Correct orientation of transmission front bearing

Posted by 39SixSedanMan On 2011/7/29 11:43:22

I don't think we've discussed this one before (I could not find it):

I have wondered many times about the orientation of the shield of the front bearing of the 39 and later column shift manual transmissions (I call this the front bearing, although technically it is the "clutch shaft rear bearing" 3.2091, pg 46, as the clutch shaft has another bearing: the pilot bearing, at the front of the shaft).

My observation is that the bearing shield is on the inside of the transmission, clearly shown on page 46 of the 35-41 Parts Master List. I would have thought the shield would be on the outside such that the rolling balls would be directly exposed to great oil flow. However, the design of the bearing cover, includes a flow path that aligns with a hole in the transmission, which I expect would facilitate flow in either direction. Supporting the literature is the fact that every one of the 4-5 transmissions I have worked on over the years have had the bearing arrangement as documented.

A few years ago, I read an article in the PAC Cormorant in which the author states the opposite is correct and warns of the danger of putting the shield on the inside resulting in bearing starvation, failure and massive damage.

My engineering background would agree with that author and therefore disagree with the design, but my observations of multiple transmissions, each of which had no bearing damage, seems to confirm it. I have always replaced/repaired by installing per the book. Apparently, the oil flow is sufficient.

Has anyone else made this observation? Has anyone had a failure? Has anyone else swapped the shield to the outside?