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Discussion Starter #1
Yes, my rear end (FD) failed me today.
The good news, I was only 60 miles from home.
Yesterday I was 300 miles from home.
The other good news.
My chip detector worked like a charm. I was at 80 MPH on the turnpike when the light came on so I stopped and checked it for wiggles and rode slowly home. Just a few tiny slivers at this point so it could have been much worse.

So, I'm inclined to let one of you FD gurus rebuild this thing for me. Anybody who is interested please send me a PM.

Now...... where's that 30MM socket?
 

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deanwoolsey said:
Yes, my rear end (FD) failed me today.
The good news, I was only 60 miles from home.
Yesterday I was 300 miles from home.
The other good news.
My chip detector worked like a charm. I was at 80 MPH on the turnpike when the light came on so I stopped and checked it for wiggles and rode slowly home. Just a few tiny slivers at this point so it could have been much worse.

So, I'm inclined to let one of you FD gurus rebuild this thing for me. Anybody who is interested please send me a PM.

Now...... where's that 30MM socket?
Dean, I am very sorry to hear this. I am beginning to think this 4% thing is BS. I am sure that in the future, mine too will fail. How many miles on your FD?

Robert
 

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I'm no guru, but I am sorry to hear about your trouble and glad that you discovered it when you did. I'm sure someone will offer you help.
 

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deanwoolsey said:
...My chip detector worked like a charm....
Have I missed this thread on final drives? I was unaware of any early warning devices for the FD failure. I have 2 beemers that are prone to this type of failure so I am always keeping an eye out for indications of a pending failure including more frequent than required fluid changes.
 

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Here's the thread from where I built the chip detector. I'm glad I had it. Otherwise I would still be riding it (or not) for another 4000 miles to the next scheduled fluid change. It was just checked at 45,000 when I did the valves and engine oil. 46,300 at failure. I do the FD oil every 10,000 and it looked fine other than the slivers and very little fuzz on the drain plug which I check with the engine oil changes every 5,000.
It was pointed out in the other thread that this is really a "your final drive just failed light". While that is true, it allowed me to make an educated decision on how to proceed with the problem. It also informed me of the problem at what is likely the earliest stages of the failure so my chances of serious damages are much lower, I hope. I'll let you know how it works out.

http://www.bmwlt.com/forums/showthread.php?t=43720&highlight=final+drive+warning
 

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Dean,

Maybe I was just tired when I read the thread, but I did not see a how-to in there. Did I miss it, or is it something you have not, and prefer to not share? For others this may seem like a straightforward project, but not for me. WIth basic instructions I could do it, however.

Care to share?
 

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Congratulations of the success of your chip detector. I admit I have been skeptical of various efforts to provide early warning of FD failure, but it sounds like you got a warning before the roughness and eventual lube leak indicated a problem.
That earlier warning would no doubt give you more "altitude" to work with before you had to get "gear down".
Good work! Now that you have a documented success you'll have to go into production, everybody is going to want one. :)

Addendum: Dean, can you post pics of the drainplug magnet or metal particles in the lube so we can see what kind of chips set your chip detector off?

deanwoolsey said:
Yes, my rear end (FD) failed me today.
The good news, I was only 60 miles from home.
Yesterday I was 300 miles from home.
The other good news.
My chip detector worked like a charm. I was at 80 MPH on the turnpike when the light came on so I stopped and checked it for wiggles and rode slowly home. Just a few tiny slivers at this point so it could have been much worse.

So, I'm inclined to let one of you FD gurus rebuild this thing for me. Anybody who is interested please send me a PM.

Now...... where's that 30MM socket?
 

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deanwoolsey said:
Here's the thread from where I built the chip detector. I'm glad I had it. Otherwise I would still be riding it (or not) for another 4000 miles to the next scheduled fluid change. It was just checked at 45,000 when I did the valves and engine oil. 46,300 at failure. I do the FD oil every 10,000 and it looked fine other than the slivers and very little fuzz on the drain plug which I check with the engine oil changes every 5,000.
It was pointed out in the other thread that this is really a "your final drive just failed light". While that is true, it allowed me to make an educated decision on how to proceed with the problem. It also informed me of the problem at what is likely the earliest stages of the failure so my chances of serious damages are much lower, I hope. I'll let you know how it works out.

http://www.bmwlt.com/forums/showthread.php?t=43720&highlight=final+drive+warning
Dean I would be interested in final drive light warning also;would like a little information on it.

Thanks Gary
 

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Discussion Starter #11
Thanks to everyone for the PMs. I'll decide what I'm going to do and get them all answered in the next day or two. In the meantime, here's a couple photos of a sliver. As you can see the slivers are literally the length of a pin head. I got one in my digital caliper and it does not register a thickness above 0.000, so less than a thousandth of an inch thick. Pretty sure it's the classic spalling caught at a very early stage. I neglected to take a photo of the drain plug or the chip detector when I pulled them but the magnet on the drain was still visible with just slight fuzz and maybe ten slivers around it. For some reason the majority of the slivers were drawn to the detector, maybe because I used a rare earth magnet to build it. There were probably only about 20 or 30 pieces total. I will at some point post some instructions on building the detector. It's nothing much more difficult than drilling a hole in a drain plug and running a machine screw through it. If you have a drill press you can do it. I'll see if I can take an exploded diagram of the components.
 

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Discussion Starter #12
Pulled the drive, took it apart, not much in there for debris. The chunks you see in the photo are globs of fuzz or maybe seal. Very little sharp metal. That makes me happy. So Guru question........... how much pre-load should the bearings have on them?
 

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Just like the book says 0.05 to 0.1 mm of pre load. All of the failed ones had twice this.
 

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Thanks John, didn't see that in my Clymers. Too big of a hurry I suppose. Measured 1.4MM post mortem.
 

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jzeiler said:
Just like the book says 0.05 to 0.1 mm of pre load. All of the failed ones had twice this.
deanwoolsey said:
Thanks John, didn't see that in my Clymers. Too big of a hurry I suppose. Measured 1.4MM post mortem.
Dean... is that 1.4mm or .14mm? This first is 14 times higher than max spec, and the latter is 1.4 time higher than max. Either way, bad news, but wondering if 1.4, was the extreme excess was caused by failure or a major FUBAR at assembly time.
 

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It's 1.4 mm, about the diameter of a pencil lead. I do not think that a failure would cause this, but I've never pulled one apart until yesterday. My bearing is still pretty smooth. I was quite surprised at how far it is off when John told me .05 to .10. Amazing it lasted as long as it did.
 

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You had a pre load of 1.4mm or a gap of 1.4mm? That is some serious pre load. How many shims where there and how thick?
 

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deanwoolsey said:
It's 1.4 mm, about the diameter of a pencil lead. I do not think that a failure would cause this, but I've never pulled one apart until yesterday. My bearing is still pretty smooth. I was quite surprised at how far it is off when John told me .05 to .10. Amazing it lasted as long as it did.
I have cut open many bearings that felt so smooth I doubted that they needed to be replaced. You really do have to cut them open to visualize the races.

I'm not sure what you measured to come up with 1.4mm but that makes no sense to me for either the preload amount, or the total shim thickness. In over 50 drives, I have removed only one 1.0mm shim; I have never seen a combined shim thickness of 1.4mm. It doesn't make sense to me.

(Addendum: Hummm..... maybe you are measuring the shim behind the tapered roller bearing? In that case 1.4mm makes sense. However, that shim is used to adjust crowngear/pinion gear backlash, it is not the preload shim. The preload shims are thinner, much larger in diameter, and usually found stuck in the crownwheel bearing recess in the FD cover.)

What was the existing shim thickness? There would have been one or two shims in the crownwheel bearing seat of the FD cover. If there are two, one of them is very likely a 0.15mm shim. The other is likely to measure between 0.20 to 1.0mm.

Now that you have the FD disassembled, I suggest you pull the bearing off the hub if you have not, and cut it open for inspection. Since your chip detector warning is the reason you are into the FD, we are very curious as to what the extent of bearing degradation is. I hope you'll be able to post pics of the bearing.

Inspect the FD housing for the "creeping input pinion needle bearing race" (see earlier posts for pics of this). Also check for the "loose tapered roller bearing".

Having ruled out the presence of either of these two occasionally coincident problems, press on a new crownwheel bearing. Press the new bearing on using only the inner race or you will damage the bearing. Alternatively, heat the new bearing to 250F and put the crowngear hub in the freezer for 30 minutes and the bearing should drop on without resistance. Careful you don't get the bearing canted or cockeyed on the hub.

Once you have the new bearing on the hub, you are readly to start measurements for shim thickness. My video, which has a few errors and poorly edited still shows a valid and reliable method of measurement as originally shown to members of this board by DMAN.

Alternatively, you can use the method described in the BMW Service manual which requires a special tool to stabilize the bearing for accurate measurement. The bearing, being a "sloppy" Class C bearing, will tilt significantly when one side is pushed down. This tilting of the bearing will cause a huge measurement error. (I suspect that this factor may have been a factor is BMW have set up so many FDs with excess shim thickness.) Because of the tendency of the bearing to tilt when making measurements for the BMW Service Manual method, the bearing needs to be stabilized and multiple measurements taken on opposite sides of the bearing (180degrees from each other) to ensure that identical measurements are obtained around the bearing.

HTH

Addendum: I just reviewed the Tapered Roller Bearing Preload Check section in the Clymer's Manual. (I have always used the BMW Service Manual and had been unfamiliar with the write up in Clymer's.) Clymer's is basically a repetition of the BMW manual and simply states: "A measuring ring (BMW part No. 33 4 601) and a vernier caliper or depth gauge are required for this procedure." Does anyone have this BMW tool? I've never seen one, and only a diagram rather than a photo of it is shown in the manuals. I have wondered to what extent this tool prevents bearing tilt during measurments.
 

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Discussion Starter #19
Perhaps I don't understand what constitutes preload on these. What I am looking at is the distance between the case halves with the o-ring removed and the hub seated back on the tapered bearing. I have not removed the hub from the case yet, I am simply measuring the distance the case flange will have to deflect to seat flush with the bolts installed.
 

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deanwoolsey said:
Perhaps I don't understand what constitutes preload on these. What I am looking at is the distance between the case halves with the o-ring removed and the hub seated back on the tapered bearing. I have not removed the hub from the case yet, I am simply measuring the distance the case flange will have to deflect to seat flush with the bolts installed.
Dean,
Ahhh.... so that's what you are measuring. That dimension is of no value and isn't used in any method of calculating shim thickness for the preload. (We all wish it were that easy.)

The gap you have to measure is that between the crownwheel bearing seat in the FD cover and the outer race of the crownwheel bearing with the cover installed and no shims in place. After the dimension of that gap is determined, you add 0.05-0.10mm (the preload amount) to the measured gap and that gives you your needed shim thickness. Since that gap cannot be measured directly with the FD assembled, two methods are available to make the measurement.

I suggest you read the "Tapered Roller Bearing Preload Check" section in the Clymer's Manual. This will help you understand what gap needs to be measured in order to calculate the shim thickness for preload.

Then if you watch the video I made some years ago, you'll understand an alternative method of calculating shim thickness the does not need the BMW special tool, but rather relies on the use of a dial indicator. The two methods that I know of for calculating shim thickness are: 1) the method first demostrated by DMAN which I refer to as the "dial indicator" method and is described in my video. 2) The other method is the BMW Service Manual (same as in Clymer's) which uses the BMW special tool and a depth micrometer. I have used both methods on many rebuilds and found that they yield similar results. HOWEVER, both methods are technique sensitive and you should repeat your measurements multiple times to ensure you are getting consistent results.

HTH
 
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