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Old 08-26-2023, 09:35 PM
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Front Driveshaft Question

Hello,


I obtained a new front drive shaft to replace one that has more wear on the splines than I would like and have a question about where the 'dust seal' is supposed to sit. Most pics I've seen show in a fixed (pressed on?) position on the drive shaft behind the splines. When I received my new drive shaft (with 1" longer splines) I had to epoxy my dust seal on because it did not have the press fit that my old dust seal did on the old shaft. But one picture and one video I've seen recently showed something different. It showed the dust seal as 'floating', but pushed over the shaft coming out of the transfer case. Which is correct? Should I have not epoxied my dust seat to my drive shaft? I'm not really sure this thing does much anyway because if it slips over the shaft coming from the transfer case water will enter between it and the splines on the driveshaft. On the other hand, with it where my original was, and where I put the replacement, it will seal positively on the drive shaft, but not the output shaft from the transfer case. On my old shaft where the splines enter the transfer case output shaft were clearly exposed. At the time I thought although the design as a whole is just stupid, better to have it exposed so moisture can easily evaporate than to create a sheltered pocket that would contain moisture just the same and let rust become more of an issue. On top of that, if it slips over the transfer case output shaft there isn't anything really holding it there, like a snap ring or anything, as would be standard design practice. If BMW had done this correctly there'd have been a molded rubber seal that would have gone between the dust seal and the drive shaft, and a snap ring to affix it to the output shaft. I attached a random picture of what a spline seal would look like. In retrospect, I thought of a third option that I like most of all. Slip it over the output shaft and use some adhesive lined heat shrink tubing between the dust seal and the drive shaft. That would (hopefully) leave you with a junction that is both sealed and securely fixed in place. No matter what I decide I will pack in some water proof grease...
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Old 08-27-2023, 06:13 AM
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I'm pretty sure that shield is meant more for dirt/rock protection exactly like the one for the front wheel hubs. It's not meant to be like the drive shaft seals going to the differential.

It's meant to have a couple mm at least of play in/out so if it was meant to seal it would have to seal radially not axially.

I think there's a seal like you are describing on the rear dif coming from the rear drive shaft.
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Old 08-28-2023, 07:11 PM
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Ah, I see. I'll leave it as it is then. It's still a bad design:/
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Old 08-29-2023, 02:37 PM
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I'm happy to say the new front shaft fits better than the one I had in there previously. The old shaft was an all new piece, left the dust seal so far back the spline to TX case interface was exposed, which left me to ask what the point of it was anyway. The new shaft, which is an OE item that has had the old splines cut off and a new end welded in, both positions the dust seal where it should be, and has MUCH deeper spline engagement. The new shaft is about 6-8mm longer overall. I do wonder about the front flex disc, however. Anyone with a BMW of any kind has heard it said again and again that you MUST counterhold the bolt and turn the nut (which is against the drive flange of either the output shaft or the driveshaft), with the aim being to not subject the steel inserts in the flex disc to the torsional stresses of torquing the fasteners. On the front driveshaft this is impossible, as there are NO nuts on the differential side, with the drive flange having threaded holes, and yet it's completely glossed over in my Bentley manual, and TIS. I attached a picture from Pelican's site to illustrate this (even they don't say a word about it). The most I can figure to do is put a dab of anti-seize on the heads of the bolts so they're as slippery as possible. I will also use blue Loctite on the threads because there are no locking nuts. Does this all sound correct?
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