I was out riding my 1980 XLH and I notice that the bike is perfectly smooth up to 50mph. As I get to 55 I start to pick up vibrations in the seat and an overall rougher ride. I have no vibrations in the Handlebars and any speed. Now the RPMs at 55 are just about 3000 I think. Is this the normal sportster shake. I believe the vibrations have more to do with the RPM's then the actual speed. So I think I can rule out tire balance. The shaking is not excessive just rougher feeling. Thanks for your help!!!

 

Sounds about like my '83. I put a 23 tooth transmission sprocket on it to lower highway rpm's. It hurts the acceleration a little, but 3000 rpm's get me to a little over 60 mph with that gearing, which is pretty smooth. It's actually not too bad at 70 mph, either, which is about 3400 rpm now.

 

could be wheel bearings pull rear wheel and make sure they turn smoothlyor change them out.i also read do not wash your bike at carwash high pressure will wash out grease from your bearings over time.also make sure everything is tight.or could be bearings in swing arm.

 

I too use the 23T front sprocket, 51T rear sprocket on my 1980. It is an ideal combination. "All the ironhead guys" around here use it.

Probably not a problem. But you should check out the usual things as already suggested anyway, especially if this is a new developement.

Wheel bearings, ignition timing, chains too loose or too tight, broken/loose engine mounts, tire pressure, loose spokes, fork oil [try 15W], set rear shocks up one level tighter, not sure what else.

 

Thanks for the suggestions. I have a feeling it's the normal high RPM shake. I may consider the 23T gear. Will the sprocket cover still fit with that gear and a O-Ring chain?

 

You'll probably have to grind a little off the cover mounting bosses. I did, and I'm not using an o-ring chain. They're big and thick, so I don't think you'll be compromising the cover.

 

Here's my sprocket cover, showing where i ground off the boss, and where the chain did some grinding of its own at the top when it was too loose.

 

Here is sample how older sportster crank case and sprocket cover need to "modify"
when you are using O-ring chain

Crank case



Sprocket cover