Wobble/occilation at 70/75mph+, am i expecting too much from old bike?

[KHEEREMA129911]

After a few months of '75 R90 ownership and a fair amount of highway cruising, I've noticed the bike can wobble/occilate a bit at highway speeds around 70mph if i hit any bumps, pavement overlaps, grades, etc. It kind of feels like a side to side movement or flex, and this can be a little bit disconcerting.

I've changed the front fork fluid with BMW 7.5, overfilled by 10cc's or so to stiffen up a bit, and I have Koni rear shocks set with the minimum for preload which seems to be adequate for solo riding (I'm 205 lbs.) with no cargo. Overall, I'm satisfied with how the bike soaks up bumps and performs in general with the exception of this wobble. I've changed the steering damper from 0 to 2 and vice versa, and i can't tell a difference. My tires are in good condition, good PSI, and I don't believe my frame/forks/rims to be bent from visual inspection, but I guess I could be wrong. I can take my hands of the grips when riding 30mph ish and the bike tracks straight.

1) Am I expecting too much from an old airhead, and should I just hold on tighter?

2) How can I tell if my steering damper needs to be replaced, and which setting on the twist knob is "more stiff"? Is this component replaceable with a new unit?

3) Does this bike have ball bearings in the triple tree that can be upgraded to the taper type bearing units like Hondas of this era?

Overall, its not too bad of an occilation, but I'm just wondering if this is normal for these old beasts, or if a few tweeks could help me cure this symptom. I am using the bike for highway commuting, and any advice/thoughts would be appreciated.

 

[RandyB]

Tighten up the subframe and luggage rack mounting bolts. That helped settle my RT down.

 

[OHScot]

Put the bike on the center stand and check the dampener by turning the forks from side to side. Should dampen from first movement, if worn it will move and then kinda catch. 0 is no damping 2 is more. But I would check tires, balance and make sure the bike is aligned front to back wheel. Check for any unusual tire wear. I ride mine with the shocks on the softest setting, dampener at 0 most of the time and no problem. Might try leaning forward and back to load front and rear of bike see if any change. I don't claim to know it all just experience with my bike. Good luck try not to fall down fooling around with the steering.

 

[flash412]

Your steering head bearings may be dry or adjusted too tightly.

 

[boxerkuh]

If you put your bike on the centerstand, move the handlebars slightly... see how much force it takes for the handlebars to fall over. It should take minimal effort. If it makes more, you need to repack the steering head bearings. You may also want to check if it is "notchy". If that happens you need to replace the bearings. How old is the grease, or better asked: When was the last time you serviced the steering head bearings? I am not aware of any different bearings out there. Now, also, do you run a fairing or windshield? That may play a factor in it. Let us know what you find...

 

[kbasa]

Your steering head bearings may be dry or adjusted too tightly.

My guess.

 

[testinglogin]

Your steering head bearings may be dry or adjusted too tightly.

Generally, a high-speed wobble would be a symptom of the bearings adjusted too loose. A low-speed wobble would be too tight. I had this issue initially after cleaning/regreasing my steering head bearings. Everything would be fine until I hit any small bump while even slightly leaned over at speeds over 60mph. A slight deceleration would stop it, but it felt TERRIBLE. Very scary. This was with otherwise properly adjusted swingarm, newer (and properly maintained) tires, and good forks/rear shocks.

The steering damper can make things harder to diagnose, of course. I don't have one, and I like it that way.

Other people mentioned accessories causing problems. I have a bar-mounted windshield that doesn't cause any problems, but I hear some do. I also notice my saddlebags can cause some weaving when I'm behind/next to a semi. Nothing crazy, and not as bad as the too-loose steering bearings. Carrying weight in my saddlebags amplified the steering problems I had.

It COULD be bad bearings if they haven't been serviced in a long time. They are already tapered roller bearings, BTW. At least, the ones on my /7 are. I think they ALL are.

If you don't feel comfortable adjusting this yourself, it may be worth a few bucks to find a shop with a GOOD Airhead mechanic (or a knowledgeable Airhead friend) who can look at this for you. Steering is not something you want to have a problem with!

 

[James.A]

I have seen more than one /6 sub-frame with a cracked weld on the crossmember just in front of the rear fender. On one bike, it was impossible to see and was only discovered when dropped on the garage floor and made an unusual sound. The owner of that bike said it was un-stable at highway speed.

 

[jgr451]

am I expecting too much from my R90?

In a word ,yes.

I had a 1971 R75/5,well enough maintained but not improved.Leaving the Montana rally in 1998 I was completing a high speed(75 mph )pass,with the bike fully and badly loaded and I fell down hard with just the oscillation of which you speak.It happened very quickly...I knew that I had overdriven the old technology,and I was lucky to be as uninjured and undamaged as I turned out to be.
Update the frame with a stiffening kit,maybe a steering damper,steering head bearings,new shocks,new swingarm bushings.THEN let er rip.The motor will go but the frame and suspension in original kit are not up to high speed touring.

YMMV.

 

[testinglogin]

In a word ,yes.

I had a 1971 R75/5,well enough maintained but not improved.Leaving the Montana rally in 1998 I was completing a high speed(75 mph )pass,with the bike fully and badly loaded and I fell down hard with just the oscillation of which you speak.It happened very quickly...I knew that I had overdriven the old technology,and I was lucky to be as uninjured and undamaged as I turned out to be.
Update the frame with a stiffening kit,maybe a steering damper,steering head bearings,new shocks,new swingarm bushings.THEN let er rip.The motor will go but the frame and suspension in original kit are not up to high speed touring.

YMMV.

Going to and from the VT rally, I had my bike loaded quite a lot and did not experience this oscillation. As I said, it was present before I found some help adjusting the steering head bearings. I did some pretty fast and hard riding on my way out of the rally and everything was rock solid. I know a number of other people who have done similar things without problems. There are a lot of people who ride their airheads FAR more aggressively than me. There are a lot of different things to be checked (swingarm adjustment, steering head adjustment, fork rebuild/check for stiction, possible need for new rear shocks, etc etc etc). You should not be getting any type of steering oscillation at any speed that would lead to a crash, and if it's happening it needs to be fixed.

 

[SEMUTA]

Could this be the same type of oscillation described by Duane Ausherman here?

http://w6rec.com/duane/bmw/wobbles.htm

 

[testinglogin]

Could this be the same type of oscillation described by Duane Ausherman here?

http://w6rec.com/duane/bmw/wobbles.htm

That surely could be the problems with an older /5, but not with the R90 that started this thread. That's a scary issue, for sure!

 

[SEMUTA]

Good to hear, I wasn't entirely sure when that was resolved.

 

[testinglogin]

Good to hear, I wasn't entirely sure when that was resolved.

The "problem" modes were the easy "short wheel base" /5's. The long wheel base model was the factory "fix" for the early problems they had with handling. The SWB models run from 1970 to mid-1973. Duane has some photos to tell the difference on his website:

http://w6rec.com/duane/bmw/whbase/index.htm

I HAVE heard people talk about how nice the SWB models are to ride; very "flickable". I guess if you could get one set up correctly it would be a nice ride. I'd probably be too worried about it to enjoy myself...

 

[KHEEREMA129911]

OK, thanks everyone for the tips, keep them coming! I have checked the subframe bolts/nuts about a month ago, but I will double check all of the tension on these bits and pieces and make sure they are torqued. I'll check for any cracks in any of the supports as well.

I think someone recommended me checking the tires...I just want to say that they are Pirelli Strada tires, and they look brand new, no sidewall cracks, plenty of tread, they came on the bike when I bought it a few months ago. All I've done is make sure the psi is up to what is recommended on the sidewall. I don't think its tire related unless the Pirelli tires I have are not good tires or have poor high speed characteristics. I am not sure about this.

I put the bike on the centerstand, and i could easily move the handlebars side to side. I don't think the bearings are too tight, if anything i think too loose.

I don't have a fairing, and this is NOT caused by overloading the bike, unless my fat 205 lb. @$$ is considering overloading the bike I do ride with the saddlebags, but I don't think its caused by them or passing trucks.

I an unfamiliar with the rear swing arm alignment, I must admit. As far as steering bearing maintenance/lube, it is safe to say this has either never been done, or has not been done in over a decade. the bike has 36K original miles, and was not used regularly for the last 10 years with the PO, and he was definitely not a maintenance freak by any stretch. The PO before the PO seems to have been a pretty hands on guy, and might have done it, but i have no way of confirming.

This is my plan:

1) Torque all subframe mounting bolts/nuts
2) Service steering bearings according to the manual if I can do myself with basic tools
3) Check rear swing arm alignment if i can with basic tools

I will complete these tasks and report back on this thread, it might take me two weeks as i'm leaving for vacation shortly and the old lady prevents me from doing all the wrenching when I'd like too Thanks for the advice everyone, I'll see what I can do so I feel a little more stable at 75MPH...

 

[BENWAY999]

"All I've done is make sure the psi is up to what is recommended on the sidewall. I don't think its tire related unless the Pirelli tires I have are not good tires or have poor high speed characteristics. I am not sure about this."

what actual tire pressure do you have?

I think the sidewall pressures are the maximums.

you can probably get the recommended tire pressures from the pirelli website

also, what size are the tires?

hope that helps

 

[ISAMEMON]

if I knew the tires were good
then steering head bearings is the next stop
all the wobble and klunk to my scooter, when I first bought it, was in the bearings

 

[APEXERIC]

I'm having the same problem with my 71 R60/5 but mine begins to wobble at 30mph and disappears at 35mph+.

I put new Metzlers on the front and rear hoping that the wobble would go away. But it didn't.

My head bearing seems ok but I'm going to take it apart to grease it and reset it.

If that doesn't work then I am going to replace the fork oil and probably replace the springs.

I don't mean to hijack the thread but I think that my questions are related.

There are three types of fork springs listed in Bob's catalouge: standard, heavy duty and Progressive.

What type should I consider to order for replacement? And, is it necessary to replace the rear shocks at the same time?

Hey, this might be getting expensive!!

Also, is it possible to remove to wobble from these SWB bikes? Or am I going to die for sure at 75mph+?

I am still relativly new to this compared to many of the members here at MOA so any advise is appreciated.

Thank you.

Eric

 

[SEMUTA]

apexeric-I think that lengthening the wheelbase was BMW's response, but in that link I posted previously they solved the wobble by maintaining exacting tolerances for front fork alignment.

 

[BOKRIJDER]

Saddle bags, hmm. I had a 74 R90S while living in Europe and did a fair amount of higher speed riding with it. The bike was in perfect condition, but with bags installed it would behave as described. Not a true wobble, but more of a very low frequency snaking of the rear. I could never 100% pin it to wind or gusts, but had a suspicion that it was provoked by a combination of speed and road surface. Either a slight reduction or increase in speed would settle it down, though a reduction always seemed more prudent. The bags on the European R90S were placarded with a speed stability warning.

Motard