I had some spare odometers around and thought I'd see if I could get some working - I needed one, a friend needed one ... I ordered some new gears from eEuro.

One by one I took them apart, reflowed the 3 solder connections as indicated in one the post "Art Benstein on Fri Jul 2 09:12 EST 2010" and an earlier Art B post with pics. I blew the dust/pieces out with air and mechanically removed some bits with a small pick.

I ended up getting a few units to work. Test bench is running a car in gear on a lift.

These three stand out (dates on back of odo unit)

1. A 1989 odo would not work with a new gear but did work with an used gear.
2. A 1988 worked with an old gear and a new gear
3. A 1990 worked with a new gear but not an old gear.

By "gear" I mean the small 25-tooth inner gear. I had one new and several used outer gears and swapped them around above with no difference eg. (3) worked with a new 25-tooth gear in multiple large gears.

I infer gear & odometer manufacturing tolerances are at work here, however, I noted the following differences between the new and old gears.

Using a calipers, the center spindle of a new gear appeared slightly thicker and taller than some older gears. (You'll have to trust me on this - even on macro, my camera won't show the difference).

So, if a new replacement gear is slightly thicker, it's possible that it would bind inside some units. This doesn't explain (3) of course - and, yes, the used gear from (3) worked in another unit.
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240 drivers / parts cars - JH, Ohio

I tried a few more combos of speedo-odo units and gears: Re-flowed some more solder joints, blew them out lightly with air, inspected carefully for broken bits, micro-drop of grease, checked assembled units by spinning the rotor with a pick ....

Similar results to before: one 1989 odometer works with an old 25-tooth gear, in multiple 15-tooth pods, but does not work with any of the new gears (including one not from odometergears.com) on various pods and with various rotors. This remains a mystery to me.

During these inspections I noticed something I'd overlooked: One of the odometergears.com 25-tooth gears did not have a boss* on the bottom. So the bottom of the gear was flush instead of being raised and the rotor had to turn it on this larger surface.

I exchanged emails with Dave Barton (davebarton.com) and Jeff Caplan (odometergears.com). Both were helpful. When I identified the problem with the one gear, Jeff mailed a new gear immediately no questions asked.

What I haven't done:
1. Tried the newest gear
2. Followed Ken C's suggestion that I try a matched gear set

(my test bench is installing a unit, sans case/bezel, in a car and running it on a lift)

*Boss: not sure what the right word is here. The gear should have a slight extension on the bottom that the gear rotates on.
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240 drivers / parts cars - JH, Ohio

Your speculation about tolerance interference between old and new gears may be valid.

I've had to fix three "electronic" odometers (rather than cable) over the years, and using OdometerGears.com as a source, have never had the problem you described, but I've always bought them as a set: the smaller gear plus the larger gear. For a few extra bucks, it's been worth the precaution -- I order the pairs before dismantling the odometer because I want to avoid the car's "down time" (waiting for the parts), so I don't know in advance which is broken. Once, the problem turned out to be the solder joints, but I also replaced the gears anyway.

My point, which I can finally get to :-), is that perhaps replacing both gears (from the same source) would eliminate the tolerance issue that you've observed. The real cost of the repair is the *time*, not the purchase of the gears, so isn't it worth the precaution to buy a pair of gears each time?

Thanks for the comments Ken. That's a good suggestion: I'll buy a couple of sets next time I order parts.

I used to replace as a set but the cars are old now and it's hard for many to justify much spending. If it's a low-mile car, I sometimes replace as PM.

But you're right about the parts mismatch potentially causing a problem. I really should keep a set I can install to test the unit 1st. I should have thought of that but I haven't had this many problems before.
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240 drivers / parts cars - JH, Ohio

hello ken jon starkie and other sages- been following this thread with interest since back in 11 i did this same job . also bought a pair of gears from odometergears.com . teeth were missing from the old gears. curious about one thing though. if it isnt the gears but the little magnet motor is shot- is that replaceable? havent seen it on the suppliers list like fcp. have any of you replaced it? want to anticipate where i might get it and not get soaked at the cleaners. thanks tons oldduke

I've only experienced 3 repairs personally, but relying on this forum's history for a long time, I can't remember an actual motor failure being reported. It's usually been either the gears' teeth or a mere solder joint crack (sometimes annoyingly intermittent) -- easily fixed with a soldering pencil and a fresh dab of solder. Before blaming the motor, have you tried resoldering?

Yes, I'd reflowed the solder joints all of these.

If you nose around some of the odometer threads, you'll see refs to other faile eg. if you plug the tack wire into the double-spade, it fries some circuitry - a capacitor I think.
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240 drivers / parts cars - JH, Ohio

re: "...if you plug the tack wire into the double-spade, it fries some circuitry ..."

Ah, but that isn't a case where a motor stops working "out of the blue" -- if you screw up the wiring, you can't blame the motor for that.

I've never identified a bad rotor in the unit but there are threads here about some not turning freely. I'm not had any that felt tight.
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240 drivers / parts cars - JH, Ohio

Thanks for the comments Ken. That's a good suggestion: I'll buy a couple of sets next time I order parts.

I used to replace as a set but the cars are old now and it's hard for many to justify much spending. If it's a low-mile car, I sometimes replace as PM.

But you're right about the parts mismatch potentially causing a problem. I really should keep a set I can install to test the unit 1st. I should have thought of that but I haven't had this many problems before.
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240 drivers / parts cars - JH, Ohio

Thanks for the comments Ken. That's a good suggestion: I'll buy a couple of sets next time I order parts.

I used to replace as a set but the cars are old now and it's hard for many to justify much spending. If it's a low-mile car, I sometimes replace as PM.

But you're right about the parts mismatch potentially causing a problem. I really should have a set I can install to test the unit 1st. I should have thought of that but I haven't had this many problems before.
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240 drivers / parts cars - JH, Ohio

Thanks for the comments Ken. That's a good suggestion: I'll buy a couple of sets next time I order parts.

I used to replace as a set but the cars are old now and it's hard for many to justify excess spending. If it's a low-mile car, I sometimes replace as PM.

But you're right about the parts mismatch causing a problem. I really should have a set I can install to test the unit 1st. I should have thought of that but I haven't had this many problems before.
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240 drivers / parts cars - JH, Ohio

hi jon- did this job on my 240 back in 11. you may want to call jeff caplan at odometergears.com who sent me the gears. remember after doing the job , installing the new gears(2) and blowing out the fragments, it didnt work.asked dealer and he said to bring it in and they would fix it for $800. then called caplan about it and he said to let the unit run while driving the car and it may eventually start. i did for about 3 days and it did and has run right since. apparently the unit which uses what is called a magnet motor turns slowly with very little torque and may take a while to start after sitting. just my $.02. ps- what do you think i should do with the $800 i didnt spend? regards oldduke

Thanks for the comments. I've seen notes here on that problem: you replace the gear, it doesn't work for a few/20/100/more miles; then it starts working. I had that happen once but it started working in less than a mile.

I had another one d it; work for ~500 miles, then quit. Removed it to find the gear was bad.

More often, I've had this: I replace a gear and the speedometer works for 9/10 mile every now and then.

A couple of these recent units I put in cars and drove to no avail.

What was consistent here, multiple times, one odometer: Gear A, odometer doesn't work; Gear B, odometer works; Gear A, odometer doesn't work; Gear B, odometer works; ... repeat a few times.

I can understand how a slightly-oversize new gear might bind; when I don't get is why a new gear would work but a used one wouldn't - when that same used one worked in a different odometer.
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240 drivers / parts cars - JH, Ohio

I can't explain it either but my experience is that simply disassembling/reassembling the unit with the same new gear will sometimes result in the odometer working after initially not working with the new gear.

Randy