DOWN Shifting

Clutch is used for Starting/and backing-up. No book will teach you to shift, Its all RPM`s. Practice, Practice, Practice.

 

I use to float gears when I was a highway driver and that's all it's meant for,highway driving. There isn't a driver alive that can pull a 12% grade from a dead stop loaded and grab a gear without using the 3rd pedal and that's just the start of off road driving. Using a 250 rpm split w/ a double clutch is a core skill application. Not to mention Jake shifting and power braking off of +30% grades.

 

just look at the speedo...add the two numbers of your speed together...*35mph* you should be in or shifting into 8th...etc...hit the throttle..in low range..a little *luv tap*...in high range...nail the throttle...and the shifter will slide into place

 

What kills me is rookies who double-clutch on upshifts. You should have the engine at the proper rpm for the next gear, then all you do is tap the clutch (once, not twice) and slip it in the next gear. If you have to double-clutch to upshift because it won't go in, that means you have no idea where the rpm's should be for the next gear and are making up for it by synchronizing the transmission to your poor shifting skills. Or you are just clueless and like to press the pedal twice because it makes you feel like a big-rigger.

The only reason or time to double-clutch is on downshifts, because the transmission gears are going faster than the engine crankshaft. In order to synch the two up, you have to manipulate them. Disconnect power (one clutch stab) move it to neutral, hit the throttle to synch engine rpm to transmission road speed (stab the clutch again) reconnect power, go.

Double-clutching on upshifts is wholly unnecessary. Once clutch stab is enough.

 

Here is a good explanation of how and why to double-clutch (partial from Wikipedia):

Non-synchronous transmissions are engineered with the understanding that a trained operator will be shifting gears in a known coordination of timing. Commercial vehicle operators use a double-clutching technique that is taught in driver's trade schools. The most skillful drivers can shift these transmissions without using the clutch by bringing the engine to exactly the right rpm in neutral before attempting to complete a shift, a technique called "float-shifting."

Double clutching (commercial motor vehicle)

Operators of 18-wheelers, farm equipment, tractors and other heavy equipment learn to float the transmission in and out of gear, beginning with dis-engaging the clutch by pressing the clutch pedal only part way, enough to pull the transmission out of gear, re-engaging the clutch in neutral (between gears by letting the clutch pedal all the way back out) to let the engine revolutions decelerate enough for the idle sprockets to shift, and free gear shafts to slow their revolutions per minute (RPM), then dis-engage the clutch again (by pressing the clutch pedal only part way to the floor) a 2nd time, and float the higher gear into engaging the drive coupling and fly wheel and engaging the clutch plates. Once an operator is familiar with range, range selector, rpm, velocity, and torque of heavy equipment like an 18-wheeler, they can begin to anticipate when to shift gears. Operators become familiar with ranges of gears. They also learn not to leave their foot on the clutch while driving, because these types of transmissions use the clutch for several very different purposes. The depth the clutch is depressed to the floor will determine what the clutch will be doing as a synchronizing function.

Clutch brake

Unlike any other type of transmission, non-synchronous transmissions often have a mechanism for slowing down, or stopping an idle gear. In commercial motor vehicles, this mechanism is called the clutch brake, and is used by depressing the clutch all the way to the floor. This is useful in 18-wheelers that have just started their diesel engines, and are releasing parking locks, and engaging the transmission from a stop. The clutch brake not only slows or stops the idle gear axis, but can also prevent shifting into gear until the clutch is lifted a few inches off the floor. In order to shift into gear, the clutch must be half way off the floor, otherwise the clutch brake will prevent the transmission from being shifted into or out of gear. Mechanics must often repair or replace the clutch brake in a non-synchronous transmission when an inexperienced operator wears it out, it becomes inoperable, or has lost its function.

 

I drive a Volvo 670. When single shifting down (one gear) I slow to about 1000 rpm.. go to neutral, clutch out, rev to 1500 and shift to next lower gear. Works every time with no grinding.

 

the prostar i drove had a 1600 rev limiter abd shifted around 950-1200 it was a frustrating drive for me because i kept missing the shift range

 

So many people throw out their RPM numbers and think all trucks are alike. The engine and transmission combination will give you your RPM range (engine power band) and RPM's between gears (transmission specs). Your gear ratio and tire size will determine the speed you travel in any gear. There are many similarities, but each truck is different. You need to become familiar with your equipment.

 

yup.... I only posted what works in my case. It is important to know where the power band begins and ends on each truck.

 

I cant remember the last time I had to Double Clutch.
Maybe, and Maybe, if I get into another truck, that im not familiar with, I might, or might not Double Clutch, I just might get pizzed off and jam the darn thing.