Shutting car off while in gear

[HR9121]

Originally Posted by Mack Reeves

I asked the same question to someone I consider an expert and his opinion is that the neutral on a forward shift is a natural neutral but not a "clean neutral. Something about the path of the fluid in a natural neutral is totally different from a "clean neutral". He has both types of valve bodies and still recommends the clean neutral for shifting on the top end. I bought the clean neutral one for myself. Even though I had to purchase a new shifter also. Oh the PPP is now my shifter of choice.

Thanks, I didn't realize this. I guess I better ask my transmission guy some questions.

[Lou Jeffery]

Could somebody explain what "clean neutral" means. I have a reasonable understanding of automatic transmissions and have heard this term many times but never an explanation. Thank you, Louis Jeffery

[jmantle]

Originally Posted by Lou Jeffery

Could somebody explain what "clean neutral" means. I have a reasonable understanding of automatic transmissions and have heard this term many times but never an explanation. Thank you, Louis Jeffery

Clean neutral valve bodies dump the forward clutch and keep the direct clutch applied so all the gear train rotates at the same speed. The engine has to be kept running (idling) to keep the direct clutch applied.

Jim Mantle V/SA 6632

[buzzinhalfdozen]

I've put many runs on both a Coan XLT-350 and a Pro-flite with clean neutrals shutting off above 10,000 RPM. Never had an issue with either, tear down at end of season shows no signs of unusual wear. I have noticed it seems to take longer for the T-350 to "let go" of the engine not sure why but never caused a problem.

[ss3011]

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.