Bad parts from my BB transaxle..

I promised several months back to provide updates about my 365BB transaxle rebuild experience, but as usual things have moved at a snail's pace. That said, everything is disassembled and cleaned now, and the last of the new parts should arrive shortly. So it seemed like a good time to show the 'bad' parts found inside...

The first suspicious discovery was the 'small' differential bearing spacer (RH I think) that must have been brought to final thickness by lathe, rather than by surface grinder - see image #1. It was probably a convenient short cut to having the perfect adjustment shim (or shim pack), or a properly ground unit, but it clearly wasn't the right approach. The unit found was originally 3.2mm - apparently Ferrari part 103426; the lathe work reduced its effective thickness to 2.9mm.

The next discovery was a highly compromised inner race on the adjacent tapered roller bearing (image #2, this is one of the main differential bearings). This inner race is visible only if you cut the tapered roller cage off the assembled bearing to allow inspection. I was amazed by the level of deterioration and glad to have bothered cutting the cage free! Unfortunately the other main bearing got trashed without similar inspection.

Image #3 shows the two other compromised parts. Note the galling between the stub axle and the differential housing; this was the issue that precipitated tear-down in the first place - - the car was getting hard to push around the garage! Anyway, the infamous weld on the housing appears to be fine. Even without all the galling, however, that housing part would have gone straight to the trash.

Wild guess diagnosis?.....I suspect whoever was in the transax previously set the differential pre-load WAY too low. When the powertrian got warm, this created more excessive clearance in the tapper roller bearings, and pounding conditions. Over time this lead to fretting of the bearing race, and excessive movement (or perhaps steady rubbing) of the stub axle on the diff housing, until it started galling.

IF this is true, it's probably an anomalous failure that isn't a concern on other cars. However, differential bearing pre-load is a critical setting and getting it wrong can happen on any car. When I actually get to that operation, I'll add comments to this thread, and let everyone know how it goes! Regards, Nate Stevens.

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Thanks David, after digging through a box of scrap parts tonight I found the outer race, and it showed clear signs of spinning. There is some discoloration on the shim (suggesting high temps) and that seems consistent too. So you are 100% correct - no drunk baboon on a lathe, just a spun bearing that chewed away a lot of shim material. Here is an image of the outer race, showing the similar damage. I remain positive that somebody was in the box previously, and would love to know exactly what they were looking to address.
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