Calibrate Speedometer on '79 Motobecane 50V

Anybody know how to calibrate a speedometer on a 1979 Motobecane 50V?

I'll be going top speed down a slope and the fastest the speedometer will show is 23-25mph. I know that I'm going faster than that. So I'm thinking I just need to calibrate it. Any tips or advice on how to go about this procedure?

Thanks,

Blair

Re: Calibrate Speedometer on '79 Motobecane 50V

Blair,

Calibrating speedos is tricky work. Getting it apart and back together is half the battle. The little Huret speedo on the motobecane has a chrome bezel, with little bent tabs that hold it in place. Getting these tabs skillfully unbent and rebent requires a careful touch..

I've never looked inside a Huret, but most simple speedos have a hairspring that is attached to the needle shaft on one end, and a moveable plate on the other. You rotate the moveable plate to increase or decrease the tension on the spring. Normally, more tension = lower reading.

Since you probably don't have a dyno to use for calibration, about all you can do is make a small change, and check the results. You might have to make several adjustments before you get it correct.

If you have any of those "You are driving this fast" radar display signs in your area, that might be a good way to check it.

Hope this helps.

Re: Calibrate Speedometer on '79 Motobecane 50V

Your reply has definitely helped me realize that this particular operation might be a bit out of my league.

By the way - I went to the locksmith to replace my fork lock. He got it out, no problem. And the new one slid right in. It was great.

Thanks,

Blair

Re: Calibrate Speedometer on '79 Motobecane 50V

Yeah, as long as the speedo works John Law will be happy with it. I don't mean to dissuade you from trying it, but then again, knowing what to leave alone is part of being a good tech ;-)

Great news on the fork lock, glad I could help. Did he charge you much?

Re: Calibrate Speedometer on '79 Motobecane 50V

The locksmith was a good guy - he didn't know what to charge me at first. I said, "well the guy on the phone earlier said $10-15." He replied, "$10 it is. Come on in, I'll write you up."

I wish all service techs could be that easy to work with!

Re: Calibrate Speedometer on '79 Motobecane 50V

It's possible someone put the wrong drive gear on the wheel or speedo head on there. OR the drive gear could be skipping(teeth worn).

don-ohio (:^D

Re: Calibrate Speedometer on '79 Motobecane 50V

Good point. For that matter, it might have tires with a slightly taller profile to them than the original ones. Since the tire has to turn more slowly for the same road speed, that will make the speedo read low.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account