4+3 Overdrive question
Thread Starter
Cruising
Joined: Apr 2005
Posts: 11
Likes: 0
From: Manchester CT
My car will shift into overdrive as i go from first to 2nd for the first time after i start the car up. If i switch it off it will not come back on unless i restart the car but i have to have it go on to switch it off.
Instructor
Joined: Jul 2007
Posts: 118
Likes: 0
From: Plumas Lake CA
That doesn't sound right. You should be able to shift through the manual gears without the OD ever coming on until you command it. Once you turn it off, can you turn it back on whenever you need it? You should be able to use the OD in 2nd, 3rd, and 4th gears. I'm not sure why it would "reset" to "on" everytime you recycle power on your car though.
There may be a problem with the switch. Is it located on the shifter or on the console (I supposed I should have asked what year....)? My '85 was originally in the shifter but has been relocated to the console. One time the wires came off the back of the switch and I couldn't control my OD. I just soldered them back on and everything has been fine since. But with mine, it had been stuck "on" and since the switch was disconnected, I couldn't turn it on or off.... so definitely different, but may be a place to start.
There may be a problem with the switch. Is it located on the shifter or on the console (I supposed I should have asked what year....)? My '85 was originally in the shifter but has been relocated to the console. One time the wires came off the back of the switch and I couldn't control my OD. I just soldered them back on and everything has been fine since. But with mine, it had been stuck "on" and since the switch was disconnected, I couldn't turn it on or off.... so definitely different, but may be a place to start.
Drifting
Joined: Feb 2003
Posts: 1,614
Likes: 163
From: Davis CA
Different years function differently. Mine will come on automatically after each restart when the temperature reaches about 128 and I am in anything but first (1986). I only have to turn it off once after the temp reaches 128 and it will stay off until restarted. I would like to restrict it to operate only when I choose to engage it but it hasn't been enough of a bother for me to do the wiring mode or have a chip made.
It only really bugs me when I have it switched off and accidentally switch it on when doing a little track driving. I don't realize that I have switched it on and I think that my transmission has screwed up when it engages. The momentary fright is not helpful.
It only really bugs me when I have it switched off and accidentally switch it on when doing a little track driving. I don't realize that I have switched it on and I think that my transmission has screwed up when it engages. The momentary fright is not helpful.
Instructor
Joined: Oct 2002
Posts: 121
Likes: 0
From: Hanover Ontario
I have an 87 and I can tell you that it will automatically come on after the car warms up to 50 C. The problem I have is that my switch is almost dead so I really have to hit the switch to get it to turn off.
Drifting
Joined: Dec 2003
Posts: 1,492
Likes: 94
From: Westfield MA
Different years function differently. Mine will come on automatically after each restart when the temperature reaches about 128 and I am in anything but first (1986). I only have to turn it off once after the temp reaches 128 and it will stay off until restarted. I would like to restrict it to operate only when I choose to engage it but it hasn't been enough of a bother for me to do the wiring mode or have a chip made.
It only really bugs me when I have it switched off and accidentally switch it on when doing a little track driving. I don't realize that I have switched it on and I think that my transmission has screwed up when it engages. The momentary fright is not helpful.
It only really bugs me when I have it switched off and accidentally switch it on when doing a little track driving. I don't realize that I have switched it on and I think that my transmission has screwed up when it engages. The momentary fright is not helpful.
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Pro
Joined: Sep 2006
Posts: 702
Likes: 2
From: Conyers Ga
Same as my 88. There's a writeup here that details how to make it a completely manual OD unit by disconnecting two wires at the ECM. I just don't feel like doing circus gymnastics to get the darn thing out.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
This link shows how all years of the 4+3 OD units operate.
It would take some wiring mods and a change in how the computer sends a command to the OD solenoid to keep the OD from engaging if you wanted to have it off by default.
This was a subject of discussion about 5-6 years ago and the CF member who was working on it is gone. IIRC, there was something that he came up with that would have the OD default to off when the ignition is turned on.
The easiest way to keep the OD from engaging at the 1-2 shift is to use the percentage of throttle or RPM needed so that the OD does not engage immediately. That's in the linked chart. But once you shift into 4th, the OD will engage anyway.
It would take some wiring mods and a change in how the computer sends a command to the OD solenoid to keep the OD from engaging if you wanted to have it off by default.
This was a subject of discussion about 5-6 years ago and the CF member who was working on it is gone. IIRC, there was something that he came up with that would have the OD default to off when the ignition is turned on.
The easiest way to keep the OD from engaging at the 1-2 shift is to use the percentage of throttle or RPM needed so that the OD does not engage immediately. That's in the linked chart. But once you shift into 4th, the OD will engage anyway.
Intermediate
Joined: Feb 2008
Posts: 49
Likes: 0
From: Langley British columbia
O.D comming on
I got sick of this happening when I would drag race (huge pain!) so I paid about $100 and had a tranny shop put in a true manual overide switch, that I think removes the power to the overdrive unit when I switch it to the 'off' position. work well for me I just put it to the off position when don't want any possiblity of the O.D coming on, and yes I did have all the relays for the O.D replaced prior to this but to no avail.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Two choices;
Cut switch into ECM control wire to relay as mentioned to stop ECM operating O/d until you want automatic engagement
Or wire fused 12V through switch to relay (delete ECM wire ) so as to give true manual control over O/d.
Switch on = O/d , switch off = none.
Team Owner
Joined: Jan 2003
Posts: 20,301
Likes: 240
From: Summerland B.C. Canada
Pissed me off too. Changed it in the PROM 2 years ago(default off). 
No more accidental bog when going into 2nd.
Good mod for those whose memory forgets to hit the switch after 120*
No more accidental bog when going into 2nd.
Good mod for those whose memory forgets to hit the switch after 120*
