4+3 Overdrive Cutout Switch
Thread Starter
1st Gear
Joined: Aug 2010
Posts: 1
Likes: 0
From: Milwaukee Wisconsin
4+3 Overdrive Cutout Switch
I've only owned my 1984 Corvette with 4+3 trans for a few months. The one thing that I'm not crazy about is when the car decides to shift into overdrive. It seems that whenever I take off aggressively in first gear, then shift to second, the trans goes into overdrive as soon as I let the clutch out. I've been careful not to hit the overdrive button but it goes to overdrive anyway.
I've heard there's a way to install a cutout switch on the OD so I can turn it on and off with a toggle switch. Any help with how to do this is appreciated!
Maurice
I've heard there's a way to install a cutout switch on the OD so I can turn it on and off with a toggle switch. Any help with how to do this is appreciated!
Maurice
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
I rewired my 84 to do that when I had the 4+3. Have the console switch intercept the lock up wire going to the tranny. I can't remember off hand what wire to tap into. You'll need an FSM. The overdrive light on the tranny still worked, and the overdrive would only engauge with the switch flicked. In essence, I bypassed the computer. It's a good mod to do and costs nothing.
Drifting
Joined: Jun 2009
Posts: 1,286
Likes: 448
From: Upstate NY
With mine off, no matter how hard I drive it or hit cruise, the OD will not engage until I turn it on.
Instructor
Joined: Mar 2009
Posts: 230
Likes: 0
check the connection on the trani . if it is just 2 pins, disconnct harness andtie out of the way. Make a jumper wire between the 2 leads on trani . this will make overdrive switching completely switch controlled. takes computer out of it .shouldnt get check light. Now you can even shift into overdrive in 1st gear
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
O/d will automatically engage once correct programmed conditions are met; engine temp / TPS / road speed/etc
Already have one; need to hit O/d switch before driving off to disable
All you are doing is bypassing the 1st gear lockout switch.
O/d relay control still comes from the ECM.
See '84 O/d diagram below
No feedback to ECM from O/d for check engine light.
O/d light on dash only shows ECM is "trying " to turn O/d on; does not indicate that it is actually engaged
Switch takes out power to the O/d regardless of what the ECM is doing
I rewired my 84 to do that when I had the 4+3. Have the console switch intercept the lock up wire going to the tranny. I can't remember off hand what wire to tap into. You'll need an FSM. The overdrive light on the tranny still worked, and the overdrive would only engauge with the switch flicked. In essence, I bypassed the computer.
Join blue to pink / blk at relay, bypassing relay.
Switch is now only thing controlling O/d giving full manual control ( with 1st gear lockout unless also you bypass the 1st gear switch as noted above).
Light will still come on when ECM tries operating the relay but as the relay is bypassed , nothing will happen
Last edited by vetteoz; Aug 23, 2010 at 07:18 PM.
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
^^What are you guys talking about?
On the '84 there is a rocker switch on the console. If that rocker switch is in the off position the O/D will not come on automatically when you start the car or by default.
What this sounds like is the OP does not know, maybe due to the silk screen being rubbed off the console...or whatever.....The OP does not understand what that switch does.
Also, the switch itself may be defective and the O/D is stuck in the ON the position. Therefore the OP does not believe that the rocker switch does anything.
On the '84 there is a rocker switch on the console. If that rocker switch is in the off position the O/D will not come on automatically when you start the car or by default.
What this sounds like is the OP does not know, maybe due to the silk screen being rubbed off the console...or whatever.....The OP does not understand what that switch does.
Also, the switch itself may be defective and the O/D is stuck in the ON the position. Therefore the OP does not believe that the rocker switch does anything.
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
Before you go crazy cutting up your wiring, why not diagnose what is wrong. A cheap Radio Shack rocker switch may be all you need to get the results you are desiring.
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Drifting
Joined: Jun 2009
Posts: 1,286
Likes: 448
From: Upstate NY
I leave mine off and use it as a regular 4 speed around town. When I go on the highway, I get into 4th and then turn on the OD.
The OD even kicks off and then back on if you punch it to pass etc.
It works great for me!
