Yes, in fact, gears can never collide in ANY transmission I have worked on, provided the shift forks do not become mis-adjusted, and/or one manually attempts to place it in more than one gear at once. I suppose there could be exceptions, but I am unaware of them of the several auto and truck designs I've rebuilt through the years.George Ryals wrote:I think the reason we can down shift our airhead transmissioms without very close matching of engine rpm, is the size of the holes the shift dogs engage to lock the respective gears to their shafts. The holes are close to one and one half times the width of the dogs that slides into the holes to engage the gear. There are four dogs and four holes so it is a pretty coarse situation compared to the spacing on synchronizers. Any crashing/grinding heard from an airhead trans is the dogs banging the edges of the holes, not the gear teeth themselves. The dogs will and do break off of the slider that moves between the meshed gears as we shift.
I have no-doubt the interface in question, dogs-to-holes in these and any other straight cut transmission is the ONLY real weakness, other than simply wearing the bearings out and such, but I am still unclear for certain as to why there are these two critical differences in what would appear be the very similar designs. One being not HAVING to spin them up on down-shifts and two, well while we have already covered how unfriendly it may be on our BMW's transmissions, why I can't run up near the red line, preload the shifter "burp the throttle" and jam it into the next higher gear, that is without expecting to NOT hit every shift that way. I know the transmission would not "last" this way, but also feel it would unlikely be able to hit up shifts every time without the use of a clutch.
I have expanded technical views of the BMW transmission and somewhere (other than in my head) I have a similar blow up of one of the sequential shifting, straight cut boxes I used to race with. If I can find the old diagram, perhaps I can post both here, or look more closely and see that difference for which I have missed all of this time. It would be quite interesting to know why they behave differently; this could lead to some additional "hardening" of our beloved BMW boxes, for which I'll be doing a few this winter...
Thanks for posting.
