4x3 overdrive woes.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
4x3 overdrive woes.
I got the overdrive button to work again. I was having problems getting the "overdrive" light to illuminate but that was another issue that is now solved.
So here is what I happened and what is currently happening
Going down the freeway, the OD kinda fell out and then back in then out again maybe three times and then it was done. I toggled the switch but the light wouldn't come back on.
Later I discovered that there were other electrical problems that had to do with the 10a fuse for the gauge panel being blown. This is what kept the OD light from coming back on. So Once the fuse was replaced the OD light started working again (After the car warmed up). This tells me that the switch is still good.
From what I have researched the next issue that needs to be checked is the Relay
What I need help with is.
A.) Where is the Relay bank
B.) How to identify the Relay within the bank.
C.) any advise you have for checking the fluid level way up under there.
I can order the relay from XYZ auto parts but I need to check and see if a bit of corrosion has gotten in between the contacts. If you guys have any other suggestions I would appreciate it.
So here is what I happened and what is currently happening
Going down the freeway, the OD kinda fell out and then back in then out again maybe three times and then it was done. I toggled the switch but the light wouldn't come back on.
Later I discovered that there were other electrical problems that had to do with the 10a fuse for the gauge panel being blown. This is what kept the OD light from coming back on. So Once the fuse was replaced the OD light started working again (After the car warmed up). This tells me that the switch is still good.
From what I have researched the next issue that needs to be checked is the Relay
What I need help with is.
A.) Where is the Relay bank
B.) How to identify the Relay within the bank.
C.) any advise you have for checking the fluid level way up under there.
I can order the relay from XYZ auto parts but I need to check and see if a bit of corrosion has gotten in between the contacts. If you guys have any other suggestions I would appreciate it.
Team Owner
Joined: Jan 2003
Posts: 20,318
Likes: 248
From: Summerland B.C. Canada
The OD relay is beside the brake booster. There are 2, the OD is the one closest to the motor, the other is fuel pump relay. You may have a short at the connector. The wires insulation may have shrunk back and now look like this. 
Here is some insight
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
http://members.shaw.ca/agent86/Overdrive-manual.pdf
Here is some insight
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
http://members.shaw.ca/agent86/Overdrive-manual.pdf
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
The OD relay is beside the brake booster. There are 2, the OD is the one closest to the motor, the other is fuel pump relay. You may have a short at the connector. The wires insulation may have shrunk back and now look like this.
Here is some insight
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
http://members.shaw.ca/agent86/Overdrive-manual.pdf
Here is some insight
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
http://members.shaw.ca/agent86/Overdrive-manual.pdf
Thank you so very much.
I'll give a report ASAP.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The dash light is powered by the same relay. Definitely check those connections, it could easily be shorting out.
Here's mine:
For a new one, head to the parts store and ask them for a fuel pump relay, it's the same p/n. In fact, you can test the relay by swapping the overdrive and fuel pump harness, the overdrive relay is in front, the fuel pump relay is behind it.
Here's mine:
For a new one, head to the parts store and ask them for a fuel pump relay, it's the same p/n. In fact, you can test the relay by swapping the overdrive and fuel pump harness, the overdrive relay is in front, the fuel pump relay is behind it.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
All that is good....No....Great info. Thank you all for helping out. This OD thing has been weighing heavy on my mind for about a month.
Fortunately, Its been real busy for me during the Holidays and I haven't had any time for the Vette....Driving or Wrenching
Fortunately, Its been real busy for me during the Holidays and I haven't had any time for the Vette....Driving or Wrenching
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Also, on this exact type of connector, I've seen where the pins on the harness can get spread out and not make good contact with the relay.
I depinned mine and slid some 1/4" shrink tubing over it. It's a little too big, but the best I could do without snipping wires.
You can also just buy a new harness connector. I believe the p/n is Dorman #85162.
Don't fret about the overdrive unless it quits working but the light is still on. Then worry.
I depinned mine and slid some 1/4" shrink tubing over it. It's a little too big, but the best I could do without snipping wires.
You can also just buy a new harness connector. I believe the p/n is Dorman #85162.
Don't fret about the overdrive unless it quits working but the light is still on. Then worry.
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Verdad Gallardo
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Joined: Apr 1999
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From: North Yorkshire, England
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John,
If the light is working you're beyond the Relay, the 1st Gear Switch and the OD Switch I'm afraid. All that's left now is wiring to solenoid, pressure switch in the OD or the solenoid. Check the fluid level as low fluid can cause the pressure switch to open.
If the light is working you're beyond the Relay, the 1st Gear Switch and the OD Switch I'm afraid. All that's left now is wiring to solenoid, pressure switch in the OD or the solenoid. Check the fluid level as low fluid can cause the pressure switch to open.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
If the gear switches were bad, the overdrive light wouldn't come on.
You can test the overdrive light by putting 12V to pinF on your diagnostic connector (top left). Make sure the shifter is not in first gear and the overdrive switch is on and car is parked.
Anyhow, if it kicks out of overdrive, but the light is still on, that means the computer is commanding overdrive, but the trans isn't doing it's job.
The most common and likely culprit is low fluid or a torn filter grommet allowing air to be sucked into the overdrive pump, which trips the pressure safety switch. It could also be a bad circuit between the dash switch and the transmission, most likely the connector at the trans is coming loose.
If it's none of that, it's either the pressure switch in the overdrive pan failing, or the solenoid failing, or the overdrive failing. One symptom of a dead overdrive is you lose reverse gear.
You can test the overdrive light by putting 12V to pinF on your diagnostic connector (top left). Make sure the shifter is not in first gear and the overdrive switch is on and car is parked.
Anyhow, if it kicks out of overdrive, but the light is still on, that means the computer is commanding overdrive, but the trans isn't doing it's job.
The most common and likely culprit is low fluid or a torn filter grommet allowing air to be sucked into the overdrive pump, which trips the pressure safety switch. It could also be a bad circuit between the dash switch and the transmission, most likely the connector at the trans is coming loose.
If it's none of that, it's either the pressure switch in the overdrive pan failing, or the solenoid failing, or the overdrive failing. One symptom of a dead overdrive is you lose reverse gear.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
this is all really really good.
Bad for me 'cause the OD is still out but the discussion is fantastic. Thank you guys for lending a hand....seriously. This thread is turning out to be a step by step Trouble shooting guide for ODs thanks to you.
The Reverse is working without a hesitation. It never changed in performance.
Low Oil is a probable culprit as the car sat idle for almost 10 years before I bought it. Not that it leaks or anything, but I am sure the system has not been checked by the previous owner. She kept every receipt for service in a folder and then she gave that too me when I bought it. Nothing in there about Tranny service at all.
Can anybody describe the tranny fill procedure? I know the oil fill is under the car.
What I mean is, When changing the motor oil for the first time. One CF member mentioned how easy it was and described just reaching under the car for the drain plug and filter. And Yes, it is just as easy as that. It takes mere minutes to change the oil in the baby's, you don't even have to jack it up.
Is there a procedure like that to check the Transmission fluid? Or do I need to jack it up.
Bad for me 'cause the OD is still out but the discussion is fantastic. Thank you guys for lending a hand....seriously. This thread is turning out to be a step by step Trouble shooting guide for ODs thanks to you.
The Reverse is working without a hesitation. It never changed in performance.
Low Oil is a probable culprit as the car sat idle for almost 10 years before I bought it. Not that it leaks or anything, but I am sure the system has not been checked by the previous owner. She kept every receipt for service in a folder and then she gave that too me when I bought it. Nothing in there about Tranny service at all.
Can anybody describe the tranny fill procedure? I know the oil fill is under the car.
What I mean is, When changing the motor oil for the first time. One CF member mentioned how easy it was and described just reaching under the car for the drain plug and filter. And Yes, it is just as easy as that. It takes mere minutes to change the oil in the baby's, you don't even have to jack it up.
Is there a procedure like that to check the Transmission fluid? Or do I need to jack it up.
Last edited by jhammons01; Jan 7, 2007 at 01:52 PM.
Le Mans Master
Joined: Nov 2001
Posts: 8,793
Likes: 1,938
From: LONG ISLAND
2025 C3 ('68-'73) of the Year Finalist - Unmodified
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4+3 = 7 
4x3= TRI POWER
4+3 TRANS = JUNK !!!
I HAD IT IN MY 84 NEVER EVER WORKED DEALER COUD'NT FIX IT TRADED CAR FOR NEW BENZ !!!
4x3= TRI POWER
4+3 TRANS = JUNK !!!
I HAD IT IN MY 84 NEVER EVER WORKED DEALER COUD'NT FIX IT TRADED CAR FOR NEW BENZ !!!
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The overdrive has no drain plug, just pull the pan to remove the old fluid.
Filters can be had at the local parts store, reuse your filter grommet if it is good.
http://forums.corvetteforum.com/show....php?t=1079461
Don't use a gasket to reinstall the pan, use TheRightStuff rtv instead. Be careful, as the ATF will drip onto the gasket surface as you are trying to put the RTV on.
Fill it with ATF until it comes out the fill plug. Some say you have to rotate the rear wheels while in neutral (to prime the system) while filling it to get all the specified fluid in. You'd need to get the rear on jackstands to do it. I haven't done that the last few times, because it seems like the cooler lines stay full of fluid during servicing.
Filters can be had at the local parts store, reuse your filter grommet if it is good.
http://forums.corvetteforum.com/show....php?t=1079461
Don't use a gasket to reinstall the pan, use TheRightStuff rtv instead. Be careful, as the ATF will drip onto the gasket surface as you are trying to put the RTV on.
Fill it with ATF until it comes out the fill plug. Some say you have to rotate the rear wheels while in neutral (to prime the system) while filling it to get all the specified fluid in. You'd need to get the rear on jackstands to do it. I haven't done that the last few times, because it seems like the cooler lines stay full of fluid during servicing.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
http://forums.corvetteforum.com/show....php?t=1079461
Fill it with ATF until it comes out the fill plug. Some say you have to rotate the rear wheels while in neutral (to prime the system) while filling it to get all the specified fluid in. You'd need to get the rear on jackstands to do it. I haven't done that the last few times, because it seems like the cooler lines stay full of fluid during servicing.
Fill it with ATF until it comes out the fill plug. Some say you have to rotate the rear wheels while in neutral (to prime the system) while filling it to get all the specified fluid in. You'd need to get the rear on jackstands to do it. I haven't done that the last few times, because it seems like the cooler lines stay full of fluid during servicing.
Now,can I just fill the resevior to see if the problem is low fluid or do I need to fully service it immediately?
I want to service it just not today. would that be ok?