I just did some reading on the Torque to yield bolts. Very interesting. And I'm glad you mentioned it, as now I know about it and have learnt a bit more. However, as another fellow here said, and I don't mean to knock your post, but it is not relevant in our ol' skool world, unless we used them on aluminum heads. And also, just because they are not TTY bolts on the crown wheel, is not really a reason to not replace them. If you knew the full history of the vehicle and exactly how it has been driven, eg if you had owned the car from new, and the diff had never been worked on, or if it had and you knew the bolts were all correctly torqued etc, then you could confidently reuse the bolts. But otherwise, for the cheapness of them in the USA, it would be just good practice to replace them. The mistaken overtorquing trying to undo them due to the LH thread is a very good reason to replace them. My main reason for asking in the OP is why, in normal circumstances, would they need to be replaced. To save time at the dealership is a very good reason but how much load are they under in normal circumstances? They must be under some considerable load for the service manual to say to always replace them. As the pinion exerts load on the ring gear, it is only one particular area that is under load each time and I would guess, only about 3-4 bolts each time are taking the force of the pinion. The load would not be evenly distributed on each bolt. I think (and I'm only guessing) that there would be both a shear and a tensile force component on these few bolts. As I read that the gears ride up and down on each other under load and on coast etc. Sorry for the long post.
