I was just talking to a friend who called me from work and asked me to search the forum for him becuase his overdrive stopped working.
He said the car does not go into overdrive in any gear and the light does not come on.
He was hoping there was something he could do before the hour long drive home on the highway.
He is not at a computer so if anyone has any ideas of what he should check I will call him and pass the info along.
Is there a fuse, wire that often comes loose, or anything else that could be a simple fix?
Thanks in advance for Rick.

 

Hello Rick,

The most common causes for no OD operation are low ATF in the OD section, a bad OD relay, or a broken wire at the OD switch that is touching the other pole of the switch.

If you're uncertain about the last time the OD filter and fluid was changed I'd start there as it is good preventive maint. If the OD still does not work with the proper fluid level, swap the fuel pump relay with the OD relay. They are the same part and are right behind one another on the firewall next to the brake booster. If the car doesn't start then you can be pretty sure you have a bad relay which is one of the most common reasons for erratic or no OD operation. If the problem persists remove the shifter trim plate and boot and inspect the wiring of the OD switch. In 86 this was a momentary switch that simply tells the ECM OD on or off.

My father's 86 had a broken wire rendering the OD button useless. My 86 had two problems related to the OD. I found that my relay was bad, however after replacing it the OD went from intermittent to not working at all. Fortunately the problem was simple, the wiring on the OD switch broke and was touching the other side of the switch. This caused the OD to turn off and stay off each time I started the car. If the wiring is intact use an Ohm meter to measure continuity across the switch. When touching the meter probes across the outer poles of the switch (Ground and N/O or Normally Open) it should read open, you should read continuity when pressing the switch. Hopefully one of these will be the cause however it could also be the low pressure switch on the side of the OD or it's wiring.

Good luck,

Steve

 

Thanks Steve,
I will try to get this info to Rick at work.
Left him a message just now.
I hope he can figure this out before it's time to head home. He said the rpms are real high on the highway with no overdrive.
Jeff

 

Just got home. Man she sucked back ALOT of gas on the way home. I have never been passed so much in my life. A few years back I had a similar problem, and it turned out to be the switch. I dont think its the low ATF as I just changed the fluid and filter. The car is maintened.

I will check tomorrow the switch. This comes at a BAD TIME, as I have organized a dyno day on saturday(cdn events), and I want to dyno my car.

FTI. I have a chip in my car, It lets me manually override the OD unit etc....I guess I could put back in the stock chip, but I dont think it would work on the dyno if I can manually switch the OD ON and OFF!


Anyone else have this problem? OD wont work, and light wont come on. On the way to work everything was working A+ like normal and when I started the car up at work and merged onto the highway, I pushed in my clutch to engage 4th OD and nothing happened.

 

ttt!

 

if you just changed filter did you plug the wire back in?

 

I had the same problem about two months ago. It turned out to be a fuse believe it or not. I think it was the CTSY fuse. I would check that before getting too deep into it.

 

Check your gage fuse and wires at OD relay connector.
http://members.shaw.ca/agent86/Overdrive-manual.pdf

 

UPDATE:

Got up early this morning too try and fix this problem. Put the STOCK chip back in the car, and now its shifts into OD. Went for a spin and at WOT now it shifts into the 4 spd gears, and then back into the OD unit when you ease out of it. Car is driving just like it was 4 years ago when I bought it, but with the stock Chip. BUT, I cannot control whether I can manually command the OD just like the other chip I have and thats a **** off!

Thanks for the posts. I really want to get it to the dyno tomorrow. Want to get somewhat of a baseline before I start modding her.

 

Thanks, but PC wont allow me to open that. I will look at my book and check those things. First switch last for 16 years, and I changed the last one 2 years ago. I didnt think it was the switch but it very well might be. I love 4+3's .

 

thanks, but i doubt that is the problem.

 

Nonsense. You can do 150mph without a working overdrive. Ask me how I know.

The overdrive relay could also have failed.

 

not with a stock motor u cant!!! 4th gear at 5000 isnt even close to 150mph. maybe for your scorp since u can rev to 6000 or there about's. u must of been in 4th at 6000 at 150 then? cant be done with a stock motor dude.

btw, fixed the car. one of the wires just under the switch came loose.

thanks guys!

 

This is an easy fix! Look here www.keislerauto.com you'll be amazed at the overdrive and fuel mileage increases you'll get and it can handle it all!

Thanks,Matt

 

i get 28mpg, i doubt i will get alot better mileage. plus not made of $$$$, those arent cheap!

 

I was just thinking it is a nice replacement. But actually you'll get better gas mileage just because the final overdrive RPM's are a lot lower with the five speed as opposed to the 4+3(w/3.07's at 2200 rpm's and the 4+3 you'll be at 55mph and w/the 5 spd you'll be at 81 mph) so at about 70 mph in the 5 speed the rpm's would be lower thus giving you a better gas mileage for your Vette!

But I do agree w/you in today's times money is tight and it's not easy just to go out and buy something new! I too am on a budget and realize it's not easy! so I hope all goes well and it was only my opinion based on what others have done w/the 5 spd over the 4+3.

Thanks,Matt

 

This is a general statement, it all depends on your rear end gear ratio...

 

Stock gearing, just another 1000 useable RPM.

 

exactly. well i dont have another 1000 rpm's. a motor acts a little different when its reving at 2600 rpm's for 65 miles when there is only 2000 more usuable rpm's. ask me how i know.

 

An L98 will hum along at 2600 all day long without issue. Its just a little louder. I had to drive my car a week to work without O/D (550 highway miles at that time).