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Debunking the trip odometer reset myth once and for all.

I saw this enduring forum myth mentioned yet again the other day.

Pressing the trip odo reset button while moving does NOT break the odometer!


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Last edited by sugarwood; 11-26-2016 at 02:42 PM..
Old 11-26-2016, 01:05 PM
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Not a Myth

Hi , yes if your speedometer`s plastic gears are not old and soft like mine were, it will not break the speedometer, BUT if your plastic gears or drive cogs are soft and weak from nearly 47 years of use then your in for trouble. My odometer reset drive gear just sheared off as I pressed the reset after refueling and while moving along at just 20 KPH. Be careful as age takes a toll on these gears and yours maybe just around the corner of failing ,depending on how old and how much work they have done. Also forgot to mention was the type of grease used on these plastic gears when assembled definitely weakened the integrity of the material used to manufacture them over the years ,new replaceable plastic gears sold over here in Oz need no grease upon reinstalling . Just my own experience with the failure and repair of my own speedo .
Cheers Brett L
Old 11-26-2016, 01:45 PM
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If there was a mechanism that breaks the gears while moving, it would break them regardless of age.

The most obvious explanation is that your gears were going to break anyway.
You just happened to be moving at the time.

It is called a coincidence or post hoc fallacy.

It's like if someone dies while wearing a yellow shirt
and the rest of the family is convinced wearing a yellow shirt is what killed him,
so no one wears yellow shirts anymore.
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Last edited by sugarwood; 11-26-2016 at 02:43 PM..
Old 11-26-2016, 02:25 PM
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They usually turn on their shaft rather than break, and become out of mesh with the other gear. The grease used originally softened the plastic after many years.
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Old 11-26-2016, 02:58 PM
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Sugarwood,

Sorry to disagree, but the gears become weak because of the absorption of the original lubricant used by the factory. When you disassemble the unit, it is obvious. The other "white" gears are still strong. The "yellowed" gear just breaks apart at the slightest touch. Pressing the reset while moving meshes the two gears together causing the weak teeth to break.

However, if you have the ability to change the spark plugs on your 911, then you have the ability to replace the odometer gear. Only $25 from our host and about 2 to 3 hours from start to finish.

See previous posts for my photos and additional details: ?s re odometer repair on 86 Carrera.

Last edited by RAW911; 11-26-2016 at 03:07 PM..
Old 11-26-2016, 03:03 PM
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Our water cooled VW's also did this. Quiet common

I'll still wait to push my reset until stopped.
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Old 11-26-2016, 05:54 PM
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Happened to me.
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Old 11-26-2016, 06:07 PM
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Is bunk the opposite of debunk?
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Old 11-26-2016, 06:52 PM
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No more yellow shirts for me I suppose.......
Old 11-26-2016, 07:26 PM
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Step back Sugar...happened to me twice...

MattR
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Old 11-26-2016, 07:31 PM
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Quote:
Originally Posted by pmax View Post
As the saying goes, your mileage may vary.

Sorry, couldn't resist.
Get back in the drawer dull knife....


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Old 11-26-2016, 07:42 PM
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Yellow Shirt

Every July in France the yellow shirt is a winner.Orange not so good.
Old 11-26-2016, 08:05 PM
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Quote:
Originally Posted by RAW911 View Post
Sugarwood,

Sorry to disagree, but the gears become weak because of the absorption of the original lubricant used by the factory. When you disassemble the unit, it is obvious. The other "white" gears are still strong. The "yellowed" gear just breaks apart at the slightest touch. Pressing the reset while moving meshes the two gears together causing the weak teeth to break.

However, if you have the ability to change the spark plugs on your 911, then you have the ability to replace the odometer gear. Only $25 from our host and about 2 to 3 hours from start to finish.

See previous posts for my photos and additional details: ?s re odometer repair on 86 Carrera.


Sugarwood,

If you have not rebuilt an odometer, try a few and examine the plastic gears. Due to age and brittleness of the odometer gears, resetting the odometer while in motion adds stress in gear meshing and prematurely breaks the old and brittle gears. This is only a myth for the uninformed.

Tony
Old 11-26-2016, 09:28 PM
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Maybe it's better to state that it increases the likeliehood of the breakage ocurring.

JR
Old 11-27-2016, 05:49 AM
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Can we all agree that with a brittle gear you'll eventually experience a failure?

And though I admittedly have never rebuilt an odometer so I am not an expert, I'm guessing that the gears of the odometer aren't spinning at a rate so high that the nylon gears would be forced together in a catastrophic manner. You push the reset and the gears are 'disengaged' and it's on releasing the reset stick that the gears reengage, yes?

So that means failure would be expected on releasing the reset, thus reengaging the gears. It seems to me that the spring tension mechanism coaxing the gears back together after reset wouldn't be high enough to jam the gears back together.

But again, I'm no expert...
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Old 11-27-2016, 06:02 AM
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Wayne, you may enjoy this clever variation on that trick
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Old 11-27-2016, 08:00 AM
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Sugarless

I think this myth has lost it`s sweetness What size Tee shirt and I will send a yellow one for Xmas mate.
Old 11-27-2016, 04:14 PM
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Moving or stopped? Don't press the reset button... ever!

After breaking the gear in the first 50k miles of ownership, I never touched the reset button ever again, no problems since.



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Old 11-28-2016, 05:56 AM
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Dunno. I reset mine while moving and it died. May have been coincidence, but I no longer reset unless stopped.
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Old 11-28-2016, 06:18 AM
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Gotta fix mine. I guess it has to come out to figure out exactly which gear to use.


Old 11-28-2016, 06:25 AM
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