Then my advise to you is to not skip gears. I disagree with your assessment of the gears and synchro's relationships, and thus, I will continue to drive as I always have, knowing (at least I think this) I am doing no harm what so ever beyond normal wear..

 

Vehicle speed is calculated at the transmission so it does give you an idea of how fast the internals of the transmission slow down... None of the internal components become "disconnected" when the car is in neutral and the clutch isn't depressed...it's just that none of the shift forks are engaged. The transmissions gears are in full contact with one another on their respective shafts(minus reverse) and there is very little drag inside the transmission. Calculating the fluid viscosity and the natural friction down I supposed you could calculate the gears spin-down rate just like anything else in a car can be calculated. What is the need though? Transmission RPM is related to engine RPM as the transmission is ALWAYS spinning from the moment you start the car just no drive is being transferred to the output shaft of the transmission Nuetral doesn't disconnect the engine from the driveline, It just takes all the Synchro Hubs/Sliders and puts them all in a non-engaged state, the gears are all still spinning at the RPM you expect them to. The CLUTCH takes the load off the input shaft to allow the gear to be selected(while it's still spinning, via the Synchro) and then with the Clutch released the power is sent through that gear ratio to the Output of the trans multiplying torque and etc etc...

If you attempt to wind up the engine to say 7000rpm and quickly clutch in the transmission loses nearly all of the mass it had accelerating it to that speed and it very quickly dies down from 7000rpm as just the mass of the clutch disk on the input shaft spinning it through the friction of SIX OTHER GEARS with bearings all turning with one another at the same time in a thick thick film of lubricant. The transmission spins down FASTER than the engine, go out and try for yourself. Even if you still don't trust it, if you clutch up before you shift while in neutral(double clutch) then select the gear you can ensure the engine speed is in fact the trans speed.

The transmission doesn't care what gear it came from, it only cares what the RPM difference is that the Synchro will have to make up for and thus causing wear. If you Shift 1-2 at redline and wait for the RPM's to drop down around 3000-3500 and then shift to 6th gear it will slide right in just like you came from 5th. However if you try to push it into 6th quickly after a 1-2 at redline you will feel the transmission slow the gear down and then let it go in, which is very bad for the life of the Synchro's. Just driving and getting to know the car will show you exactly where the smoothest shift points are, skipping gears or not.

Skip shifting is only bad if you have no clue what you're doing, I do it all the time and have had zero issues with my AP1 and AP2 over many many tens of thousands of miles. It will sound just like nothing ever happened if you do it correctly, do it wrong and you'll hear the engine wind down faster as it is matched out of sync. If you want to cheat the skip-shift you can just clutch up in neutral to check the transmission speed to engine speed then just clutch back into the next gear, 6th or whatever.

 

Now that we basically have 4 arguments for and 4 against, I would be interested in what the topic starter thinks:

Is fullvnrg willing to try skipping gears, or did we just make him regret asking?

There's not been a word out of fullvnrg since starting this thread.

 

This isn't correct. When the clutch is disengaged (clutch pedal to the floor) AND the transmission is in neutral, the clutch friction disk and input shaft (at a minimum) are disconnected from the engine AND output shaft (at a minimum). If the car is rolling while in neutral with the clutch disengaged, the output shaft will be turning, but the input shaft will not.

I had the misfortune of getting a terrible transmission rebuild in my S2000 18 months ago, which makes it very noisy. While I'm at idle, my transmission makes about as much noise as my motor. However, when I disengage the clutch, the noise stops quickly. All this happens while the car is parked (output shaft not moving). I've crawled under the car while it idles, and can hear the noise coming from the transmission case. There is no way possible for this to occur if the input and output shafts were not diconnected from each other while in neutral.

Basically, vehicle speed only gives a measure of the speed of the output shaft while in neutral, and engine RPM only gives a measure of flywheel speed when the clutch pedal is depressed. Therefore, unless you are in gear OR the clutch pedal is NOT depressed, then there's no way to know what the speed of the input shaft is.

 

I'm aware of how the transmission spins with clutch in/out in neutral, I explained that above. What I am saying is that with both the engine and transmission completely separated and both spun up to 7,000rpm and let go the transmission would spin down BEFORE the engine, spinning down faster because of less rotational mass. If you want to check the transmission speed to the engine speed while skip-shifting all you need to do is clutch up once while in neutral then shift like normal into 6th. My favorite is probably 4th to 6th, Butter smooth every time.

Go out and put the car in neutral, then rev it out to about 7,000rpm - now quickly put the clutch to the floor which should "disconnect" the internal movement of the transmission to the engine at least on the input side. Now let the engine wind down to 2000-3000rpm with the clutch still depressed and you'll still find that the next gear you try to engage will go in just as smooth as if you'd shifted normally. The transmission does not just "take off" on its own and continue spinning at speed because there is too little momentum/mass and too much drag with six gears in constant mesh turning through fluid, etc etc.

If you let the clutch out while in neutral between say 1-2 and 6th it will ALWAYS check the transmission speed to the engine speed allowing a safe correctly RPM timed shift no matter what gear you want to go into next.

As I said before, the transmission DOES NOT care what gear it just came from...it ONLY cares about the speed and pressure required to slow that gear down until the synchro slider/hub is able to lock in place and the gear is selected. You have ALL OF THE TOOLS YOU NEED directly at your feet to put the transmission at any RPM into any gear you want safely. That's why the pedals do what they do.

 

I mentioned that in post 7, but I don't think the OP was talking about skipping gears while double clutching to rev match. I realize that the input shaft of the transmission will slow down, but I don't think it will slow down as fast as the engine. When you lift throttle, the engine has more than just friction slowing it down, and I don't think the moment of inertia of the flywheel is as significant with respect to all the moving parts in the engine as the moment of inertial of the clutch fiction disk with respect to the moment of the input shaft. When I burned up the 5th gear syncrho in my Integra, I had to wait seconds before shifting into 5th without a grind.

 

I think comparing the Integra Transaxle to the RWD Transmission of an S2000 is a bit far fetched IMO, the transaxle has much more moving mass due to having a differential in the mix of things spinning around inside. Be that as it may do you really think that Honda would design a transmission in their flagship RWD roadster that spun down SLOWER than the engine? That would mean that every single normal shift would happen out of the optimal range for the synchronizer to work in and not retain excess wear because the transmission shaft RPM is staying higher than engine RPM during the process of the shift. Either way, the process of skip shifting can be achieved multiple different ways...it just takes some knowledge to do correctly.

 

Gentlemen (Gernby and Froth),

I found a couple things:

1) SKIP SHIFTING IS BRUTAL ON SYNCHRONIZERS

HONDA SERVICE NEWS
Reference Number(s): HSN0106-01, Date of Issue: January 1, 2006
SERVICE INFORMATION

Gear ratios in 6-speed manual trannies are spaced close together so you can keep the engine speed in its optimum range for max power and acceleration. Shifting to the next higher or lower gear in a close-ratio tranny causes small changes in engine speed. Shifting a close-ratio tranny through its gears by the numbers puts a very small load on the synchronizers since they only have to make small changes to the speed of the mainshaft and the clutch disc.

Some drivers, though, like to skip shift so they don’t have to work the clutch pedal and shift lever as much. They like to accelerate in 1st gear, then pop it into 3rd gear, then into 5th or 6th. Skip shifting, though, is really brutal on synchronizers; it puts a higher demand on them than they were designed to take. Skip shifting can cause premature synchronizer wear that can cause the gears to grind when you shift up or down.

If you’ve got a vehicle in your shop for repeated damage to the synchronizers, go for a test-drive with your service customer to see if he or she is guilty of skip shifting. If that’s the case, remind him or her skip shifting can be an expensive habit to break. Any repairs due to skip shifting may be reviewed and debited by your DPSM."

For more, see this S2KI link: https://www.s2ki.com/s2000/topic/717...th-after-woot/

2) MORE INFORMATION FROM A HONDA SERVICE ENGINEER

"I am the woodwork and I work for American Honda.. I am writing this to hopefully help S2000 owner/drivers understand the importance of shifting properly to minimize the damage to 2nd gear synchronizer rings. I'm not the Warranty Police but will from time to time quote warranty policy when I read things like "Shifting without the clutch".

My overall objective being in the woodwork is to keep S2000 owners from hurting themselves and hurting their cars. Everytime a transmission or engine gets replaced in an S2000 I get the part. I've seen a lot of damaged transmissions.

You have an engine that revs to 9000 RPM. That means that the transmission mainshaft and clutch disk are also revving to 9000 RPM. When you disengage the clutch (push in the pedal) to shift from first to second the engine and the transmission are disconnected. The engine will slow down from compression when you lift off the throttle. The mainshaft of the transmission is not connected to the engine any more so it is freewheeling in the transmission. Given enough time the mainshaft will slow down but not as fast as the engine. The countershaft is connected to the rear wheels and the speed stays constant during the shift.

When you shift into 2nd gear the synchronizer of the 2nd gear must SLOW DOWN the transmission mainshaft to match the speed that the engine WILL be going when the shift is completed and the clutch is engaged.

The transmission mainshaft and the clutch disk together weigh 19.75 lbs. (not including the pressure plate and flywheel that are connected to the engine) When you shift from 1st to 2nd at 9000 RPM the engine speed drops to 5900. That means that the little brass synchronizer rings have to push on the 2nd gear to slow the mainshaft from 9000RPM to 5900 RPM. It not only has to slow down the mainshaft it has to do it in the time that it takes you to shift. So if you have a tendency to shift fast you may be making the sleeve blow past the synchro rings before it has a chance to do it's job and it will smash into the 2nd gear.

The early '00 cars needed a little change to the sleeve to make the synchros work a little harder. That is what the new parts in the service bulletin are for. Cars after VIN YT006255 already have the new parts. Grinding in a car produced later than 6255 is possible if the synchros have been damaged and now are not able to slow down the mainshaft properly.

Shifting without the clutch, or, shift too quickly and not letting the synchros do their job may permanently damage the gear, sleeve and synchros and make the 2nd gear grind more often.

It makes sense that if shifting at 6000 makes the engine speed drop to 4300 RPM, (1700) into 2nd gear then you should give the 2nd gear synchro twice the time to do the shift from 9000 RPM.

If your car does grind once in a while you may not want the transmission removed, disassembled and a new 2nd gear put in. If it does it quite often, show it to the dealer and have it replaced.

If you hesitate for another 1/2 second while putting constant pressure on the shifter while the 2nd gear synchro does it's job, I'll bet many of your cars would not grind any more. Try it. You might like it.

Added 5-2-03:
Skipping gears:
I have seen many 6th gear sleeves that have been damaged.

The typical story is this: Stop light, 1st gear, engage the clutch, rev to 9,000 RPM, shift quickly to 2nd, rev to 9,000 RPM, same into 3rd, look down and find the car going 80 MPH on a city street and the engine noise is screaming, recognize that any cop is going to write a ticket. Shift to 6th quickly to lower engine noise.

Dragging the mainshaft speed down from 9,000 RPM to 4,000 when going from 3rd to 6th takes time. 6th gear has only a single synchro ring and it doesn't like it. It will grind if you are shifting hard and fast. By shifting hard the synchro ring does not have time to slow down the main-shaft and the sleeve will slip over the synchro and grind the gear. If the sleeve is ground enough in 6th then it will not slide the other way to engage 5th.

So if it is hard to get your car into 5th or 6th it may be because the sleeve is being damaged by skipping gears. Hope this makes sense.

For more, see this link: http://www.standardshift.com/forum/v...hp?f=6&t=13489

MY ASSESSMENT

For what it is worth, there is risk to synchronizers when skip shifting. However, this risk increases with aggressive driving and should be lessened, if not eliminated, at lower RPM. Apparently, skip shifting hard and fast at wide open throttle will damage synchronizers, but skip shifting at lower RPM and giving components sufficient time to slow down could have no ill effect. As a result, I believe the potential harm that could be caused by skip shifting is largely a function of how aggressively the driver is revving the engine and slamming the shifter into gear.

I'm open to counterpoints.

NOTE: "Woodwork" post updated to better reflect original, and that original post linked here:

https://www.s2ki.com/s2000/topic/196...gear-synchros/

 

For the AP1 that information may be correct, I find that the AP1 engine spins down MUCH faster than the AP2 F22 because the AP1 has only a 13lb flywheel while the F22c has an immense 22lb flywheel! Perhaps this was to combat some issues they found with skip shifting? Will we ever know? Probably not. I find personally that in the AP2 the transmission spins down as fast if not faster than the engine.

If you were to skip shift after 1-2 at Redline then just move the shift lever over to 6th OF COURSE you're going to cause wear because the transmission is still spinning 4-5000rpm faster than the gear expects. However if you slow that shift down, even with the clutch depressed the entire time and you wait until the RPM's fall naturally to 3000-3500 you will find that the transmission engages exactly as if you are shifting from 5th to 6th at 60mph which is the area of speed the transmission is expecting during the shift with no increased effort or extra "winding down" of the transmission.

If you shift the S2000 normally, 1 to 1.5 seconds between gear changes the synchro's do NOT slow down the transmission as they are at the optimal placement for the shift to occur when this behavior is used to shift. I re-build manual transmissions, I have been inside the S2000 transmission and I can tell you from my own personal experiences that skip shifting is ONLY AS BAD as improperly shifting!!!

If you are skilled enough with the shifter and clutch you can narrow down the shift window to nearly 100rpm where it will slot in miraculously smoothly, so smoothly in fact that the clutch does not NEED to be used if done properly. I have personally shifted 5th to 6th THOUSANDS of times without using the clutch over many many thousands of miles and I can tell you that my 4-5-6 shifts do not notice AT ALL.

It seems the "Don't skip shift" information supplied by Honda and from the "Honda technician" are geared towards the layman who would simply Jam the gear lever into whatever gear they please. I am an ASE Certified technician for a living, My hands are made to work on cars and drive them as they are meant to be driven...I'll stick to shifting the way I know works.

As I have said MANY times, the transmission DOES NOT CARE what gear it comes from...It has no idea what gear was before the one that has just been selected the ONLY thing the transmission cares about is how much it has to make the Synchro's work in order for the gear change to occur. Shifting properly, even skip-shifting properly will NOT HARM THE TRANSMISSION. Just shifting the car IMPROPERLY through the normal 1-2-3-4-5-6 can create BOATLOADS of wear and there's no discussion on that because it's all chalked up to the driver and their habits. If you make it a habit to ensure the transmission sees as little wear as humanly possible then shift however you like...

 

Thanks for posting the info! I tried finding that post from Woodwork, but couldn't. Do you have a link to that thread he started? He is not a Honda Mechanic. He is a Honda Engineer. Whenever there were "out of the ordinary" warranty repairs, the defective parts were / are sent to him for inspection.

Froth, the transmission wouldn't "care" if you replaced its oil with water.