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Old 07-19-2018, 07:38 PM   #1
mj4276
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Question 26 tooth odometer gear in a 1986 240?

Hi all, I set out to fix the odometer in my '86 244 the other day. I took it all apart, found the broken gear, and counted 26 teeth. I counted again, 26. I counted eleven more times. 26.

I'm aware that all 240s from 1986-1990 are supposed to have 25 tooth gears. Ignoring this, I ordered a 26 tooth gear for a 1991-1993 240, and surprise! It is about half a millimeter bigger in diameter than the old gear.

Should I bother taking apart my dash to see if it fits? Should I just order a 25 tooth gear? Have any of you ever seen a 26 tooth in a pre '91 car? Do odometer gears shrink with time? Have I forgotten how to count?


Here is a picture of the two gears:
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Old 07-20-2018, 12:14 PM   #2
freevolvos
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i just took apart a 1986 dash.i will count the teeth when i get home
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Old 07-20-2018, 12:22 PM   #3
GeneralBurrito
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FCP has a 25 tooth gear for my 87 240. I've had it for a few months and it's perfect.

https://www.fcpeuro.com/products/vol...th-240-240gear
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Old 07-20-2018, 02:20 PM   #4
mj4276
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I went on and installed the gear anyways, and it seems to work. I drove around the block and the odometer was ticking up. I'm still not sure why there was a 26 tooth gear in an '86 though.
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Old 07-20-2018, 07:48 PM   #5
freevolvos
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counted both mine 25 86 and the 1990 has 25 ones a wagon the other a sedan
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Old 07-20-2018, 07:55 PM   #6
mj4276
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I went for a drive and compared the odometer reading to google earth. The odometer seems to be about a 4% fast. Considering that 26 is roughly 4% more than 25, I'm thinking that maybe 25 would have been the way to go. Although I still don't know why the original had 26.

eh, Ill worry about it the next time the odometer breaks
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Old 07-20-2018, 07:57 PM   #7
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Quote:
Originally Posted by mj4276 View Post
I went for a drive and compared the odometer reading to google earth. The odometer seems to be about a 4% fast. Considering that 26 is roughly 4% more than 25, I'm thinking that maybe 25 would have been the way to go. Although I still don't know why the original had 26.

eh, Ill worry about it the next time the odometer breaks
Apparently, the trip reset button is one of the main causes of breaking the teeth. I removed the entire button and my odo/trip have been working perfectly
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Old 07-20-2018, 10:04 PM   #8
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Doh! I just remembered that my tires are smaller than stock (aspect is 65 instead of 70). That would account for the difference in my test. All is good.


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Apparently, the trip reset button is one of the main causes of breaking the teeth. I removed the entire button and my odo/trip have been working perfectly
That's interesting, I guess I'll be more conservative with my button mashing there.
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Old 07-21-2018, 12:49 PM   #9
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Check with a mechanical engineer, but I don't think the tooth count on the planetary gear matters as long as it fits correctly. I think the reduction ratio is just (sun gear tooth count / ring gear tooth count).

Maybe a PO replaced the odo gear with the wrong one?
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