View Single Post
      11-29-2009, 05:52 PM   #26
dougman
Second Lieutenant
dougman's Avatar
12
Rep
228
Posts

Drives: '07 E92 328 --> 2010 E92 M3!
Join Date: Apr 2007
Location: Bay Area

iTrader: (0)

Quote:
Originally Posted by MMMorish View Post
Your tranny is fine. I had TONS of grinds in my first tranny, that thing was a lemon. But after BMW replaced it, I had a "lazy" grind happen to me once between 1st-2nd at about 3k rpm as well. The car is fine! The syncros in these trannies are made of CF, so they should withstand a lot of abuse.

Hey Harris, take your car on a test drive with a BMW tech and replicate the problem, they'll change your tranny without any questions asked. My second tranny is not plagued by the 1st-2nd grind. Thank God!
CF Syncros??? I don't think so. CF would be a terrible friction material, and would shred and leave fibers in the tranny as it wears. Syncros are brass or steel.

The gears themselves are always in mesh. The syncros are cones (see last pic and you can see the cone) that speed up or slow down the shafts to allow the "dogs" to mesh, at which point the gears are locked to the appropriate shaft.

Syncros prevent the interlocking teeth of the collar from engaging until it is spinning at the same speed as the one it is going to mesh against.

When syncros wear down/wear out, they either slip or don't engage soon enough to get the collars spinning at the same speed before the teeth engage.

When you "grind your gears" you're actually hearing the collar grinding. The gears themselves are always in mesh so you're not hurting them. There is still the potential for damage over time, but it's not the same as

Here's a link:

http://auto.howstuffworks.com/transmission1.htm
Attached Images