1985 4+3 overdrive problem
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 28
Likes: 0
From: Lawton Oklahoma
1985 4+3 overdrive problem
Hello,
I am a newbie to the Corvette. Saturday I bought a 1985. During the testdrive everything worked fine, including the overdrive. During the 250 mile ride home, all of a sudden the overdrive would not shift into gear. In order to make sure I didn't do any further damage, I turned off the overdrive and still managed to average 18 MPG (shock me). I want to check the fluid in the overdrive, but I don't know the procedure or locations of the plugs. Any other ideas would be greatly appreciated. I love the car, just want to get this fixed.
suks2bu37
I am a newbie to the Corvette. Saturday I bought a 1985. During the testdrive everything worked fine, including the overdrive. During the 250 mile ride home, all of a sudden the overdrive would not shift into gear. In order to make sure I didn't do any further damage, I turned off the overdrive and still managed to average 18 MPG (shock me). I want to check the fluid in the overdrive, but I don't know the procedure or locations of the plugs. Any other ideas would be greatly appreciated. I love the car, just want to get this fixed.
suks2bu37
Last edited by suks2bu37; Dec 6, 2007 at 09:57 AM. Reason: misspelling
Slingshot
Joined: Dec 2001
Posts: 3,817
Likes: 24
From: Charlotte NC
Check OD switch
Frequently, this problem is a faulty OD switch. If after checking to make sure that all your wiring is snug and secure and ground wires are in good shape, consider changing out the OD switch. The attached WORD file will give you all you need to change our this switch.
Good luck
Good luck
Last edited by pmihaltian; Nov 26, 2007 at 09:26 AM. Reason: clarity
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 28
Likes: 0
From: Lawton Oklahoma
1985 4+3 overdrive problem
The old girl ran at a constant 175-185. The last time it went into overdrive, it took three or four times of pushing in the clutch to get it to engage. I am excellent turning wrenches, just need some guidance.
Suks2bu37
Suks2bu37
Pro
Joined: Sep 2006
Posts: 702
Likes: 2
From: Conyers Ga
You can't really "check" the fluid level. Best place to start is drop the pan and replace the filter. Most people overlook 4+3 maintenance. While the pan is off you can check the pressure switch for damaged wiring and also the solenoid. And whatever you do do NOT use the gasket that comes with the kit or you're begging for a leak. Use black RTV. Once you know that's been taken care of you can start diagnosing the switch. Just remember speed and temperature are important in what controls the OD.
I'm not sue about the 85 but doesn't the dash have an OD light to tell you when it's engaged? If the light is lit yet the unit not engaged then that'll help with the diagnosis also.
I'm not sue about the 85 but doesn't the dash have an OD light to tell you when it's engaged? If the light is lit yet the unit not engaged then that'll help with the diagnosis also.
Last edited by Yellow2015; Nov 26, 2007 at 04:46 PM.
Intermediate
Joined: Nov 2004
Posts: 40
Likes: 2
From: Mt Vernon IL
If you expect to spend money, why not spend it on some small things first? The OD relay switch costs about $16, while the OD switch itself may be 8-10 times more expensive than that, and the relay is much easier to install, too.
Possibly the act of unplugging and replugging the relay might fix a bad connection (even cheaper).
Possibly the act of unplugging and replugging the relay might fix a bad connection (even cheaper).
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 28
Likes: 0
From: Lawton Oklahoma
The OD light does come on in the dash. Tommorrow I will put it on stands and drop the pan. Now that I think of it, it was pouring down rain when the OD quit. Could be a electrical problem.
suks2bu37
suks2bu37
Pro
Joined: Sep 2006
Posts: 702
Likes: 2
From: Conyers Ga
Then the switch sounds as if it's ok. Once you drop the pan, change the filter, (don't lose the magnet inside) then you might want to check the OD relay. This is where an FSM book pays for itself. Mine is for an 88 so I don't think it would be much help here.
FYI: I just had my OD completely rebuilt along with a new clutch. $2600.00...........so check the small stuff first.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Drifting
Joined: Feb 2003
Posts: 1,978
Likes: 2
From: San Antonio Texas
Relay is always the first place I look. I've replaced the switch once. The OD is full when fluid runs out the plug hole. Some fill, then rotate the rear wheels a few times, and top it off. Do a search on the fluid change.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
If the dash light comes on when you hit the switch, your switch and relay and ECM and sensors are perfectly fine.
You need to check the wire and connection on the left side of the overdrive casing (it should be getting 12 volts), and check the fluid level inside the trans (spin the rear wheels in neutral when topping it off). Those are the two most likely causes. If this doesn't fix it you'll need to pull the overdrive pan to get to the rest of the parts.
You need to check the wire and connection on the left side of the overdrive casing (it should be getting 12 volts), and check the fluid level inside the trans (spin the rear wheels in neutral when topping it off). Those are the two most likely causes. If this doesn't fix it you'll need to pull the overdrive pan to get to the rest of the parts.
Pro
Joined: Dec 2002
Posts: 522
Likes: 3
From: Rolling Meadows IL
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 28
Likes: 0
From: Lawton Oklahoma
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The counterboy shouldn't have to know or be concerned what material the filter is, the FMX filters are all the same. That trans was used on late-60's to early 70's Ranchero's, Merc Montegos and Cougars, and some F-150's.
When you replace the filter, you will have to re-use the rubber grommet that is on the old filter. Get two quarts of Dexron III ATF (not synthetic) for refill. Make sure the pan rails are clean and straight. Don't tighten the bolts too tight; the book calls for 11-ft lbs. Use a good RTV sealant like "The Right Stuff" or go to a Dodge dealership and get a tube of their MoPar RTV Sealant.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
No, there are mesh filters and paper/felt FMX filters. Get the brass mesh one, this is what came from the factory. I think I got my last one from Napa. It came with a pan gasket that you throw away.
I tried that Mopar transaxle sealant and wasn't impressed by it. I'd stick with The Right Stuff.
I tried that Mopar transaxle sealant and wasn't impressed by it. I'd stick with The Right Stuff.
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 28
Likes: 0
From: Lawton Oklahoma
Ok, dropped the pan on the overdrive. OMG. Only got about 3/4 of a quart of some type of liquid out of the overdrive. The stuff was a chrcoal color with metal glitter in it. When I cleaned the pan, I found large chunks of thin metal. Since I am not a transmission man, I can only describe it as being similar to the metal plates in between the clutch discs on a motorcycle clutch. I have posted pictures here:
http://usera.imagecave.com/suks2bu37/IM003516.JPG
I have looked at the overdrive rebuild kits from several manufacturers and none contain any of the metal parts. I filled the fluid and changed the filter(since I already had it) and the car still drives perfectly, except no overdrive. Any ideas?
I was thinking of finding another overdrive unit and scavenge both to put together one decent (functioning) one. I have a friend that builds trannys and he will help me out and build it for beer.
suks2bu37
http://usera.imagecave.com/suks2bu37/IM003516.JPG
I have looked at the overdrive rebuild kits from several manufacturers and none contain any of the metal parts. I filled the fluid and changed the filter(since I already had it) and the car still drives perfectly, except no overdrive. Any ideas?
I was thinking of finding another overdrive unit and scavenge both to put together one decent (functioning) one. I have a friend that builds trannys and he will help me out and build it for beer.
suks2bu37
Last edited by suks2bu37; Dec 6, 2007 at 10:11 AM.