Subject: [Fot] GT6 differential failure follow-up

From: Scott Janzen <[email-masked]>
Date: Sun, 19 Jul 2015 18:46:34 -0400

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Pulled my differential out and apart today - did not find what I =
expected. =20
The input/pinion shaft is sheared off just forward of the pinion gear. =20=

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.

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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
"><div>Pulled my differential out and apart today - did not find what I =
expected. &nbsp;</div><div>The input/pinion shaft is sheared off just =
forward of the pinion gear. &nbsp;</div><div>The crown wheel has barely =
a mark on it, all teeth intact, no signs of damage.</div><div>The inner =
tapered bearing race on the pinion shaft is just mangled and there are =
roller bearings all over the place. &nbsp;However, the outer races for =
both pinion bearings look fine - no sign of discoloration or =
overheating, significant damage, etc.</div><div>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&nbsp;minimal sign of rotational damage to the =
driveshaft - just a couple of paint scrapes. &nbsp;It was essentially =
unsecured at the rear, but perhaps the outer/forward pinion bearing kept =
it centered.</div><div>Both the shaft and the gear rubbed against each =
other so much there's no way to see any fracture marks.</div><div>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. &nbsp;I had just topped it up before the =
weekend, and there was no sign of oil under the car throughout the =
weekend. &nbsp;Guess I'll be tapping the next diff for two more bolts, =
so there are six securing the spring next =
time.</div><div><br></div><div>Photos attached.<img =
id=3D"8c0b48cd-c54c-4581-af0d-373d8167de5b" height=3D"1022" width=3D"766" =
apple-width=3D"yes" apple-height=3D"yes" =
src=3D"cid:9F694021-28EB-46FB-8EC6-BB5C950D9848@home"></div><div><br></div=
><div><img id=3D"06eec5c3-97f4-4a7c-b08a-536811669de3" height=3D"1022" =
width=3D"766" apple-width=3D"yes" apple-height=3D"yes" =
src=3D"cid:0B882439-6950-4FC9-B980-BB60DF264B8A@home"></div><div><br></div=
><div><img id=3D"162eff64-7ae5-4a63-8e45-1eef295ce5a9" height=3D"575" =
width=3D"766" apple-width=3D"yes" apple-height=3D"yes" =
src=3D"cid:4C47ABF7-0265-468B-9061-153C138BE531@home"></div></body></html>=

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