slow shifting

[mugwump]

hi folks, hoping someone can enlighten me... is it normal for the shift from 1st to second gear at high revs (eg redline) to be slow and difficult to engage? i almost have to force the stick in. however when i do, it doesn't make any noise. 2nd to any other gear is ok. i haven't noticed any clutch slip, but then again i'm a pretty docile driver most of the time (petrol prices too friggin high). as you might imagine, its really frustrating when gunning it because the slow shift really corrupts the acceleration and also the revs drop too much by the time 2nd has engaged

[mike_d87]

yeh, mine does that too. kinda like putting it into 1st from anywhere above about 40-50 kmh? gotta be careful coz sometimes it can crunch. very embarassing!

[-BraXta-]

i get that from 2nd to 3rd =P

and it clunks too =D

[mattyd]

hey mugwump, where abouts in melb you from? id love to see your car. im driving a black v6 too.

[skippy]

Yeah 1st to 2nd is slow in my V6 aswell,

No sounds just a bit of umm delay,



a Docile driver at Redline, hmmmmmm

I find 3500 is the best shift point, all things concerned,
unless your having a bit of fun at the lights in which case there is no fun below 4000.

[89sp1.8]

i get the same thing in my 4 cyl hatch.only between 1st & 2nd though

[andrewgrazier]

SAAAAAAAAMee here

[mugwump]

looks like i'm not the only one!! ok i asked a colleague today, i figured since he drives race cars he'd know... its definitely not the clutch, its probably the design of the gearshift itself, given that when you step on the clutch at 7000rpm it takes a while for it to slow down given the inertia from its weight, or something like that. sometimes, when shifting quickly its also easy to mis-time the clutch. he says his sti is no different...

just this evening when driving home i changed very quickly at redline from second to third and yet, it gave a little bit of a crunch.

moral of this story, step firmly on the clutch when changing and slow down the shifts!!!

mattyd i live in the western suburbs but i'm often in the eastern as well. to be honest my car is nothing much to look at... its completely stock, and really needs a good once over at a professional detailer!!!

[Rupewrecht]

i think it's because you're getting close to beating the synchros!

or your synchros are starting to get worn, as 1-2 get used the most and take the most abuse

[mrpayner]

This is where you take the course on "Double Clutching".. Take it slow to begin with, then when you've got it down pat start living a quarter mile at a time

AP

[skippy]

Therory of double clutching,
I dont get it,
but i think that is because it was explained to me by someone who doesn't get it but was happy to teach me anyway.

[Fro-Daddy]

doubling is pretty much pointless in a newer car (a car with synchomesh) isnt it? coz they ado all the work for ya...or so i have heard

[Astro Boy]

its fairly (but not entirely) pointless on the up shift yes... but on the downshift, certainly not..

a. it SIGNIFICANTLY reduces gearbox and clutch wear, and
b. maintains smooth (ie controlled) downshifting, preventing loss of control due to drivetrain jolt...

When racing, i don't use the clutch at all upshifting, but i do double clutch if i'm going 4-2 or 3-2, but i don't clutch at all going 4-3... that mainly stems from the fact that i brake with my left foot, but it does place LOTS of strain on the gerabox...

[Nate]

Originally Posted by skippy

Therory of double clutching,
I dont get it,
but i think that is because it was explained to me by someone who doesn't get it but was happy to teach me anyway.

Double Clutching.

1. Push Clutch in
2. Put gearbox into neutral
3. Release Clutch
4. Rev the engine
5. Clutch in
6. Select gear
7. Clutch out

the whole idea of double clutching is to match the revs of the shafts in your box (what a syncro does), double clutching does it a lot quicker . if you dont have you foot off the cltuch all your are doing is reving the engine ... which does SFA. you need to have the gearbox engaged to the engine to spin the gears up!

[skippy]

Nate,
I now understand the theory, I was told very similar but it was to get the engine up to speed and I thought but clutch in and rev and it, it is up to speed so whats the diff, but I get it now.

Originally Posted by Bourne Boy

i don't use the clutch at all upshifting,

how does that work???

[mrpayner]

Theory of Double Clutching..

Stolen from What's all this Double-clutching, anyhow??
Let's say you're accelerating in second gear. When you're ready to shift into third, you decide not to use the standard approach, which is just to tromp on the clutch, take your foot off the gas, shove the shift lever into third, and let the clutch back out. Instead, you opt to double-clutch properly:

First, you take your foot off the gas and kick in the clutch. You shift into neutral, AND let the clutch out. You wait perhaps 0.3 to 1.0 seconds for the engine to slow down from its high revs, depending on how fast you were revving when you started to shift and how much inertia the engine has to slow down. THEN you kick in the clutch and shift into third, and let the clutch out quickly, feeding the gas appropriately. If you have judged it right, when you let the clutch out, there isn't any JERK. And when you shove the lever into third, the gears and engine are at a synchronized speed, so there's minimum wear on the synchronizers, which are the tiny clutches that bring the clutch plate and the gears into smooth synchrony. There's also usually less wear on the clutch plates.

What's the big deal? The main point is that when you try to shift into third gear, the engine has slowed itself and the clutch plate down to the right speed—just about the same speed as the gearbox—so it saves wear on the synchronizers and the clutch. It can also save shock and strain on the whole drive-train, because the speeds are just about synchronized when you let out the clutch.

Well, big deal, you say. Cars haven't needed double-clutching since the synchromesh transmission was popularized 50 years ago. Why bother? Why fool around with anachronistic motions? Isn't it just buying trouble? Even Tom and Ray Magliozzi* claim that double-clutching is silly and stupid and wasteful of energy. Ah, but I can give you reasons why it is beneficial.

First, in most cars, the actual gears are always in constant mesh, and the synchronizers only decide which pair of gears to connect to their shaft. But many trucks and some racing cars are still set up with a non-synchromesh gearbox. With trucks, because they have so many gears, it's noticeably more efficient not to have all of the gears in mesh all of the time. So with the "crash-box," you HAVE TO double-clutch, or you will not be able to shift. The same holds true for racing cars—to gain the last couple percent of efficiency, only one set of gears is in mesh at any time, and you have to actually synchronize their speeds or you can't get it in gear. Despite the obvious drawbacks of having to double-clutch, the gearbox is stronger and more efficient than a comparable synchromesh one, and has less tendency to overheat.

Other reasons for double-clutching: Because it is the right way to operate the clutch. Because it saves wear and tear on your synchronizers in the long run, if you're planning to run your car over 200,000 miles, as I do. Because it is fun to do. Because in very cold weather, (-10° F, for example) you may have to double-clutch to shift gears at all, at least for the first few miles.

One very important reason is that, if your clutch linkage ever fails, you can still shift and get home by double-clutching, getting the engine and gears' speeds synchronized and then just EASING the shifter into the right gear. In the last 1,050,000 miles of driving VWs, I have lost my clutch about 3 times, and each time, with careful planning, I've been able to drive home safely. One time I pulled into the Customs House at Calais, Maine, and discovered my clutch was out. I eased along carefully and managed to get all the way home, 350 miles, to Boston, where it was convenient to put the car in the shop to have the clutch repaired—much more convenient than in the middle of a vacation, or the middle of Maine.

Another reason is that on some old cars, first gear isn't synchromesh, so if you need to shift into first without coming to a full stop, you have to double-clutch. Also, a lot of cars these days are made with weak, chintzy synchros, so they soon wear out, and to drive them gracefully, you need to double-clutch.

Note, when down-shifting, you have to shift into neutral and then blip the throttle momentarily before you shift into the lower gear. It requires practice and a good feel, a good touch, to do it right, especially considering the embarrassing noises you make if you miss your shift into a low gear on a crash-box. For example, you should aim to have the revs just a little high, so if you miss, the engine will soon slow down, and then gears will be at the right speed to mesh and the cogs will slip in....

OKAY, Pease, I'll try this double-clutching some day; but why do you bring up all this stuff in an electronics magazine? Ah, there's an excellent analogy: In most conventional switching regulators, the power transistor turns on while there's lots of voltage across it, and after it turns off, the voltage usually increases to a large voltage. When the transistors turn on, the diodes are already carrying significant current, and the transistors have to turn the diodes off. This is all somewhat stressful, and causes the transistors and diodes to have large turn-on and turn-off surges—pulses of power on every cycle. Of course, diodes and transistors have been designed to withstand these stresses and surges with excellent reliability; we see them all the time.

Still, people have specially designed "resonant mode" switchers to have zero-voltage and zero-current switching. In these regulators, most turn-on and turn-off stresses are eliminated, because the transistor is at a very low voltage when you turn it on, and at a very low current when you're ready to turn it off. Consequently, most voltage and current transients are greatly decreased. Less filtering and shielding is therefore required, enabling the complete regulator to have low Radio Frequency Interference (RFI). Now, to design such a supply takes a more complicated controller IC, more expensive parts, a very careful layout, and a lot of expertise in the electrical design. So while you get some advantages, you have to pay for them.

Now, when you want to build a compact, high-performance, switch-mode regulator at switching frequencies up to about 1 MHz, conventional switchers can do at least as well as resonant ones in terms of cost, size, and performance. But if you need a switcher even smaller and faster than that (most users do not), when the switching frequency rises above 2 MHz, the resonant-mode switchers begin to show real advantages.

At this time, National doesn't make these resonant-mode switchers, so I can't offer you any detailed info about all of their advantages and disadvantages. But I have explained most of their key features. And now you can see why the smooth, stressless turn-on and turn-off of the transistors and diodes in these resonant-mode switchers are analogous to double-clutching your shifts.

AP

[Astro Boy]

Originally Posted by skippy

I was told very similar but it was to get the engine up to speed and I thought but clutch in and rev and it, it is up to speed so whats the diff, but I get it now.

the PRIMARY purpose is to match the input and output shaft of the gearbox, so that a. if engages quickly, b. prevents undue wear and tear... its SECONDARY benifit is a matched engine rev which means very little (if at all) clutch wear...

Its done exactly as nate said, and when you want to get fancy, and need to grab 2nd (or first) in a REAL hurry, you do what called 'heal and toe' by reving the engine (step 4) with the heel of your foot while the ball is still braking...

[MitchEG]

so when u suggest heal and toe-ing on the downshift, is that with a double clutch or just a straight throttle blip only. I try it often and am wondering if i am creating undue wear somewhere from not double clutching on the downshift...i assume i am matching the engine to the speed the clutch will be at in the next gear, so the synchros are doing all the work here...?

[Astro Boy]

YES! You have to double clutch!!! If you don't you're puttting more wear on stuff than if you don't blip the throttle at all!!! By not double clutching it means the engine isn't connected to the gearbox at the point where you rev the engine... i'll try and explain it this way: i'll use 4th-3rd...

- Engine~Inner Clutch Plate (1)- Outta Clutch Plate~Input Shaft (2)- Output Shaft~Wheels (3)-

So that's the three inline connections we're talking about... you want all three to match 'at the point where you release the clutch after selecting the lower gear'...

I'll explain it mechanically in two steps:

1. To match the input shaft to the output shaft (ie, the wheel speed)... this is done by revving the engine in neutral (because you can't rev it in gear), and since the gearbox needs to be connected to the engine, the clutch must be out... so that forms the first part (clutch from 4th into neutral, then clutch out)

2. to select the lower gear while the engine is at a similarly matched *falling* rpm... (clutch from neutral in 3rd, then clutch out)...

Now the problem with not double clutching is that parts 1 and 3 are at road speed, whilst the inner 2nd part (input shaft) is at idle (or the previous gears' speed), so this wears both ends of the inner connection... firstly because you're relying on the synchros's the match the two shafts of the gearbox, and secondly the the clutch, because one side is at a falling RPM, and the other is at a rising RPM.

[goldsp]

with new cars its the biggest waste of time and if you were lining someone up at the lights its the quickest way to be behind after the first shift.

bourne boy i know you think you know alot and think you can drive however if you doulbled clutched against a car with equal power you would lose.