Rear Instability?

[bobbydyabb]

Hello R65ers, perhaps you can help with this sticky issue I have.

Bike runs straight and true on the street to 50 mph.  On a freeway section that's fairly grooved where I can test repeatedly, I get an intermittent wobble (and scary to a newbie like me) at 55+ mph that seems to involve the rear wheel too.  I just cannot tell whether the rear wheel instigates it or not.  Has this happened to any of you and what was your resolution?  If not, any insights?

Other clues ---

Tire, Avon Roadrider, 110x18, 4K miles, mildly cupped on the left half, balanced with 1/4 oz.

There's a feeling of a short rear wheel wiggle under load (during spirited left turns at less than 40mph).

Rear wheel shake test exhibits no obvious looseness, although I can detect a slight movement at the gap between the brake drum and rear drive housing even with axle nut torqued to spec.

TIA,

[Barry]

A squared off worn rear tire gave mine the wiggles on grooves but that was at 6 - 7000 miles.

You can't always attribute behaviour at one end of the bike to a fault at the same end. It could just as easily be a problem at the front that causes the back to misbehave and vice versa.  I think I would also be checking adjustment of the head bearings and maybe fork alignment.  Having said that if the bearing has the correct pre-load there really shouldn't be any play between the rear drive housing and the drum. I just gave mine a tug to check and there's no feel of movement at all. Maybe stressing the wheel changes the gap a thou or two at the most but that's it .

[Crossrodes]

I had the same symptom a couple of years ago.  I checked the head bearings and the swing-arm adjustment.  It was neither of those.  What it turned out to be was the rear shock absorber preload.  I increased it a couple of notches and the problem went away.

[Bob_Roller]

Getting an uneasy feeling on a grooved road surface is not too uncommon .

Some tread patterns are a little more prone to it than others .

What tire pressures are you using ?

If you are a little bit of movement on the rear wheel/tire, you may need to check the bearing preload adjustment .

There are spacers and shims between the wheel bearings, sounds like you may have to adjust it a bit .

[bobbydyabb]

@Barry, thanks for checking your brake drum to rear drive housing gap when doing the rear wheel shake test.  That's what I get too.  No axial play, just a little (very little) increase in the drum/housing gap.  I suspect that my problem only happens under load.  That sort of opens up possible scenarios, unfortunately --- cracked something (wheel bearing, swingarm, subframe, mainframe) that's only felt under loads greater than what my hand shake tests are capable of generating.  

@Crossrodes, I too checked my steering bearings (lubed them too) and swing arm bearings, and they seem to be fine.  I've adjusted steering bearings from loose (easy handlebar flop) to tight (slow weave at 20-30mph), same wobble at speed result.  But I've forgotten about shock absorber settings.  I have Konis and I'll play with tweaking the preload setting just as you did.

@Bob_Roller, I've tried pressures from 30/35 front/rear to 35/40.  Same result.  Actually much rougher at 35/40.  The grooved section where I do my repeatable test appear to give my rear tire a slight nudge which starts the wobble which gets worse if I don't slow down a little.

Thanks again everyone, I'll keep you posted.

P.S.  Regarding frame/subframe cracks, is there a list of where they usually occur on an R65?  Also reminds me, bike had a "Luftmeister" type front engine mount untorqued when I got it at 71K miles.  I've replaced it with metal washer/s after inspecting the frame section around it for cracks.  

[Barry]

P.S.Regarding  cracks, is there a list of where they usually occur on an R65?  

I think there has been the odd one like engine mounts but no pattern of frame/subframe cracks that I've heard of.

On a related issue I've always been puzzled by the factory torque value for the subframe mounting bolts. I forget the figure but I think it's 11 ft/lb which seems low in relation to the 18 ft/lb for a standard 8.8 spec 8mm bolt.  The only thing I can think off is it's a very dangerous place for a bolt to shear if it's overtightened so maybe they played very safe with the torque figure. Anyway at that low torque and I think without locking washers of any sort it's just possible they might have loosened off.

[montmil]

Bob, Your test have been well investigated but the wobble problem continues, correct?

I would suspect the rear wheel bearings are worn and/or loose from wear. Wheel bearings and seals are inexpensive and simple to replace. A close inspection of the bearing's outer races might also confirm the need for replacements.

I bought one of my R65s well knowing the rear wheel bearings were shot. Talk about a wobbly goblin!

Monte

[trolle]

For the last two seasons I have had a front wheel wobble at 40 mph. I gave up finding the cause, but this year I had new tires put on both front and rear and now the wobble has disappeared completely. So before checking the difficult and expensive parts, I would check the balancing of the wheels and tires.

greetings from a sunny and warm north

[bobbydyabb]

...
I would suspect the rear wheel bearings are worn and/or loose from wear. Wheel bearings and seals are inexpensive and simple to replace. A close inspection of the bearing's outer races might also confirm the need for replacements.

Thanks Monte, this would be my next step after the shock absorber preload test.

When you did your wheel bearings, did you use Cycleworks' race remover?  Also, how did you recalculate/redo the wedding ring/shim size?

[bobbydyabb]

...
 So before checking the difficult and expensive parts, I would check the balancing of the wheels and tires.

Trolle, mange tak, you validated the recent tire balancing I did using a Brian Curry/Largiader/Hugh Kenny inspired pocket wheel balancer.  Front needed 1oz and rear, 1/4 oz.  It did improve the ride but unfortunately,  the wobble continues.

[Bob_Roller]

To recalculate the shimming requirements for the bearings, here's a general overview .

With the bearings and races clean of any grease, apply a light oil to the the bearings, reassemble the 'top hat' spacers that contact the bearings themselves, bearings and spacer, wedding ring spacer in the wheel , insert axle tighten the nut to the specified torque, then use a spring scale to see how much force is required to move the wheel, by attaching it to one of the 'spokes' of the wheel, where it connects to the outer rim . .

Front wheel is no problem to do  this, but the rear wheel obviously can't be done on the bike .

I rigged up a fixture of sorts, by securing the axle to a pair of automotive jack stands .

I needed to get a piece of pipe to take up the 3 inches or so of axle that goes through the final drive, so I could torque the axle nut and bring all of the parts together, like it would be if it were installed in the bike .

In Snowbums BMW tech site, he gives the whole process in detail .

Mike V and myself, had a few threads about this around August or September last year, do a search, I think just about all of your questions will be answered in these postings about bearing adjustment .

[montmil]

When you did your wheel bearings, did you use Cycleworks' race remover?  Also, how did you recalculate/redo the wedding ring/shim size?

A propane torch, played gently around the wheel hub, will allow you to then use a long drift punch to easily remove the outer races... Piece o' cake.

To fit the new outer races, place each outer race in in a zip-lok baggie and toss it in the freezer overnight. Mark the bags and the cardboard bearing packages so as not to mix up the bearing sets.

Reheat the wheel hub to a "spit sizzle" temperature, square up the outer race to the wheel hub, then use a matching size metric socket to drive the new races into position. S-o-o easy a caveman could do it.

See the other posts to help answer your additional questions... although I personally believe the entire bearing preload angst is highly over rated. I have my own technique that's served me well for the years I've owned my brace of R65s...

Monte

[bobbydyabb]

I had the same symptom a couple of years ago.  I checked the head bearings and the swing-arm adjustment.  It was neither of those.  What it turned out to be was the rear shock absorber preload.  I increased it a couple of notches and the problem went away.

Finally tested this yesterday --- and ---
It did help significantly.  The wobble still occurs on that particular strip of freeway but it's much tamer now.  Having recently rebuilt the Koni rear shocks, a two notch increase (to "3") was too stiff, and so I set it to "2" for the major portion of the test ride.  

Looking back at it, I suppose the rear wheel had too much undamped boucing and coupled with the deep freeway grooves on "my" test strip, resulted in significant lateral tugs that started the front wheel wobbles.  I don't know.  Just surmising, plus there's the tire cupping at 4K.

So, many thanks Crossrodes.

[bobbydyabb]

... although I personally believe the entire bearing preload angst is highly over rated. I have my own technique that's served me well for the years I've owned my brace of R65s...  

Monte, I still plan to do the rear wheel bearing job (and front fork alignment) and would be interested in your bearing preload  technique.