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Thumpin_426

Clutch needed while downshifting????

15 posts in this topic

I keep hearing alot of people saying how they never use their clutch when they downshift the 426. What's up with that?? I know it can be done but after a while won't that tear up your gears? I agree, it is much easier to hang on without pulling in the clutch especially through some knee deep breaking bumps but is this really OK??

I've heard just about everyone's opinion that I know so please, let the mechanics reply. I need answers from the "Wrenchers".

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You wont hurt anything. I dont even use the clutch up shifting much.

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If I am hangin on for dear life I never use the clutch afer the start.

What I mean fo rdear lif is WFO, pedal to the metal, cahona's in your throat type of riding.

When I am putzing around I use the clutch.

The bike was built to race, the tranny can take it

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Im a mechanic....well, part time....Downshifting without a load on the tranny has not hurt mine. I have a couple hundred hours on the bike. I always upshift with cluth though....Im just am so used to using the clutch to upshift its habit now. Again just be sure to let off the gas when not using the clutch to downshift.

Mike

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I`m not exactly sure but I think it`s one of the thingnies on the left side of the bars....I`m not quite sure what it`s for though...

:D:)

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It's a clutch, thats what it's there for! Sure you can shift without it-but it's just a matter of time when your tranny blows! Your just putting heavier loads on your gears or chipping them away prematurely. You don't shift your stick-shift car without using your clutch?Maybe you don't! If your a factory rider who doesn't have to pay for the parts-go for it!

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I have shifted both up/down without the clutch since I began racing bikes back in 1975. On the "wrench-head" issue; I have worked as a motorcycle dealership technician, then service manager, and eventually as a full-time crew chief on a professional car racing team for 12 years. This experience has led to the following conclusion.

Motorcycle transmissions use a "dog-block" design to engage/disengage individual gearsets. This is very different than car tranny's, which use fine-pitch synchronizer rings. The advantage for dog-blocks is that they are rugged, they shift very fast, and very tolerate of RPM mismatches. The advantage for fine-pitch synchronizers are that they provide less backlash and a tighter driveline feel--which is nice in a street car.

Dog-style trannies are used exclusively in serious racecars (IRL, CART, Winston Cup) and it is common practice for these guys to shift, both up/down, without the clutch.

Also, if you've ever driven a outboard or sterndrive boat you've shifted a dog-style tranny clutch-less. These designs have no friction clutch whatsoever--when you shift from nuetral to Forward (or Reverse), you are slamming the transmission shift dogs together and causing instant acceleration of the gear train. This is much more harsh then shifting your MX bike w/o using the clutch.

Bottom-line:

Is shifting w/o the clutch harder on the gear train, compared to using the clutch? Obviously.

Is this beyond the design capability of the transmission?

No.

Will this cause your tranny to fail sooner? Maybe. It depends on how well you match RPM with the throttle during the shift, how positively you use the shifter, and what other types of damage you subject your tranny to in the meantime (bent shift forks during a jump landing or crash).

Steve :)

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if shifting your bike without the clutch is so accepted why in the name of god would someone make and market with the hopes of selling the rev-loc? could it be that just maybe it does indeed do extra damage to the transmission on the bike afterall. I know the pros don't shift with it. They don't have to becasue their race trailers have enough spare parts to build 10 brand new bikes and they do not have to pay for it or do the work themselves. If you like donating money to yamaha and turning wrenches in your free time, don't use the clutch, otherwise do use it and you also just might build up enough strength in your left arm so you don't now need a hydraulic clutch either.

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Bambislayer,

Your reference to the RevLoc clutch actually defeats your argument. The RevLoc is a centrifugal-type clutch. Once the RPM is up the clutch is locked-up solid, therefore any shifting that takes place under hard acceleration is just like riding a standard bike with w/o using clutch.

The design intent of the RevLoc is to eliminate the need to manually modulate clutch slip while attempting to keep the RPM up in a slow corner. A wothwhile objective, but it has no effect on easing the stress of clutchless shifts, as you suggested.

Steve

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I seldom use the clutch when upshifting, but I use it when I downshift. I have been told that the rewlimiter doesen't kick in when you downshift, so if you downshift to quick w/o the piston can hit and bend the valves. Anyone else heard this??

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GYT-Rider,

The rev-limiter concern is valid--but mostly for vehicles operating on pavement. Dirt bikes aren't really at risk.

Here's the deal: the rev-limiter controls RPM only by reducing engine power (via ignition changes). However, this does nothing to prevent the rear wheel from backdriving the engine when you shift into a gear too low for the speed you're carrying. On high traction surfaces--this can force the engine to spinup past the redline.

Dirt offers a safety margin because the compression braking of the engine more easily cause the rear wheel to begin sliding against the ground before it can over-speed the engine. This is a result of the reduced traction of the dirt surface, the lighter static weight loading on the rear tire (MX bikes are lighter then street bikes), and the MX bike's high C.G. which causes a substantial reduction in the dynamic loading of the rear-wheel during deceleration--especially if you're using the front brake as you should be (Nose-wheelies anyone!).

The risk of downshift induced over-rev can be avoided completely (even on pavement) by simply:

1) Don't downshift when you're already revved-out.

2) Avoid downshifts until your groundspeed is appropriate for the lower gear that you wish to select. Use common sense

Again, on 99% of the dirt surfaces we ride on, this just won't be an issue. No matter what, the wheel will slide before the engine over-revs.

Steve

:)

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Thanks for the info Steve. I ride mostly in sand/gravel so I guess I don't have to worry. :)

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