doug nash 4+3 shift button
Thread Starter
7th Gear
Joined: Oct 2011
Posts: 7
Likes: 0
doug nash 4+3 shift button
I am new at this but was able to rebuild my 1985 C-4...4+3..my question is ...How are you really supose to shift this trans..IE; mine works fine 1st gear is no OD..clutch in...now if I want to stay in 2nd low I have to keep my finger on the button..."then push clutch in and let off button...2 OD kicks in 3rd and 4th are the same...I thought the ECM should keep me out of OD...and the pulse switch was to put me in OD...IF I dont use the button the car stays in OD thru all 2-3-4....I changed OD the relay by the fuel pump relay and that did not help....Any ideas out there...T10 is working fine.
Last edited by dougsspeed; Oct 11, 2011 at 10:52 PM.
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
Not sure what year you have but my 85 has the OD switch in the console. OD is always off unless the switch is activated and it operates in 2,3,4. I am not sure about later years. Fill out your Forum profile or mention your year in the post and folks can help ya better.
Thread Starter
7th Gear
Joined: Oct 2011
Posts: 7
Likes: 0
how to shift a 4 +3
Sorry!! This is a 1985 C-4 with the OD button on the ****...the overdrive has all the upgrades..the shop service manual show I have everything wired right..could it be possible this is a early 1985 and the switch should work like a 1984 ==power on==low range==power off==OD...thank you
Drifting
Joined: Apr 2011
Posts: 1,925
Likes: 441
From: Albuquerque NM
My transmission is a replacement DN 4+5 that my grandfather bought from some guy in brooklyn new york almost 10 years ago. he had a mechanic install it. the car is an '85. wierd thing, the button mounted overdrive unit manually toggles overdrive on and off. when i push the button, the little (D) light on the console lights up and when i push the button the light goes off. This works in 2nd, 3rd, and 4th gear but i only use it in 4th gear. There is no automatic component. Not sure exactly what is going on.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Once the ECM sees correct conditions are met (engine temp , road speed , TPS ,etc) it will engage O/d.
O/d should disengage once you open the throttle over a certain % and in some cases re-engage after you lift off.Operation varies by year
Button disengages o/d and gives you manual control.
If you push the button before driving off you have full manual control
Exactly as setup by the factory for fuel economy reasons
see above
So yours has been wired to bypass the ECM control giving full manual operation
Last edited by rodj; Oct 12, 2011 at 02:15 AM.
Le Mans Master
Joined: Jun 2009
Posts: 6,528
Likes: 752
From: South Dakota
My 85 has the button on the shift **** also. I think they changed it in mid 85 from the console to the shift ****.
On mine the button turns (toggles) the OD system on or off.
In the on setting, the light comes on and the OD works automatically so that it is in OD at light throttle (& other conditions like temp over 144°) and downshifts like a powerglide if you give it enough throttle. This automatic operation is only available in 2nd, 3rd, and 4th gears.
In the off setting the light is not on, and there are no OD or downshift functions.
In practice I find that I don't like the automatic function, so I keep it off until I would use it like a 5th gear.
On mine the button turns (toggles) the OD system on or off.
In the on setting, the light comes on and the OD works automatically so that it is in OD at light throttle (& other conditions like temp over 144°) and downshifts like a powerglide if you give it enough throttle. This automatic operation is only available in 2nd, 3rd, and 4th gears.
In the off setting the light is not on, and there are no OD or downshift functions.
In practice I find that I don't like the automatic function, so I keep it off until I would use it like a 5th gear.
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
My 85 has the button on the shift **** also. I think they changed it in mid 85 from the console to the shift ****.
On mine the button turns (toggles) the OD system on or off.
In the on setting, the light comes on and the OD works automatically so that it is in OD at light throttle (& other conditions like temp over 144°) and downshifts like a powerglide if you give it enough throttle. This automatic operation is only available in 2nd, 3rd, and 4th gears.
In the off setting the light is not on, and there are no OD or downshift functions.
In practice I find that I don't like the automatic function, so I keep it off until I would use it like a 5th gear.
On mine the button turns (toggles) the OD system on or off.
In the on setting, the light comes on and the OD works automatically so that it is in OD at light throttle (& other conditions like temp over 144°) and downshifts like a powerglide if you give it enough throttle. This automatic operation is only available in 2nd, 3rd, and 4th gears.
In the off setting the light is not on, and there are no OD or downshift functions.
In practice I find that I don't like the automatic function, so I keep it off until I would use it like a 5th gear.
Thread Starter
7th Gear
Joined: Oct 2011
Posts: 7
Likes: 0
Thank you very much!!! These are the answers I needed...In different years the button could be a +12vt on...or...A 12vt pulse...Mine I am sure now is a early 85 and I think it needs to be +12 ON...And I control the OD...Oh by the way...On the my rear hatch window wont open question someone posted... pass this along...On the 1985 manual trans corvetts...Center console button for rear hatch==Open one door...put car in nutral and apply emergency brake...pop rear hatch
Last edited by dougsspeed; Oct 12, 2011 at 09:15 PM.
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Drifting
Joined: May 2006
Posts: 1,428
Likes: 7
From: Chewelah Wa
I have a 85 with a 88 replacement OD (85 T10), My switch is on the console. I got tired of the games the ECM was playing, and went to straight manual control of the OD by grounding the OD relay through the console switch. The ECM controls the OD the same way, by grounding the relay. If you do what I did, you have to remove (cut) the wire from the ECM to the relay and wire it directly to the switch, then to ground (which it already is BTW). One of the best mods I have done. This may just apply to 84-early 85 cars.
Thread Starter
7th Gear
Joined: Oct 2011
Posts: 7
Likes: 0
I think this is what the last owner did to a tee!!! I also have heard of being able to have a transmission shop trick the ECM so the same thing will happen..I agree I like to be in full control of the car when it comes to shifting...Thank you.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Difference is on the early cars the switch was on the wire between relay and solenoid
Whereas on the later cars , the switch was a input to the ECM so you would have to splice in a new higher amp switch into the solenoid wiring.
Putting a switched 12V supply to terminal F on the ALDL connector gives manual control
( so long as you remove said control wire from ECM )
Navigator
Joined: Apr 2016
Posts: 9
Likes: 0
how to use overdrive
Just a quick question I have an 86 with the doug nash 4+3 just wondering if it's necessary to use the clutch when engaging/disengaging the overdrive? I only ever use the overdrive when I'm in 4th gear on the highway. I've read that some people use the clutch when engaging the overdrive, I never do, I don't really see the need to but just wondering if I'm supposed to?
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Just a quick question I have an 86 with the doug nash 4+3 just wondering if it's necessary to use the clutch when engaging/disengaging the overdrive? I only ever use the overdrive when I'm in 4th gear on the highway. I've read that some people use the clutch when engaging the overdrive, I never do, I don't really see the need to but just wondering if I'm supposed to?
I always used to use the clutch when going in and out of OD on my old '87. But like you, I never really used the OD when driving in city traffic. As soon as the coolant temp was high enough to laet the OD work, I shut it off with the button.
I used 3rd gear and OD on roads where the speeds were around 40-50 MPH. 3rd and OD is a lower RPM than 4th and no OD.
The "downshift" feature in 4th with the OD ON can be used without the clutch. Just let off the gas when going back into OD.
Navigator
Joined: Apr 2016
Posts: 9
Likes: 0
It's not necessary, but using the clutch does reduce the shock of going in and out of OD to the driveline.
I always used to use the clutch when going in and out of OD on my old '87. But like you, I never really used the OD when driving in city traffic. As soon as the coolant temp was high enough to laet the OD work, I shut it off with the button.
I used 3rd gear and OD on roads where the speeds were around 40-50 MPH. 3rd and OD is a lower RPM than 4th and no OD.
The "downshift" feature in 4th with the OD ON can be used without the clutch. Just let off the gas when going back into OD.
I always used to use the clutch when going in and out of OD on my old '87. But like you, I never really used the OD when driving in city traffic. As soon as the coolant temp was high enough to laet the OD work, I shut it off with the button.
I used 3rd gear and OD on roads where the speeds were around 40-50 MPH. 3rd and OD is a lower RPM than 4th and no OD.
The "downshift" feature in 4th with the OD ON can be used without the clutch. Just let off the gas when going back into OD.
Safety Car
Joined: Oct 2007
Posts: 4,426
Likes: 229
From: Pennsylvania
thanks for the reply, i know what you mean, i do notice that it does kind of thud into gear when i turn the overdrive off thats why i try not to do it until im down to about 1000 or 1200 rpms, does seem kind of inconvenient to have to use the clutch tho, so is it the overdrive itself that you're preserving by using the clutch or is it other components of the drive train? i dont really know much about these trannys, only owned the car for a year, ive read they can be problematic if you dont take care of them, which was why i was curious. Does chevrolet recommend using the clutch for the overdrive, or is that something owners have just adopted on their own?
Burning Brakes
Joined: Dec 1999
Posts: 984
Likes: 154
From: Columbia MD
Here's an excellent summary of the Doug Nash 4+3 transmissions for each production year:
http://www.5speeds.com/43table.htm
I've owned a 1985 and now own a 1988 and they do behave differently. This chart put my mind at ease.
http://www.5speeds.com/43table.htm
I've owned a 1985 and now own a 1988 and they do behave differently. This chart put my mind at ease.
