1975 BMW R90/6 speed wobble problems. HELP!!
 

Hello there,

I have a 1975 BMW R0/6 that is in great shape, purchased it from an english fellow who rode from alaska to new orleans. It runs great and all is well except one major problem.

When I get up to around 70 MPH there is a fairly unpredictable wobble that begins randomly. speeding up makes it worse, slowing down to under 70 cures the problem. Sometimes I can up to 80 or more without it occuring, but then out of nowhere, it happens.

I have noticed that when I add a good amount of weight (ie second passenger, or my camera gear (45pounds) to the rear seat of the bike, there is no wobble issue.

So I loosened the rear shocks a bit but that didn't seem to cure the problem

any advice or knowledge would be greatly appreciated.

Thanks!

Max

R90/6... ahhhhh an engineered motorcycle. I'm assuming you have checked for chassis problems like worn or over-tight steering head bearings? Get the front wheel off the ground and turn handlebars slowly to feel for tight spots or lumps. Grip front wheen and try to pull it back and forwards. Grip top and bottom of each wheel when off the ground to check the wheel bearings don't have play.

These bike are very sensitive to tyre type, tyre wear and tyre pressure. What sort of tyres are they and and how worn? What pressure?

Regards

Nigel in NZ

Hi Nigel,

You are describing a damaged speedo cable/wire, and/or hypoid connection.

Here is the speedo set-up:
http://www.realoem.com/bmw/diagrams/c/w/16.png

RealOEM.com * BMW K51 R60/6 SPEEDOMETER SHAFT/REV-COUNTER SHAFT


Here is the connection of the speedo set-up:
http://www.realoem.com/bmw/diagrams/d/y/10.png

RealOEM.com * BMW K51 R60/6 Cover


Here is the hypoid drive connection for the speedo:
http://www.realoem.com/bmw/diagrams/e/a/4.png

RealOEM.com * BMW K51 R60/6 Short Engine

Begin with checking that the wire is ok.

The connection into the instrument house - it happens that the wire get unscrewed...
Rare, but it happens, the "sprocke-drive" inside the speedo in the speedo-gauge can have been damaged/worn-out. (should last >>X00 000 miles...)

The problem with the crank-connected speedo is very well known. The newer shaft connected has a reputation to be far better.

...did you mean vehicle wobble and not speedo wobble?...

Yes simple!
* new steeringhead bearing
* steeringdamper - install or renew if broken
* new swingbearings

Renew bearings since if you have gotten wobble and not touched them, they are worn (badly?). You will be wasting your time if you only try to reset the bearings preload and torque-down pressure.

Too large play at steeringhead and swing-arm attachment will result in wobble.

IF your shocks have lost their shock-absorbation (=broken oilseal and no oil left in them) - this will also cause wobbel at higher speeds. Overhaul or renew.

If you've got broken forkseals - lost oil. It may cause wobble. Renew seals, Fill with Omega 699 Automatic gearbox oil (5W/20) and Omega 917 seal improver => same daping cold as hot and the seals are "protected" and will last several times longer.

Sub-frame loose at connection under the tank/seat => will cause wobble.

Sprocket broken in wheel, or sprockets unevenly tighten; wheel not round and skewed => will cause wobble.

My experience is that the bearings are the prime cause to suspect.

There is a joker cause also:
- if your steeringhead bearings have rusted solid and you have used chain-oil or similare sticky slippery grease fluid to the the steering to operate - that will cause wobble at higher speeds since the bearing is no longer a ballbearing... oh, yes - I've tested this and passed our yearly vehicle (e.g. TÛV) inspection several years in a row before I realized/discovered the problem... yes - no BMW mechanic found the problem either(!)...

Did you find the problem?