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Topic: Over drive on automatic

in Forum: C4 Driveline Components


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Over drive on automatic (1/5)
 2/28/17 4:21pm
aldocar
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Joined: 12/3/2016
Posts: 92

Just went for my first ride of the season its been nice and all the snow for now is gone. Is the overdrive meant to be used on the turnpike?  The reason I ask there is slight vibration when accelerating but if I use the d1 there is no vibration at all.   I just purchased the car in late November it runs great except for the slight vibration in overdrive. I use d1 driving around town.    Take care.

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Re: Over drive on automatic (2/5)
 3/4/17 9:46am
Adams' Apple
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Duncanville, TX - USA

Vette(s):
1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.


Joined: 3/18/2009
Posts: 2201

O/D can be used anytime....the system is designed to "know" what gear is appropriate for the situation.
If you feel a "vibration" on acceleration in O/D, most likely what you are feeling is a torque converter "shudder", OR an engine misfire. My suggestion would be to have someone do a diagnostic scan to see if there are any engine related codes set, and go from there.


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Re: Over drive on automatic (3/5)
 3/6/17 3:43pm
aldocar
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Thank you for your input I will take your advice.

Al


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Re: Over drive on automatic (4/5)
 3/11/17 12:34pm
wolfuser
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1987 C4 convertible 350ci auto white / red / white top appx 18k mls


Joined: 11/15/2012
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Hi,

if you go to "overdrive", 2 things happen. first, the torque converter lockup clutch is activated and will provide a direct drive thru the converter, eliminating slip. this is noticeble as rpm comes down when the clutch engages. however, locking the torque converter removes vibration damping from the drive train, so that a slight resonance is encountered at appx 1100-1200rpm when accelerating on a light throttle. as soon as the throttle is opened a bit more, the lockup clutch disengages, rpms rise as the torque converter permits "slip".
and the 2nd thing.... only in OD is the 4th gear available. thats why a little reminder lights up in the road speed readout should one forget to change from D to OD and tries to go faster.

D is fine for city driving or winding roads where one might encounter that 1100rpm period more often. 

cheers
Wolfram
Re: Over drive on automatic (5/5)
 3/12/17 2:37pm
aldocar
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Joined: 12/3/2016
Posts: 92

Thank you I must be senile but it makes that noise at around 40 at 1100rpm not at start up and when I give it gas it stops this is all in OD.  I took it out a few days ago as the weather was nice and it drove fine in OD it seems to like a heavier throttle at lower speeds.  We are expecting some bad weather so car is back in hibernation.  I have not driven it much as I bought the car in November.  I did not see any light in D I must have been below the limit. Thank you.  The car idles fine and has no skips I think I was to light on the gas in OD.  I do love the feel of the car it makes me smile a lot. Take care Al.

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