JB's FD - BMW Luxury Touring Community
 
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post #1 of 10 Old Apr 11th, 2011, 6:51 pm Thread Starter
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JB's FD

This drive came to me as a working drive for a preemptive rebuild.

The tapered roller bearing was loose on it shaft and came partially off by gravity as I removed the crownwheel assembly from the housing.

Further analysis reveals that the tapered roller bearing inner race has been spinning on it shaft and on the shim that is located under the tapered roller bearing. This shim is used to set the gear lash between the crown and pinion gears.

Pics show the wear of the shim and the scoring on the inner race of the tapered bearing. Clearly this FD was on its way to a failure of the tapered roller bearing. When this type of failure occurs the crowngear assembly is toast, and the drive is basically trashed because the cost of a crowngear assembly/input pinion gear set is pretty expensive and required a complete rebuild of the drive. In this case the tapered roller bearing is stable on the shaft, its just that the inner race spins on it seat. I'll rebuild with a Loctite product designed for this type of application after I reshim the tapered roller bearing.
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Last edited by CharlieVT; Apr 11th, 2011 at 7:03 pm. Reason: drive history updated/corrected
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post #2 of 10 Old Apr 11th, 2011, 9:26 pm
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Re: JB's FD

Quote:
Originally Posted by CharlieVT
This drive came to me as a working drive for a preemptive rebuild.

The tapered roller bearing was loose on it shaft and came partially off by gravity as I removed the crownwheel assembly from the housing.

Further analysis reveals that the tapered roller bearing inner race has been spinning on it shaft and on the shim that is located under the tapered roller bearing. This shim is used to set the gear lash between the crown and pinion gears.

Pics show the wear of the shim and the scoring on the inner race of the tapered bearing. Clearly this FD was on its way to a failure of the tapered roller bearing. When this type of failure occurs the crowngear assembly is toast, and the drive is basically trashed because the cost of a crowngear assembly/input pinion gear set is pretty expensive and required a complete rebuild of the drive. In this case the tapered roller bearing is stable on the shaft, its just that the inner race spins on it seat. I'll rebuild with a Loctite product designed for this type of application after I reshim the tapered roller bearing.
Hi Curtis

Are you able to get an accurate OD measurement on the shaft anywhere to compare to the ID of a new bearing? Sure sounds like an undersized shaft but would be interesting to see how much.
Jim

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post #3 of 10 Old Apr 12th, 2011, 5:22 am Thread Starter
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Re: JB's FD

Quote:
Originally Posted by RealWing
Hi Curtis

Are you able to get an accurate OD measurement on the shaft anywhere to compare to the ID of a new bearing? Sure sounds like an undersized shaft but would be interesting to see how much.
Jim
Hi Jim,
Yes it is an undersized shaft. BMW made a bunch of these around 2005 just to mix up FD failures a little.
I've seen a few drives with this "feature". A couple were trashed because the shaft was worn and the bearing loose. In a few others, the loose tapered roller bearing was an incidental finding secondary to opening the drive for crownwheel bearing inspection or repair. In those cases the shaft for the tapered roller bearing looked fine, but a replacement bearing just slips on. No doubt there has been some wear/polishing of the shaft but it isn't scored and the bearing fits snugly, it just isn't a press fit; it doesn't wobble, but it slides on and the race can spin on the shaft.
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post #4 of 10 Old Apr 12th, 2011, 7:46 am
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Re: JB's FD

Could you elaborate on the symptoms an owner would have when these happen?
Thanks
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post #5 of 10 Old Apr 12th, 2011, 10:08 am Thread Starter
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Re: JB's FD

Quote:
Originally Posted by krider08
Could you elaborate on the symptoms an owner would have when these happen?
Thanks
Noise, vibration, maybe an oil leak when they get bad enough.
In the early stages, pretty hard to tell without opening and inspecting.
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post #6 of 10 Old Apr 12th, 2011, 11:33 am
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Re: JB's FD

I think Curtis is on to something here. BMW probably started undersizing the shaft in an attempt to bleed off the excessive shim on the bearings.
Loose here + tight there equals just right........ Yea, that'll work.

Curtis I've used that Loctite for loose fittings on wheel bearing races. It's good stuff. I fixed an old Mustang where the outer race was completely loose in the hub. I could spin it and it would coast. If your race is real loose a few hits with a center punch on either the race or the shaft will pull it out nicely to hold the race until the Loctite sets. Maybe you already knew that...


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post #7 of 10 Old Apr 12th, 2011, 12:43 pm
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Re: JB's FD

i bought a fd for a preventive rebuild how much does it cost to have you do it. if it is in decent shape(gears & houseing in good shape). i might be jumping the gun my 02 has under 15K on it. the drive i bought has about 30K on it & is also from an 02
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post #8 of 10 Old Apr 12th, 2011, 4:11 pm Thread Starter
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Re: JB's FD

Quote:
Originally Posted by bobst2
i bought a fd for a preventive rebuild how much does it cost to have you do it. if it is in decent shape(gears & houseing in good shape). i might be jumping the gun my 02 has under 15K on it. the drive i bought has about 30K on it & is also from an 02
Hi Bob,
I used to have an ad in the classified section that said I'd do a preemptive rebuild for $300 including return shipping. Too many times I ran into the unexpected so I don't quote a cost before I've seen the drive. I pretty much do these as a community service to members of this board. (I used to give a discount to those who have contributed to this site but have sort of lost track of doing that.) Canada is also a challenge because of import/export duties. I've done a few from north of the border, some guys from Quebec have just driven down with the drive, when we've shipped the customs guys have extracted a fee that seemed unreasonable to me. If someone wants to ship me a drive, I try to treat them more than fairly, meaning I try to do the best rebuild I can, and I try not to lose money in the process. This isn't a money maker for me, rather a hobby, enjoyable when I'm not too busy, an incovenience when I am. I've never declined to rebuild someone's drive to the best of my ability, but I don't go looking for them either. If you want to ship me a drive, send me a private message on this site.
Cheers from the Deep South of Vermont,
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post #9 of 10 Old Apr 13th, 2011, 8:53 pm
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Re: JB's FD

Quote:
Originally Posted by CharlieVT
Hi Jim,
Yes it is an undersized shaft. BMW made a bunch of these around 2005 just to mix up FD failures a little.
.
curious,
how many miles on JB's fd?
also,
I would assume the only time a bearing would spin is an undersized shaft or a bearing seizing up?

I replaced my taper bearing... just because I was in there... but I am happy to say it needed to be pressed on .

also, also, what would the harm be if you left the bearing as is? I mean , if the bearing still spun... the race wouldn't spin much... but maybe continue to slowly erode and elongate??

interesting stuff...
thanks for posting.

True Wisdom Only Comes From Pain.


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post #10 of 10 Old Apr 14th, 2011, 5:16 am Thread Starter
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Re: JB's FD

Quote:
Originally Posted by johnT
curious,
how many miles on JB's fd?
also,
I would assume the only time a bearing would spin is an undersized shaft or a bearing seizing up?

I replaced my taper bearing... just because I was in there... but I am happy to say it needed to be pressed on .

also, also, what would the harm be if you left the bearing as is? I mean , if the bearing still spun... the race wouldn't spin much... but maybe continue to slowly erode and elongate??

interesting stuff...
thanks for posting.
The drive was purchased used by the current owner, mileage history unknown.
The shaft of the bearing seat is undersized. (You could say the bearing it too big, but BMW buys the bearing and manufactures the crowngear assembly the bearing is pressed onto.)
The harm of leaving it? Several cases of final drives failing because of this problem. A steel bearing race, spinning on an aluminum shaft will eventually chew up the aluminum.
Additionally, if you look at the pics, you can see where the shim under the bearing is worn from the spinning bearing. The part of the shim that wasn't worn measured 2.75mm. The worn section measuered 2.50. That's 0.25mm of measurable wear that had already occured. It would have eventually failed if not identified during this "preemptive" rebuild.

Last edited by CharlieVT; Apr 14th, 2011 at 5:27 am.
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