate engine 325hp. When I'm doing about 45mph or over and am in 3rd gear and I floor it do get around another car, should the transmission down shift to 2nd gear, and accelerate quickly? Right now, it stays in 3rd gear and accelerates rather quickly, but not as quick as a down shift would. Is it supposed to down shift?
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Well, you have a Turbo-Hydramatic 350 and, yes, it should downshift. There is a 'kickdown' switch mounted on the accelerator pedal which send a 12 volt signal to the tranny when you ask for WOT. That signal then powers a small solenoid valve mounted to the tranny valve body. So, you first need to determine if the kickdown switch is working (providing 12 v. when at full throttle); then you need to see if that 12 v. signal is actually getting to the tranny [could be a wiring problem]; then you need to drop the sump pan and check out (or replace) that solenoid valve. Sometimes the valve is functional but the valve orifice is clogged up with clutch plate particles (normally worn off the plates). Hope you can get it working again.
Melting Slicks
Joined: Mar 2006
Posts: 2,248
Likes: 67
From: Warrington PA
Finalist 2020 C4 of the Year - Unmodified
My 75 has a Turbo 300 automatic connected to a GMPP crate engine 325hp. When I'm doing about 45mph or over and am in 3rd gear and I floor it do get around another car, should the transmission down shift to 2nd gear, and accelerate quickly? Right now, it stays in 3rd gear and accelerates rather quickly, but not as quick as a down shift would. Is it supposed to down shift?
I had the same problem with my 74 Coupe from years ago. The trans kick down solenoid (switch) is probably at fault. I don't remember the exact speed that the trans won't kick down, but it is not @45mph, I think it was around 60-65 mph. So yes, it should kick down into 2nd gear when you hit WOT in 3rd for passing gear, or even partial throttle, should still drop the trans into passing gear at that speed, won't be as pronounced as a WOT passing gear, but you would still feel the difference.
