Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Speedometer drive

Speedometer drive

Post Mon May 26, 2014 7:42 pm

Posts: 1654
I'm just looking at the speedo drive for the 45" project bike.

Right now this bike has two speedo drive points, and a problem. The problem is that the frame, having been subjected to a lot of cosmetic work, has lost the tunnel through the frame backbone for the speedo drive.

I can see various solutions, but they all start with a 90deg adapter from the speedo. These are available from various car restoration parts suppliers. I've established that the threads on a Shovelhead are 5/8" x 18 and unsurprisingly, this seems to be a stock adapter size. So, I could drive it from the Shovelhead front wheel but this leaves a rather awkward looking cable route.

The next option is to drive from the back wheel. I already have a 2:1 reduction Shovelhead speedo, somewhere about. I don't have a 45 drive cable. Is the thread on the drive cable compatible with a Shovelhead speedo, ie 5/8" x 18? Knowing HD, it probably is but I thought I'd ask before proceeding as someone is bound to know, or have the parts to check?
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Jun 30, 2014 2:29 pm

Posts: 222
Location: Virginia

Not sure what you have for components, but the 45 frame didn't hold the speedo drive unit, it was held in place by the 45 rear brake backing plate.

Post Tue Jul 01, 2014 9:46 am

Posts: 1654
No, I know that, I was thinking about the speedo and connection. The tunnel through the neck forging has been blocked for cosmetic reasons by a past builder, so I need another cable route. I was looking at a 90deg adapter (there is room for this because the top tube is now flush, where the cable tunnel formerly projected ) but because I have the option to drive it from the Shovelhead front wheel or 45 rear wheel, I was asking a question about drive ratios and thread sizes.

The preferred option is probably to use a Shovelhead speedo and drive it from the front wheel. The cable route looks a bit challenging either way but I think the front wheel drive is slightly better. However I'd like to use an older type repop speedo if the drive ratios and thread sizes match
Shoot, a man could have a good weekend in Dallas with all that stuff...

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