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docc

ANSWERED Drive shaft failure

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The "crime scene" has no doubt been compromised, but is there anyway to tell if the fracture surface has evidence of being cracked for sometime? (ie: one side clean and the other dirty) I'm with the others suggesting yolk failure and still am wondering why. Is it possible to tighten one side enough to crack it? The other bolt holding as long as it could. Through over torque, inaccurate wrench, and/or flawed casting. I wish I had more confidence in the torque wrench "process", especially the lite spec bolts. Then there's that thread stress thing where some bolts are only good for one torque use. :huh::unsure: 

 

how's it go?     "Moto :mg:  Guzzi ... turning riders into mechanics for 100 years" :luigi:     (and, mechanics into  :rasta: + :drink: + :oldgit: )

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Docc, Have you checked UJ alignment?

 

I had v similar failure.

Don't trust the factory paint marks, that supposedly show alignment.

Mine were wrong, & in fact shaft collar/UJ's were welded so as to be impossible to align correctly.

Roper was always banging on about stresses set up by wrongly aligned UJs.

 

KB

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Docc , scrolling thru this thread : you stated you installed a different pinch bolt due to crossed threads ? The replacement bolt was the same size , thread pitch ? Was the bolt still in place or close by ?

 Can you post pics of the damamge yoke ? It does NOT look like the u-joint it self failed but the yoke failed . Does the fractured yoke show any rusting or is the break new ?

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That's over 100,000 miles on that driveshaft before fatigue, right? 

 

Good that you already have a replacement on the way. Off with the swingarm... and this is a good time to put a relief in the front collar for easy access with grease gun. Or did you already do that?

 

Yessir. On the cusp of 108,000 miles.

 

I still actually can't figure out where to make that cut (?)

 

I guess it's out of warranty?

They came with a warranty?

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Yeah, what's up with my twenty year warranty? :grin:

 

@Andy - yeah, there was something different about the RedFrame. Can't remember what it was.

 

@Chuck - I do have a beam that I got to cover this "in between" range for another job. I'll use it this time and verify the collars are tightly clamped onto the shafts.

 

@Gene - original bolts. My replacements didn't work out. One of these got re-cut pretty substantially after the cross thread mistake.

 

@Baldini - I remember your misalignment and checked mine then. I’ll get a careful look at the replacement. Thanks for the reminder!

 

I'll get another image up of the failed yoke. Wow, but there is not much metal there considering what that piece does!

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I'm guessing, of course..but..

 

One of these got re-cut pretty substantially after the cross thread mistake.

is likely the culprit. :2c:

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I'm guessing, of course..but..

 

One of these got re-cut pretty substantially after the cross thread mistake.

is likely the culprit. :2c:

 

Even if it isn't it sounds guilty.

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Docc , if you were able to reach & maintain the torque value I would rule this out .

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So, a couple things . . .

 

Red arrow points to the largest broken surface that does not look as fresh and shiny as the other breaks. Blue arrows to the threaded surfaces that look pretty flattened to me. These things are soooo easy to cross thread on re-assembly. Ignition key is there to show just how small this part is and how little metal is there! :o

 IMG_6196.jpg

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Yeah that was deffo broken before now. 

My '97 has 10 (?) spline shafts, and the yokes were loose on the splines on both ends. All four of the pinch bolts were hella tight and came out with the factory threadlocker on them. I wish I had tested them to see how much they had to turn to tighten up before I removed them, but upon reassembly everything tightened up nicely. I didn't torque them, but an educated guess with a 6" 3/8 drive ratchet says about 30-35 lbs-ft. And red loctite 'cuz they're staying in.

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Yes docc looks like it has the classic "beach marks" that define a progressive fatigue failure.

 

Ciao

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Can you post pics looking straight into the cups ? What condition is the cross ? 

The darker portion of the break is the first crack and the beginning of the failure .

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Can you post pics looking straight into the cups ? What condition is the cross ? 

The darker portion of the break is the first crack and the beginning of the failure .

IMG_6198.jpg

IMG_6197.jpg

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The marks on the cross do not go all the way round the mating surface, only about 25% around. Pretty much what you see there.  The other cap was destroyed in the bashing about.

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