M6 trans grinds during 1-2 shift when cold
Thread Starter
Racer
Joined: Apr 2008
Posts: 270
Likes: 8
From: Michigan
M6 trans grinds during 1-2 shift when cold
'12 Grand Sport with M6 trans, when the car is 'cold' there's a harsh grinding/grabbing sensation through the shifter when shifting from 1-2. It only happens the first minute or two of operation, once things warm up a little bit all shifting is smooth. If I shift from 1st, put it in neutral, and then shift to 2nd around a second later, I don't have that sensation when everything is 'cold'. Any ideas what the issue could be? Synchro? (Could a bad synchro get better with temperature?). I'll take it to a dealer later this year since it's still under warranty; but it's done this ever since I bought the car (used with 7500 miles), so I'm concerned it could be from abuse from the previous owner, in which case it might not be covered.
Last edited by Kozzzz; Jun 28, 2014 at 11:45 PM.
Burning Brakes
Joined: Dec 2001
Posts: 1,244
Likes: 13
From: Laguna Woods, CA
'12 Grand Sport with M6 trans, when the car is 'cold' there's a harsh grinding/grabbing sensation through the shifter when shifting from 1-2. It only happens the first minute or two of operation, once things warm up a little bit all shifting is smooth. If I shift from 1st, put it in neutral, and then shift to 2nd around a second later, I don't have that sensation when everything is 'cold'. Any ideas what the issue could be? Synchro? (Could a bad synchro get better with temperature?). I'll take it to a dealer later this year since it's still under warranty; but it's done this ever since I bought the car (used with 7500 miles), so I'm concerned it could be from abuse from the previous owner, in which case it might not be covered.
Race Director
Joined: Oct 2005
Posts: 14,999
Likes: 200
From: Bay Area Ca.
Normal should be better when warm.
Not really a grinding but more of a notchiness.
A real gear grinding, not meshing could be another problem but I am betting you have the normal notchiness going from 1-2 gear.
Not really a grinding but more of a notchiness.
A real gear grinding, not meshing could be another problem but I am betting you have the normal notchiness going from 1-2 gear.
Thread Starter
Racer
Joined: Apr 2008
Posts: 270
Likes: 8
From: Michigan
I'm not sure if this is what I'd consider a 'notchy' feel. The shifter doesn't have any issue getting into the correct position, but the engagement feels bad. It feels and sounds like what I'd imagine it'd sound like if a gear was trying to mesh with a gear that's already spinning, it feels/sounds like the teeth of one gear are clattering off the tips of the teeth on the other gear a couple times before engaging. Granted, I can't see what's actually happening, but the feel and sound of it makes me visualize something like that in my head. Is that what you guys all experience too?
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Team Owner
Joined: Jun 2005
Posts: 46,295
Likes: 2,596
From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
The usual response of normal is almost always correct especially due to design (but there was some redesign to trans synchro materials I think in your car's year). But it could be other things, too You are familiar with CAGS lockout at low rpm/speed, right? It can also be synchro, bad fluid (unlikely), possible shifter issues, and (unlikely) prior user abuse.
Team Owner
Joined: Mar 2008
Posts: 21,502
Likes: 462
From: Southern Utah
Don't worry about possible abuse from the previous owner...it is unlikely this but also undetectable by the dealership even if it was abused. I would bet that with few miles and possible babying by the previous owner, it is more likely a break-in issue rather than the opposite.
Pro
Joined: Sep 2013
Posts: 644
Likes: 53
From: Metro Detroit
Thats not abnormal, and is quite common with the T56 and TR6060. Every one I've ever driven has done this a little when cold. The carbon fiber blocking ring for 2nd gear was supposed to resolve this issue in 2011, but I've heard rumors of some 2012 transmissions being disassembled, and finding the old style in there.
I like Royal Purple Synchromax in the trans (and I'm not a RP fanboy). It is a GL4 gear oil, rather than an ATF, but is still VERY thin. Lighter than SAE 30 motor oil. Shifts are definitely smoother than with DEX III.
I like Royal Purple Synchromax in the trans (and I'm not a RP fanboy). It is a GL4 gear oil, rather than an ATF, but is still VERY thin. Lighter than SAE 30 motor oil. Shifts are definitely smoother than with DEX III.
You will be glad you did
Safety Car
Joined: Nov 2007
Posts: 4,148
Likes: 392
I'm not sure if this is what I'd consider a 'notchy' feel. The shifter doesn't have any issue getting into the correct position, but the engagement feels bad. It feels and sounds like what I'd imagine it'd sound like if a gear was trying to mesh with a gear that's already spinning, it feels/sounds like the teeth of one gear are clattering off the tips of the teeth on the other gear a couple times before engaging. Granted, I can't see what's actually happening, but the feel and sound of it makes me visualize something like that in my head. Is that what you guys all experience too?
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
There is nothing wrong. Once you drive a mile or so and the trans fluid warms up the notchiness and grabbing go away. Until it warms up you just need to shift slowly to avoid the feeling.
Bill
Bill
Burning Brakes
Joined: Dec 2001
Posts: 1,244
Likes: 13
From: Laguna Woods, CA
When my GS is dead cold, I frequently shift from first to third, avoiding second altogether for the first couple of shifts.
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
Document it with the dealer. You may even get a free fluid change.
I tried a aftermarket fluid in my '08 and didn't see any change. I then changed to the current GM recommended fluid, and it got a little better. If you have a '12, you probably have the newest recommended fluid.
Shifting technique can help alot. Try shifting at different rpms. Shift 1-neutral-2. Shift 1 to 3, etc.
52k miles here and it's not getting any better or worse, just a minor agravation.
I tried a aftermarket fluid in my '08 and didn't see any change. I then changed to the current GM recommended fluid, and it got a little better. If you have a '12, you probably have the newest recommended fluid.
Shifting technique can help alot. Try shifting at different rpms. Shift 1-neutral-2. Shift 1 to 3, etc.
52k miles here and it's not getting any better or worse, just a minor agravation.
Thread Starter
Racer
Joined: Apr 2008
Posts: 270
Likes: 8
From: Michigan
Thanks for the input guys! I feel better that there's no actual problem (I had some concerns about the car's previous history since it was bought back by GM from the original owner, and the engine was replaced under warranty prior to me buying it, so I was wondering if maybe there was some abuse or something in the past).
Any ideas why it only behaves that way when 'cold' (is it even due to temperature?)? Mine usually only does it for the 1st 1-2 shift. It might last for 2 1-2 shifts at the most before it seems to engage smoothly.
Any ideas why it only behaves that way when 'cold' (is it even due to temperature?)? Mine usually only does it for the 1st 1-2 shift. It might last for 2 1-2 shifts at the most before it seems to engage smoothly.
Team Owner
Joined: Jun 2005
Posts: 46,295
Likes: 2,596
From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
Thanks for the input guys! I feel better that there's no actual problem (I had some concerns about the car's previous history since it was bought back by GM from the original owner, and the engine was replaced under warranty prior to me buying it, so I was wondering if maybe there was some abuse or something in the past).
Any ideas why it only behaves that way when 'cold' (is it even due to temperature?)? Mine usually only does it for the 1st 1-2 shift. It might last for 2 1-2 shifts at the most before it seems to engage smoothly.
Any ideas why it only behaves that way when 'cold' (is it even due to temperature?)? Mine usually only does it for the 1st 1-2 shift. It might last for 2 1-2 shifts at the most before it seems to engage smoothly.