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

91t4,
No mixup, but the crown gear torque specs have changed:
Suspect you're got 10.4Kg-m from 308GT4 WSM.
I'm using the 308QV/328 WSM's torque spec. of 80 N-m/8.15 Kg-m/59 Ft-lb (See 308QV/308 WSM differential image w/torque specs on it in my 2nd post in this thread.)

ham308,
Tnx, your recommendation makes sense. Also perf. class 10.9 bolts are a lot more readily available.

tbakowski,
Umm,
Think you have something. Just might be able to force it. I can see the stud's bottom thread when the cover's all the way up. So, maybe 10-12 mm of thread is all I've got to get past. Might just be able to pry the cover off with a long pry bar & a couple of pieces of oak to protect the cover-base mating surfaces. A lot will depend on if the stud will bend a bit under pressure & how sloppy the hole in the housing is/will be when the end of the stud gouges it a bit. Your angle is a tad off tho,Think I'll need to pry at more like 45 degrees(LOL)... Will try tomorrow or Fri. night as have a NASTAR race tonite.

 

Got it!!! Owe you a cold one if we ever meet! A long pry bars in between two mall oak blocks abutting the stud, and wiggling the cover while prying up got it off in about 3 minuites!!! Wish I'd known that would work before I put in 10-12 hours on the #$%^ stud.

The stud came right out 1st try with my stud puller, very little break-loose force! Must have broken it loose on my last try & hadn't realized I had done it(sigh)! Anyway, it's out at last.

Reference attached images:
Groove in diff. cover - Note that it starts at the cover's edge & stops at the groove thru the cover, then reappears at the other cover's edge. The bolt's nut end was jammed into the groove when I pulled the cover off. No wonder I couldn't turn the wheel by hand in one direction to see if the bolt was still in the crown wheel!

Vy strange, Really looks like it literally just happened!

I think I must have stressed this somehow just as I was getting the car up on the blocks for the lift. It didn't quite stop soon enough, ran up on the ridge that keeps it from going too far fwd. &, started to roll backwards. I hit the brakes, to stop it, then let out the clutch & pulled it up to center it on the boards. Don't remember it jerking or anything tho.

BTW, Malcom West's (Ferrari.uk) email informed me that they're out of the crown wheel bolts & don't have a source!!! Now I've really got to find an alternative part!!!

Anyone know if the Ferrari differential was used on another car? Who makes it for them?
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Had a chat with a local machinist today. He's also a car buff ('vettes, & does classic VW beetle restorations as fill-in when his machine shop business is slow.)

He kept looking at the bolt & muttering something like: "I can't see any thing other than over-torqueing that would have caused this to fail this way."

Looks like a grade 10x1 80-mm grade 12.9 bolt down, turn a small boss on the head, and extend the threads by a few mm, then re-heat treat it. IF the original hardening isn't so hard that it can't be machined.

Am also thinking about having the bolt head & end drilled for safety wiring. - Any comments?

So I'm looking for some grade 12.9 metric bolts.

Initially thought the bolt was machined. However, after looking at it out of the car, I believe that it was rolled, then the shaft was slightly machined to ensure exact diameter & surface finish. It's very possible that it was made from a std. part the same way we're thinking about doing.

Will post the drawing & other spec details in hopes that someone will come up with a closer match.

BTW, Malcolm said that the differential is mix of Ferrari unique parts & ZF std. pieces. Anyone know what other cars used ZF differentials? BMW? VW? P*?...

My son works in a BMW parts dept, am going to ask him to see if he can get some likely crown gear bolts in. Might just be able to match one up.

Also, is there any way to contact ZF to see if they have something that'll work?

re: castellated nuts - These have much thinner slits than I'm used to seeing in nuts where a pin or safety wire is intended to ensure they stay in place. I suspect that the castellations are bent inwards to make them into lock-nuts. Ferrari seems to use that a lot, eg: the timing drive ring nuts, & the half-shaft nuts are this kind of lock-nuts. Can tell better when I pull out one of the intact bolts.

Anyway, will use blue loctite on reass'y fer sure.

 

Malcolm West was kind enough to generate this drawing of the crown wheel(aka ring gear) bolt to help in sorcing a replacement.

If anyone can identify a replacement, or even a close match, please post a response to this thread & send eMAIL to: [email protected]
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Yes, tnx, sent you email an hour or so ago.

 

Found a table cross-referencing various steel alloy standards. Here's the list of equivalent standard alloys for the crown wheel bolts:

EN: EN24 Alloy Steel:
BS: 817M40
DIN: 34CrNiMo6
IS: 40NiCr4Mo3
SAE/AISI: 4340

That's one tough alloy, Machinery's handbook describes the 4300 series as a 'high case & core hardenability alloy" recommends it for applications such as axle & other heavy duty shafts!

 

IMHO, the shaft diameter (10mm +0/-0.015) is very important. The bolt must be a snug fit, ensureing that the crown gear & spider housing halves can't move back & forth with changing load. Otherwise they'll start wearing the holes & the bolt, leading to failure. The primary forces acting on these bolts are shear forces where they're transferring the main driveline engine power from the crown gear to the spider gear housing.

The drawing's specs are derived from the Ferrari purchase spec. ones, including the alloy and bolt tensile strength grade. Note my earlier post in this thread (01-05-2005 04:31 PM) about the torque spec changing from 102N-m for the GT4 & early carb'd cars down to 80 N-m for the QV & 328. Suspect the torque spec was reduced because field failures were being encountered.

While ideally this would be made as a rolled bolt, It looks possible to make this part from an ~80mm std bolt with a washer head by slightly machining the body to ensure the OD isn't greater than 10mm, cutting some add'l threads, and cutting the length down. Thus preserving most of the characteristics of a rolled bolt. Of course the alloy used by the std bolt would have to have claracteristics very close to EN24/4340

 

Steve, You're right , it's +0/-0.15, had decimal point in wrong place. Tnx for catching my typo. The fingers & head weren't synched.

 

tbakowski,
TNX,
Rcvd the 4 bolts yesterday PM. "The check is in the mail'...

Am going to continue to look for sources, would like to replace all 8 & add them to Unobtainium's list of products.

 

One bolt mfg responded with:
"8 pcs, would be $156.50 each [$1252 total]"

I thought FNA prices were high! I did NOT tell them anything about the application other than it was an automotive differential.

Am going to call to see if any non-critical part of the spec. is driving the price thru the roof.

 

Have been getting quite an excellerated education on fasteners. Also have learned that both the parts currently in my car, and the ones tbakowsky had made are very close to each other, but differ significantly from the spec drawing. Also that I may be able to use standard

spent several hours yesterday discussing the ring gear bolts with Spider348, and his father Ed. Ed is a retired tool & die maker grade machinist. Ed really knows his stuff. I learned a lot about high strength fasteners in a hurry!!

After looking at the spec, Ed said that what I should be looking for is a a 'Hex Head Cap Screw', not a metric bolt for these reasons:
- The washer face is std on hex head cap screws.
- The std 10mm cap screw's body diameter tolerence of +0/-0.22 is close enough to the 10677 ring gear bolt's +0/-0.15 tha it's highly likely that off-the shelf screw bodies would meet the spec. (assuming that the screw mfg. tunes his process to 10mm-0.11 - the center of the tolerence range).

Hex Head Metric Bolts do not have washer faces, and they have body much looser diameter specs, eg +0.58mm/-0.58mm for a 10mm bolt.

Ed's recommendation was to get a standard 10x1x70mm class 12.9 hex head cap screw, verify that the body diameter met the spec, and then cut off 8mm of the threads.

This would produce a 62mm long screw with 18mm max thread length instead of the spec's 15mm, thus the body length would be 44mm instead of the spec's 47mm. He said that the extra 3mm of threads wouldn't be significant in this application.

Ed also asked about the 19mm head spec. I told him that I was pretty sure the broken bolt had a 17mm head, but would measure it to be sure. He said that the standard head size for a 10x1 Hex head cap screw will be fine, especially since the 80N-m torque spec is well below the yield point spec for a class 12.9 screw.

Definitely want rolled, not cut threads, and a tighter thread fit is definitely desirable also as it provides larger surface contact between the mated threads. (ham308, did tell me this earlier in this thread.)

TODAY I FOUND OUT THAT MY CURRENT BOLT's don't match the spec, and neither do the ones tbakowski had custom made!

I pulled one of the unbroken bolts & measured it. I wanted to determine just how close to the inner edge of the ring gear the start of the extra 3mm of threads would be.

Here's what I found:
The 19mm head can't be critical as the current bolts, & the ones tbakowsky had made, all have 17mm heads. (See images below)

The bolt with purple layout fluid on the threads is a tbakowsky bolt that I'd inserted into the differential & then painted the threads that extended beyond the gear's surface. From this I learned several things:
-Unthreaded body length on the current bolts, & tbakowsky's bolts is ALREADY 44mm, instead of the spec'd 47mm.
- ~49mm of the bolt is inside the differential/gear stack.

The other bolt is from my car of course. Note that the body length is also about 44mm!

The last image shows the differential halves that bolt to the gear are ~30mm wide, so the gear is 49mm-30mm = 19mm thick. The length of the current bolt's unthreaded body inside of the gear is 44mm-30mm = 14mm. The spec'd bolt would have 17mm inside of the body.

TBakowsky's bolts show that it isn't just a case of my car being a 1-off, or one that someone put some odd-ball bolts into.

IMHO, Ferrari was possibly doing what Ed suggested:
Buying cut-down std 70mm hex head cap screws!!!
Alternatively, they could have been buying 70mm bolts that had been cut down and ground to ensure the OD tolerence was met and form the washer on the head.
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Just did something I probably should have done in the beginning, located ZF's US web site & called them (. After being handed off a couple of times, I got the US distributor's (847-478-6868) technical guy named Roger.

Gave Roger the number off of the differential & he's looking it up on ufiche to see if they have the bolts. Will call me back w/what he finds out. Really nice person.

Hopefully it'll turn out that several other cars use the same bolts & they've got them at an affordable price.

 

Received the following form ZF. So, I'm back to selecting std 10x170mm hex head cap screws for body ODs matching the spec & then cutting them to length...

 

Sent eMAIL to Paul Hill yesterday & have just received a response indicating that the can make the bolt. Even have the proper thread rolling dies!

HEAD MUST BE 17mm:
That discrepancy between the print specified 19mm head & the actual bolt's 17mm head has been bothering me. So I went & took some measurements(See attached photos).

The first photo shows that a 19mm head would be a very tight fit at best, it might not even fit! It would have to butt up snugly against the differential body. I believe that the chamfer at the intersection of the body & the flange is such that a 19mm head's washer face would hit the chamfer instead of seating fully against the flange surface. This would introduce significant stress on the head, most likely leading to premature failure.

As you can see in the 2nd photo, the 17mm head will nicely clear the chamfer area.
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