I know this is a topic that has been discussed at some length, but I'm having a tough time finding exactly what I'm looking for. Only a few days ago, we picked up a 1974 R75/6, which I rode home about 90mi. We bought it from the second owner, who has a ton of paperwork from the original owner of more than 40yrs. I've looked through those papers and not found anything useful to this issue.
The speedometer reads about 50% high at all times, which among other things, makes for tougher mental arithmetic when riding than just being a set number of miles fast. The Final Drive casing marks match the W number on the speedo dial, so it hasn't had the Final Drive casing replaced. But I question if the gearing in the Final Drive or the transmission may have been changed, as that would seem to be the simplest explanation. Though I'd have expected to find a record of that amidst all the detailed maintenance records I've got.
My questions are: what is the best way to determine if the final drive or transmission has had a gearing change that could account for the inaccuracy? If it is a gear change, would it be possible to adjust the speedo and/or get a replacement with an appropriate calibration? And is there an obvious speedometer issue I'm missing that could account for the behavior if, as all appears from the outside, the gearing remains stock to the '72 R75/6
Funnily enough, we seriously considered several airheads before settling on the particular one we purchased, and one of the other bikes, an R65, has the exact same speedo behavior, reading about 50% high
Welcome Aboard !
I believe you may be looking in the wrong place. Map out a 10 mile loop with Google Maps or some similar GPS type mapping system. Then go ride that exact loop and compare odometer readings. If you have the correct odometer readings, then the problem is not with gear ratios.
The odometer is directly gear driven, but the speedometer is driven magnetically, which means it's open to outside influences which will vary its reading. Outside influences like coagulated 40-year old lubrication, loss of magnetism, bad pivot bearings, etc.
If that is the case, then the gauge needs to be cleaned and re-lubricated by a specialist you can find listed in the AirMail magazine.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
If the odometer reading is correct I bet that someone took the needle off in order to take the instrument apart and did not mark the speed cup against the housing before pulling the needle.
In that case the speedo can easily be 20-30mph fast when the needle is reinstalled at the 0 mph position.
You can adjust that by holding the spindle at the speed cup with needle nose pliers, rotate to for example 50mph and force the needle back to 30mph by hand.
Thank you SO much! It hadn’t occurred to me to check the ODO, I just assumed it was fast like the speedometer.
I just did a test ride, and the odometer is reading bang on accurate. Now I’ve got to look more into what you’re talking about with resetting the needle.
I just did a test ride, and the odometer is reading bang on accurate.
Hey, that's great !
Now I’ve got to look more into what you’re talking about with resetting the needle.
Removing the needle is not only dangerous to the needle, but useless if the needle pivots haven't been re-lubricated.
The correct way to remove needles is shown in this watch video (at min ~7) and he also shows how to make the tools at the beginning.
https://www.youtube.com/watch?v=bKIKLsid5lk
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
just to make sure I did not mislead. Do not take the needle off. You are asking for trouble.
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