Guys, I bought a used 07 Base MN6 with 9000 miles and as soon as the temps at night dropped below 50 degrees I started having this problem.

When I first start the car in the morning and drive down my street it is very hard to shift into 2nd unless I wind out 1st to about 2500 rpm. Once in 2nd and sometimes in 3rd the car "bucks" slightly every now and then until I drive it a few miles. I know its not engine related as it feels like it's something in the drive line. Can cold, thick fluid cause a slight bucking feeling?

I have also noticed after warm up that sometimes the shifts feel as if there is inadequate lubrication and things aren't meshing well. I do have a C5 Hurst shifter installed with the Anti Venom detent mod.

I took it into the dealer and naturally they said that they couldn't repeat the problem. While there they showed me a paragraph from GM, basically stating that the car won't shift right with cold transmission fluid. Please realize I live on the Texas-Mexico border so I am thinking something has to be wrong for the trans fluid be this temperature sensitive.

Now here's my question: Would switching to redline synthetic trans fluid solve any of this. I can see it addressing the viscosity issue at startup but what about my bucking problem?

Anyone else experience these symptoms?

 

I believe the problem you are having is not really a problem but is really the CAGS (computer aided gear shift) that prevents you from shifting to 2nd or 3rd (hence the 1-> 4 light in the instrument display) in order to save gas. When certain criteria are met, the solenoid locks out the 2nd and 3rd gears. For me usually its when the oil is warmed up and when I am between 2,000 and 2,500 RPM. The owner's manual describes it in more detail. You can shift into 4th then back into 2nd or 3rd or just keep it in neutral until you are back out of the "criteria." This can be eliminated with a CAGS eliminator for $20 or pulling a fuze, but the latter has caused some to throw codes. Best $20 investment ever. As for the 2nd to 3rd shift, don't know what to tell you other than sometimes its hard to get smooth shifts until you get used to it, and even then it isn't always smooth.

 

I have installed the CAGS when I did the shifter. Sorry I didn't mention that in my mods. Thanks for the response though.

Mainly I am comparing this car to my 01 Z06 which never bucked whatsoever.

 

Virtually EVERYONE experiences difficult shifts with the MN6 when the fluid is cold. The symptoms are shifter sluggishness and resistance when moving to second and then to third, and possibly some minor gear clashing depending on how fast you insist on making the shift. Bucking?!...No, bucking does not make sense as being directly caused by lubricant viscosity.

But...this sounds like it could be incomplete gear engagement before you release the clutch, and perhaps this is related to lubricant viscosity; the "buck" may be occuring as the gear is fully positioned under torque. If this is the case, you are going to create transmissions problems for yourself. Avoid hard, swift shifts for the first few miles until the fluid warms a little. In Mission, it shouldn't take that long. I would definitely NOT do any "winding out" shifts until the engine oil temp had stabilized at normal operating level...I keep my DIC display on oil temperature for this purpose.

Some aftermarket lubes will help with this problem...I prefer to wait a few minutes until the fluid warms up. Maybe if I lived up north where temps were regularly in the teens and twenties, I would consider a lubricant change.

 

I may just do a 1-3 shift until the trans is warm. I am planning on doing a swap to Redline because I can't see it doing anything but helping.

 

Do yourself a favor, and confirm the aftermarket lubricant meets the GM spec for manual transmission fluid...if you do have transmission problems, a lubricant not meeting their specs could cause you warranty problems.

I forgot to mention, but the symptoms I described begin to appear for my car at any temp below about 50-60 deg.

 

Change the MN6 fluid to Royal Purple Syncromax. There will be a drastic improvement in cold weather shifting.