Originally Posted by c00k1e
This is VERY interesting (having had 6 failed FDs and bought a brand new one from BMW). I hope to do a tech session at the 1st UK LT do,on the old FD based on your vid. Is this new technique going to be more accurate?
Have you ever done a rebuild on a failed FD from your old technique?
Is the "new" technique going to be more accurate? I think that this technique, which basically follows the BMW service manual, is more prone to measurement error due to the number of measurements, how they are taken, and the multiple calculations that must be made. However, I have no basis to say that one technique is going to be "better" than the other as far as being able to properly calculate preload shim thickness. Having done it both ways, I prefer the technique that uses the dial indicator that was introduced by Dman and is shown in my video. But in any future rebuilds, I will use both methods because I am curious and want to continue to compare the results.
Have I ever done a rebuild on a failed FD from my old technique? I don't know of any of my rebuilds that have failed, if that is what you are asking. But I don't have good follow up on them. I hope if one of my rebuilds fails, the owner will notifiy me (as opposed to sending me a letter bomb)
. I would really like to look at such a drive. Many (most?) of the drives I have rebuilt are sitting on shelves as "spares" where the owner replaced their drive and sent me the failed one for rebuild to keep as a spare. I have +40K miles on my own rebuilt final drive. That was a preemptive rebuild, not a failed drive, but it was shimmed using the technique in the video. There are a couple (few?) drives I have done which are being ridden and have not failed as far as I know; I have no idea what miles have been put on these drives.
Regarding reports from people like yourself who have experienced multiple failures, I have often queried as to whether the new bearing was just installed using the old shims or if measurements were made to check for proper preload. I am very suspicious that many of these rebuilds were done without checking preload, and if done by a BMW service department, if queried they'll say they did measure for preload, but does anyone really know if they did? [Now ranting here] I frankly doubt them even when it was reported that they claimed to have down the measurements. My guess is they just slapped in a new bearing. In the early days they didn't know it was going to fail again. It wasn't until there were enough failures and repeat failures here in the US that BMW of NA started telling dealerships to replace the whole drive rather than rebuild it when doing warranty work. (I am just guessing that BMW made that decision based on reports that folks with failed drives were getting whole new drives). But even then, no one knew if the "new" drive was assembled any better than the one that failed, and I believe there we several people who got a factory new drive that went on to fail.
Good data is pretty hard to come by with respect to reasons for failure and success rates of rebuilds, that's why there is so much speculation.