TD in DC

http://auto.howstuffworks.com/transmission.htm

OK, this is what I mean.



Let's look at each of the parts in this diagram to understand how they fit together:


The green shaft comes from the engine through the clutch. The green shaft and green gear are connected as a single unit. (The clutch is a device that lets you connect and disconnect the engine and the transmission. When you push in the clutch pedal, the engine and the transmission are disconnected so the engine can run even if the car is standing still. When you release the clutch pedal, the engine and the green shaft are directly connected to one another. The green shaft and gear turn at the same rpm as the engine.)

The red shaft and gears are called the layshaft. These are also connected as a single piece, so all of the gears on the layshaft and the layshaft itself spin as one unit. The green shaft and the red shaft are directly connected through their meshed gears so that if the green shaft is spinning, so is the red shaft. In this way, the layshaft receives its power directly from the engine whenever the clutch is engaged.

The yellow shaft is a splined shaft that connects directly to the drive shaft through the differential to the drive wheels of the car. If the wheels are spinning, the yellow shaft is spinning.

The blue gears ride on bearings, so they spin on the yellow shaft. If the engine is off but the car is coasting, the yellow shaft can turn inside the blue gears while the blue gears and the layshaft are motionless.

The purpose of the collar is to connect one of the two blue gears to the yellow drive shaft. The collar is connected, through the splines, directly to the yellow shaft and spins with the yellow shaft. However, the collar can slide left or right along the yellow shaft to engage either of the blue gears. Teeth on the collar, called dog teeth, fit into holes on the sides of the blue gears to engage them.


So . . . if you have the clutch depressed,then the rate of the gears is determined by the rate of the rotation of the wheels of the car . . . so shifting through the gears will have no impact on the internal rotation speed of the gears of the transmission.

If you do not have the clutch depressed, then the rate of the gears is determined by the RPM of the motor. Just make sure you have the right gear selected so you still have a motor!

Without a synchro, you have to double clutch to get the car out of one gear and into another. With synchros, you don't have to do that.

So the only issue is to make sure that RPMs of the motor exceed the RPM of the selected gear and rotation speed of the wheel when you release the clutch pedal, or, the resistance of the motor will act like a brake on the driven wheel UNTIL the motor can "catch up"

I think I have this right. My point is that if you do not release the clutch pedal, it doesn't matter what you do with the shift lever . . . you will not speed up or slow down anything in the transmission, and blipping the engine will not do anything either . . . unless you release the clutch crisply before the blip has fallen too much . . .

Veloce Raptor

ZACTLY

Alan Herod

I understand what some pros do and I have observed it. Some bang it through the gears; but, do not try this with an old 915 transmission with 100 track days on it; unless you want to accelerate your rebuild frequency. Do not compare what somebody in a GT3, 996, 993, or Boxster does with what is good for the life expectancy of your 915. A transmission rebuild is 3 sets of track tires. As I said at the beginning heel-toe is a mandatory technique for promotion beyond Blue with very few exceptions. There is generally no need to go through 4 gears in less then a second, if you are heel-toeing, you just begin your shifting earlier.

Larry Herman

Not exactly. In the example above, if you push the shifter into a lower gear with the clutch disengaged, the syncros will spin the gear, layshaft and clutch disk up to matching speed, and then the lever will slide over the dogteeth and lock the gear to the output shaft.

TD in DC

Absolutely true. I didn't describe what I was trying to say very well.

What I mean is that if you have synchos, it doesn't matter whether you row through the gears or go directly from 5 to 2, because the synchros do the same work anyway -- one method is not "harder" on the transmission than the other. Of course, if it (a) helps prevent you from making a money shift, (b) enables you to get back on the gas midshift in the event of an emergency, or (c) makes it easier to stop quickly or in a more settled manner, that is a whole other subject.

With respect to rev matching in order to prevent your tires from chirping and upsetting the car when you release the clutch pedal, nothing matters apart from the relative speed of your motor and the gear you have selected at the time you release the clutch pedal . . . nothing you do before that moment (e.g., blipping the motor as you row through the higher gears) will change anything.

Right?

cooleyjb

Which video of his?

FWIW I've ridden with a pro driver who will skip gears at some points and at other points will grab them all.

I think it boils down to a matter of preference more than anything else.

Greg Fishman

http://gscdownloads.com/race.wmv

http://gscdownloads.com/leh/roadatlinrs.wmv

993inNC

Maybe its just me, and this is meant as no disrespect...yada yada yada, but it seems that banging throught the gears is a huge waste of time. If you know your car, you should be able to go right to the necessary gear at the appropriate (broke to) speed. The ONLY time I go through a couple of gears is if I completely over shoot a corner and need more braking power than the brakes can offer in a short distance. I'll use the motor (still speed appropriate) to help woe it down, other than that, its top gear....hard on the brakes, strait to second, lift and back on the throttle lickitty split.

For instance, top of the carosel at VIR.......flat out down the back strait, lift at 3 marker, slam on the brakes at 1(ABS kicks in when done right ), down shift at the same time into second (correct speed has been reached), turn in, lift of brake and right back to gas down the hill......why go thru gears?

Greg Fishman

Part of it is to develop a rhythm. The only track I ever skipped gears in my 993 was at Road America coming into turn 5 in 6th and needing to get to 2nd. I would go 6th-5th to 2nd. The braking point was so critical that I wanted to focus on that. Did the same into Canada Corner.

tkerrmd

what's great about this forum is to read all the posts from you guys with tons of experience, skill, and knowledge. Thanks for taking the time to share it with the rest of us mortals!
I cant pretend to understand all of the discussion points and certainly many views. Appears as with most things in life there is more than one way to do something and personal preferences abound.
My take on the entire heel toe thing and 5 to 2 shift is summed up by Chris ^^^^^^ above and that goes with what I have been doing.
I never got the 5-4-3-2-1 thing with 14 inch rotors anyway.
So unless someone says Chris is incorrect I am going with his method.
great discussion guys!!!!! I am really learning alot!

Veloce Raptor

(shrugging) Well, different strokes. As I said, I can go 5-4-3-2 in a second. Doesn't seem like a waste of time when I am braking for at least that long, if not longer.

forklift

Not for me. I have had a problem w/ my ABS coming on early w/ the stiffer springs, especially at Summit Point, but VIR also into 1. If I go too deep it will activate and it sucks. Really sucks. ABS feels like it decreases braking power by 40% or more. I try my best to stay out of ABS and until they pave Summit that means braking earlier and lighter (relatively speaking). When I moved to RS19s from the 14s up front that helped at VIR, but not Summit. I was told this might also be a rebound problem so I need to look at that.

Slamming doesn't sound good either....with all due respect.

TD in DC

I usually shift from 5-2 rather than rowing from 5-4-3-2 when I want to use the braking zone to create a little space between my back and the seat in order to get that "special" feeling from cold water circulating up your back through the cool shirt. Hard to row with the "O" face.

Veloce Raptor

I hate using ABS.

Todd gets 2 extra points for using "O-face" in this thread.

penguinking

just so ppl know what kind of car/transmission im using - i'm driving a 996 C2.

i do the 5-4-3-2 downshift by rowing the gears. sometimes i go 5-2, but usually thats if i overcook it. honestly, if you can maintain threshold braking while bliping the throttle at the same time, no harm in rowing the gears.

there was a long thread discussing "rowing the gears" a long time ago where Leh contributed heavily to this and explained his method on the videos.