Incubus

I see ya'll's point,

...but the original point of this thread is to find out whether we'll DAMAGE synchros while skipping gears. I say, if you double-clutch (and get it right; that doesn't always happen), you won't damage the synchros. On the other hand, if you DON'T double-clutch, then the synchros may get damaged.
In Wisconsin's scenario, the more experienced driver may win...but after 1000 autocrosses, he'll need to rebuild his tranny. All the while, the double-clutched car is still going strong.

xviper

I'm going to go with Incubus on this one.

Here is a PM from someone I'll not ID asking about this sort of thing:
[QUOTE]on the subject of skip shifting.

slipstream444

Double clutching does help (at least a little)... but can sometimes take the same amount of time to accomplish as working through the gears properly. However, it can help partially resolve the shaft momentum issue that can damage synchros when skip-shifting. It's not a complete solution for the problem though.

Skipping gears puts stress (up or down shifting) on the selected synchros because the synchros of the gear you're skipping to have to slow down (or speed up) the input shaft (including the clutch disk) to the throughput speed (ratio/gear selected) of the output shaft. Matching revs won't help this issue either, because the processes involved deal with internal speed changes in the transmission - independent of what the flywheel is doing.

The most commonly reported example of skip shifting associated with failures is the 2nd gear redline shift to 5th. At the point you push in the clutch pedal, the input shaft (and clutch disc) are spinning at around 9000 RPM. When you begin to shift into 5th, the 5th gear synchros have to slow down the input shaft to around 3000 RPM. That's a lot of energy the 5th gear synchros have to absorb and dissipate. If you've ever seen the synchros in an S2000 transmission, they're not that big. They're not that big in any passenger car for that matter. Rotational inertia is not a linear function either (especially acceleration components of this type of problem).

The problem is similar for down shifting (say a 5th to 2nd shift) in that the synchro now has to speed up the input shaft. This is assuming you are deliberately doing this within 2nd gear engine limits (but that's a different thing all together if you're not). This type of shift is probably not done often. A 4th to 2nd shift (much more common) is not nearly as hard on the synchros - but not recommended by Honda either.

I believe Honda published you should never skip-shift - select all gears sequentially and cycle the clutch every time. However, I think much of the problem is resolved simply by working through the intermediate gears and letting those synchros help slow (or speed up) the input shaft. In other words, if you were going to do a 2nd to 5th shift, make sure you row through 3rd and 4th (clutch still in) to help slow the input shaft down.
Here's the caveat: I don't recommend doing anything contrary to procedures or recommendations from Honda.

I personally 'half-clutch' it (don't fully let out the clutch), match revs and always row through each gate when I want to expedite to a gear past the next in cue. I have no problem getting to the desired gear as quickly as possible.

xviper

I'm going to have to agree with Slipstream, too.
As I've said in other threads, we cannot rely upon the fact that eveyone will be able to understand how and why you would double clutch a skip shift, therefore, the general recommendation is to NOT do it all. Hence, the general statement "Skip shifting is bad", is a good recommendation. Seeing the pictures of damaged syncros that Woodwork provided me to post, is a real world confirmation of this.

BryanH

This is why I have a light touch on the shifter when driving normally. If for any reason the synchros are not up to what I'm asking, I'm not forcing anything. And when I drive on the track, I always shift sequentially -- obviously up, but downshifting as well. During heel/toe I let out the clutch and engage each gear as I approach the corner.

I'm not a fan of short shift kits because of their increased effort. I want to shift with a light, smooth motion.

slipstream444

Okay, I see your point. But your 'light touch' is a subjective and unknown value. You have no way of knowing how much force you're actually putting on your synchros. However, your light touch is a lot better than banging your transmission into gear.
I don't agree with your position on short shifters though. The longer the shifter, the greater the leverage (and resultant force) on your synchros. A short shift kit actually reduces the amount of force you can put on your synchros (reduced leverage). This is why they require higher effort to shift.

I was not a fan of short shifters until recently. I changed my mind after speaking with a few people with them installed in their S2000s. Folks that have them installed claim a better sense of control during shifting. They state they can almost feel the synchros engaging. More effort yes. But I'd say that produces a better sense of control.

apex2k

All good points from good people. I see what Wisconsin S2k is saying but Slipstream and Incubus really spell out what I am thinking. I really think if I have to force something on this car I am probably doing something wrong, and by wrong, I mean using it in a way the people who designed and bolted it together had not intended. (Not that there is anything wrong with that, if you can afford it. ) As for the short shifters, I like the idea of less leverage=more feel and shorter fore-aft shifts. What I don't like is the fact that shorter fore-aft throws also equals shorter left-right distances in a tightly gated, mis-shift sensitive auto. I will stick to standard shifter with a subjectively light touch.

jin ba itai

Wisconsin S2k

I see your point. IMO if you're keeping the car long enough for the tranny to fail using either method, then either way eventually you're going to have to rebuild the tranny.

BryanH

You're right, it's all subjective. I guess my point in bringing that up was that a heavy hand isn't necessary for shifting most of the time. I've noticed friends doing it, so I thought maybe I'd share my experience. I frequently shift with my fingertips, rather than grabbing the shifter with my whole hand.

I had a short shift kit on my MR2 for a few months. I took it off -- I didn't like the increased effort. It seemed to me the difference between this extra effort and a reluctant synchro wasn't as high as I'd like it. It felt like I was forcing it every time.

Believe it or not the most direct shift feel I've experienced was in my father's AE86. You might as well be rowing a boat, but you really could feel the synchros working (and they weren't in great shape on that car).

smyroad

SKIPPING 5th GEAR is BAD FOR THE S2000 and other HONDA/ACURA 6 SPEED TRANSMISSIONS!!!!!

the reason is that 5th and 6th gear share the same synchro sleeve. Every time you engage 6th, the 5th gear syncro mushrooms. The mushrooming is knocked down when 5th is engaged, too much mushrooming will prevent entry into 5th.

Better explanation

I'll post the info this afternoon when I get more time.

DON"T SKIP 5th GEAR!!!!!!!!

NHTSA web site has a new TSB about skip shifting. Without the text I'm not sure what it says.