I think I just answered my own question......


Mistake #4: Improper Downshift Technique
More correctly, this should be called "Improper Brake and Downshift Technique," since it is difficult to separate the two. I would like to explain the entire sequence of heel-and-toe braking and downshifting; that would be an article in itself, however, so I will not.
Simply put, the theory of the heel-and-toe downshift is this: When braking and downshifting prior to a corner, you must brake in a straight line while simultaneously clutching the car, revving the engine to match the speed of the drive wheels, putting the car into a lower gear and then releasing the clutch without upsetting the tire contact patches and suspension in the process.
For those of you who do not know how to heel-and-toe downshift, you may want to go to Bob Bondurant's or Skip Barber's driving schools. For those of you who know how to heel-and-toe downshift, but are still not doing it as smoothly as you would like (i.e.: you are chirping the tires when you downshift), here are a few tips:

With your car in neutral and with the engine running, practice putting pressure on the brake pedal with the ball of your foot while swinging your heel and the outside of your foot over onto the gas pedal. Please, do not touch the shift lever!

Using constant brake pedal pressure, try to rev the engine up to a reasonable rpm and hold it there. Repeat the process, pivoting your foot from left to right until you feel you can do this with consistent repeatability. Your tire chirping problem is probably due to your lack of revving your engine up high enough or blurping the throttle and downshifting too slowly.
Practice your downshifts at your next autocross event or on an uninhabited back road. Better yet, take a refresher driving school course until you have your heel/toe downshift perfect. Good braking and downshifting is essential if you want to improve your lap times. (Not everyone, however, is impressed with a good heel/toe downshift technique. Mr. Holland, my high school driver education teacher, marked me off for doing it.)

 

I tried double clutching it, it would still do it. I'll try blipping the throttle every time I downshift. Might be kinda awkward at first but I'm sure I'll get used to it. Wish i had known about the M12 before. But the whole tranny didn't go out, just the snychros and cones. So I doubt GM would have replaced the whole thing.

 

When you downshift, you need to be mentally cognizant of 2 things BEFORE you start the downshift: 1) what RPMs are you currently at, 2) what is the ratio between this gear and the next lower gear. The M12 trannies have about 1.4 ratio between each gear. So if you are in 3rd at 4000 and want to be in 2nd, you need to add gas quickly* (blip) so that the (post blip) rpms are close to 4000*1.4 or 5600 RPMs. Anything between 5300 and 5800 will lessen the stress on the synchros to almost nil!

If you can see the nose of the car rise of fall during a dwonshift, you are not doing it right. If you notice the car accelerating or deceleraing as you let the clutch out, you are doing it wrong! Smoothness-grasshpooer--smoothness.

But really, we used to downshift older cars because the brakes plus engine would stop the car faster then the brakes alone. Such is not the case today. The brakes are strong enough all by themselves to stop the car without any help from the engine. All you need to have acomplished is to perform the shift without upsetting the chassis so that as you ease off the brakes, you can ease on the gas to balance the car for maximun cornering forces.

I suggest you get the tranny fixed, and then learn to use it properly at less than 1/2 power until you can shift so smoothly that the passenger can't tell that you have changed gears. After you learn this, then slowly add power to the equation and learn to retain the smoothness as you develop car control.

* you have the same amount of time to get the RPMs up as you have time to push in the clutch and let it back out again. The blip is a quick agressive stab at the throttle then a release of the throttle. The stab brings the RPMs up to the required range, the release removes the power so that when the clutch comes back out you don't upset the car.