Swingarm failure - torque arm mounting point

[kebab19]

Had a bit of an incident this morning.
Normal road riding conditions probably doing 50 or so at the time.
Pulled front & rear brakes to slow down, heard a fairly loud crack then realised that the rear brake pedal was solid and wasn't working anymore.  I was about 2 miles from home so limped back and then had a look in the driveway.
I was disturbed to see both the rear caliper and the torque arm had rotated up round the top of the swingarm.  I thought the torque arm securing bolt had either come off or broken but then took a look under the swingarm where the torque arm mounts  :eek Brake fluid all over the back wheel after the line got twisted round.
These swingarms are alloy so it can't be due to corrosion.  I have no idea how this could have happened, everything was secured safely.  Could it be down to the bluespot rear (or silverspot in my case)? Metal fatigue?
I realise some people will suspect I was acting an eejit, locking the rear at 80 or something, but this wasn't the case.  Sobering stuff....
Anyway, I now need a replacement swingarm, RHS chain adjuster and rear brake line now  and new pants

[fazersharp]

Glad that you are safe mate - but I don't know why people want to go changing the original back calliper and arm anyway and your experience is another reason not to do so.

[Fazerider]

:eek
Scary. Lucky it didn't lever the back wheel off the road as the arm pivoted round. Guess I'll take a look at mine tomorrow to check it's not threatening to do the same thing.
Good luck with the repairs.

[His Dudeness]

Lucky escape alright. Any chance the bolt was over tightened and that might have cracked the lug on the swingarm?

[Paulfzs]

Powdercoat could hide anything, as above maybe it was too tight, suppose you might get away with making a bracket and drilling the swingarm if youre feeling brave...


This is why i kept the original torque arm.

[His Dudeness]

You could get it ali welded if you wanted

[MC680x0]

If you were doing 80 when that happened your lucky the whole thing didn't go through the wheel and send you flying into the air in a different direction to the bike. Glad you are here to do the show n tell. I won't be fitting a fancy torque arm/blue dot now.
Cheers and stay safe

[unfazed]

Fitting a blue dot caliper would have nothing to do with it as it is fitted to the standard mounts. :rolleyes

Fitting a non standard torque would be a more likely culprit.

Another culprit would be, not loosening the caliper side and swinging arm side torque arm bolts when adjusting the chain.

[Skippernick]

Fitting a blue dot caliper would have nothing to do with it as it is fitted to the standard mounts. :rolleyes

Fitting a non standard torque would be a more likely culprit.

Another culprit would be, not loosening the caliper side torque arm bolt when adjusting the chain.

Sorry don't get that unfazed, why would you need to do that? If the torque arm is undone but the calliper bolts aren't and you realigned the rear wheel/chain tension the torque arm would still be in the same place. It's all a fixed point.

[His Dudeness]

The angle of the torque arm changes as you adjust the chain. You really notice it when you go from an old stretched chain to a new one.

[fazersharp]

Fitting a blue dot caliper would have nothing to do with it as it is fitted to the standard mounts. :rolleyes

Fitting a non standard torque would be a more likely culprit.

I always thought (from reading past posts )that if you were fitting a blue dot then the OEM arm was the wrong length and so you also need a different arm to match.

[MC680x0]

And thus if you don't loosen the calliper end torque bolt, the arm is stressed under tension, and this applies a shearing force to the other end of the torque arm mount... where yours has sheared off !!

[fazersharp]

If you look at this picture the area around the mount point on the face of the swing arm looks ground off a little, also the welding on the mount point dosent look like a factory neat job,has this already been re welded in the past I wonder, I also see a different shock and dog bones as well as the non oem caliper and arm .
I wonder if its a combo of all these things was just too much of a change in speck for the OEM mount point
 

[unfazed]

The angle of the torque arm changes as you adjust the chain. You really notice it when you go from an old stretched chain to a new one.

And thus if you don't loosen the calliper end torque bolt, the arm is stressed under tension, and this applies a shearing force to the other end of the torque arm mount... where yours has sheared off !!

Eureka  :thumbup :thumbup :thumbup



Nothing to do with suspension

[fazersharp]

[quote author=His Dudeness link=topic=14772.msg167448#msg167448 date=1411296336]
The angle of the torque arm changes as you adjust the chain. You really notice it when you go from an old stretched chain to a new one.

And thus if you don't loosen the calliper end torque bolt, the arm is stressed under tension, and this applies a shearing force to the other end of the torque arm mount... where yours has sheared off !!

Eureka  :thumbup :thumbup :thumbup



Nothing to do with suspension


[/quote]

Hmmm -- I pulled my wheel back a few months ago by about 2mm (yes) do you think I should now go and loosen off the caliper-side arm bolt, and then re tighten to realease said stress

[MC680x0]

Mmmm

[fazersharp]

Sorry I dont get you tweety ?

[MC680x0]

LoL
Soz. I was pissin around a bit. 4give.
Loosen the bolt AND the calliper hanger bolt, THEN adjust chain, and then tighten up to the torque specs

[fazersharp]

Ok, I sort of knew I should losen the arm bolt but from my memory of the manual there is no need to lossen the caliper hanger bracket.

EDIT or by caliper hanger do you mean caliper hanger side of the arm.

[midden]

Should loosen both ends of the torsion bar for adjustment  :rolleyes