Author Topic: AirDyne odometer (speedometer) replacement for 1988 Schwinn Air-Dyne AD3  (Read 878 times)

Offline Air-Dyne

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I have a 1988 Schwinn Air-Dyne AD-3.  The ergometer broke after about 33 years.  Spare parts are hard to find.  I searched but could not find the wheel size to use for a bike computer.  I borrowed from my Dad’s AD-2 to get mine working again.  I setup a bike computer to compare and find what the wheel size should be.  I set the circumference to 846 millimeters on a Sigma Pure 1 wired bike computer.  This shows the correct speed, distance and time on the bike computer.  Here is more detail and a much longer explanation with pictures. 
https://www.amazon.com/review/R3FTGRX4UGRN7M/ref=cm_cr_srp_d_rdp_perm?ie=UTF8&ASIN=B017800L2G

I found these, so I put this in the same place.
https://www.schwinnbikeforum.com/index.php?topic=36124.0
http://www.schwinnbikeforum.com/index.php?topic=38384.0

Offline JenniferC

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Welcome to the forum. Andy (acg_Schwinn) is our resident speedo guru but there might be others that can help you find parts.

Offline acg_schwinn

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Welcome to the forum. Andy (acg_Schwinn) is our resident speedo guru but there might be others that can help you find parts.

Ah-hah. I did see this earlier but wasn't sure if I could contribute anything to the topic; I was misunderstanding what the problem was with the ergometer. I finally read the Amazon posting linked above, and I see that it's just the usual drive hub failure on the plastic Taiwanese drive hubs that replaced the original metal Huret units. The plastic housing splits open, after which the ring gear slips out of position and no longer turns the output shaft properly.

I'm not sure if those fail due to plastic fatigue or to increased turning resistance on the drive cable (caused in turn by need for some lube on the impeller shaft in the ergometer head). If you (Air-Dyne) are able to remove the drive cable and the ergometer head from the AD-3, try putting a few drops of penetrating oil in the cable outlet on the underside of the head, aiming for the side between the inner barrel (which turns, via the drive cable core) and the outer barrel (which doesn't). Use the end of the drive cable core to turn the ergometer head by hand, and be sure that there is not too much turning resistance.

Regarding the drive hub, there have been some variations over the years. The original units are die-cast metal from Huret, from the same molds they used for the bike speedo hubs, but at a higher output ratio to drive the Stewart-Warner ergometer head. Markings on it should read "2,6" (the output ratio of 1:2.6 in French notation) and "G" (Gauche, or left-hand rotation). These were later replaced by plastic drive hubs, bearing the same markings but made by (I think) King I Industries in Taiwan. These are the ones that split open after some years of service.

Complicating things a bit further, I have also come across a batch of Huret hubs bearing the same AD-3 specs, but fitting a 1.8mm drive cable core instead of the usual 2.5mm. I have never heard of an Air-Dyne using a 1.8mm drive cable (perhaps with a 2.5mm square tip at the upper end), but that's exactly how these hubs were made. Perhaps you could check to see if your ergometer and drive cable will turn better after some penetrating oil for lube (do not use grease), and if so, what size of square tip is on the lower end of the cable where it meets the drive hub.

Offline Air-Dyne

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Thanks, I guess I didn't do a very good job of making it clear what this was about.  I am OK using the replacement bike computer.  I don't need any replacement parts anymore.  I figured out the correct circumference to use for the bike computer so the odometer shows the same distance as the Schwinn odometer.  I saw a few questions asking what wheel size to use, but no answers.  Anyone with an old Air-Dyne can use 846 millimeters circumference on any bike computer that can be set that small instead of trying to find old obsolete parts.  That is if you are don't mind getting MPH instead of pedal RPM and Load.  Cat Eye Velo 9 can’t be set that small.  Sigma Pure 1 can.  I haven’t tried any others.

Offline acg_schwinn

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Okay; sounds good. Just to be clear, though, the Air-Dyne parts for the Load Indicator, hub and cable are still available, even if technically old or obsolete, such as via multiple sellers on eBay. (Those sellers don't always know the difference between Air-Dyne parts and bicycle parts, especially for the drive hubs, but they are still out there if needed.) Thanks to the Intertubes, you can find practically anything you need, indefinitely.  ;)