Odometer gear replacement surprise

[Otter74]

So I’m replacing the broken odometer gear in my SC’s speedometer. I’m referring as I go to the video that was helpfully posted on an earlier thread. I get the frame that holds the odometer and trip odometer off, ready to remove the other two gear sets so that I can remove the one I need to replace, and I run into this surprise:



the gear set that directly drives the odometer, instead of being retained by a pin that I can push out with a pick, is as seen below. The shaft of the red gear and that of the white gear both fit within the housing, and the red looks like it fits inside the white. And I have no idea how to remove them. I can’t get the other two gears off until I get this one off.

Any suggestions? I had not seen this retention in any of my research prior to starting this.

[jbell959]

Looks like you have an 75/76 speedo. They switched to the pin sometime in 77. The earlier ones like yours had gears that are plastic welded in place. These are definitely more tricky to work with. You basically need to break those 2 gears apart to be able to change the top gear.

I very carefully cut off the plastic weld and use a hot iron and a piece of parchment to get them back together. Even when being very careful I have had issues with the new plastic weld not holding.

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[Otter74]

Ah. Thanks, John. Since my car is an 80 SC it originally had an 85mph speedo, so I knew this one wasn’t original. But of course I didn’t know where it came from. All I knew was that it hadn’t been apart before I took it apart.

Where did you apply heat to break the weld? There is what looks like a witness mark for the weld at the center of the red gear. And can you describe the process by which you weld it back together?

Only after I have it apart do I learn that this one would have been worth sending to you, LOL.

[jbell959]

I use a razor blade to cut off the plastic around the square shaft. I dont use heat to get it apart.

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[Otter74]

Do you mean the little nub of plastic at the hub of the red gear?

[Otter74]

Thanks - I was able to get it off. I’ll figure out getting it back on once it’s ready.

[Otter74]

I think what I may try is carefully clearancing the relief in the center of the red gear so that a little bit of the keyed end of the shaft on the white gear is exposed, giving me something to mushroom over when I put heat on it.