Welcome to the 'everything about sloppy gear-changes' thread. Yeah, my first grind.

[MMMorish]

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!

[J08M3]

Originally Posted by elp_jc

By the way, removing the spring on '08 cars (they only have one) reportedly creates problems with the cruise as the cruise deactivate switch is all the way to the top of the clutch pedal travel, and removing the spring causes the pedal to drop enough as not to allow cruise to engage, or disengages at the least provocation. Folks doing that mod should test their cruise. Owners of '09 cars can always install the '08 spring for better feel. The '08 clutch spring seems like the best compromise. Besides the cruise issue, folks who drive in heavy traffic might not appreciate a heavy clutch over the long run. A matter of personal preference.

I've had my spring removed for over a year and not one issue with cruise and I use cruise all the time on the highway. There is another spring that holds the pedal all the way up.

Also, the clutch in my opinion is not heavy at all without the spring, it's just more linear in feel.

[JCtx]

Originally Posted by MMMorish

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.

Thanks for the encouraging words . So the grinding sound is a synchro hitting a gear then? Need to find an exploded view of this Getrag tranny to familiarize myself with it; google didn't work.

Originally Posted by J08M3

I've had my spring removed for over a year and not one issue with cruise and I use cruise all the time on the highway. There is another spring that holds the pedal all the way up. Also, the clutch in my opinion is not heavy at all without the spring, it's just more linear in feel.

Good info man . The post I read probably didn't have that spring reinstalled. I haven't investigated that mod since I'm happy with the clutch feel myself. Thanks.

[dougman]

Originally Posted by MMMorish

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

[J08M3]

Most syncros I know of are brass, or some material softer than the gears, this way any grinding that happens damages the syncro not the gear.

[JCtx]

Originally Posted by J08M3

Most syncros I know of are brass, or some material softer than the gears, this way any grinding that happens damages the syncro not the gear.

I don't think the synchros have teeth; do they? So they only wear if you push/pull on the knob while driving, no?
Only collars and gears (not the teeth but the 'female' dogs) seem to be able to grind. Now the question is if both the collar and gear could be damaged while grinding, or one is supposed to 'sacrifice' itself for the other . When a gear 'jumps' back to neutral, means the collar 'dogs' are rounded from grinding, and can't keep itself mated to the gear. I guess it doesn't matter if it's just one or both components, as tranny has to be opened up in that case. And although gear teeth are unaffected, the affected gear has to be replaced anyway due to worn dogs.

My new question is how synchros can wear prematurely if knob is never held while driving. Hopefully both the gears and collars are strong enough to withstand some abuse, as it's practically impossible not to grind a gear at least a few times in the life of the tranny. Thank you all for your contributions .

[littleyellowm3]

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