Auto transmission mystery plug
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Instructor
Joined: Mar 2002
Posts: 174
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From: Raleigh NC
Auto transmission mystery plug
When I was disassembling our '72 I noticed what appeared to be an electrical plug at the left rear of the transmission. It was not connected to anything. My assembly manual is vague on what this connection is for. Can anyone help me?
Thanks
Thanks
Melting Slicks
Joined: Jul 1999
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From: Godspeed Mikey Hogsmak Invitational Spring Skyline Drive Corvette Cruise
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Re: Auto transmission mystery plug (Texaggie)
The only thing I can think of on a 72 that would be electrical is a backup light switch, but on my manual 69 it's on the shifter linkage. :chevy
Drifting
Joined: Dec 1999
Posts: 1,319
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From: Douglasville GA
Re: Auto transmission mystery plug (subboz)
Wasn't there a switch called TCS or something back in the early 70s? I think it had to do with altering the timing when in hi gear and cruising.
Tom Melton
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86 Z51 Coupe
Tom Melton
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From: Petaluma CA
Re: Auto transmission mystery plug (Cookwithvette)
Detent. What is the origination of this word ? To get up and out in the morning on a camping trip would be to de-tent. There was a political policy a few years back called detent. My son reads Car Craft magazine in detention. Please help. I am losing sleep. Can't go on.
Le Mans Master
Joined: Sep 2000
Posts: 5,635
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From: Orlando Floriduh
Re: Auto transmission mystery plug (Stevo)
The termonoligy "detent" refers to a wide open throttle positioning of a valve inside the trans that forces a downshft. This valve, at it's extreme has what is called a detent hence the name detent or detent valve. TH400's do this with an electric solenoid that is actuated by a switch on the carburetor OR under the gas pedal depending on year. Without this the trans will not downshift into 2nd when accelerating at speeds over about 40mph. The vacuum modulator will do that at speed under 40mph. It will also NEVER downshift into 1st (accelerationg) Lots of cars have this system not workng and the owner never knows it because the trans work fine the rest of the time and they think that's just the way it works.(no high speed downshift and no 1st gear downshift)
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Burning Brakes
Joined: Nov 2001
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Re: Auto transmission mystery plug (silvervetteman)
It will also NEVER downshift into 1st (accelerationg) Lots of cars have this system not workng and the owner never knows it because the trans work fine the rest of the time and they think that's just the way it works.(no high speed downshift and no 1st gear downshift)
This is happening to me, too! I had this working last year before the year-long suspension, caliper and steering box rebuild project. It's one week since I've been back on the road, and I can't get my TH400 to kick down into first gear on WOT.
I think I've got good vacuum to the modulator - it will hold vacuum also - and I just double-checked the electrical line to the solenoid, and it lights up just fine. I can get what I'm looking for with manually shifting the trans into low gear, but it won't do it at WOT on it's own.
So what could be causing the non-kick-down situation? Am I stuck with taking the valve body apart?
Let me know your thoughts. Miranda really wants to run, and I've got to get this figured out.
Your kind and generous consideration is appreciated. GM
Le Mans Master
Joined: Sep 2000
Posts: 5,635
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From: Orlando Floriduh
Re: Auto transmission mystery plug (mayberg)
OK... First.... You should (MUST) hear an audible "click" from the transmission pan every time you close the switch. You may have power coming from the switch but if the solenoid is bad or a wire in the trans is broken.... You can test the solenoid just by applying 12V. to it. If the solenoid is bad you will have to drop the pan to replace it. TH400's will not got back into 1st (or into 2nd at speeds over about 45mph) after they upshift without the detent solenoid functioning. Of course I'm refering to full throttle downshifts. Hope this helps.
[Modified by silvervetteman, 5:51 AM 6/14/2002]
[Modified by silvervetteman, 5:51 AM 6/14/2002]