Doug Nash 4+3 problem
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
Doug Nash 4+3 problem
Just got my 1988 on the road and never had a 4+3 before so I'm not sure how it's suppose to function.
The O.D. lite comes on and off when I toggle the button on the shifter and it seems to shift into a higher hear when toggled in 2nd and 3rd but for example on the freeway at about 65 if I engage the OD switch the light comes on but the only difference I notice is when I back off the throttle it coasts.
There is no difference in RPM's but if I slow down and disengage the OD switch it appears to downshift to a lower gear.
Also in 4th when engaged and I back off the throttle as I said it coasts then when throttle is applied it almost sounds as though its slipping until it fully engages.
Is this normal operation??
The O.D. lite comes on and off when I toggle the button on the shifter and it seems to shift into a higher hear when toggled in 2nd and 3rd but for example on the freeway at about 65 if I engage the OD switch the light comes on but the only difference I notice is when I back off the throttle it coasts.
There is no difference in RPM's but if I slow down and disengage the OD switch it appears to downshift to a lower gear.
Also in 4th when engaged and I back off the throttle as I said it coasts then when throttle is applied it almost sounds as though its slipping until it fully engages.
Is this normal operation??
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
No. Spend some time here, to start, then use the references to learn more.
http://www.5speeds.com/dne.htm
Typically, the light coming on tells you the electrical portion is okay, which is only partially good news. there's roughly a 30% reduction for O/D engaged.
http://www.5speeds.com/dne.htm
Typically, the light coming on tells you the electrical portion is okay, which is only partially good news. there's roughly a 30% reduction for O/D engaged.
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
4+3 problem
No. Spend some time here, to start, then use the references to learn more.
http://www.5speeds.com/dne.htm
Typically, the light coming on tells you the electrical portion is okay, which is only partially good news. there's roughly a 30% reduction for O/D engaged.
http://www.5speeds.com/dne.htm
Typically, the light coming on tells you the electrical portion is okay, which is only partially good news. there's roughly a 30% reduction for O/D engaged.
Just some additional info, the car only has 107K miles and was sitting in storage for some years.
What is the most likely problem in your opinion?
Thanks for the help. vette novice here!
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
One thing you should probably do very soon if you don't have any service history on the car is to change the fluid and filter in the OD unit. The OD unit uses regular DEXIII ATF and takes about 2-1/2 quarts.
The filter in the OD is the same filter used in some Ford FMX auto transmissions in late 60's to early '70's Cougars, Fairlanes, and even a few F-150's. Here's some part numbers:
CarQuest 85926
AC Delco TF184
FRAM FT1024
NAPA ATP14717
Ford D0AZ-7A098-A
Any of theses filters will be less that $10 so don't bother with the $30+ filter kits you see in the catalogs.
You will need to re-use the rubber grommet that will be on the old filter.
Make sure the pan rail is straight and both surfaces are clean, dry, and free of any old gasket material. I use a thin bead of Permatex RTV black sealant instead of a cork or rubber gasket. Clean the pan completely and remove the magnet, clean it an re-install in the same place. Make sure the pan bolts are tightened evenly but not very tight; just enough to get the RTV to squeeze out a little.
Yuo will need a hand pump to get new ATF into the unit. Add fluid until it starts to come out, then replace the plug. Turn a rear wheel for about a minute, then re-check the fluid level.
There has been lots of discussion about synthetic fluids for the OD and the 4-speed. The consensus a few years ago was to not use synthetics. Regular DexIII/Mercon fluid is widely available and cheap.
Also, you may want to drain and refill the 4-speed at the same time. For that trans (it's a Borg-Warner Super T-10) use a GL4 80W gear oil. That's a different fluid that what is used in the diff. The diff uses a GL5 75W-90 gear oil and a bottle of GM Positraction additive. Some gear oils have a friction modifier already addes, so if you use something like that, don't add the Posi additive.
The filter in the OD is the same filter used in some Ford FMX auto transmissions in late 60's to early '70's Cougars, Fairlanes, and even a few F-150's. Here's some part numbers:
CarQuest 85926
AC Delco TF184
FRAM FT1024
NAPA ATP14717
Ford D0AZ-7A098-A
Any of theses filters will be less that $10 so don't bother with the $30+ filter kits you see in the catalogs.
You will need to re-use the rubber grommet that will be on the old filter.
Make sure the pan rail is straight and both surfaces are clean, dry, and free of any old gasket material. I use a thin bead of Permatex RTV black sealant instead of a cork or rubber gasket. Clean the pan completely and remove the magnet, clean it an re-install in the same place. Make sure the pan bolts are tightened evenly but not very tight; just enough to get the RTV to squeeze out a little.
Yuo will need a hand pump to get new ATF into the unit. Add fluid until it starts to come out, then replace the plug. Turn a rear wheel for about a minute, then re-check the fluid level.
There has been lots of discussion about synthetic fluids for the OD and the 4-speed. The consensus a few years ago was to not use synthetics. Regular DexIII/Mercon fluid is widely available and cheap.
Also, you may want to drain and refill the 4-speed at the same time. For that trans (it's a Borg-Warner Super T-10) use a GL4 80W gear oil. That's a different fluid that what is used in the diff. The diff uses a GL5 75W-90 gear oil and a bottle of GM Positraction additive. Some gear oils have a friction modifier already addes, so if you use something like that, don't add the Posi additive.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The OD filter can be cleaned (it's all metal) but the typical price of one of the listed FMX filters should be under $10. I had always thought it was quicker to just get one from a parts store.
The various Corvette Accessory catalogs will advertise them for $30 and now probably more. They usually include a gasket and a replacement bushing but a good RTV sealant works much better than some cheap cork gasket. The bushing can be re-used.
In any event, the filter should be cleaned or replaced every year or every 12K miles.
The various Corvette Accessory catalogs will advertise them for $30 and now probably more. They usually include a gasket and a replacement bushing but a good RTV sealant works much better than some cheap cork gasket. The bushing can be re-used.
In any event, the filter should be cleaned or replaced every year or every 12K miles.
Instructor
Joined: Oct 2015
Posts: 134
Likes: 6
From: Osceola WI
If you have a scanner you might look at the MAP output. If the ECM sees low vaccuum it will kick out the OD if i remember correctly. Its like an auto kickdown if you floor it. Other vaccuum leaks will affect this as well.
Now, before i get flamed, not sure if the 88 has a MAP sensor but it should have something like that. The TPS may be included in the formula that the ECM uses, not sure.
Now, before i get flamed, not sure if the 88 has a MAP sensor but it should have something like that. The TPS may be included in the formula that the ECM uses, not sure.
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Advanced
Joined: Mar 2001
Posts: 89
Likes: 1
From: ca
I've only been driving my 4+3 for 20 years, but I thought I would add this for the OP who said he is new to the 4+3 and to you, hatebarkingdog, who mentioned using the OD button in your other thread.
I've been driving manual transmission cars almost exclusively since the early '60s. After buying my '87, it took me nearly a month to figure out how to drive and shift the 4+3 properly.
Make sure the trans is operating in OD and NEVER TOUCH THE OD BUTTON AGAIN. EVER.
Just simply drive the car like any other 4spd and let the ECM do the thinking as far as OD is concerned. You will appreciate the 4+3 much more if you let the Doug Nash part alone and let it do its job.
Example.
You want to pass a car so you stab the throttle and the trans goes from 4OD to 4D. That's not enough for you? Push the shift lever in 3rd, stab it and you're in 3D and moving.
Let up and it's in 3OD. Shift up and your already in 4OD. Play with that button and you'll make a mess of it.
Of course that is just my opinion, but I think it is a much better trans than people give it credit for. I think it got its bad reputation from people using that button, thinking they could out-think the ECM.
I've been driving manual transmission cars almost exclusively since the early '60s. After buying my '87, it took me nearly a month to figure out how to drive and shift the 4+3 properly.
Make sure the trans is operating in OD and NEVER TOUCH THE OD BUTTON AGAIN. EVER.
Just simply drive the car like any other 4spd and let the ECM do the thinking as far as OD is concerned. You will appreciate the 4+3 much more if you let the Doug Nash part alone and let it do its job.
Example.
You want to pass a car so you stab the throttle and the trans goes from 4OD to 4D. That's not enough for you? Push the shift lever in 3rd, stab it and you're in 3D and moving.
Let up and it's in 3OD. Shift up and your already in 4OD. Play with that button and you'll make a mess of it.
Of course that is just my opinion, but I think it is a much better trans than people give it credit for. I think it got its bad reputation from people using that button, thinking they could out-think the ECM.
Last edited by RichardJ; Mar 2, 2017 at 04:28 PM.
Oil Producer
Joined: Apr 2014
Posts: 9,364
Likes: 2,734
dogs, im new to the 4+3. can u elaborate on the bang shift at light throttle? i love the 4+3 and plan on keeping the car for a while and would like to make it last.
Intermediate
Joined: Jun 2016
Posts: 37
Likes: 5
From: Arizona
One thing you should probably do very soon if you don't have any service history on the car is to change the fluid and filter in the OD unit. The OD unit uses regular DEXIII ATF and takes about 2-1/2 quarts.
The filter in the OD is the same filter used in some Ford FMX auto transmissions in late 60's to early '70's Cougars, Fairlanes, and even a few F-150's. Here's some part numbers:
CarQuest 85926
AC Delco TF184
FRAM FT1024
NAPA ATP14717
Ford D0AZ-7A098-A
Any of theses filters will be less that $10 so don't bother with the $30+ filter kits you see in the catalogs.
You will need to re-use the rubber grommet that will be on the old filter.
Make sure the pan rail is straight and both surfaces are clean, dry, and free of any old gasket material. I use a thin bead of Permatex RTV black sealant instead of a cork or rubber gasket. Clean the pan completely and remove the magnet, clean it an re-install in the same place. Make sure the pan bolts are tightened evenly but not very tight; just enough to get the RTV to squeeze out a little.
Yuo will need a hand pump to get new ATF into the unit. Add fluid until it starts to come out, then replace the plug. Turn a rear wheel for about a minute, then re-check the fluid level.
There has been lots of discussion about synthetic fluids for the OD and the 4-speed. The consensus a few years ago was to not use synthetics. Regular DexIII/Mercon fluid is widely available and cheap.
Also, you may want to drain and refill the 4-speed at the same time. For that trans (it's a Borg-Warner Super T-10) use a GL4 80W gear oil. That's a different fluid that what is used in the diff. The diff uses a GL5 75W-90 gear oil and a bottle of GM Positraction additive. Some gear oils have a friction modifier already addes, so if you use something like that, don't add the Posi additive.
The filter in the OD is the same filter used in some Ford FMX auto transmissions in late 60's to early '70's Cougars, Fairlanes, and even a few F-150's. Here's some part numbers:
CarQuest 85926
AC Delco TF184
FRAM FT1024
NAPA ATP14717
Ford D0AZ-7A098-A
Any of theses filters will be less that $10 so don't bother with the $30+ filter kits you see in the catalogs.
You will need to re-use the rubber grommet that will be on the old filter.
Make sure the pan rail is straight and both surfaces are clean, dry, and free of any old gasket material. I use a thin bead of Permatex RTV black sealant instead of a cork or rubber gasket. Clean the pan completely and remove the magnet, clean it an re-install in the same place. Make sure the pan bolts are tightened evenly but not very tight; just enough to get the RTV to squeeze out a little.
Yuo will need a hand pump to get new ATF into the unit. Add fluid until it starts to come out, then replace the plug. Turn a rear wheel for about a minute, then re-check the fluid level.
There has been lots of discussion about synthetic fluids for the OD and the 4-speed. The consensus a few years ago was to not use synthetics. Regular DexIII/Mercon fluid is widely available and cheap.
Also, you may want to drain and refill the 4-speed at the same time. For that trans (it's a Borg-Warner Super T-10) use a GL4 80W gear oil. That's a different fluid that what is used in the diff. The diff uses a GL5 75W-90 gear oil and a bottle of GM Positraction additive. Some gear oils have a friction modifier already addes, so if you use something like that, don't add the Posi additive.