How do you determine the tooth count when the gears have turned to dust.

I've yet to find that info.

If you have the device and one gear, you can find it from GEAR RADIUS 1 plus GEAR RADIUS 2 = SHAFT SPACING, or MISSING GEAR RADIUS = SHAFT SPACING minus KNOWN GEAR RADIUS. If you have neither gear, you are shunted onto the "trail of tears" siding.

Note that the outside diameter of a spur gear is LARGER than the pitch (the actual spot of true contact) diameter, or the pitch diameter is smaller than the measured outside diameter. Just to keep things interesting. The pitch diameter is what is used to order/specify the gear, NOT the outside diameter. Or instead of pitch diameter, you can specify it as module (spacing, or pitch) and number of teeth. Same-same.

For very small gears (with few teeth), it helps us that the variance from one tooth causes a perceptible change in the gear size. Such as, from 9, to 10, to 11 teeth makes a visible error. If it was, say, 99-100-101, you would be hating life to try to guesstimate that dude.

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k

Odometer Gears - Mercedes-Benz - 126 Chassis 79-91 Diesel

If you read, you will discover that thare are two types of the bigger gears. The gear on the motor, is always 12 tooth, no mater what. Upon dissassembly of my odometer, the larger two gears were largely intact, just missing a tooth or two each. I was able to determine how many teeth they should have had quite easily. I was then able to measure their diameters, widths, bores, etc. and order the correct ones. However I had to guess on the motor gear, and I was wrong.

But Boisebenz is also correct. There are formulas for spur gears, I just tried using logic I'd learned during some projects in my younger years.

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1984 300sd auto with 246,000 miles

I was wondering what the E3 tooth count would be for the 3.07 vs 2.88 diff W126s.

just nice to have the parts in hand before pulling the cluster.

On other cars I've messed with (70-83 Datsun Z(X) is example) the speedometer drive is mechanical and the required speedo drive gear is determined by the differential gearing. The Datsun drive gear is located in the trans.

Where is the pick up for these cars? It may be that the speedo is the same and rear end ratio is compensated some place else.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Hi

I just did a tooth count on a 88 560SEL speedo:
Black gears 48/12 and 44/34
Clear gear 48/16
White gear 26

And then on a 300SD unknown year.
It 's the speedo that reads up to 85 Mph:
Black gears 48/12 and 48/36
Clear gear 48/12
White gear 24

I need a set of gears for a 82 300SD (Speedo reads up to 120 Mph)
Don't know the tooth count yet, but if you guys do a group buy please let me know.

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76 240 D. Bought in 1998 for $25.
85 300D. Got it for free with a bad engine. ( Sold )
60 Unimog 404. What was left of it, was given to me. Now powerd by 617A.
88 560 SEL. Bought without engine and trans. Now powerd by 617A.
67 250 SE. Cuope. For resto or sale.
64 220SE. For resto.

Hello,

On my 84 300sd with the highest written number on the spedometer being 120 (125 indicated by the line count), I had a 12 tooth motor gear, and 12/48 for the two gears right after it. I know there may be other factors like gear ratios, manual / auto, etc. but that's what worked for me on my automatic.

I would organize a group buy if anyone was interested, it should save them lots of $$ on shipping, but I'm not sure the places I've found have a gear for every mercedes spedometer, I'll have to take a look and see if they have ones with all the different teeth counts.

Just ordered motor gears, can post up a how to when I'm finished

Cheers,
Mike

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1984 300sd auto with 246,000 miles