'84 4+3 trans o/d overide
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Joined: Mar 2001
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From: Hacienda Heights, Ca. USA
'84 4+3 trans o/d overide
Anyone out there know how to over ride the ECM overdrive control on an '84? I'd like to have the overdrive switch on the console be a direct on/off switch. My problem is that the car runs at about 160-163 degrees on the freeway, and the ECM doesn't allow the o/d to engage until it hits 165 degrees. Sometimes I'll get over that temp but as soon as the o/d kicks in the temp drops below 165 and the o/d disengages. Anyone who can help with this out there?
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From: Cincinnati, Oh USA
Re: '84 4+3 trans o/d overide (john25)
Here is another reason why you should not run a 160 F thermostat. The overdrive is controlled by a shift solenoid. You could use a switch that would select between 12 v on the solenoid or the ECM. This is very dangerous to the transmission because the ECM won't allow the overdrive to engage until a number of conditions are met, such as, proper engine temperature, vehicle speed above 35, throttle not wide open, OD lubricant pump producing proper pressure, etc. Forcing the OD on with a manual switch will most likely shorten your OD life and GM no longer supports the 4+3 transmission. The OD was made by Doug Nash and no parts are available any longer.
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From: Hacienda Heights, Ca. USA
Re: '84 4+3 trans o/d overide (jfb)
I don't see this as a reason to not run a 160 degree thermostat. I only have this problem in the winter. I had an '85 with the 4+3 trans and the ECM on that car turned the o/d on at 143 degrees. I called Hypertech and they told me that their thermomaster chip which uses a 160 degree thermostat, does not change the o/d engagement temp. So that took care of that idea. If I go to a direct on/off type of set up, the o/d would only be used at freeway speeds, which is when I use it now.
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Re: '84 4+3 trans o/d overide (john25)
I've got a 160 thermo and a Hypertech Stage II chip in my 85 Z51 4+3. Everything works as desired. You can
setup a SPST relay and a small toggle switch to send power to your OD, but be careful. You should not send power to the OD at low-rpm and you should wait until the engine warms up a bit. IMO you should turn off the OD before downshifting into second and anytime you are going less than 30 MPH.
Connect relay terminal 30 to OD solenoid.
Connect relay terminal 87 to batt power.
Connect relay terminal 86 to +12v key on.
Connect relay terminal 85 to one terminal of a small SPST switch. Mount the switch in the car.
Connect the other end of the small SPST switch to ground.
setup a SPST relay and a small toggle switch to send power to your OD, but be careful. You should not send power to the OD at low-rpm and you should wait until the engine warms up a bit. IMO you should turn off the OD before downshifting into second and anytime you are going less than 30 MPH.
Connect relay terminal 30 to OD solenoid.
Connect relay terminal 87 to batt power.
Connect relay terminal 86 to +12v key on.
Connect relay terminal 85 to one terminal of a small SPST switch. Mount the switch in the car.
Connect the other end of the small SPST switch to ground.
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Joined: Dec 2001
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From: Syracuse NY
Re: '84 4+3 trans o/d overide (rbartick)
I can't tell you why, but my O/D kicks in when the coolant hits 119 deg F - like clockwork. I do remember when I was low on coolant, it did not kick in until a much higher temperature (150 - 160???)
As far as not being able to get parts. I don't think this is true. I just rebuilt the manual part of my 4+3 and I was in contact with S-K Speed to get parts for it. Since I didn't touch the OD (except for replacing the rear seal), I can't be sure they have the parts, but I think they do. I talked to a guy named Brian there - his advice was invaluable.
As far as not being able to get parts. I don't think this is true. I just rebuilt the manual part of my 4+3 and I was in contact with S-K Speed to get parts for it. Since I didn't touch the OD (except for replacing the rear seal), I can't be sure they have the parts, but I think they do. I talked to a guy named Brian there - his advice was invaluable.
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From: Cincinnati, Oh USA
Re: '84 4+3 trans o/d overide (jshope)
The 4 speed part of the 4+3 transmission is a Muncie unit. GM no longer supports this part either. A company in Texas bought all the stock and tools and supplies parts for the 4 speed, but no one is supporting individual parts for the overdrive. A company in Chicago sells rebuilt 4+3's but does not supply OD parts. Manually selecting the OD will destroy the OD if the pump fails or the lubricant is low. You are taking a chance with a manual OD switch.
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Re: '84 4+3 trans o/d overide (john25)
The '84 was designed to engage @min temp. of 80c/176f
Check: http://www.gearzone.net/dne.htm for information
[Modified by Ky_Vette, 11:21 PM 2/23/2002]
[Modified by Ky_Vette, 11:21 PM 2/23/2002]
Check: http://www.gearzone.net/dne.htm for information
[Modified by Ky_Vette, 11:21 PM 2/23/2002]
[Modified by Ky_Vette, 11:21 PM 2/23/2002]
Team Owner
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From: Boston, MA
Re: '84 4+3 trans o/d overide (jshope)
I can't tell you why, but my O/D kicks in when the coolant hits 119 deg F - like clockwork.
This is correct for 86-88. :) It is actually 122, but commonly you will only see 119 on the gauge by the time the tranny sees the higher temp. :)
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Re: '84 4+3 trans o/d overide (jfb)
>Manually selecting the OD will destroy the OD if
>the pump fails or the lubricant is low.
The OD has a pressure switch inside the unit. If the pressure falls due to low ATF or a bad pump the OD will disengage.
>the pump fails or the lubricant is low.
The OD has a pressure switch inside the unit. If the pressure falls due to low ATF or a bad pump the OD will disengage.
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Re: '84 4+3 trans o/d overide (scorp508)
This is correct for 86-88. :) It is actually 122, but commonly you will only see 119 on the gauge by the time the tranny sees the higher temp. :)
Don't you mean "by the time the ECM sees the higher temp. :)"?
