Shutting car off while in gear

ss3011 · 08-10-2015, 12:00 PM

The reason it takes so long to dump the clutch at high rpm is due to the fluid in the clutch drum. As the drum spins the fluid is centrifically forced to the OD of the drum and effectively creates a higher pressure on the clutch piston. The feed for the clutch is closer to the centerline of the piston. When you want to dump the clutch, a valve opens and exhausts this feed channel, the problem is that the spinning drum keeps high pressure at the OD of the piston, and limits how much oil can be moved to the centerline of the piston. Most pistons or drums have a small check ball that is machined close to the OD of the drum. When the clutch pressure drops to a designed value the check ball comes off its seat and exhausts the clutch oil. At high rpm the clutch centrifical oil pressure may be too high to unseat the check ball and basically keeps the clutch on. Some tranny builders know this and drill a small hole (constant bleed) near this check ball, That is a "fix" to try and get the clutch off quickly, and is unaffected by rpm.

08-10-2015, 12:00 PM	#14
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Shutting car off while in gear The reason it takes so long to dump the clutch at high rpm is due to the fluid in the clutch drum. As the drum spins the fluid is centrifically forced to the OD of the drum and effectively creates a higher pressure on the clutch piston. The feed for the clutch is closer to the centerline of the piston. When you want to dump the clutch, a valve opens and exhausts this feed channel, the problem is that the spinning drum keeps high pressure at the OD of the piston, and limits how much oil can be moved to the centerline of the piston. Most pistons or drums have a small check ball that is machined close to the OD of the drum. When the clutch pressure drops to a designed value the check ball comes off its seat and exhausts the clutch oil. At high rpm the clutch centrifical oil pressure may be too high to unseat the check ball and basically keeps the clutch on. Some tranny builders know this and drill a small hole (constant bleed) near this check ball, That is a "fix" to try and get the clutch off quickly, and is unaffected by rpm.