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  #1  
Old 06-08-2000, 12:26 AM
akry's Avatar
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Join Date: May 1999
Location: Burnaby, BC, Canada
Posts: 960
I thought I might as well bring this up here. I had an arguement with my friend over this issue for a while now. He's a die=hard double clutch(and good at it)guy, while I insisted that newer manual trannies have synchros, and double clutch is NOT necessary any more, and will just bring more wear to the clutch.....

Benzmac, Lee, anyone?? What do you guys think??

Andy Kuo

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  • 1992 Mercedes-Benz 400SE
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  #2  
Old 06-08-2000, 08:28 AM
LarryBible
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Akry,

So, what kind of eighteen wheeler does this guy drive for a living?

Double clutching was a pretty good skill to have in the sliding gear transmission days. In my opinion, double clutching is 100% unnecessary with a modern, all synchro gearbox. However, there are a few people who probably should start doing it, or something, to keep from destroying their gearbox. For long transmission life, it is necessary for the clutch to be COMPLETELY disengaged before moving the shift lever. If there is still torque when moving the lever, the corners of the synchro rings will wear out in no time.

Good luck with your disagreement,

------------------
Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[This message has been edited by LarryBible (edited 06-08-2000).]
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  #3  
Old 06-08-2000, 01:04 PM
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Join Date: Aug 1999
Location: ajax, ontario, canada
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double-clutching is still necessary for racing applications, or just plain exuberant driving. This is especially true if your transmission has widely-spaced gear ratios and you are downshifting from a gear in high rpm to a lower gear, after sufficiently slowing the car down so the engine would not exceed redline upon engagement with the lower gear (slowing the car down while double-clutching requires heel-and-toeing).

even if your transmission has closely-spaced gear ratios, you will need to double-clutch if you downshift by 2 gears, e.g., in a hairpin turn.

if you rely solely on your synchros, without double-clutching and rev-matching, you will induce engine braking, which can upset your car's attitude in a high-speed corner.

i've wondered for some time what the tickmarks on the speedometer indicating the maximum speeds for gears 1 through 3 were for (e.g., in 3rd gear i can run 160kph at redline), considering there is also a tachometer. I've realized that these are useful when you are heel-and-toe downshifting at high speeds: e.g., from 5th or 4th gear at 180kph, brake until the speedo needle is below the tickmark for max speed at 3rd gear (160kph), at which point it is safe to engage 3rd gear, but of course after blipping the throttle for the tranny and the engine to match revs.

as the vehicle speed increases, the differences in rpm between 2 adjacent gears increases linearly. This means that at higher vehicle speeds there is a greater need to synchronize the gears before they engage.

i have a 5-speed 190e2.6 and from time to time practice my heel-and-toe double-clutching, which is useful considering the wide gear ratio spacing of the stock transmission. It is also quite satisfying when done smoothly.

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  #4  
Old 06-08-2000, 02:52 PM
akry's Avatar
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Join Date: May 1999
Location: Burnaby, BC, Canada
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Thnx for the replies. I practiced double-clutch with my 240SX, and it sure feel good when it's done properly. But the most common problem with recent cars(even some so-call sports car)is that the gas pedal is pretty far away for heel-toe....

BMW is pretty easy to do heel-toe with, but Mercedes!!??? Bobbyv, you must be REALLY good at heel-toe...

Andy Kuo

------------------

  • 1992 Mercedes-Benz 400SE
  • Pearl Grey/Black Leather

ICQ#26950002
Mercedes Owners ICQ ActiveList ID#61730549
Mercedes S-Class Page
http://akry.web.com
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  #5  
Old 06-08-2000, 03:44 PM
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Join Date: Aug 1999
Location: ajax, ontario, canada
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akry,

i'm not an expert heel-and-toe-er, and it is not yet programmed into my reflexes.

however, the pedal placement of the car makes it easy to heel-and-toe: the gas pedal is hinged at the bottom (sometimes called organ pedal-type) and is slanted to the right, with the brake pedal slightly above the hinged bottom.

This makes it easy to leave your right heel where it is, rotate your foot to the left to brake, slightly raise your right heel to blip the throttle, and perform your double-clutching.

i first learned the technique on a VW Beetle, which has the gas pedal also hinged at the bottom.

for gas pedals that are hinged at the top (called pendant-type), a variation of heel-and-toeing is used: instead of using your heel to blip the throttle while braking, use the right side of the ball of your right foot. I have difficulty doing it with these types of pedals.

I believe there are aftermarket parts for certain cars that are attached to the gas pedal, increasing their surface area, making it easier to heel-and-toe.

happy heel and toeing ...
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  #6  
Old 06-08-2000, 06:04 PM
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I used to have to double clutch when I had my Triumph TR6. In a modern car, it isn't necessary, except, of course, as some of you mentioned, for spitired driving. Double clutching does decrease wear on the synchros though, in a modern car. A good technique to know for SCCA track racing. I usually would stab the gas really quickly and hit about 1,800 rpm before the actual shifting, and at that point, you're hooked up 1:1 with the tarmac and you're ready to tell the other guy "check out my chrome tailpipes, dude". Crude, but works every time.


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Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
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