High speed wobble

[bbelk]

My 1975 R90/6 has developed a wobble. It presents itself somewhere above 75 MPH. It is not consistent and responds to road surface and wind. It is not violent, it is just a couple inches of full body wobble and its damn scary.

Tires are new. Fork oil is fresh. Back shocks are nine year old progressives with maybe 50K on them and no apparent leaks or binds. What is the life expectancy of rear shocks?

I have not checked the back wheel yet, but I have checked the front one pretty carefully as its brand new. It has no humps, lumps or out of round issues and is balanced per my neighbors home balancer.

The front end is tight in all directions but it does have a barely perceptible notch in it. Could this be the culprit?

Thanks
Brad

[Rob]

Is that a dynamic balancer? I won't ride a bike with only statically balanced tires.

Fork fluid is equal on both sides?

Duane will probably ask if you have removed all accessories and retrying. As I recall, this bike has a large, aftermarket fairing?

Could be the steering head bearings. Could be the swingarm bearings.

Please note my bottom-most signature line...

[bbelk]

Is that a dynamic balancer?

No

Fork fluid is equal on both sides?

Yes

removed all accessories and retrying. As I recall, this bike has a large, aftermarket fairing?

No and Yes. Windjammer fairing has been there longer than the wobble. I will recheck its tightness everywhere.

Could be the swingarm bearings.

Guess I will go check that.

Please note my bottom-most signature line...

Do you warranty your information?

[Rob]

Do you warranty your information?

No, I will only add, wear ATGATT. (that is never a lie!)

[Steve in Golden]

Duane will probably say "Google it".

[2valve]

My vote goes to the steering head bearings. Also had a bad shake on my 1976 /6 long time ago at very high speeds and everthing seemed to check out OK by feel by me. But talking to a retired classic bike mechanic (great bloke)said to replace the steering head bearings after he had a look over the bike himself and he was right. Actually in the end he gave me a huge framed hand drawn picture of a 90S which was hanging on his workshop wall that i admired which was dated 75 when drawn , which is the same year as my 90S ! Sorry to hijake the thread.

[Rob]

Never apologize for a great anecdote, 2valve! Picture of your picture?

Yeah, if the history of the bearings is unknown, it might be time for a look-see.
And it is SO much fun!

[bbelk]

Back wheel spins true. I ran it up to about 60 on the centerstand and it wasn't jumping around.

I found about a 16" (1.5mm) of back and forth play in the swing arm, but no looseness.

[Rob]

I found about a 16" (1.5mm) of back and forth play in the swing arm, but no looseness.

So you are saying you have 1.5mm of play side-to-side? I don't know how the preload works on that model, but on my R65, I don't remember having any side-to-side play that could be felt. If the play is fore/aft, I don't see how that would be a good thing.
Do you have the shocks detached for these measurements?

[2valve]

Never apologize for a great anecdote, 2valve! Picture of your picture?

Yeah, if the history of the bearings is unknown, it might be time for a look-see.
And it is SO much fun!

Not a problem Rob , but have no idea how to load it on this site could you flick am a email and i'll send it to you ?