Diff failure

[Colin Byrne]

My dad was running this 4.55 diff  with an LSD Centre for a while but swapped back to a standard 2000 4.1 diff as the 4.55 developed a noise and started blowing oil out the breather.  I was keen to use it with my new gearbox ratio's so I pulled it apart this arvo to take a look.

Turned out the pinion had a broken tooth, not sure how it happened anyone seen this happen before?  I've got another old diff centre with a good crown wheel and pinion to replace it with but reading the manual looks like there needs to be some very careful measurements made to get the correct shim thicknesses.

[Barry Edmunds]

Colin

I have got a 4.55 diff/complete in the collection that is surplus to current requirements.

Crown wheels and pinions are matched so extra care needed with clearances/shims etc

Barry

[Frank Musco]

Colin

Haven't seen it in a 105, although my Alfasud track car broke half a tooth off the pinion, like your photo shows. Happened a few years ago, and it wasn't making a noise. Only found it after removing the sump to inspect the shift mechanism.

[Colin Byrne]

interesting, did you ever work out why it happened, i don't want to just replace the crown wheel and pinion if there is an underlying problem  and have it happen again.

[Frank Musco]

Unfortunately I couldn't find a reason. Both pinion and crown looked in good condition, ones you would use if it wasn't broken.
Again, it wasn't noisey, for what you can hear in a race car flat out, and definitely no noise that made me think it was a broken pinion tooth. Pinion-crown clearance was normal.

I have broken one in ten years, so...who knows? I put it down to bad gear changes (I've still got it), general abuse and then metal fatigue.

I'm no diff expert, though spend heaps of time shimming the fricken things up and painting teeth.

[aggie57]

Colin - years ago I chipped a crown wheel in a GTV6 at an AROCA DECA day. Made an almighty knocking sound, so much so that I flat towed it home. Turned out to be the smallest indent you could imagine. Tidied it up with a dremel and put I back together. No further problems over several years of competition use.

Guess it's down to luck. I'm pretty sure my problem was caused by a wayward synchro tooth which of course doesn't apply in your case.

[Colin Byrne]

Sounds like it's a pretty uncommon issue, I wonder if some foreign body made it's way into the housing, I didn't find anything but the oil looked very metallic when I drained it.

The manual shows a huge amount of very special tools required to correctly re-assembly the unit, might have to get some external help on this one

Barry-I'll have a chat with you about that Diff at the driver training day cheers

[colcol]

I broke several teeth of the crownwheel in the 33, while driving up the back straight at Winton. made an allmighty bang, and jumped out of gear and then made a whining noise, drove it the rest of the day, back to Melbourne, to work the next week, to the Rob Roy hillclimb and competed, drove home, could not select 5th gear, drove it home, pulled sump off gearbox, NINE broken teeth in sump, got second hand crownwheel and pinion, could not set it up, because as i later found out, a tooth had got jammed between the crownwheel and pinion and cracked the gearbox, thats why the the clearances kept altering, got another seconhand gearbox casing, and had it set up by a professional, [not me!], and put it back in my car, reason it broke wasn't because of too much power from the 33, they turn so many Billion times then they break, Colin.

[aggie57]

I'm pretty sure Vin has the necessaries to set them up. We used to get him to do our Alfetta ones.