Wobbling at 15 to 25mph

SPRIDDLER · Post by **SPRIDDLER** » Mon Mar 28, 2005 5:08 pm

Tks Rohan - The wobble / oscillation certainly increases when I brake - and with one hand off and signalling it even frightens oncoming drivers. I've put the pressures up to 21 front and 24 rear which is noticeably better. I'll try a bit more. Must get back out into that sunshine, NOW!

Rohan B. · Post by **Rohan B.** » Wed Mar 30, 2005 2:39 am

Neville,
I think you need to have a long hard look at everything that might cause this - doesn't sound right (or safe) to me, and tyre pressure alone shouldn't do this either.

If you get the front wheel up off the ground and spin it, does the wheel spin true ? Is it out of balance ? With the wheel out of the forks, can you rock the fork sliders (alloy bits) on the fork tubes - worn fork bushes ? Off the ground, does the steering flop easily side to side - or is stiff or notchy to turn ? Loose or tight or notched or dry steering bearings could easily be the culprit. Hard to get to them I know, but need to be perfect...

You mentioned swing arm. Are the Jampots in good order - weak or fading damping could just do this too. Rear chain not too tight ? Frame bolts all tight and correct ? Gearbox adjuster bolts tight ? String line along the wheels shows them in line and pointing in the same direction ? Not gripping the tank too tight with your knees in terror ? (just kidding - but I have seen this....).

Its there somewhere - you just have to find it before it maybe bites...

hopethishelps,
happy cycling.
Rohan.

SPRIDDLER · Post by **SPRIDDLER** » Wed Mar 30, 2005 10:14 am

Thanks Rohan, G'day.
I'll do some serious checking this weekend - I've already checked the alignment with string, chain tension (on and off the centre stand), wheel's not buckled and tyre runs true. Frame bolts are all tight (in fact I replaced two across-frame bolts as the threads were knackered). The steering head is free and smooth. I'm not sure how th check the jampots except by bouncing up and down on the seat - as I would to check a car's shock absorbers. I guess I'll have to take them off.
I'm an ex Greeves scrambler (35 years ago) so I'm used to wrestling a 'bike along, and am quite relaxed as long as we're both going approximately in the right direction, but I must say that I can't understand how these machines were so successful in trials - I have difficulty threading through traffic, never mind how they managed trickling along rocky streams and sharp turns over greasy tree roots at 2 mph!
I've covered 1600 miles during this winter (I bought the bike last October) and it goes like two of dripping - except for the wobble!
Neville

itma · Post by **itma** » Wed Mar 30, 2005 4:05 pm

neville , you sure got something wrong with your bike, i`ve had lots of these and never had anything like this, they`re usually pretty solid whatever else their faults are, my thought at first were with tyres, those jap dunlops are crap, i had one on my rigid and it did`nt like it at all.
they seem to be far too supple[unlike me] the brit dunlops were less flexible, the proof being in the ease of fitting, of the jap tyres, i found conti`s or metzlers better but dearer.
but nothing was as bad as you have, sounds frightening,you sure you`ve not got a frame defect/one thats not easily seen, a crack or summat like? have you had a second opinion ride it
seeing as you`ve only had it since october, did you buy it from a known source? it seems to me, as a cynic, that the answer to your problem could well be in the previous owners [in] competence with the spanners

Rohan B. · Post by **Rohan B.** » Thu Mar 31, 2005 4:42 am

Unhelpful comments. "[in] competence with the spanners" is something that has to be able to be measured or observed to be wrong. Thus far we have neither.....

Modern tyres are generally far better than those hard old things of days past - and far more forgiving. Which is not to say all tyres will suit all bikes, or riders.

Jampots can maybe only be tested by substitution. Although taking them off and seeing if they have any damping action may be a start. I seem to recall reading mention of fading damping even when these units were new - didn't the compy riders use disguised Girlings or Armstrongs or something ?

If this were my bike, I'd then have the front end off and have a good look at the steering bearings. And grease them while there, these would have to be the most neglected item on a bike ? Although wandering steering is the more usual fault with a trace loose steering bearings, rather than a shimmy...

Hmmm, hope your frame has not had some sort of accident damage that has affected the steering geometry, this could be very hard to assess. In AMC bikes, the frame front can be changed out -relatively easily even - as a last resort....

hopethiselps,
Cheers,
Rohan.

SPRIDDLER · Post by **SPRIDDLER** » Thu Mar 31, 2005 10:24 am

Ken, Rohan, Hmmm, thanks.
I'll press on and give some more thought to these suggestions - esp. the tyres. We had a Sussex section Bun Run last Friday and I asked a couple of the guys to have a try - but none of those that had been following me were very keen. Can't think why...............!
The bike was repatriated from the Rhodesian Police 6 years ago and I bought it from its second UK owner. I assume the first owner was the importer. Whatever it needs it'll get. I swear it wags its tail whenever I go into the shed. Don't always have the time to take it out though.
Next instalment after the weekend no doubt.
Neville

itma · Post by **itma** » Thu Mar 31, 2005 12:34 pm

believe me rohan after 40 yrs working with/ on these, and having seen some of the shiny horrors that are about, i reckon i can spot spanner incompetance from 20 paces, and believe me this one has all the hallmarks, if were mine it`d be in small bits for a looksee pronto,
sorry neville

Mike Plant. · Post by **Mike Plant.** » Thu Mar 31, 2005 7:05 pm

I had what sounds like a similar "speed wobble" on a Douglas Dragonfly,the front tyre suspected though looked OK. Problem went away with a brand new tyre,but is gradually returning after about 600 miles.. In my case,between 25 and 36 mph. Put down to the Earles forks,the weight behind the wheel--but that would not apply in your case... Good luck in solving it,eventually!.

itma · Post by **itma** » Thu Mar 31, 2005 8:19 pm

[?] ..why would anyone go to the trouble of bringing one of these back here when the uk`s full of them I ask myself?.....it must have had a hard life out there...not too many motorways and probably none too hot on the maintenance side; after years of sanctions against what was his name the spares situation must have been dire, and I doubt keeping the thing in original condition for posterity was foremost in their mind...
I regularly used to see a similar situation with brit bikes bought back from spain by amateur optimists, only worse .
My advice to neville is get it to bits and scrutinised before you come a serious cropper....downtime in the shed is preferable to downtime in hospital or a coffin... some of us are a bit too near the coffin as it is[:(]

Merlin · Post by **Merlin** » Thu Mar 31, 2005 11:20 pm

Thanks for the last thought Ken will go to bed now a happier man[|)]