This may be an answer to anyone getting broken speedos/odos perhaps a "little too often", note, this is a speculation but I think it has value,
makes some sense to me.

Speedo breaks, get another, that one breaks, get another, etc. So,whats going on? This of course is an opinion but makes sense I think. Speedos are getting older and older. The little gears inside getting more and more brittle. The shafts they turn/rotate on getting gummy-er. Step on the gas hard, then wonder why the little brittle gear goes "byebye"?

One solution, drive easier. Next, take that next odo, clean it thoroughly and any and all "shafts" the gears turn on. Then clean and lubricate as many little gears as possible. After having done so, drive easier.

hi sages- good advice art b and others. smart to not change tripmeter numbers on 240s in motion. my speedo in the 92 245 has two new gears which i put in 5 years ago . the gears were from odometergears. the old gears had teeth missing and were very soft and crumbly. no problem with them except have to occassionally tap the cluster when rolling to restart them. happens less frequently when cold. trip meter still works but no reset since button lever crapped out. figure the solder points on the cluster back have a crack or two .will solder them one day when i get a needle nose soldering piece for my weller. btw its very useful to shake out and blow out the cluster since busted gear teeth and related debris may be in there from the old gears . like when its late at night and a nam type monsoon suddenly hits on tobacco road and you stall and then have to dry the distributor cap and rotor and shake out carbon debris. thanks tons oldduke

Hi there, long time since I whisper to you!

I'm thinking you idea about not pushing on the gas so hard is quite humorous. I'm sure those gears care less about the speed they turn unless you approach the speed of sound going down the road. (:-)

I have about six whole instrument clusters at home. Two are them are cable driven. No problem with them and they are older and the cars go just as fast.

The others have those with pulsing motors that have problems with the gears.
I found them all in junkyards for what I would pay for one of the aftermarket gears offered.
I was lazy and used the gears out of them, until one day I gathered up my collection and realized I needed to stop this!

Since I have the capability of making some, I figured I could make ten in the same time I can make one. That is, except for the bore, then it fell to three at a time to cut off from the round length of Delrin rod. It is in the nylon family side of plastics with a slightly different polymer chain with different qualities.

I have to say the original gears are made out some lousy "plastic" for lack of a better defining name, besides junk that turns to rubber!
In the process of doing measurements I saw another major flaw in the gear train. It's very shaky!
The larger counter weighted center gear acts more like a floating saucer.
It has no support except from its bore and the driven and drive gears faces when they are in mesh.

I also thought about those pulses again, jerking the gears about.
In the my trade, that can be considered shock loading. Something that's not good if you have excessive backlash to add into the movements.

So when I made my gears I increased the thickness to widen the face that engages outer ring gear.
The width of the gears face, determines its horsepower rating and it's got a whole lot in there! (:)
There is not much room but I managed to make it about 25% to 30% wider.
I also increased the pitch diameter by only a few thousandths for good measure to take up a wee bit of backlash.
There are no adjustments like an idle gear in a planetary gear system, especially when it missing two more gears!

I had to be careful on that as that is the last thing one needs for the assembly to be too tight!
From the way those speedometers are working from the factory they must have had trouble calculating for tolerances or material shrinkage(s) and just left it loose.

When making gears by hand you don't measure the pitch diameter very accurately until you are halfway around. These guys are the tiniest gears I ever tried to make. For the most part of my career, I made huge things!

I used, as I remember, about a .020 drill rod to get the measurement for my depth on the first tooth measuring to the opposite side of the blank. Imagine old eyes and some Trump hands doing that! (:-)
Still, with all that, I made them all on my first piece of stock. I was feeling pretty smug until I got careless.
I had a few, at the end of the lathe work, where the bore wandered a few thousandths. They ended up being not as concentric as I wanted but with all the slop in there, it may not matter.

I planned on ten but my length gave me about fifteen. The boss (me) got what was needed to repair the cars and the shelf models.

I might have one cluster with a bad motor. I have not had the time to check it out by using Arts powering up and frequency method.
I have to sit down with quiet time, to do that kind of stuff!

If I wasn't away from home again, I could see my way to send you a good one. Maybe two! One of the not so good ones and let you experiment with them. Your speedo might be worse with play?
I use a toothpick, to tickle them, to check out the play in it. There is plenty, IMHO.

The speedo's are probably made in Italy, where, "it's like my Maria, gotta be loose or she don't ..ah.. go!" (:)

It will be near next month before I'm back, if you are interested. They will get lost inside a letter size envelope. So the postage is squat to me and the gears are just extras for nothing as well!

I didn't get that you are into doing your own repairs of these or not? Seems you are pretty sick of it though!
I have been running my experiment, with these, for about six months now!
Let me know.

Phil

so a K9800 speedo requires a 25 tooth gear? I saw somwething on the internet about 26 tooth option? I need to replace mine soon. Is there an easy way to roll forwad the odo to reflect the approximate true mileage?

I've never heard a new gear has broken in a 240's electronic odometer, regardless if machined Delrin or molded nylon. Never. The only broken gears in my experience are the original 20+ years old turned-to-powder VDO gears. Once replaced, I reset the trip meter every fillup and have no fear whether I think of doing it while writing the mileage on the gas receipt or remember to do it while driving away.

Kudos to you Phil for even attempting to machine a part that small. Your skillful hands must be the guarantee there's no problem.


--
Art Benstein near Baltimore

"I have to use an 18 to 24 inch *1/2 inch drive extension* powering a flex-socket -this is ONE INSTANCE where a "snap together chain" of universals and sockets WILL NOT WORK you need to get ALL OF THE TORQUE you can into the bolt and NOT 'soaked up by the chain of floppies'...drive THAT with an 18" cheater and throw down on the friggin bolt...be CAREFUL...it will be 'tighter 'n crabs ass' until just before it lets go - at which point it will *POP* and come loose carving deep blue ripples in the tissues of your mind...Uh OH...flashback...." - TrickMick