1985 4+3 overdrive question

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May 9, 2006 | 10:33 AM

BillFla

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1985 4+3 overdrive question

I'm having problem with the overdrive on my 4+3 transmission. What happens is that I get up to highway speed, switch on the overdive and nothing happens for a couple of minutes (no overdrive light indicator either). Then after a couple of minutes, the overdrive kicks in an the overdrive light, on the display, lights up.
Can anyone shed some light on this for me.
Any help is appreciated.
Thanks,
Bill

May 9, 2006 | 12:35 PM

bills1985corvette

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From: Troy Illinois

I have read on this forum that this can be caused by the relay going bad. My 85 OD did this a couple of times so I got a new relay but by the time I received it I was no longer having the problem so I didn't install it. They don't cost much so I would give it a try.

May 9, 2006 | 02:56 PM

FlyboyZR1

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From: Minneapolis MN

What's your coolant temp when trying to engage OD? On my '86 it must be at least 120* to engage. If you get on the highway right after starting up a cold engine the OD might not engage right away.

May 9, 2006 | 04:00 PM

rubberman

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I agree with FlyboyZR1. The coolant temperature must be up before the overdrive works. That's the way it is on my '88.

May 9, 2006 | 04:13 PM

BillFla

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Thanks-
Come to think of it, the car really wasn't warmed up before I jumped on the highway and tried the overdrive.

May 9, 2006 | 06:00 PM

q2blaster@work

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From: Elgin Minnesota

4+3 temp

The 85 has to be 136 degrees fahrenheit before the overdrive will engage!

May 9, 2006 | 06:12 PM

scorp508

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From: Boston, MA

140* on an '85 for overdrive to engage I believe.

May 9, 2006 | 06:21 PM

CentralCoaster

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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed

Quote:

Originally Posted by scorp508

140* on an '85 for overdrive to engage I believe.

Also, the computer and the dashboard don't read coolant temperature from the same place. So you might see 144F on the dash before the overdrive comes on.

As long as the overdrive works whenever the overdrive comes on, its something simple.