Doug Nash Cooling
Thread Starter
Racer
Joined: Jul 2012
Posts: 262
Likes: 12
From: South Lyon, MI
Doug Nash Cooling
I'm not asking this question to be ignorant, but does the overdrive unit on the DN 4+3 NEED to have lines going to the radiator, or can it be bypassed to itself? I have not had any luck (yet) with the overdrive on mine functioning. I have the pan off of it to change the filter/fluid and things look great up in it, and at this point I'm cleaning up all of the electronics so the switch could be at fault for it not working, but I currently only care about the T10 gearbox. So, has anyone bypassed the radiator, not used it, and had any issues?
Instructor
Joined: Nov 2012
Posts: 120
Likes: 6
From: Phoenix AZ
As a former owner of an 84 Z51, I can say DO NOT bypass the trans cooler. I ran my auto dry when a line blew on a long road trip (in the rain). I knew the auto quit, but the heavy rain washed the fluid off the undercarraige and I couldn't figure out what was wacked. When the tranny shop looked at it, my guy said "good thing you didnt run it manual only, as the drag would have worn out your syncros in a month".
Your money, but I would fix it. FYI, when my OD wouldn't light up, it was a bad ground .....needed a new ECU.
Your money, but I would fix it. FYI, when my OD wouldn't light up, it was a bad ground .....needed a new ECU.
Thread Starter
Racer
Joined: Jul 2012
Posts: 262
Likes: 12
From: South Lyon, MI
Yea, I plan to keep fluid in it. I was just curious as to whether the unit itself would have overheating problems when not in use and if that could effect just driving the car. What I'm getting from your reply is you had an incident running it without fluid yes?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I can't imagine why you'd need a cooler; you're not running a tq converter . There would be some heat generated with a relief valve, but man...can't see it being that bad.
But to answer your question, I have not tried one w/o a cooler, so can't say for sure.
But to answer your question, I have not tried one w/o a cooler, so can't say for sure.
Instructor
Joined: Nov 2012
Posts: 120
Likes: 6
From: Phoenix AZ
My tranny guy said that I couldn't run it for long in "coast" mode as it would were out the 4 speed. Others can validate if thats the truth or not. Is it not working?
Thread Starter
Racer
Joined: Jul 2012
Posts: 262
Likes: 12
From: South Lyon, MI
Well, currently everything isn't working, but that's because I've been chasing an electrical short which has turned into a mild restoration... 
However, when I bought the car almost a year ago to date, when I was driving it the overdrive wouldn't engage, even when I pushed the switch on the console. I don't intend to drive with it engaged honestly. I just like the 4-speed and i'm not necessarily aiming for mpg's with this ride
However, when I bought the car almost a year ago to date, when I was driving it the overdrive wouldn't engage, even when I pushed the switch on the console. I don't intend to drive with it engaged honestly. I just like the 4-speed and i'm not necessarily aiming for mpg's with this ride
Thread Starter
Racer
Joined: Jul 2012
Posts: 262
Likes: 12
From: South Lyon, MI
Tom, your point makes sense. To me all the fluid does is lubricate and engage/disengage the parts. I don't think things would get hot with it disengaged and spinning, but, I don't know enough about these units. I know enough to realize the common failure parts but that's it
Instructor
Joined: Nov 2012
Posts: 120
Likes: 6
From: Phoenix AZ
Well, currently everything isn't working, but that's because I've been chasing an electrical short which has turned into a mild restoration... However, when I bought the car almost a year ago to date, when I was driving it the overdrive wouldn't engage, even when I pushed the switch on the console. I don't intend to drive with it engaged honestly. I just like the 4-speed and i'm not necessarily aiming for mpg's with this ride
However, when I bought the car almost a year ago to date, when I was driving it the overdrive wouldn't engage, even when I pushed the switch on the console. I don't intend to drive with it engaged honestly. I just like the 4-speed and i'm not necessarily aiming for mpg's with this rideCorvette Stories
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Drifting
Joined: Jun 2009
Posts: 1,286
Likes: 447
From: Upstate NY
I'm not asking this question to be ignorant, but does the overdrive unit on the DN 4+3 NEED to have lines going to the radiator, or can it be bypassed to itself? I have not had any luck (yet) with the overdrive on mine functioning. I have the pan off of it to change the filter/fluid and things look great up in it, and at this point I'm cleaning up all of the electronics so the switch could be at fault for it not working, but I currently only care about the T10 gearbox. So, has anyone bypassed the radiator, not used it, and had any issues?
Just wanted to be sure that you had this info also, because when I bought mine, it had a 160f thermostat and if it was cool at all, the temperature would not get high enough.
Thread Starter
Racer
Joined: Jul 2012
Posts: 262
Likes: 12
From: South Lyon, MI
Gotcha. I didn't know that part of it, but i've had it up to temp plenty of times and nothing. Like I said though, I'm not too concerned with it working and using it, more of will it be alright to just run the cooling lines to themselves instead of to the radiator and back. When I swapped engines over the summer I cut the pre-bent lines pulling the engine and trans and was going to build my own back to the radiator, but it doesn't seem that there is really a need for it, considering I don't plan to use it. I could be wrong though, that's why I decided to ask here, haha 
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Reverse gear uses the direct clutch plates and packs in the OD unit. If they get too hot, you will most likely lose reverse. Also fluid pressures in the OD when it's working can hit up to 125psi. Fluid can get hot real quick at those pressures with no cooling.
As far as coolant temp levels that allow the OD to work, it's far different between the 84 and the 86-88 units. For the later cars, coolant temps only need to be around 122 degrees to allow the OD to work.
It really doesn't hurt anything to keep the coolant lines in place. Replacement steel lines can be fabricated easy enough, both for the proper bends and the flares and nuts. Just make sure you use the right type of steel tube that will handle the fluid pressures.
With the pan off, you can see the pressure switch and the OD solenoid. It's possible that either of these parts can be bad. The FSM has diagnostic procedures for testing the OD components, both electrical and mechanical.
As far as coolant temp levels that allow the OD to work, it's far different between the 84 and the 86-88 units. For the later cars, coolant temps only need to be around 122 degrees to allow the OD to work.
It really doesn't hurt anything to keep the coolant lines in place. Replacement steel lines can be fabricated easy enough, both for the proper bends and the flares and nuts. Just make sure you use the right type of steel tube that will handle the fluid pressures.
With the pan off, you can see the pressure switch and the OD solenoid. It's possible that either of these parts can be bad. The FSM has diagnostic procedures for testing the OD components, both electrical and mechanical.
Instructor
Joined: Nov 2012
Posts: 120
Likes: 6
From: Phoenix AZ
Reverse gear uses the direct clutch plates and packs in the OD unit. If they get too hot, you will most likely lose reverse. Also fluid pressures in the OD when it's working can hit up to 125psi. Fluid can get hot real quick at those pressures with no cooling.
As far as coolant temp levels that allow the OD to work, it's far different between the 84 and the 86-88 units. For the later cars, coolant temps only need to be around 122 degrees to allow the OD to work.
It really doesn't hurt anything to keep the coolant lines in place. Replacement steel lines can be fabricated easy enough, both for the proper bends and the flares and nuts. Just make sure you use the right type of steel tube that will handle the fluid pressures.
With the pan off, you can see the pressure switch and the OD solenoid. It's possible that either of these parts can be bad. The FSM has diagnostic procedures for testing the OD components, both electrical and mechanical.
As far as coolant temp levels that allow the OD to work, it's far different between the 84 and the 86-88 units. For the later cars, coolant temps only need to be around 122 degrees to allow the OD to work.
It really doesn't hurt anything to keep the coolant lines in place. Replacement steel lines can be fabricated easy enough, both for the proper bends and the flares and nuts. Just make sure you use the right type of steel tube that will handle the fluid pressures.
With the pan off, you can see the pressure switch and the OD solenoid. It's possible that either of these parts can be bad. The FSM has diagnostic procedures for testing the OD components, both electrical and mechanical.