4+3 0verdrive ?
Thread Starter
Intermediate
Joined: Feb 2002
Posts: 42
Likes: 0
From: Woodbridge VA
4+3 0verdrive ?
I have an 88 coupe with a 4+3 OD, when I get to 70mph my car jumps in and out of OD. I have had the tranny serviced and no luck, I was told that I could have a bad Electronic Overdrive Switch. Could someone please tell me where to find this switch, and would I be able to fix this without dropping my tranny?
Thanks :mad
Thanks :mad
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Re: 4+3 0verdrive ? (JonM)
Can you manually select the overdrive using the button?
If so the switch is OK . The problem then might be in the ECM which controls the automatic engagement of the O/d depending on load , speed ,
throttle position.
If the switch is the problem , you can get a similar switch from a electronics store like Radio Shack an adapt it to fit. It needs to be a "momentary "contact switch as in it only makes contact when held down.
If so the switch is OK . The problem then might be in the ECM which controls the automatic engagement of the O/d depending on load , speed ,
throttle position.
If the switch is the problem , you can get a similar switch from a electronics store like Radio Shack an adapt it to fit. It needs to be a "momentary "contact switch as in it only makes contact when held down.
Burning Brakes
Joined: Jan 2001
Posts: 1,234
Likes: 175
From: IN
Re: 4+3 0verdrive ? (rodj)
Two things:
1) you can run a ground directly from the lead on the gear shift. If the switch is bad, this will still engage the O/D unit. You are basically just taking the switch out of the equation at this point. If it doesn't engage with the grounding, we go to number 2.
2) Change the fluid/filter. Not many people know(or knew) that the O/D unit has it's own fluid and filter, just like an automatic transmission. Many people would inspect the 4-speed part of the gearbox, but leave the O/D unit unchecked. Guess what?
The pan seal had a tendency to leak over time, the O/D unit would run dry and bam, no more O/D and expensive overhaul. The single best thing you can do for a 4+3 O/D trans is check/change that fluid/filter often. Now, if you've run the O/D unit dry, it could be rebuild time. Changing the fluid/filter may get you by for a while but it's probably worn out and will cause problems in the near future.
The people that had the problems with 4+3 ODs at 30, 40K miles had a failure due to the problem outlined above. As long as that unit has fluid it's going to be fine. I had a '84 4+3 for a brief period with 150K miles on it and the O/D had never been replaced, just maintained. Hope this helps!
1) you can run a ground directly from the lead on the gear shift. If the switch is bad, this will still engage the O/D unit. You are basically just taking the switch out of the equation at this point. If it doesn't engage with the grounding, we go to number 2.
2) Change the fluid/filter. Not many people know(or knew) that the O/D unit has it's own fluid and filter, just like an automatic transmission. Many people would inspect the 4-speed part of the gearbox, but leave the O/D unit unchecked. Guess what?
The pan seal had a tendency to leak over time, the O/D unit would run dry and bam, no more O/D and expensive overhaul. The single best thing you can do for a 4+3 O/D trans is check/change that fluid/filter often. Now, if you've run the O/D unit dry, it could be rebuild time. Changing the fluid/filter may get you by for a while but it's probably worn out and will cause problems in the near future.
The people that had the problems with 4+3 ODs at 30, 40K miles had a failure due to the problem outlined above. As long as that unit has fluid it's going to be fine. I had a '84 4+3 for a brief period with 150K miles on it and the O/D had never been replaced, just maintained. Hope this helps!
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
Re: 4+3 0verdrive ? (ZR WON)
More than likly it is either the OD switch or the OD relay. The switch is mounted on the stick, under the boot. The relay, not sure on an 88, should be mounted on the firewall.
If you have access to a scanner, you can see what the ECM is trying to do, (control the OD).
If you have access to a scanner, you can see what the ECM is trying to do, (control the OD).
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Re: 4+3 0verdrive ? (szukrider)
Basically when in a higher gear (2nd, 3rd, or 4th) the OD is controlled by the position of the TPS. OD will disengage when the throttle is opened past a certain point. Like an automatic kicking down to passing gear. Then re engage when the throttle is let up. Like an auto going back up to a higher gear. Sounds like maybe your TPS is out of adjustment. It is kicking down when it should not be. The TPS may have a dead spot in it or just need adjustment. Adjusting the TPS is cheap and easy. I would check that first before you start replacing any parts. The adjustment procedure is in the manual. if you cant find it repost. I can fax it to you if needed.
Race Director
Joined: Apr 2000
Posts: 11,259
Likes: 6
From: dfw TX
Moderatrix
Cruise-In IV Veteran
Re: 4+3 0verdrive ? (ZR WON)
2) Change the fluid/filter. Not many people know(or knew) that the O/D unit has it's own fluid and filter, just like an automatic transmission. Many people would inspect the 4-speed part of the gearbox, but leave the O/D unit unchecked. Guess what?
Brian you rock! Guys, Brian here is my own personal 4+3 tech support, HE is the one that told me to check my fluid 2 years ago when I first had problems with the 4+3. He knows his stuff :yesnod:
Thread Starter
Intermediate
Joined: Feb 2002
Posts: 42
Likes: 0
From: Woodbridge VA
Re: 4+3 0verdrive ? (ZR WON)
Thanks, I have checked the fluid levels and they are fine. as for the toggle switch It was working until I replaced my shift ****. However I was having the problem before then.
[Modified by szukrider, 4:20 AM 6/11/2002]
[Modified by szukrider, 4:20 AM 6/11/2002]
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