JCtx

Since day 1 (2,900 miles now), '12 GS 'crunches' in the first one or two 1-2 shifts when engine is cold. A few times it hasn't done it. I don't feel absolutely any resistance on the lever, but can clearly hear the 'crunch' as I shift into 2nd. I'm stumped by what it is. By the 3rd shift, even though tranny is obviously not hot, zero issues. Tried shifting to 1st and 2nd gear before taking off, and the first time no crunching, but the last time I used the car, it did. So not the solution. I also have to say gears don't 'click' into place while doing this. I have to try once or twice before gears engage all the way (with engine running). Reverse is also not easy to engage. After a try or two, I have to 'shove' it a little bit until I feel it clicks into place. I wouldn't say there's anything wrong with the tranny, but remember rowing the tranny on a showroom Vette (maybe an '11), and all gears went right in, even with clutch pedal out and engine off...which should be harder to do. Can't do that on my car.

My first question is: WHAT IS CRUNCHING? Is it the gears that need more break-in miles to mesh in? Or Is it the synchro? If so, why crunch at such a low rpm, and only once or twice when engine is cold? Again, tranny shifts perfectly afterwards. I know this tranny is no Graziano or ZF, but it shouldn't be crunching IMO. Previous Vette and GTO (T56) never did. I'm very close to changing all fluids, at which time will replace tranny fluid with fully-synthetic one. Haven't bought it yet, but I'm leaning towards Amsoil (need to order it), based on reviews here. Hoping that will eliminate the issue, but honestly doubt it.

My second question is: DO ANY OTHER VETTES DO THIS? It'd be nice to know I'm not the only one. I also want to know if whatever it is can lead to potential problems down the road. And no, I'm not going to take it to a dealer now. It's not a problem yet. If it continues for a year or two more, then I might do that before warranty expires. Could be a break-in issue due to crappy tolerances, but only time will tell. If it's a problem, it should get worse with time. Thank you for your comments folks.

JoesC5

Common complaint with the TR6060. Some are worse then others. My 09 seems to fit in the middle. GM went to another synchro material in '11, I think.

I originally changed over to the Rpyal Purple transmission fluid and it made the problem worse, so I drained it and went with the Mobil1 synthetic Dex III ATF. It seemed to help a little.

TINCANMAN

my 05 has the same problem when cold. after one or two shifts everythings ok. changed fluid no difference.

JCtx

So that's an issue with T56s too? Never had that on the C5 or GTO. Hey, how many miles on your car? So guess nothing happens to the tranny over time, huh? BUT WHAT THE HECK IS IT??? Is it something slightly misaligned? Not a typical synchro noise, but could be. Want to know what is it more than anything. And figured synthetic fluid wasn't going to correct the issue; you just confirmed it. Thanks for your help man.

C6RaceCar

It is lack of warm trans fluid completely circulated through all the parts. Just hesitate between shifts until the trans is warm. No need to force shifts between gears when cold.

Bill Dearborn

It really isn't an issue. In 54 years of driving I have had several transmissions that did the same. Including the ones in both of my C5s and now in my 08Z. The older transmissions were really bad because they used thick synchromesh transmission fluid. Not only did the gears grind some they did it longer and the shifter moved like it was enmeshed in glue.

There is nothing wrong with the transmission it can go several hundred thousand miles with the gears doing this.

Bill

JUIC3D

You could try a better transmission fluid--redline or amsoil and see if it helps.

JCtx

I actually shift like a grandma when cold, and at a very low rpm. And never rush shifts, even when hot; this tranny doesn't like to be rushed .

Excellent news; that's what I wanted to hear . But what exactly is happening inside? I'd like to know.

As I said, that's exactly what I plan on doing in a few days . I don't know if it's going to help with the crunching, but it should definitely help with the notchiness. Plus a full synthetic fluid is always better than dino .

And a big thanks to everyone who contributed .

Bill Dearborn

Here is an article that has an explanation:
http://www.rsgear.com/articles/2007_10.pdf

Read down to the explanation about the synchronizers being wet clutches and how they are affected by changes in lubricant viscosity.

Bill

AORoads

synchros. synchros were added (as well as gear cut angle) to ease transition fr. gear to gear. even synchros however need fluid warmed. depending on ambient temp, this has happened to non-synchro trans as well as synchro trans for ever. even legendary muncies of "midyear" 60s corvettes. as dearborn sez, it's happened in many many cars.

two ways (three actually) to avoid it: warm up car---actually trans oil--until it doesn't do it; shift to neutral betw. 1-2 and then to second gear slowly; double clutch (let out clutch in neutral, then shift to second gear). usually, first method is not recommended and car/trans oils warm up quicker when moving at low load. therefore, second or third methods are the way to go.

my opinion is, depending on car, trans design, and how long you do this, the more you bang the gears while they crunch, the higher the chance that sometime sooner than later you will have a chance of needing trans repair.

C66 Racing

If you do opt for the AMSOIL, more than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.

Mike's LS3

My 08 had a slight nip in 2nd gear when cold, but after a couple of shifts it was gone. As I put on mileage, it went away completely.

JCtx

Thanks Bill, but that article didn't tell me anything I didn't know already.

Found an analogy that I'd like comments if they're similar. On my bikes with wet clutches (synchros are like a wet clutch too), they 'clunk' rather loudly when you shift to 1st gear when stopped. That's the noise gears make when meshing together after the input gear is abruptly stopped from 1,200 rpm. On my car (and others), the output gear is the one turning at about the same differential, but the synchro is not grabbing due to cold oil, so the 'crunch' is the gears also mating at a different speed. On the bike, as horrible as that phenomenon sounds, it doesn't hurt the transmission. That's probably the same on our trannies, right? They're pretty robust. What I don't understand is why only SECOND gear, when all others change perfectly, even though the fluid is just as cold. Hmmmm.

I actually let the car warm up a little, but obviously not until fluids get warm. But I always use your second option, shifting very slowly AND at very low rpm from 1st to 2nd. But no, haven't tried double-clutching yet, nor do I want to. That's why we drive a freaking synchronized tranny in the first place .

I'm ordering from you man, so don't worry . Had to do a million thngs, but I'm finally about to send you a PM to order the fluid and a pump. Many thanks.

Your first sentence is exactly my issue, and that's why I'm not worried now. Your second statement, however, is music to my ears. And that explains my theory that the 2nd gear synchro has a little bit of a mismatched surface that will take longer to wear/break in. I certainly hope that's the case. Tranny is perfect when hot, so everything is fundamentally right in there. It's just this one freaking synchro. And the T-6060 has been improved after '08, and this shouldn't be happening. Wonder if other 2012 MZ6 (or MN6) owners are having this same issue. Thanks again to all of you .

CO Lightfoot

Lots of cars suffer with a crunching 1-2 shift when cold. My long-gone 03 Mach1 was terrible.

Sometimes I would skip 2nd... shift 1st-to-3rd.

Or just start in 2nd gear until it warms up.

5W30

Mine doesn't "crunch" into second when cold per se but it is notchy and stiff. I don't like it. To avoid it I don't use second gear until the car has warmed up. In fact even once the car is warmed up I still use 1-3 shifting on most occasions unless I'm feeling frisky.

Shdwops

Warranty . U get 5 years on the trans

Flying24

Short shift on cold morning

Boomer111

My 08 with 31,000 miles still exhibits this cold shift, usually disappears after a few blocks. My 3 speed manual in the mid year '63 Pontaic 326 Tempest Le Mans sifted about the easiest all all my manuals. Or so as I remember it.

JCtx

I always short-shift when cold, and still does it. I've been just pausing the shift (allowing rpm to drop) and that worked. Slightly annoying, but I prefer that than a 1-3 shift, since I'd have to rev it higher in 1st. Shifts beautifully after a few miles, so I won't do anything about it. Will sell the car before warranty is over, in case new owner wants to do that. It's the stupid odd 2nd-gear synchro Tremec uses, so why tear down a new transmission and the same thing happen again? What's clear to me is that 'crunching' or 'scratching' can ruin the synchro in the long run, so we need to avoid that with whatever method we want to use .

I remember a Cobra kit car with the TKO 5-speed that shifted like butter hot or cold. And it was also a Tremec. All of my Tremecs (GTO, Vettes, and Mustangs) have always had that stupid trait of being notchy as hell when cold, 'crunching', or both. I'm not going to buy another car with a Tremec again.