Twitchy Forks - weaving at 45 mph

[SJRoome]

Hi

I have a 1989 R100GS and I am finding the front end a bit twitchy. If I go into a bend on the correct line at the right speed and accelerate out of it the front end is steady as a rock. However if I have misjudged it and I have to roll off the throttle during the bend the front end seems to get a bit twitchy.

I have carried out a few experiments and the twitchiness is detectable when rolling off the throttle if you are looking for it even when on the straight. I have tried going hands off the handle bars and at speeds up to 40 mph it appears perfectly happy. However if I go hands off at 50 it goes through a period of fairly gentle weaving at 45 mph and then stops as the speed reduces.

I have checked for play in the front steering head bearing and forks I cant find any. I am using the Millichap cocktail for fork oil.

Is this behaviour normal, or is there something I should be checking?


Steve

 

[nud1e]

check the rear shock, I've found that many front end problems start at the rear

 

[John Armstrong]

Tyre pressures ok? Tyres plenty of tread left and not squared off? Clamps on forks secure? Back end bolts secure? Barn door fairing fitted? Rear suspension pre-load set up ok? Rear shock ok?

 

[toadjam]

my 95 100 gs pd is the same . i,ve had it 4 years now , doesn,t matter what tyres ,tyre pressure , shock settings or my position on bike .
if i take my hands off , when the speed gets down to about 40 the bars start to wobble .
i just asumed it was normal .
the last page in motobins hints and tips section says this means the bearings are too tight .

 

[DrFarkoff]

I hate to say it I've had quite a few airheads this last while and everyone of the feckers wiggled thier noses @ 40 miles and hour if you only had light pressure on the bars

The Cure for me was to remove the top triple clamp and clean and inpsect the bearings and to rebuild with fresh grease and to tension it up so that there is slight drag in the bearing lock to lock rather than just flipping side to side with great ease, whilst the front is supported

If you have little vertical straight lines in the casings then yer bearings buggered get new ones in

It works for me

NOTE Be careful don't overtighten the top nut!

Do it in increments and move the forks several times lock to lock each time when you stop to expel excess grease and settle the bearings

If you're too rough you may damage the bearing face ( Everyone says you can so who am I to say Nay?) My feeling is go softly softly catchy monkey and come slowly to your desired point rather than passing and having to slacken and retstart

 

[Beemerboff]

Good advice on the head bearings - I like them that way too.

The paralever bearings like to be that way too, and play in the rear pair can give your symptoms.

So can the wrong profile on the tires - I like a really rounded tire both front and rear, your may be too flat.

 

[(RIP) Proff]

Easy answer.
DO NOT throttle off in a bend, cog it down one and ring it's neck, as they drop down when you throttle off and lift when you ring their necks..
Even more noticeable on a mono or twin shock non paralever

It's called "ShaftJack"

 

[electric_monk]

Easy answer.
DO NOT throttle off in a bend, cog it down one and ring it's neck, as they drop down when you throttle off and lift when you ring their necks..
Even more noticeable on a mono or twin shock non paralever

It's called "ShaftJack"

Would I be correct in assuming that if the driveshaft is deteriorating this "Shaftjack" problem may be amplified.
My paralever developed the same symptons over the last six months and the driveshaft is knackered

 

[shafted]

It's been said before - head bearing's too tight.

Safe riding Karl.

 

[SJRoome]

Hi

In answer to people wanting more information. The tyres are Metzler Enduro 3 Sahara. The front has 2mm tread at the lowest point (the centre) and is at a pressure of 2.2 Bar. The rear has about 50 miles wear from new and is at 2.5 Bar.

The rear shock is original and at the lowest setting. It does not leak, and appears to damp effectively.

The bike is close to original and a photo of it can be seen here. http://www.ukgser.com/forums/showthread.php?p=1778692#post1778692

I have seen lots of posts on the internet about complicated ways of adjusting the steering head bearings on airheads and its effect on weaving at various speeds but they dont seem to agree. I have also seen posts saying that this is normal airhead behaviour.

Steve

 

[shafted]

The only time I have had a weave on a BMW, is when I adjusted new head bearing's too tight. None of mine weave at any speed or a closed throttle. One has a sidecar attached and the other (solo) has an RT fairing.

It should not be a usual practice for a BMW to weave (unless it's a short wheel base).

It is not hard to adjust head bearing's.

Safe riding Karl.

 

[SJRoome]

Hi

Well I have spent a long time reading about adjusting steering head bearings on airhead BMWs on various internet posts. There does not seem to be any form of consensus on this. One well respected pundit indicates that steering head tension on an airhead is a compromise between too tight and you get a weave at medium speed and too loose and you get a potentially fatal tank slapper at high speed and the way I have adjusted mine is about optimum.

I would be intersted in actual ride reports from similar bikes. Its easy - just ride at 50mph on a good surface in a straight line and take your hands off. Before you do so you need to be confident your bike is well set up and the tyres are at the correct pressure.

I am going to try changing the steering head tension in small increments and see what happens.

Steve

 

[Archie Adv]

I have been experiencing the very same symptom on my GSPD, and like you have ready every article I can find on it. It is also worthy of note that neither Clymer nor Haines give much info on this subject neither in their manuals nor for that matter does the BMW handbook. Does that tell a story in itself?

Anyway I've just had my bike MOT'd again and the steering did not cause it to fail. However I have been unhappy with it and my wobble comes on at exactly 60Kph or 36Mph. Not below or above. So effectively and according to some they would say whey worry. Well I don't worry but no matter what anyone says it is not meant to wobble at any speed and I want it to be right. Okay I'm a pedantic Barsteward.

Jaythro mentions little black vertical lines in the outer casing and that being the case says there shot. I don't disagree or agree providing the lines are not actual grooves which you would feel when turning the steering. These grooves would be more pronounced if the bearing were tightened. No argument there then!

Well after many discussions with my mate MickDB1 I decided to have another go. I mean Beemer are no different in this particular area than any other bike. IMO only.

So yesterday I stripped the lot down cleaned them and yes there was slight vertical lines on the outer casing in the top set only. I cleaned it up repacked the bearing race and casing with fresh grease and nipped it up until I was happy with the level of tension. It doesn't flop to the side like a limp dick now..!! Which it has done from the day I bought it about 20 months ago. I would hasten to add that I honestly don't think it had ever been apart from the day it rolled of the factory line in 95/96. The grease had hardened. So as I said above I cleaned them up repacked them and it was a case of job done. The steering does not wobble now at 36Mph or 60Kph. In my case I would put this down to lack of adequate maintenance on the PO’s part and on my part. It did take a an 2’ crow bar to prise off the top yoke from the steering stem once the lock nut and lock screw had been removed but rather that then knocking the sh1t out of it with a hammer. Gentle persuasion rather brute force and ignorance.

Slightly off topic but worthy of note and it may have been discussed on here a few years ago. When I had an 1150 GSA I had a similar effect on a new Metzler front tyre. This was down to a bad batch from the OM which was known about. My dealer tried to convince me it was by bearings or my rear shock. I checked them out to no avail. Finally I took the bike to and independent fitter bought a new tyre and had it fitted. Bingo won problem after then new tyre was fitted. I took the other one back to dealer and received a refund credit.

I hope I haven’t stolen anyone’s thunder and have not deliberately tried to annoy anyone by my posting on this thread.

Just my two penneth for what it’s worth….

 

[(RIP) pastyman]

Many years ago when on my advanced course we were shown a clip of film . I believe it was from the transport lab guys. It was called" wobble and weave"
It explained the difference and showed various bikes suffering weave at speed.It also discussed "wobble" and showed a BMW displaying this trait when slowing down and with the rider either letting go of the bars or holding them lightly. This wobble got progressivly worse but control was imediately regained by a firm hold being taken of the bars. This was not limited to Beemers but bearing in mind that the frame was not changed much , even later airhesds are likely to suffer. I managed to get a copy of this film but as it is on video, I cant post it.
Both my g/s and the 100 gs will do it if I let go of the bars. ( moral is,,, dont do it) otherwise the handling is fine at any speed and the bearings do not "drag"