I am resurrecting this 71 75/5 to make it roadworthy. With the bike on the center stand and in gear, how much,if any, "backlash" should there be in the drivetrain by rotating the rear wheel back and forth? Any input would be greatly appreciated. Thanks in advance.
It's a gracious plenty ! Maybe 20° or more. Most of that is adding up all the slop in the splines and straight-cut gearbox cogs. That amount of free play sounds like a lot, but this is not usually a problem area. If you do have an issue, then you'll usually hear a whine associated with, or related to, road speed.
► The No 1 problem area is the splines connecting the final drive to the rear wheel. If those splines get dry, then they wear. Remove the rear wheel and add a water-resistant grease to the male and female splines. And every time the rear wheel comes off, do it again. You never want to see those splines go dry.
► For the oil change, don't go by the manual because oil technology has improved. I can seriously suggest a change to synthetic multi-grade gear oil for the gearbox, drive shaft and final drive. (All 3 the same grade & type.) The gearbox will shift better and the final drive will run cooler. The gearbox alone takes 1 qt, so you'll need to buy 2. I've been using synthetic Valvoline 75W-90 with excellent results. Change it once a year.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
@wobbly thank you for the reply. It was very helpful. I am looking forward to wrenching on this project. The backlash is less than 20 degrees, so probably normal. I will check all splines as it gets a good going over this winter. Cheers. Dave.
@dave-jensen No problem and very glad to help.
I was going through 1 or 2 rear tires a season, so inspecting that wheel spline every time the rear wheel came off was the best way for me. But that inspection should definitely be at the top of your check list for a new-to-you bike.
Back in the day, my parents and thousands of others thought nothing of riding 1800 miles a rally, just to turn around and come back 4 days later. That meant getting caught in a lot of rain, and not all lubricants were water-resistant back in the 70's. So there was a list of very specific, very tenacious, water-resistant greases to use on those splines. Since most people aren't going that far from home anymore, and definitely wouldn't set out knowing there was rain, we can relax the spec a little. The main requirement now is that both sides of the spline stay totally grease-coated between inspections. This because replacing either or both splines is major dollars.
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Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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