86 4+3 Speed Vette's Overdrives wont come on anymore. Any ideas as to where or what I should look into.

 

I had the same problem but had no one to ask. My symptom was no overdrive and no drag on trailing throttle. When I let off the gas it free-wheeled. This was caused by the gasket between theT-10 and the overdrive unit leting the two different lube oils mix. It was a $1300 meltdown for the overdirive only and I took it into the shop. Richmond Gear (not sure about the exact name) has/had a nifity replacement for not to much more than fixing the old unit. You can count on a substantial amount to bring the T-10 up to spec. So the total bill can easily top $2000.

On a positive note, the overdrive unit is working flawlessly. Removing the transmission is not just a job, it is an adventure! Not for the faint of hart.

 

If the overdrive unit is very low on transmission fluid, there's a lockout that won't let it engage. I'd recommend that you check the fluid level first.

Also, I've been told that if the O/D fluid is black in color, that's an indication that you have a leaking seal between the tranny and the O/D. (don't know if that's true or not)

 

I just recently had all the tranny fluid topped up so I know its not low on fluid.

 

is the light working on the dash???

 

I have this "thing" about folks who check my fluid levels. After having been burned once a long time ago, I started checking after them. And I've found on several occasions that I'm glad I did! If you can believe it, some folks actually tell untruths about checking those things!

(Sometimes they also top off fluids with the wrong type!)

 

No the Overdrive light isn't working.
Does it not only come on when your car is in one of the overdrive gears or should it be on all the time when the overdrive in engaged.

 

OK - let me set the record straight. I had overdrive failure. I have completely rebuilt my overdrive unit and have researched it. For more information please see 4 speeds.com.

1) the reverse housing gasket between the transmission and the reverse housing actually lets fluid past into the reverse housing cavity. If that gasket is bad you will not have a problem with the overdrive, nor will you have a problem if the gasket between the two units is bad. The fluid can mix if the overdrive input sun gear seal goes bad. That will cause problems.

2) Black fluid is not from gear oil and ATF mixing. It is from ground up metal. Black fluid in the overdrive is an indication that the planetary gear carrier bearing is going out. Check out 4 speeds.com.

3) If your overdrive unit has not been redone by someone that knows what they're doing - namely SK Speed, plan on your overdrive unit failing at some point. When I bought my car at 48,000 miles the fluid was black. It took about 30,000 miles for it to get bad enough for the overdrive to begin making noise. Bad deal. I spent over $900 just in transmission parts and did the work myself. That didn't include the clutch and a bunch of other stuff.

Hope this helps.

 

I typed the wrong address. Here's a link:
http://www.5speeds.com/dne.htm

 

I uploaded some info for you. Its right out of the bible
http://members.shaw.ca/agent86/Overdrive-manual.pdf

 

Thanks for all the info on the Overdrive question I posted, I found the problem, it was a defective Overdrive relay located on the firewall.

Problem is now solved

Thanks again

 

Nice work. That relay is a bugger. Take a 2nd look at the wiring and see if any of the wires are exposed. The insulation on that one tends to shrink over time.