[Fot] GT6 differential failure follow-up

[Jason Ostrowski]

Wow, I have not seen that happen before. For me, Usually it's ring and pinion, which often destroys the case. 
In terms of bearings, We have always used good looking and working original stock ones as well. I suspect this one just went as a result of an high revving extreme load under the conditions you describe. As knowing your attention to setup details are spot on the factory manual methods. That is our way too (less the welded spider gear). I think it's just a failure more racing related which just happens when you are trying to go fast and shows you are doing a good job of trying to drive harder ( can't be mad about that). 

I've been told by some of the best that the 4 bolt spring attachment is fine and will be fine. Yet I agree with you completely and feel that the 6 studs are necessary and a proper choice for the GT6. 
Thanks for the update.
Keep doing what you have been doing with the differential. 
And maybe it's best to just try to keep it in third for the descent and shift again way later. Just use second (if you must) after a nice blip once you are all slowed down and ready to accelerate again. 
Jason Ostrowski
Friendly Ghost Racing

Sent from my iPhone

> On Jul 20, 2015, at 7:08 AM, Scott Janzen <sjanzen at me.com> wrote:
> 
> Bearings are what was in it.  If bearings look good/feel good, I tend not to replace them. Figure old used stock is probably best, but maybe not.  Pre- load, always suspect.  The diff I have "ready" to put in is going to be disassembled and reassembled just to confirm. Shims and spacers at the ready - !
> 
> Sent from my mobile device 
> 
> On Jul 20, 2015, at 7:58 AM, fubog1 <fubog1 at aol.com> wrote:
> 
> Scott I realize it's after the fact, and that thing is pretty torn up, so I'm a little hesitant to speculate... but when you rebuild it make sure NOT to use the crap bearings on the market, Timken only, and make sure the preload is correct...
> Glen
> 
> 
> -----Original Message-----
> From: Scott Janzen <sjanzen at me.com>
> To: 'Friends of Triumph' Triumph <fot at autox.team.net>
> Sent: Sun, Jul 19, 2015 6:54 pm
> Subject: [Fot] GT6 differential failure follow-up
> 
> Pulled my differential out and apart today - did not find what I expected.  
> The input/pinion shaft is sheared off just forward of the pinion gear.  
> The crown wheel has barely a mark on it, all teeth intact, no signs of damage.
> The inner tapered bearing race on the pinion shaft is just mangled and there are roller bearings all over the place.  However, the outer races for both pinion bearings look fine - no sign of discoloration or overheating, significant damage, etc.
> It did fail when I was decelerating in second gear at high RPMs down the steep downhill on the new course in Pittsburgh, so the engine promptly slowed down - still, amazingly, there is minimal sign of rotational damage to the driveshaft - just a couple of paint scrapes.  It was essentially unsecured at the rear, but perhaps the outer/forward pinion bearing kept it centered.
> Both the shaft and the gear rubbed against each other so much there's no way to see any fracture marks.
> One of the four bolts securing the spring to the top of the differential had cracked the housing, and it clearly leaked some oil there, but judging by the lack of oil on the underside of the car, I don't think this contributed to the failure.  I had just topped it up before the weekend, and there was no sign of oil under the car throughout the weekend.  Guess I'll be tapping the next diff for two more bolts, so there are six securing the spring next time.
> 
> Photos attached. <FullSizeRender.jpg>
> 
> <FullSizeRender.jpg>
> 
> <FullSizeRender.jpg>
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