I am having a problem with my Doug Nash Overdrive. It will not engage. The switch turns on/off the light in the dash. The wiring seems OK. It worked in the past.

The fluid level is correct (new fluid)

I assume it could be the O/D is bad or a solenoid, or a sensor? Or....

How can I go about figuring out exactly what it is?

Also, if it is a mechanical issue and it requires a rebuilt - Would another transmission be a good idea? Tremco T5 or a 6 speed? I am not in love with Doug Nash's O/D - pain in the $&%^

 

Probly electrical. Not sure where the solenoid is but its probly at fault if your wiring is all intract. Hopefully someone with more knowledge will chime in.

 

Did it start failing when you changed the fluid?

Chuck

 

The solenoid may be bad but check the connector to make sure it's not corroded and that the wires are connected to the tabs in the connector.

First thing to check is the fluid level Did you put in about 2 quarts??
Does the speedometer work?
Check for a bad solenoid: Raise car so rear wheels are off ground. With engine at operating temp, shift from 1st to 2nd gear at 15MPH and check for 12v at the connector at the OD.

There is a low pressure switch in the valve body that could be bad. Remove the pan and it's on the passenger side of the valve body.

It's also possible that there is enough debris in the valve body that the solenoid is not working or the solenoid check ball is stuck. How long had it been since the last fluid change?

I have a 4+3 in my 87 and I like it. I usually turn the OD off with the switch and engage OD depending on speeds. The 4-speed part is the same as a Borg-Warner Super T-10 so it will handle decent power and abuse. The OD doesn't like to be abused.

Keisler has two versions of a 5-speed that are complete bolt-in replacements including shifters. The difference is in the amount of HP they will handle. But figure on $3000 or so for the trans and then install labor if you don't do it yourself. I think that Richmond Gear has a 6-speed made for C4's but this is also pricey. A ZF-6 from later C4's can be swapped in and others have done it. Do a search on something like "ZF6 conversion" or similar search terms.

The OD unit can be had for around $1200 as a reman unit.

 

I took it (working) to a shop for other work. The shop was extremely slooow and it sat for 5 months. The guy tells me it was leaking and low. He told me he drained it, refilled it. It now does not work. The car has about 200 miles more on it than when I dropped it off

I don't think I want to go back to that shop.

 

First thing to check is the fluid level Did you put in about 2 quarts?? Full up to the bolt

Does the speedometer work? Yes, as does the tack, the O/D light, and the O/D switch

I will check the electrical - Thanks

If I found a Camero or Firebird L98 with a T-5. What parts would I need in addition?? It seems like $3K for a kit is a little high.

Thanks

 

If the T-5 you found is from an early F-body (early 80's) they are a very weak tranny. Back then, those cars only had 150-190HP. Also IIRC, those T-5's bolted in at an angle; not upright like the 4+3 or ZF. This would require some fabrication to the tunnel and the shifter setup. The clutch hydraulics will most likely need some mods.

You would have to most likely change or mod the driveshaft. There will have to be a custom adapter for the C4 C-beam.

Do a search on something like "T-5 swap" I think this was discussed before and there should be threads about this type of swap.

To double-check on the OD unit, I would pull the pan and make sure the connector from the low pressure switch to the OD solenoid is in place. Did the shop that did the OD service replace the filter? He may have loosened the wire when he put the filter back in. Same with the cable on the outside of the OD.

The solenoid is inside the OD unit and if it needs cleaning/replacement, it's something that a good trans shop can do.

 

These posts do help. I am thinking it may be electrical or a loose wire or corrosion in the connectors - That would be a good thing and much cheaper to fix than a rebuilt O/D.

I am not sure the filter was replaced - but I guess it was not.

I think a good trans shop is in my future. If it is a minor component (solenoid or switch) it would be great. I also am unsure if I want a non-original transmission anyway. It would be good to get what I have to work

Thanks

 

I have a good o/d unit if you need one.

 

what is your contact info? I am f.murch@sbcglobal.net and I am in San Diego

Thanks

 

is your engine getting up to normal operating temp? i know the o/d unit will not engage in my 84 unless the engine is above 174 degrees. i'm not 100% sure what the coolant temp has to be, but i do know that GM did this for emissions reasons and accelerated engine warmup.

 

O/d light on indicates ECM is operating the O/d relay when you hit the switch.Need to check wiring
from relay to terminal on O/d case
There is a 1st gear switch ( open in 1st ) that can go bad on the circuit between relay
and pressure switch / solenoid
switch is on the trans side cover on 1/2 selector shaft

 

If you need any questions answered I found that SK Speed on the east coast is the expert so to say ask for Brian... They ship all over the country and seem to know what they are doing..

 

Do your diagnosis, and PM me if you need it. I live in Florida.