Hard Shifting on '08 6 speed manual

Originally Posted by c4c5specialist

HI there,
Degradation of the clutch fluid meaning lower lubricity to keep things moving freely or slow moisture contamination.
Either way, clutch fluid should be changed every 2 years/24000 miles unless raced.
Fact is, different fluid cause different issues.
Syncromesh is designed for bronze frictional surfaces in the New Process/Getrag transmission. In the six speeds in Corvette, the paper(pre2001) and the carbon composition frictional surfaces are not designed to accept the lubricant.
Not to mention the tolerances of shafts to support bearings are actually LESS, so the lubricant doesnt lubricate the bearings correctly under high stress conditions.
This is why GM didnt recommend it for the T56.
Allthebest, c4c5

Are you sure the 6060 has carbon? Tremec directly told me they had Bronze & the Synchromesh wouldn't hurt them...

Tremec also advised to NOT run the Dex6 replacement fluids that some GM dealers were telling people to use, as it is too thin.

The previous 2 "best" feeling fluids I tried were the Amsoil ATF and Redline D4 ATF, but when the trans wasn't up to full temp it still shifted like @#$! so I decided to try a few other fluids. Overall, I think the Redline was next in line for best shift feel.

[c4c5specialist]

HI there,
Yes, they are carbon composition. These were specific for GM in the design.
Second, DEXRON 6 should NEVER be used. And its the same viscosity as the old Dexron 3, but its the friction modifier package within the fluid that is different and NOT compatible.

88861800 is the transmission fluid that should be used in these transmissions now, since Dexron 3 licensing is no longer valid.

Specifications from GM on transmssions fluid, document 1788842: 88861800

Allthebest, c4c5

Originally Posted by c4c5specialist

HI there,
Yes, they are carbon composition. These were specific for GM in the design.
Second, DEXRON 6 should NEVER be used. And its the same viscosity as the old Dexron 3, but its the friction modifier package within the fluid that is different and NOT compatible.

88861800 is the transmission fluid that should be used in these transmissions now, since Dexron 3 licensing is no longer valid.

Specifications from GM on transmssions fluid, document 1788842: 88861800

Allthebest, c4c5

I highly respect your opinion on many Vette items, but I believe in this case there may be an error. I contacted my source at Tremec again, and he stated that 100% of all TR6060's used in every 2008+ C6 contain "sintered bronze" synchros, as the carbon lined ones went away with the T56. He even went out to look at a tranny to double check & said "yep, I can see their surfaces are yellow metal...". He stated that the new ones are a German design that is thinner, which was required to maintain the same overall gear stack up since wider gears are now used for increased torque, but the case is still the same size. He said the synchro assembly is also using new springs, washers & blocker rings and the spring path is the only thing that really requires a fairly thin fluid, but slight viscosity changes shouldn't be a problem. Since we were racing, they advised that we need to consider the general operating temps of the trans, and if seeing primarilly track use a slightly higher viscosity ATF equivalent could be used for greater gear/bearing protection. He also said just don't run a Type F fluid as their FM package has the reverse friction characteristics with regard to speed, and will make shifting worse.

HTH

[c4c5specialist]

Hi there,
Ok, well, in order to confirm this.
I have ordered 2 parts, frictional cone surfaces for 1/2 and 3/4 syncronizers for the 2008 Corvette.
Once they are in, I will post pics and part number and we will see.
Maybe the information within GM is incorrect.
However, I will NEVER deviate from the fluid specifications within SI.
They have had Syncromesh on the shelf forever, if it would work reliably, they would specify it.
Allthebest, c4c5

[cwmoss]

I bought a new 08 last March. One of the first things I noticed, was the 1-2 and 3-4 shift problem. I checked the corvette forum (I didn't know of this one yet), and saw that this is a common problem. After reading all I could, I replaced the original fluid with Mobil 1 ATF, and what a difference it has made. Cold, it still has just a bit of the "grinding" between the 1-2 and 3-4 shift, if you shift quickly, but it is noticeably less, and after it gets to operating temperature, hardly any. I only got a little over 3 qts out when I drained it, so, I am going to change it again after another month or so.
Just my experince with this wonderful car,
Daryl (cwmoss)