Where is a 10mm bolt used in in the 308 Transaxle?

Speaking of unwelcome 'surprises' in sumps,
I just pulled my trans sump cover to do a shift shaft alignment. I found the head of a 10mm bolt (ie: hex socket size 17mm). The bolt was sheared off flush with the bottom of the head. Head is black metal.

WHERE IS IT USED?
Looked all over the trans & couldn't see where it might have come from, couldn't spot anything.

Then went all thru the FPC trans & diff pages. I haven't been able to spot where a 10mm bolt is used in the entire trans/diff. Found lots of 8mm & the ring gear bolts are 12mm. What am I overlooking?

Only place I'm familiar with a similar 10mm black metal bolt being used is to secure the flywheel to the crank. Can't envision a way a bolt head could migrate from the bell housing into the transaxle tho.

Confusedly,

 

John,
The ring(driven) gear bolts were my first thought also (see cross-section dwg below). However, I could not find any specs on them other than the torque spec.

However, when I saw the torque spec I figured I'd found where it came from. Given an 80N-m(59ft-lb) torque spec and Ferrari's consistency in using the same torque values wherever the same thread size & pitch are used, I'd expect the ring gear bolt to be the same size as other bolts with the same torque specs. eg: the half-shaft bolts are 10mm, & the torque spec is 8Kg-m(57.5 ft-lb). Thus most likely the ring gear bolts are also 10mm.

Uncertainty crept in:
The cross-section drawing indicates that the ring gear bolts have long shoulders that are larger diameter than the threads. making the shoulder most likely 12mm dia, thus the break at the head would be 12mm not 10mm.

Of course, the cross-section could be exagerating the size of the shoulder, relative to the threads & the shoulder is really 10mm. Another (IMHO unlikely in a high stress application like this) possibility I thought of is that the shoulder was undercut at the bolt head.

The other possible contra-indication is that drawing shows the half-shaft flang bolts are shown as similar in size to the ring gear bolts. The torque spec section of the WSM lists these bolts as 12x1.25 torqued to 9Kg-m(65 ft-lb).

So, does anyone know what size the ring gear bolts are?
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Tnx Tom,
Went back & looked again. Took a while to get the angle & light right. Rotated the ring gear & sure 'nuff there the rest of this sucker was(sigh). Hanging mostly out of the ring gear hole & starting to cut a groove into the side of the diff. housing.

Must have just broken because the groove isn't much more than a mark, maybe 1/2 mm deep. Also there weren't any Al chips in the trans lube or sump when I drained it.

Tried to get a pix, had a lot of trouble getting light up into that spot. You can sort of see the bolt, the nut, & the groove the nut is starting to make in this image:
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Just checked ring gear bolt prices at Ferrari.uk. Boy is the exchange rate unfavorable these days ($1.92/£ )!!!Replacing all 8 bolts is going to be a tad expensive & my wallet's flat after Christmas:

[8] #106777 CROWN WHEEL BOLT
Unit price: £15.20 $29.22 USD
Quantity required: 8

[9] #104011 SELF LOCKING NUT
Unit price: £3.80 $7.30 USD
Quantity required: 8
This part supersedes: 14511, 14795

$36.52/nut & bolt pair * 8 = $292.16 !!!!

Would like to hear from the professionals as to the need to replace all 8 differential bolts vs just replacing the broken one. Also don't want to be penny wise/pound foolish.

I don't stress the differential by such things as popping the clutch with the engine rev'd, but do downshift to get engine braking on the highway. This is literally the 1st differential I've had a problem with in almost 40 years of driving cars!

 

Descr earlier:

See above.

What kind of evidence can I look for?

Not that I've found, just recommended in a prior post in this thread.

 

Well, I'll pull out the last of the studs tomorrow AM, then will have the diff's cover off. Discovered that the studs for the left side seal holder/flange can't be removed w/o removing the half-shaft flange, so had to pull the left half-shaft.

Found one of the half-shaft bolts was missing it's head! No way to tell if it's related to the broken crown wheel bolt. Looks like the head's been gone quite a while, there was some very dark old looking rust on the end, not bright red like fresh rust.

BTW, anyone know of a lower priced source for the half-shaft & crown wheel bolts?

Any idea what grade they are? 10.6 ? 12.9?
Guess I can't go wrong with 12.9 other than spend a tad extra.

 

HERE WE GO AGAIN!!!

Yesterday AM I pulled all the studs out of the diff cover, EXCEPT for the last one. It's stuck! Of course it's the one that's way in next to the block with minimal clearance! The others came out vy easy w/my stud pullers.

The last one the stud puller rounded the threads a bit, but didn't break the stud loose.

Cleaned them up with a SnapOn thread chaser, then double nutted them. Only room for top nut to go about 3/4 way on. Stripped the $!#@$ threads!

Tried my trusty small pipe wrench, not quite enough room for it to get a good bite on the threads.

Bought an S-K stud puller (one w/off-set hole & round toothed wheel driven by a 1/2" socket. Wheel's teeth were too shallow, just filed a flat on the stud.

New pair of medium vice-grips can't quite grip it hard enough to keep them from turning on the stud.

After 6 hours fighting it, called it quits for yesterday.

Ordered a set of S-K impact screw-on/drive-on stud pullers (female easy-outs). Had to buy a set to get an 8mm one. (Already had the large Craftsman set, smallest size is 10mm(sigh), should have bought the $20 smaller set.

If that doesn't get it, then will weld a nut on the end of the stud...

Next to last resort will be to lift the diff cover up until it's as high on the stud as the block overhang will allow, then saw the stud & hope I can get it out with the pipe wrench once the diff cover is out of the way.

Last resort will be to pull the engine & split the tranny/diff case off of course(deja vu fer sure...)

BTW, the T.Rutlands crown wheel list price for the bolts is ONLY $43.66/bolt, $6.35/nut. BTW, nut is same F. p/n as conn. rod nut.

Spider348, tnx for the pointer to a local supplier. Found a couple of metric suppliers here in Nashua as well. Now I just have to figure out the performance class for these bolts. So far 12.9 is highest class I've found.
(Anyone know the perf. class for conn rod bolts? S/B same for these bolts.

Sure hope these bolts don't have a machined body.

Birdman, Haven't been taking pix as too much of a PITA w/my Kodak. However, my FZ20 just arrived, but the SD card is still in route. Figure I'll take pix during reassembly. BTW, my 8 mm stud puller seems to have developed problems, may be why it didn't deal too well with the last stud. Am going to pull it apart to see if anything's fixable. It's has a lot of use between my timing driver project, the JWise timing drive project, & this one. Thought it might have gotten oil/grease inside & tried cleaning it out w/brake cleaner, but it still isn't working right. Suspect I'll end up just ordering that set w/the 3/8" drive for the smaller studs.

 

Don't have the threaded end out of the tranny yet, but I suspect it's 10x1. The WSM torque spec is 80 N-m.

Still fighting with that last stud. Couldn't whack the drive-on stud pullers hard enough to drive them down to where they wouldn't strip instead of turning the stud. Only have about 40 or 50 mm to swing a hammer, less when you deduct about 30mm for the thickness of the hammer turned sideways. Just couldn't get any momentum up.

Next step is to try welding a nut on. Maybe the heat will help loosten the stud.