Clutch Question

[Lawrence Coppari]

For the past couple of years when I run the car on the track, I get a clutch vibration in the pedal if I downshift after being at full throttle. For instance, there is one track that I go to most of the time. It has straight where I can get going quite fast. The straight ends with a 110 foot drop followed by a 90 degree curve. I come down the hill in 5th - well into triple digits. If I downshift to 4th then 3rd while braking, the clutch vibrates when I go into 3rd. At that point I'm probably going 60 mph. If I just brake in 5th without disengaging the clutch, then skip 4th, nothing vibrates. The vibration only occurs when the clutch is depressed and I only feel it in the clutch pedal.

Off the track, the clutch never vibrates unless I go full throttle. There is a hill near my home. I sometimes go full throttle up it. I can get some of the same vibration when I down shift to turn into housing area.

Think it's my throwout bearing? There is no noise and clutch does not slip.