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I have a SIR B90 tool kit and have performed the rear bearing replacement task quite a few times on Boxsters, and numerous times on other cars. I last performed this task last week, on both front and rear knuckles of one of my 1997 Boxsters.
It takes a great deal of force to break the thrust bearing that SIR includes in that kit, which I have managed to do myself. In my case, and I suspect in yours as well, the problem was incorrect selection of the disc to use on the inner side of the knuckle. That area is difficult to see, even with illumination, and is usually caked with road dirt and grease ( from either the bearing you’re replacing, or the adjacent CV joint). The key point is that the disc must be smaller than the hole in the knuckle so that it does not accidentally come to bear against the knuckle itself rather than on the bearing. If a disc is selected, of the several in the tool kit, that is too large, then when force is applied with the screw to pull the disc ( on the inside, out of sight) into the 2-piece ‘cup’ on the outside ( so that the outer edge of the bearing is also out of sight), then you are basically applying force to compress the aluminum casting.
In that scenario, something’s gotta give: either the roller thrust bearing will fail, or the aluminum knuckle will fracture. I’m betting the bearing will fail first.
So I suspect the reason you had trouble pulling out the bearing was that the inner disc was one too large for that knuckle. For the 2.5L Boxsters, I use the 8A disc, but it clears the hole in the knuckle by only about 2mm (eyeballed, not miked), so careful positioning by blind palpation is essential.
Another option would be to use the next-smaller disc #7. It will not contact the outer bearing race but it will contact the inner race, which in turn will force the balls of that race against the inner part of the outer race, to force the outer race outward into to cup, removing the bearing..
All my above recommendations are only for the base 2.5 and 2.7 cars, not the 3.2 Boxster S. The Boxster S used a larger bearing in the rear so it would likely need a larger disc to pull it out. I have not had occasion to work on an S yet.
As to your knuckle: I think if you will just dress down with your Dremel the scarred points to ensure that your new bearing seats fully, I think that knuckle will still be sound.
Lastly, when you install your new bearing, lubricate the bearing and the knuckle with some sort of grease first. Had the mechanic before you done so, you would have had a much easier time pulling that bearing.
Good luck! David Crowder
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