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Nash 4+3 Overdrive Problems

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Old 07-09-2018, 11:18 PM
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davidmcnutt
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Default Nash 4+3 Overdrive Problems

The overdrive on my 1985 C4 (manual transmission) has been giving me problems. It started misbehaving after I took a longer trip than just to and from work. The overdrive button would come on, but instead of shifting at around 50 mph, it starting shifting in the high 50's and low 60's. Now, when I press the overdrive switch, the overdrive will engage once around 63ish mph and stay engaged for about a minute, but then slip back out of overdrive. It will still kick into a lower gear if I put the throttle down, but it won't reengage into overdrive. The overdrive light comes on when I turn the switch on. I have already replaced the overdrive relay, and refreshed the fluid and filter on the overdrive unit, but that still hasn't fixed it. Any help here? Thank you!
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Old 07-11-2018, 11:38 AM
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84 4+3
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Not an expert by any means but it would sound like you may have a couple of issues. First the early ones have a kick down cable. Iirc if that goes out of adjustment it can cause weird issues. Second if you get it then drop out you're losing holding power. So there could be a pressure or clutch issue. How was the fluid whe you refreshed and what type did you use?
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Old 07-13-2018, 11:54 AM
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ihatebarkingdogs
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If the OD light is ON, it should be in Overdrive. If it is dropping, or slipping back into Direct, with the light remaining ON, or the light comes on but it does not upshift into Overdrive, There is a problem. Slipping OD clutch, or hanging thrust washer.

If the light is ON, it should be in Overdrive. Period.

The cable on a 84-85 is a Throttle Valve cable and is used to modulate the up-shift. It is not a "kick down" cable. Kick down is controlled by the ECM based on VSS and mostly TPS.
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Old 07-13-2018, 11:58 AM
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davidmcnutt
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Originally Posted by 84 4+3 View Post
Not an expert by any means but it would sound like you may have a couple of issues. First the early ones have a kick down cable. Iirc if that goes out of adjustment it can cause weird issues. Second if you get it then drop out you're losing holding power. So there could be a pressure or clutch issue. How was the fluid whe you refreshed and what type did you use?
The fluid was super black and dirty, and I refreshed it with non-synthetic transmission fluid
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Old 07-13-2018, 11:59 AM
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Originally Posted by ihatebarkingdogs View Post
If the OD light is ON, it should be in Overdrive. If it is dropping, or slipping back into Direct, with the light remaining ON, or the light comes on but it does not upshift into Overdrive, There is a problem. Slipping OD clutch, or hanging thrust washer.

If the light is ON, it should be in Overdrive. Period.

The cable on a 84-85 is a Throttle Valve cable and is used to modulate the up-shift. It is not a "kick down" cable. Kick down is controlled by the ECM based on VSS and mostly TPS.
Thanks for the insights! I'll check the light again.
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Old 07-13-2018, 09:30 PM
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ihatebarkingdogs
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Originally Posted by davidmcnutt View Post
The fluid was super black and dirty.
Super black indicates it may be slipping. If there were bronze flecks the size of coarse beach sand, that is the thrust washer. These two maladies go hand-in-hand. Hanging thrust washer causes the clutch to not fully apply, and it slips. There were a number of improvements to the overdrive unit about 2/3 of the way through the 85 model year which included the updated thrust washer and carrier bearing. My 85 is #26553, built in April 1985 and it did NOT have the improvements. If your car is earlier than mine, and the OD has never been worked on, it probably needs to be. Good luck.

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davidmcnutt (07-16-2018)
Old 07-14-2018, 01:04 AM
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84 4+3
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Originally Posted by ihatebarkingdogs View Post
If the OD light is ON, it should be in Overdrive. If it is dropping, or slipping back into Direct, with the light remaining ON, or the light comes on but it does not upshift into Overdrive, There is a problem. Slipping OD clutch, or hanging thrust washer.

If the light is ON, it should be in Overdrive. Period.

The cable on a 84-85 is a Throttle Valve cable and is used to modulate the up-shift. It is not a "kick down" cable. Kick down is controlled by the ECM based on VSS and mostly TPS.
I always think kick down for whatever reason. I don't know enough only because mine has been trouble free.

I do agree, burnt fluid means it is probably due for some work.
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Old 07-16-2018, 11:27 AM
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Thanks for the help, much appreciated!
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