gsflyer2011

Mine, 2011 GS with MN6. My friends, 2012 GS with MN6. Both car's skip shifts bypassed.

On mine the first drive after sitting all night, it resists going into second gear and sometimes gets hung up on the gate and I have to shove it in. I also noticed that when cold, the gates are not aligned, ie, while shifting into second the shifter goes few milimiters to the right. However after the car is driven for about a mile and has time to warm up the shifter acts normally, no resistance and the 1-2 shift is straight down, with no movement to the right.

My friends experience is slightly more puzzling, not only he has resistance when cold, he has gear crunch/clash evertime he tries to shift into second. Again just like mine this disapears after few miles. He also noticed this slight gate mis-aligment when cold also.

Both puzzled. Has anyone have a comment, suggestion?. Is the skip shift solenoid interfering as it is bypassed and does not get a cold/inop signal?, or is this a design problem. Like to hear from all having similar challenges but especially solutions if any.

Thanking you all in advance!

grady

I believe this is a very common problem and seems the only way to avoid it is to let the car warm up.

Just be gentle on those shifts that are struggling until everything is heated up. The skip shift is not causing the problem.

Dado5

Yes my 2012 GS does the same thing when cold.

Motorhead-47

Swap to synthetic trans fluid. Flows better in the cold.

Bill Curlee

If it were me,,, I recommend doing this:

Your MN6 is filled from the factory with normal DEXTRON ATF. You can upgrade to some Mobile 1 Synthetic ATF. Any synthetic ATF will work. AMSOIL has a really great ATF.. Contact forum member SUBDRIVER for the details.

It made a significant difference in my 02 ZO6 and I'm sure that you will feel an improvement. Give it a try.

Just for your info, there are not any gates or stops inside the shifter or shift box. All that is located inside the transmission.

If you pull the shifter off the shift box, the lever is able to be flopped around to any position.

You SHOULD inspect the shift box bushings as they are well known to deteriorate / rot. If they are deteriorated, it can and will give poor shift quality.

The only pictures that I have are for a C5 shift box but, yours is just about identical. The C5 ZO6 box has solid metal shift box bushings but yours will have rubber ones.

There are a few aftermarket places that sell the nylon up grade bushings. I think ZIP Products has them



Let me know what you find out.

Bill Dearborn

I don't view it as a problem. They all do it when cold. The viscosity of the lubricant increases when it is cold. It has to get a little heat in it before the gears will engage properly without a little coaxing. I find when it is cold I can avoid any gear clashing or nibbling by shifting very slowly but firmly on the shift from 1st to 2nd. The transmission will slide right into gear and by the time I have made the 4th or 5th shift l can move the shifter as fast as I want to.

Bill

JCtx

Hey guys, I'm having the crunching/clanking issue for the first 1/2-mile or so. Those above me saying that's 'normal', are you referring to the notchiness, 'crunching', or both? Curiously, my car exhibits zero hesitation on 2nd gear, but crunches. Wish it was the opposite, justl ike GSFlyer .

Before continuing, my car is a '12 GS with 3K miles on the clock. And just switched to Amsoil Torque Drive fully synthetic Dexron-III ATF fluid. It did NOT stop the crunching; used it this morning for the 2nd time. Anyway, want to get one thing out of the way: What's exactly 'crunching'? Probably the blocker ring teeth, but against what? And since the tranny has no load and car is going very slow (15 to 20 mph tops) when this happens, all that is happening inside is the output shaft has to speed up the input shaft (stopped due to a leisurely shift) when meshed, so that shouldn't be rounding out the teeth, right? My motorcycle sounds similar, but much more violently when engaging 1st when stopped, and you can do that all day long, and nothing will happen to the tranny; it's normal for wet-clutch trannies to do that. Is that the case in my car? And yes, I also have the weird cold 2nd gate behavior when cold. But when tranny is hot, it shifts like a dream now. I'd probably rate it as one of the best I've tried, and I've driven several exotic manual cars with Grazianos and stuff. It has a very satisfying mechanical feel, and very nice gate action. I wouldn't change anything; not even the shifter. At least now that's new . And that's why I refuse to even take it to a dealer because if they touch anything, they might screw up a perfect tranny 99.9% of the time. I don't mind myself the cold notchiness one bit. The only thing I don't like, to be honest, is the crunching. I don't want to skip 2nd, or having to double-clutch, but might try shifting at 6 mph, which would put me at idle speed in 2nd; that should minimize the crunching damage. Hopefully somebody can explain exactly what's clashing in there. Curious why only 2nd. I can shift perfectly all other gears, even when stone cold. Thanks gang. And thank you to GSFlyer for starting this .

gsflyer2011

Thank you for the input, much appreciated. I have changed my fluid to Royal Purple SM 4000 miles ago (now have little over 6000 miles on the car), and my friend went with Amsoil very recently at 3000 miles. Although it has definetely made for smoother shifts while hot, it has not made too much difference when cold. You may have a point with the bushings, my car shifted better when new (go figure). Maybe I need to get in there and lubricate the H out of it with some good syntethic grease or go with nylon bushings as you have suggested. Better yet, both

Bill Curlee

I will see if Rick Kim will tune in and comment. He is deeeeeeeeeeep into tranny and differential stuff.

JCtx

Did you mean quickly from N to 2nd? I've tried shifting quicker, but more often than not, it still crunches. The times it has not I'm probably matched input and output shaft speeds and it went in smoothly. And contrary to most Vettes, I don't have any resistance from 1st to 2nd; it just crunches. And I don't feel anything on the lever either; I only hear it in the tranny (below the tunnel).

Hey GSFlyer, can you add a poll with 'notchy', 'crunchy', or 'both', or something to that effect? Most have the notchiness, but curious how many have my issue. Haven't heard much about it. What makes me feel good is when warm, mine is a dream to shift, so I know nothing mechanical is amiss. Just wish I had a better understanding what and why can be causing my crunching. Thanks gang.

Rick@RKT Performance

The GS's have MZ6 ratio and for some reason the 2nd gear (ONLY the 2nd gear) engagement teeth are design in an angle. The corresponding 2nd gear side of the synchronizer is also different than 1st gear side in that center 5 teeth are angled to match the 2nd gear enagement teeth. The new 5th gen Camaro TR6060 have this same design and had grinding going into 2nd gear. I have replaced the 1-2 synchro with Z06 design and upgraded the blockers to compressed carbon design. This took care of the grinding or issues going into 2nd gear hot or cold.

I can't say with certainty this design is causing the 2nd gear issue but I rarely have this type of issues with Z06 MM6/base MM6/ZR1 MH3 TR6060's.

MZ6 2nd gear.



MZ6 1-2 synchronizer.



MM6 2nd gear.



MM6 Z06 1-2 synchro.

JCtx

That was awesome Rick; thanks a million. And baffling indeed, but what do you think was the reason for it? Is it beefier, less prone to misshifts, or what? There has to be a reason. Hey, may I ask you a few more questions?

1. Does that grinding hurt anything in the long run? Or is it like on motorcycles with wet clutches, that the 1st-gear 'CLANK!' makes you cringe, but nothing happens? It's a lot more subdued on the car, by the way.

2. What's exactly grinding? Is that the blocker ring's 'tabs' against the 5 elongated cavities in the gear, or the actual angled teeth you showed? And why the synchronizer isn't doing its job, and allows grinding, angled teeth or not? Is it the lack of fluid due to no pump?

3. Finally, didn't Tremec supposedly improve the tranny with 'carbon synchronizer cones' (or some crap like that) to avoid grinding? Don't see any carbon parts there. Glad to hear you can replace that pair with Z06 units, but hope never have to open the tranny, to be honest. Hope to hear from you to see if I have to find an alternative to the grinding, like shifting to 3rd or double-clutching. Or if I can continue shifting to 2nd at very low speed without any worry of potential future damage. Contrary to my hopes, it's pretty obvious by your pictures that's not going to go away with mileage . I'll try shifting at 6 mph next time, which corresponds to idle rpm in 2nd gear, to minimize grinding. With zero load on the tranny, just speeding up the input shaft shouldn't damage the gears/synchros if the tranny is worth a darn. But will wait for your expert response. Thanks a million for chiming in Rick; greatly appreciate it .

Rick@RKT Performance

1) The engagement teeth on the gear and the synchro will be worn in the long run and must be replaced if the grinding continues. I would at least test drive the car with the dealer service manager to document that your car grinds when cold. This is so that you can have it repaired under warranty if it gets worse.

2) The grinding you hear are the engagement teeth not being locked in and running across each other.

3) Tremec started using carbon blockers on 2nd gears starting in 2011 but that was hit or miss. You can use the MM6 Z06 1-2 synchro but the MM6 2nd gear is not interchangeable since the gear won't work with the MZ6 counter shaft.

Most people just live with it and let the car warm up before using 2nd gear.

We use Z06 1-2 synchros and carbon blockers (1-4) on our performance upgrades.

JCtx

I guess it makes sense. Although 'grinding' might convey the wrong message here, since it's momentary. It's a quick and subdued 'clank' I wouldn't even hear with the stereo on. It's nothing like when you release the clutch before gears are engaged; that's what I call grinding. I hope somebody else has it, so they can hopefully describe it better than I do.

But it might be a good idea to one of these days leave my car there (not checked in), go in the morning and take a tech for a quick drive so they can document the issue. I wouldn't do anything before warranty expires, but as you said, at least have the option. Thanks a bunch for all your great input .

ROD BROWN

It seems to me as I put some miles on my 09.6 speed stick with the Z51 tranie,it smoothened out significantly. I think the gears began to mesh up and there is a definite improvement.Rod: flag:

JCtx

So yours used to 'crunch' on the 1-2 shift when cold too or not? Mine hot is perfect. And cold almost the same now that I have Amsoil fluid, except 2nd for a dreaded 1/2 mile or so.

C6Vette1

Is this something the dealer would fix under warranty? I have a 2008 Z51 with 12k miles. I get a a crunching/grinding sound between 1 and 2 and the shift tends to be sticky. The problem tends to go away once the car is warm or if I blip the throttle between 1 and 2.

Another issue is that when downshifting from 5 or 6, the shifter does not immediately self center in neutral between 3 and 4. It hangs between 5 and 6 and after a couple of seconds will move left to be between 3 and 4. Has anyone had that problem or have any idea what might cause it?

Rick@RKT Performance

It should be covered under your powertrain warranty but GM dealers will only use stock parts to repair.

I would check your shifter base alignment. The newer TR6060 Have better/updated design for the shifter return to center in the transmission.

Bill Curlee

For the centering issue, you can start with lubing your shift box. If that doesn't help, you can switch to a shifter with centering springs. I use the KIRBAN shifter in my C5 and really like it.



The centering springs for the shifter are inside the transmission. The early C5s had weak 5-6 return springs but the later C5, seemed to be better.. Your the first C6 owner that I have seen a return spring from. Thats why I recommended lube clean adjust first.

When you get the console off, check out the shift box mounting bolts and make sure that the rubber isolation bushings are not damaged, dry rotted or missing.

C5 ZO6 box with the ZO6 metal bushings. Yours will be rubber:



BC

C6Vette1

is there a TSB that I can refer the dealer to? They did not think there was any problem.