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Thread: Installing transmission into pilot bearing - Won't Go!

  1. #1
    Join Date
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    Installing transmission into pilot bearing - Won't Go!

    Disclaimer: I posted this in the e46 M3 section yesterday, but with no replies, maybe this is a better place.

    Bottom line: How tight of a fit should the transmission input shaft be into the pilot bearing? Mine will NOT seat with normal transmission-installation force. I measured the pilot bearing ID at 14.95mm and the transmission input shaft OD at 15.10mm.

    More detail: I have spent all day today trying to install the 5-spd transmission into my 2001 M Roadster (not an M3 I know, but an S54, so here I am posting for help). It slides in, but just will not go the last 1/2" or so. Classic symptoms of clutch misalignment. So I spent all day tweaking the clutch position using the plastic alignment tool, since there is a tiny amount of play when installing it. Nothing had any effect. I am relatively confident the clutch is/was properly aligned with the pilot bearing.

    I replaced the pilot bearing while the transmission was out, so figured there had to be something wrong with it. I pulled the pilot bearing and tried to put it onto the transmission input shaft, and it would not go on at all. I measured both the pilot bearing and the transmission input shaft, and sure enough, a 15.10mm shaft will not fit into a 14.95mm hole.

    I've always been warned not to use the transmission mounting bolts to force the last bit of motion, but is that what is required here? Either that or I just have a defective pilot bearing. It is a BMW OEM part (p/n 11211720310 purchased from ECS Tuning).

    Any help would be greatly appreciated. Other than ordering a new pilot bearing and seeing what happens, I'm not sure where to go from here. A basic google search of interference fit tolerances confirms my suspicion that, even for a press-fit, the shaft needs to be smaller than the hole. I ordered a new pilot bearing, so hopefully the recently-installed one was just a dud?

  2. #2
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    Since you tried sliding the pilot bearing onto the shaft, out of the car, and it wouldn't fit, there would seem to be but one answer: wrong pilot bearing.

    Having looked up the part at realoem, though, I'd have to warn that you should recheck your measurements. The ID of the bearing is 15mm. It's highly unlikely that there's a duplicate bearing with a 14.95 ID, or a shaft with a 15.1 OD. Perhaps you have a burr on the shaft?

    I'd also mention that if you've truly gotten the gearbox within half an inch, the problem is much more likely to be the starter dowel, or another dowel, rather than the pilot bearing.
    Last edited by bmwdirtracer; 08-11-2018 at 05:40 PM.

    Chris Powell
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    Master Auto Tech, owner of German Motors of Aberdeen
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  3. #3
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    Thanks for the quick reply! While I would never say I'm perfect, I did measure both the bearing and the shaft at several places, and the numbers were all within a few hundredths of a millimeter. Now, I did remove this bearing from the crankshaft using a slide hammer, so it's possible that the bearing is slightly deformed, giving the 14.95mm ID.

    My plan going forward: receive the new bearing and test fit it on the shaft. If it doesn't fit, I'll take some measurements to make sure I'm not crazy, then use some emery cloth gently on the input shaft until it does. Any issues with that plan? Would also eliminate the potential of burrs on the shaft as well, I suppose.

    Regarding the dowels, I'm nowhere near engaging them. The dowels are only ~1/4" deep, and I'm still at least 1/4" to 3/8" away from them touching anything. The starter is pushed well out of the way, so I'm not touching that.

  4. #4
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    I'm not judging any more than I would judge myself, in these circumstances,

    The pilot bearing is a genuine BMW, or OEM part?

    Does your old pilot bearing fit?

    Certainly, there's no point in offering up the transmission until you have a pilot bearing that fits the shaft.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  5. #5
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    Pilot bearing is genuine BMW. Unfortunately, I do not have the old pilot bearing to test (transmission spent 3 months at the shop, so it's been a while since I did most of this work), so can't verify, but it used to be installed in it, so I would imagine it fit just fine. I never even thought about test-fitting the new pilot bearing on the transmission input shaft until I started researching this problem.

    Thanks!

  6. #6
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  7. #7
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    I finally did! The problem was a slightly "mushroomed" input shaft on the transmission. I sought out and visited McB Autosport (in Bridgeville PA) who had an old input shaft for me to compare to. No way to know for sure if it happened during the transmission's recent trip to the transmission shop or much earlier (car has 220k miles). The solution was about an hour with emery cloth and then fine-grit sandpaper on the shoulder of the input shaft. Worked like a charm.

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