shudder

...could be in your clutch! And You might check the tightness on ALL 'Halfshaft' bolts. A 'shudder' could be caused from the clutch disc becoming too thin, wearing unevenly, or spring(s) broken/missing. Also oil on the disc/pressure plate. Could be as simple as the clutch NOT being adjusted properly. Many things can cause it, even as far off as the rear brake(s) or E. Brake staying locked even just one sticking locked just a little! Good-Luck!...

Marlin's right about the half shaft bolts. I had a good half turn and more in some of them when I checked. I never thought they would loosen, but they do! And that's where my vibration was coming from.

Also check your engine mount and tranny mount bolts.

John

I would interpret your shudder as clutch slippage.
Considering the rear tires and it sounds like you were getting traction, I'm not too surprized with a little slip.

Personally I wouldn't even deam it a malfunction of the clutch.
Something has to give when you put the hammer down.
Race cars need to be balanced bettween tire slippage and clutch slippage to find the right bite.

Sometimes what is thought to be a momentary clutch slip isn't that at all. You are torquing the chassis and you felt the response.

...talking about 'Something has to give'; If it is NOT the clutch slipping! And it is NOT the tires breaking loose! Then it IS the rim/wheel spinning within the tire beads!! That is why you see screws threaded through the circumference of the rims and into the tire beads; on dragsters and drag cars. You can check this by applying a 'witness mark' on the tire and wheel; and see if it has moved, after the next time you do a 'Launch'...

Now that's what I call getting the car to lock up.
Maybe the shudder was chunks of pavement coming loose as the grooves are cut in the surface?

Thanks for all the help, I left out an important factor simply because I don't think about it. Here is the answer...Some of you may know that I'm disabled and use a push-button clutch actuator. Seems like I inadvertantly adjusted one of the engagement parameters to a too soft setting, thus the clutch chattered. It was only the second gear shift engage that was wrong. Don't remember doing it but it was set too soft, re-adjusted the potentiometer and I'm back to Ferrari killing. Man those Goodyears grip.
I did have the half shaft flanges checked and they are good.
Thanks again, guys.