What I suggested was pertaining to Diesel engines. It can be done effectively with all types of automatic transmissions, but must be done carefully to avoid damage and premature aging and slippage. The main idea is to keep inside of the power curve of the engine. What I mean is this, watch your tach, and try to remember at what RPM your car shifts into, or out of each gear, and at what speed. You will find that there is a place within a few hundred RPM before the shift points going into the next higher gear where your engine is performing best. Bob Bondurant is really the guy to blame for this, he was the one who taught me how to do it. That's my story, and I'm stickin' to it! If you, dear reader, don't know how to do this, or think you do, and want to be sure you're doing it right, I believe Bob covers the technique in one of his books.
This is what I do in my 300SD. My '82 has a D-S-L transmission selector. I seldom use L manually, but I will start out in S when the engine is cold to help warm it up, and/or when I want to get a little more power/speed before shifting. You need to manually shift to D before the transmission would want to shift it for you or you will get a clunk when you shift. You also will want to shift up under acceleration, and not while decelerating, or you will get the dreaded clunk too.
The second part of this is while decelerating in D, you can shift down to S to assist in braking by using the engine to slow you down. I will also drop down a gear while going around a street corner to optimize the engines torque coming out of the turn. To be smoothest, you need to match road speed, RPM, and the correct gear. So when I shift down from D to S, I add a few hundred RPM to equalize the speed of the driveshaft, crankshaft, and transmission.
Think of it like this, if traffic on a roadway going the same direction in multiple lanes is travelling at different speeds, they are not "synchronized" and therefore would not be able to freely merge in and out of each other's lanes because their speed relative to each other is different. However, if they are all going the same speed, although that speed is 65 MPH relative to a fixed object standing still, they would be motionless relative to each other, and allowing for positioning and spacing, able to freely merge in and out of each other's lanes in traffic.
This is the "secret" of shifting a manual transmission without using the clutch, and how to properly shift multigear (10, 13, 15, & 18 speed) manual transmissions in trucks. I personally have always loved the physics of it. You are taking two gears, spinning at different speeds, and adjusting their speed to synchronize so you can mesh them without clashing. This is how a professional truck driver is able to change from a radically higher gear, to a much lower one, simply by adjusting road speed, and RPM to match the gear the driver needs to select. This is also one reason that it's illegal for trucks to coast down a grade. The speed of the truck can exceed where the transmission's RPM entry point into the highest gear would be at top speed, and the brakes alone are sometimes not sufficient to slow the 80,000 Lb. (max gross) vehicle to a point where the gear mesh can take place. The result is a "runaway" truck, and that's why there are those "truck ramps" on seriously steep down grades.
Well, that's all for now, kids, but please join us next week, when our topic will be: "Why that truck driver is looking at you like that while you're re-fueling your diesel Mercedes at the local truck stop"...
[Edited by longston on 01-29-2001 at 11:42 PM]