RoatanMan

2008 Z06...

I hear a grinding sound when down-shifting just from 3rd to 2nd... It happens every once and a while no matter the RPM... Slow shifting, fast, doesn't matter... Any Ideas...?

Landru

Just one: sychros.

Any warranty left?
Here's where a valid warranty --or extended-- proves its value.
Had to have it done on my '06.
Tranny completely dropped, removed. Bad sychro(s) replaced.
Not cheap, labor cost alone sky-high.

RoatanMan

Out of warranty, it only happens once and a while...

VetteVinnie

I always blip the throttle when downshifting even on the streets. Less stress on the synchros.

JJC5

That's only if you double clutch; let the clutch out as you go to neutral and blip the throttle at the same time. That will speed up the trans and mesh with less dependence on the syncro. Blipping the gas with the clutch in only speeds up the flywheel.

VetteVinnie

Rev matching. Expensive cars do this automatically (GTR for instance).

JJC5

Rev matching is to prevent loss of traction when downshifting as when going into a corner; prevents the rear end from washing out. By letting out the clutch (engaging the transmission) in neutral, then revving, it speeds up the input shaft. Clutching again, then downshifting, the trans is already up to speed to mate to that lower gear instead of the syncros doing the work. But....you still need to rev match as you let out the clutch.

VetteVinnie

Got it. Just seems that the synchros don't whine near as much going into gear when the RPMs are higher than if you were to just leave the RPM at idle when going into gear. But what do I know. I'm an electronics engineer, not a mechanical engineer.

JJC5

I know what you mean...it does seem like it still helps. I double clutch my Z even when up shifting when it's cold. I clutch, go to neutral, let off the gas, engage clutch, clutch again and up shift. It gets rid of that notchy shift when cold.

JJC5

O.P., sorry to butt in on your thread....back to your question; your syncros are probably shot as said above and that's what is causing your grinding. Might want to consider changing your trans fluid first although I doubt that will cure it.

TAILWAG

Why are you out of warranty out of curiosity? Do you have 100,000+ miles? If it is a 2008, even super early 2008, you should still be covered under the 100k/5yr powertrain...

3LZZ06

^^^^this^^^^

0Cunningham Motorsports

my 08 only had a 3yr 36k warranty

VetteVinnie

That's the bumper to bumper warranty. Unmodified (i.e. not voided with mods and/or tuning), the Powertrain warranty is 5yrs/100K miles.

TAILWAG

Your 2008 has 3/36 bumper to bumper...but on top of that a 5/100k drive train.

The issues the OP is experiencing are most likely drive train related and should be covered under the 5/100k.

Even with certain modifications, this would still be in effect. The 2006 Zs only had 3/36, but in 2007, they bumped the cars to 5/100. Some 2007 may now be coming out of warranty...but, all 2008s should still be covered.