Hi, so i've got the four speed manual and my overdrive doesn't seem to be working that well. I've made two long trips with the car and the overdrive didn't turn on for me almost at all, maybe a total of five minutes in 18 hours of driving. But when i was at work and drove around a bit it worked fine for awhile. I recently did the ecu bypass trick and now it doesn't turn on at all. I checked voltage at the switch and it does work.

Any ideas what my problem might be or what i should check for issues? thank you

 

What year is it? There are differences in the 1084-1985 (use a cable), then 1986-88(no cable).

If it's '86 -88 I would take a fused 12v wire from ignition, and test the unit directly to the o/d unit. If it still doesn't work, you have a bad o/d unit. I'm not sure of what the cable does on the earlier model year units.

If it does work, i'd be checking the mod you did very carefully.

 

well actually it's an 85 chassis with 93 body panels and engine. So i'm not too sure what the o/d setup is, but it does have the 85 switch, if i'm correct the switches past 85 are buttons or something and will not stay flicked on or off right?

Do you know where the o/d unit is itself? I can take a look at it if i can find it. I was going to get a manual but none of the auto stores in town have any.

 

Has the fluid and filter in in O/d ever been changed?
Should be done every 12K
Is O/d fluid level correct?

 

actually i don't even know where to check the fluid, this car is so different than everything i've worked on or owned before. I just got the last week.

 

1. The overdrive is bolted to the back of the 4 speed.
2. The overdrive is controlled by the computer, but you can over ride it by putting a 12 volt wire on the little blade connector on the left side of the trans just above the overdrive oil pan.
3. nothing happens when you are sitting still. There is a pressure switch inside the overdrive that turns on the engage solenoid inside the trans. So don't get excited when you hear nothing.
4. make a wire about 10 feet long, and cut it in the middle. Then crimp on a connector that will fit on the blade connection on the trans and wire it to a switch that you happen to have laying around. on the other side of the switch, add the rest of the wire. put an alligator clip on the other end, and clip it to the battery positive. make sure the switch is OFF. Now get the car going about 30 miles an hour, put in the clutch, flip the switch, let out the clutch.
5. if the overdrive comes on, you have a wiring problem, if not, you have a trans problem.
6. do not use overdrive in first gear, it will burn up the overdrive, and rebuilt overdrives are about $1400.
It would be best to just turn it off, and go back to your garage before you get too brave here.
7. there is a first gear switch. if the first gear switch goes bad, your overdrive might never engage again. .....
8. to find out if first gear switch is good, shift the trans in to first. then ohm the switch. You should get no continuity.
8. switch the trans into second, then ohm the switch. it should read 0 ohms (full meter deflection) make sure you know which is first gear under the car. It is the rearward shift arm coming out of the trans in the forward position.
You might just have a switch on each gear position. any of those switches can go bad.

 

 

Thanks for all that advice. I wired up a switch to the solenoid and the overdrive works just fine in 2nd, 3rd, and 4th. And thanks vetteoz for the pic and diagram, i'm going to look into all the wiring and switches later this week when i get home. Oh yeah, and coupeguy, what is the purpose of putting in the clutch when turning the overdrive switch on? thanks

 

Check the O/d relay and it's connections 1st.

Pushing the clutch in on O/d operation takes the load off it and might increase it's life

 

Ok i'll do that. Is the relay under the hood? Any idea how to identify it? My fusebox isn't exactly under the hood and there seems to be a few random relays floating around

Ok, that totally makes since, thanks for the advice!

 

On firewall next to fuel pump relay.
Pull the wrong one and your engine won't run

 

 

ok awesome, thank you! I know where that one is at

 

Hello,

I realize this is an old post. I am hoping that someone can answer this. When I was under my 1984 4 plus 3 I repaired a BLACK wire. I put a new blade and connected it to the side of the left transmission just above the oil pan. I thought it was a ground. Is the black wire the wire that I am going to replace with a wire to the battery to test the OD? Thank you.

 

Pushing the clutch in every time you engage or disengage the overdrive will DEFINITELY increase the overdrive life span.

 

hello fourspeedvette,

The forum said that you posted a response to my question. But, I cannot find you on the thread. Do you know where your post went thank you, josephseremba@gmail.com

 

I don't know why it won't show up for you. Can you read the post that's two above this one? That was my response to your question.

 

Thank you. I know which wire it is.

 

OK. I'll try it again this way. Pushing the clutch in every time you engage or disengage the overdrive will DEFINITELY increase the overdrive life span.

 

Not hard to understand how it would make it last longer but at the same time I never bothered on my 86 and I drove it hard. Never had a problem with the overdrive in it and never used the clutch when engaging it. Also when you go to pass someone it downshifts on its own and your not "clutching" for that either which is 100 times more harsh than you engaging it while just cruising along with no real load on it. Again never had a problem. Hard to say if shorting the life of the main clutch is worth any savings on the life of the overdrive in the long run since the overdrive never went out.