My first 122 was converted before my time with it from an auto to manual. Recently my speedo cluster started to act kind of wonky. The "estimated" speed bar began to go all the way to the right at even moderate speeds, plus "bounce" a lot and such. Becoming annoyed with the noise, I finally unhooked the cable drive from the unit underneath the dash, I noticed it was rather loose when I did this. Later I decided to try screwing it back in and see if perhaps it had been doing this because it had been so loose in the first pace. To my surprise I discovered that the screw-on "cap" that is supposed to keep the cable engaged into the speedo-cluster did not match the thread diameter of the cluster. I was thinking that maybe there was a difference between speedo clusters for manuals and auto transimssion cars. Can anybody comment on this? I thinking I may have to track down an original manual cluster and swap it in. The old one is rather crusty anyway, so this would not neccessarily be a bad deal.

I think they changed threads in about 1964 or 65. For sure 66 and later is
compatible with threaded ones from 140, up to 1973. After 73 they were twist-
lock, needing only ¼ turn to lock, sort of like an automotive light bulb,
rather than screwing on
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George Downs Bartlesville, Heart of the USA!

Ahhhh, OK. So there are some compatibility issues with that connection then. That must be the deal, because it clearly does seem to be a different diameter between the two. My rig is a '64, but I have no idea what the M41 or cable was sourced from. I'll have to hunt down a match I think.

Thanks.

Yep, that's an early/late instrument cluster issue, and your car has the early smaller connection. When I put an M41 in my PV I needed a longer early style cable, and was able to get one from www.gcp.se (PV's never had OD's, this was for an early OD 122, just like you have). Part number 668598, $62.32 on www.gcp.se.

Of course, if your M41 has one of the sometimes troublesome angle drives, you probably don't need a longer OD cable. The longer length is made up for (more or less) by it not needing to make a right angle bend at the trans.
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I'm JohnMc, and I approved this message.

Ooops. Sorry -- I ment to say M40.

Also... the problem is actually that the cable "cap-er" deal does not fit onto the threads of the cluster because the cap-er is too small. So perhaps I have an older cable, but a replaced "newer" cluster? It certainly doesn't look new though. It's pretty crusty so I thought it must be the original!?

Ah. I think another visual difference between the clusters is the warning/indicator lights. The old style (with the small speedo fitting) has a chrome surround around each indicator, and a small inset plastic lens. The later models have a protruding larger plastic 'button' which serves as the lens.
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I'm JohnMc, and I approved this message.

No, the cluster are the same... The speedo cable is supposed to be different but it's just a length question, not a fitting or end issue... Last time I needed a speedo cable for my 122 automatic, I got the one for a 140 and it was several inches longer than what I needed but worked fine... I guess I could of gone to the local speedo shop and had one made exact to fit...