Double-Clutching

[M.D. Holloway]

Ever sense the Dallas meet and talking with Ed Hughes, I have been double clutching. As I understand it, less gear wear occurs if you do this but doesn't it wear out your clutch quicker? It is true that clutch pads are cheaper than synchros and gears but in the grand scheme of things what is the best way to go?

Also - I'm getting to where I have about a second (maybe 2) lag between engaging the gear due to the double pump action. Should the transision time between gear engagement be as short as possable or should there be about a 2 second lapse to account for an old man's coordination (of lack there of).

[ZOA NOM]

If you're doing it correctly, there should not be increased wear on the clutch plate. What is important in the double-clutch is the engagement of the clutch while the transmission is in neutral (on the way to the lower gear) and you are revving to match the input and output shafts. With the clutch engaged, there should be no wear. If you are double-clutching without revving in neutral between the gears, then you are defeating the purpose, which is to match the speeds of the input and output shafts in the tranny, not match engine RPM to car speed. Practice will achieve a smooth, transition punctuated by a short throttle blip in the middle of the process.

[M.D. Holloway]

So the "shift feel" should be seemless, the sound should have a slight delay and the actual acceleration should not feel jerky at all - if that is the case, I am doing it correctly?

[ZOA NOM]

I would describe the process as follows:

Setup: Heading down straight in 4th gear preparing to downshift

1. Simultaneously clutch in and slip gear knob out of 4th into neutral.

2. Simultaneously blip throttle and engage clutch quickly. (I imagine a button hovering above my clutch knee that is pressed when I "blip" my clutch knee up.)

3. Gear knob should almost "fall" into 3rd, and you are back on the throttle.

Engine sound should remain fairly constant, but punctuated with the quick blip in the middle, and rising as you accelerate once in gear.

[slodave]

I agree. I can't think of a better way to describe it.

Dave

[jim72911t]

The whole idea is to match revs between the engine and transmission. Double clutching can accomplish this, as can heel-toe shifting. IMHO, two different approaches to the same goal.

Some may scoff at this, but I've worked hard to at least be able to shift any of my cars without the clutch. All you do is, while driving in a straight line, with little or no traffic, try to downshift by raising the revs with the throttle while gently pushing the gearshift into the next lower gear. When (if) you have the revs exactly right, the car will snick cleanly into the lower gear.

Once you are able to do this at least some of the time, you will understand the reasons for double clutching or heel-toe shifting.

This has great benefits on the track, as you will be able to downshift before, (or in) a corner, without the car shuddering, bucking, bogging, or the like, depending on speed and gear selection. My goal in shifting is to be able to shift without a passenger even knowing I shifted, except for the change in engine RPMs.

BTW, this is great for extending the life of your clutch. And, there is nothing wrong with shifting slowly and cleanly. I never understood the guys who bang the car from gear to gear. I shift with my fingertips, not my fist.

Jim

[HardDrive]

Just had the 1/2 sycro + clutch combo done on my SC. About an even split. Clutch is expensive, but less labor, sycros cheap, but more work for Mr. Walker.


(btw, he did superb job.)

[Eric Coffey]

bottom line: Shifts should be heard, not felt.

[ZOA NOM]

Originally posted by jim72911t
The whole idea is to match revs between the engine and transmission.

This should be clarified a little. Understand, the purpose of double-clutching is NOT for matching engine revs to tranny. It is for matching input shaft to output shaft rpms WITHIN the tranny. Greater wear occurs when these two shafts are turning at significantly different speeds. I say this because many times, people think they are double-clutching when they downshift without engaging the clutch in neutral in the sequence, when in truth, they aren't. Simply revving the engine to match rpms to car speed will produce a smoother transition to the lower gear for the driver, but not necessarily for the transmission.

[}{arlequin]

lots of reading on rennlist as well. look for the "autocross and racing forum" 2nd or 3rd page contains the most recent

[Mulhollanddose]

So I take it this isn't a thread about masturbation?

[livi]

And here I have been blipping the engine with the clutch out feeling very proud of myself. Duuuh, I am such a dork.

I my defense I manage to change gears very smooth anyway.

[singpilot]

Masturbation done well is also heard, not felt.


No.... WAIT! Felt not heard......


No.... WAIT! Double Pumped, then blipped.....


No.... WAIT! Felt then heard.



More research is required. Will get back to you on this.

[stuartj]

Originally posted by tcar
Do a search, there's a long thread on this subject every 4-5 months.

Yeah, there is. And there is still, IMHO, no point in DC (assuming a modern synchro tranny in good order.)

On the track, its slow, complicated and fraught with danger.

On the road, its slow, tiring and achieves little in a synchro box.

It has its place- I confess I did use DC in my 915 car to get 2>1 while moving.

Now, heel and toe is a worthy skill. kind to the box, the clutch, the car and faster and smoother on the road or track.

My less than 2c.

[M.D. Holloway]

Stuart - help a novice out here. Why is H2T better than 2c?

[stuartj]

Lets say press on driving, at the track (ofcourse). You are in 5 at 120mph and you need 2 out of the corner at the end. You need to brake the car hard, and be able to stand on the go pedal early as possible with 4000rpm already on board in 2nd gear- and keep the car balanced.

DC clutching through 5>4>3>2 means you are going to busier than a one armed wall paper hanger while trying to threshold brake and steer the car from high speed at the same time. Every time you do it, you stand the chance of stuffing it up. Declutch-shift-clutch-declutch-shift-clutch through 4/3/2. And the guy behind you will drive right past.

Some will say, brake, then shift 5>2- the mantra being "give yourself the least number of things do to" This makes sense. The only only way to get from 5>2 and match engine/road/driveline speed is via H/T shifting, either straight into 2 at the appropriate road speed or via 4/3/2 ( because we all like the noise).

If you cant H/T while threshold braking, you will likely breifly compression lock the rears and/or unbalnce the car while its standing on its nose under brakes and very often have a spin (especially in a rear engined car), or least an untidy corner. Or worse, blow something up as the engine tries to pull 9000rpm as you engage 2nd with 1500rpm on the dial.

DC is just slow and complicated, and unneccessary. No-one, except the vintage car guys, does it. H/T allows you to correctly match engine/drive train/road speed for a smooth and importantly-balanced downshift. Good technique on the road, kind to the car- fact is, once you master it, its almost impossible to drive anything any other way.

Again just my 2c, YMMV. Hope that helps.

[Hugh R]

When I was attending the University of Massachusetts, Amherst it was said that guys that dated girls from Mount Holyoke, a nearby all girls college, were too lazy to masturbate.

[ZOA NOM]

Further clarification - I agree with stuart. About the only time I DC is from 4-3, and not during agressive cornering. It's more of a leisurely pastime for me, and sort of a habit. It does become a bit much in the twisties. My earlier clarification was for the folks who think they are performing a DC when in fact, they aren't. As for it's benefit, that debate could go on ad nauseum, but simple physics says that it will result in less wear on the gears, even of a synchromesh gearbox, with all else equal.

[M.D. Holloway]

Hugh - after spending much time in CT/MA/RI, I was under the impression that the girls at Mount Holyoke were (and maybe still are) lesbians. Not the hot, lipstick, bi-sexual I'm in trianing for girls gone wild lesbi-friends, but rather the crunchy, broken-stock sandle, softball swatter, beefy elbow bull dyke. If so, I think I would prefer to rub one out over the phone with my HS sweety as well!

[Jared at Pelican Parts]

I have a butch friend who pops off beer bottle caps with her elbow.. It's truly an amazing sight..