sudden bang and lurch - twin cam

birdseye

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odd one this. out for a ride with a pal I had a bang and a luch forward exactly as if said pal had run into my rear wheel but he was a good 20 yards behind me. I didnt stop immediately but when I did I couldnt find anything wrong. Rode on for another 30 miles or so with no issues at all. Neither of us saw anything in the road. Bike is a 2012 with jut 2k on the clock. No bevel box play.

Any ideas? Best I can think of is something to do with boots and gear change. The lurch was reall quite big.
 
I imagine you didn't select a gear properly and it dropped out into a lower one...... :nenau
 
Do you mean it suddenly accelerated, propelling you backward, or suddenly slowed, propelling you forward? If it's the latter I'd go with Schtum's diagnosis...
 
I think ( its so difficult to remember ) that I got pushed forward as if hit from behind
 
Really(?) but I guess a really big pothole could cause 4 bangs** but the rider would surely have noticed something that big.

** Front wheel in, back wheel in, front wheel out, back wheel out !!!
 
definitely not a pothole or the pal following. has to be sudden drive from the rear wheel to cause the jerk. the bang suggests that the sudden drive was the result of a sudden gear engagement as people have suggested. my alt berg boots are fairly thick and I have previously had accidental gear disengagement because of that.
 
When changing up a gear, it helps if you keep the pressure on the gear lever for a second or two after you've changed gear.

It's all to do with the weird BMW way of making the gearbox quieter or something. Steptoe posted a really long reply about it ages ago.
 
interesting. this is my third 1200gs but never had this happen before.
 
I like to preload the gearlever before shifting to take any slack out of the system. With it preloaded momentarily dip the throttle and the gear drops in as the transmission unloads. But the GS shifter seem very sensitive, so preloading can accidentally whack the gear through anyway - not good. :o
I tend avoid preloading the lever but help it with the clutch. Matched revs give a smooth shift.

Preloading the lever does seem to work for clutchless downshifts on the GS. On a closed throttle gently press the pedal until you feel the selector then momentarily (and minutely) blip the throttle. The transmission unloads and the gear drops in. I personally prefer the clutch miss-match revs blip method as its less fussy or maybe Im just better at it. :thumb
 
Bendy toy said:
I like to preload the gearlever before shifting to take any slack out of the system. With it preloaded momentarily dip the throttle and the gear drops in as the transmission unloads. But the GS shifter seem very sensitive, so preloading can accidentally whack the gear through anyway - not good. :o
I tend avoid preloading the lever but help it with the clutch. Matched revs give a smooth shift.

Preloading the lever does seem to work for clutchless downshifts on the GS. On a closed throttle gently press the pedal until you feel the selector then momentarily (and minutely) blip the throttle. The transmission unloads and the gear drops in. I personally prefer the clutch miss-match revs blip method as its less fussy or maybe Im just better at it. :thumb
Click to expand...

First you like preloading then you don't and what exactly do you think your preloading
 
Depends if I'm going up or down the box. The gear lever on bikes is centre weighted with springs. The lever moves about 1cm then the selector fork touches down. That's preloaded.

When shifting keep gentle pressure on the lever. When the transmission momentarily unloads the gear will drop in. No clutch needed.

To unload going up just dip the throttle. Going down with throttle shut a quick blip also unloads the gears. The shift happens in a fraction of a second so a clumsy throttle hand or left foot isn't good.

Pretty obviously, too much foot pressure (preload) on the gear lever will cause the gear to crash through with transmission under load.

My BMW has a more sensitive action than some bikes making clutchless shifts risky. It's safer on the gearbox to help with a bit of clutch lever.
 
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