456GT gearbox bearing failure?

Last weekend I did a short, 10km, test drive. When I got back home, put the car in neutral, opened the door and released the clutch (in that order), I noticed a sound of a rumbling bearing coming from underneath the car. I pressed the clutch and the noise disappeared, released it and the noise came back, louder this time. I got out and poked my head under the car and the rumbling became an awkward rattling within a minute. I pushed the car into my garage and onto the lift and started again, armed with a stethoscope to try hear which bearing it was. I only listened for half a minute or so as I couldn't stand the noise and my diagnosis is inconclusive.
It is definitively a bearing, sounds like a ball is split or broken. Epicenter of the noise is the front end of the gearbox although I am not 100% sure it is not the aft bearing in the torque tube. In all gearbox problem posts on here I read that the problem is most likely the tube, not the box. Anyway, I need to drop the box to investigate...
Any suggestions? Anyone ever experienced failure of bearing #3 in below diagram?
Not amused as this means yet another job this winter but perhaps I should count myself lucky as this happened in front of my garage door?


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70k km

 

Well, I bit the bullet and removed the the bearbox. There's a M14x1,5 threaded hole in the bottom of the box, exactly in the center of gravity of the box and torque tube together. I made an adapter that screws into the box and sits onto a transmission jack and with these tools removal of the box is not that difficult.
Upon opening the box, and removal of the forward two sections, the root cause of the noise became apparent. The reverse auxiliary gear is held in place by two seeger rings which sit in a groove on the shaft. The upper one seeger ring was not in the groove at all but rather at the top of the shaft, firmly pressing against the casing. How it got there is beyond me. The only thing I can think of is wrongly mounted by someone before me. Without this seeger ring the gear is free to move up the shaft and hit the gear above it, which is obviously did. Bad news.
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Now in order to disassemble the box further, I need to undo a ring nut on the differential side. In order to get there, you need to take off the oil pump. And in order to take the oil pump out you need to remove the differential/crown wheel assembly. But how???
The manual simply says 'remove diff/crown wheel assembly', but it just doesn't seem to fit.
Any help please from someone who has done this before.


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I can easily make two bushes either side of both seeger rings that positively keep these in place, as apparently Ferrari also did. But in my case the damage is done already. Luckily I didn't drive and the steel chips collected at the filter and, as far as I have now seen, have not entered any of the bearings. As far as I can now see only the aux wheel and the reverse synchromesh ring have been damaged. But I will surely flush and carefully check every other component for damage or wear and replace bearings if there is any doubt. But I have first to get the diff out and I don't see how!

 

Thanks, done that.
And I am very much aware of the difficulties and special tools required, tools that nobody has the exact specifications of. Also the WSM is of little use. Luckily the box is of rather old fashioned layout (very similar in construction to Lancia Aurelia 1-3 series, except that these had the clutch in the transaxle and were 4 speed), but obviously of very high standard otherwise. I will make the tools as I go along; I will need to wash/check all bearings anyway.
Gearboxes are the equivalent of a mensa test; getting a box back together is one thing, getting it really 100% quite another. I like gearboxes.

 

It's like one of these impossible Chinese puzzles that are actually quite simple. After struggling with this most of Sunday, tonight I walked past my workbench, gave it one more try and 10 seconds later I hold the diff in my hands...

I now have access to the third ring nut which, off course, has different dimensions to the other two so will now proceed to make a spanner.

 

I've made progress on my gearbox issues and will do a write up shortly, as I think chances are high that other 456/550 owners may have the same issue. I have seen the insides of 4 gearboxes now (2 456, 1 550 and one 575) and apart from the 575 all boxes had the same issue with the reverse gear.

@Taz, do you have the WSM for the 575M, gearbox section, and can you please share?
I'd like to check dimensions and tolerances of this 575 manual box before putting it up for sale as I can not use (or test) it on my 456.
Thanks.

 

Thanks, this will do.

 

Sorry, don't know anything about the auto boxes.