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 Motorcycle Safety
 Technical/Maintenance
 Nice tutorial on how a motorcycle transmission works.
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scottrnelson
Advanced Member
6960 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 01/08/2013 :  10:14 AM                       Like
A guy on the Honda XR650 site took a bunch of photos and put a web page together after having his transmission apart. It does a pretty good job of explaining how a motorcycle transmission works.

http://www.justxr.com/jaw/gearbox.html

And a video from a different source: http://www.youtube.com/watch?v=vq11CusULlk

I'm not completely satisfied with the video, because it shows just gears moving, while many motorcycle transmissions move a piece attached to the input shaft that just has the dogs and no gear teeth. You slide that piece along the shaft to engage with the gears that stay in place where they make the best contact with the gear they're driving. The last transmission that I opened up did not slide the gears at all, but they're not all the same, so there could definitely be some out there that slide the gears too.

Hopefully a few of you will better understand how motorcycle transmissions work after reviewing these.

kacinpa
Male Advanced Member
802 Posts
[Mentor]


Lansdale, PA
USA

Triumph

Sprint GT

Posted - 01/08/2013 :  12:29 PM
Thanks for that Scott.

It helped to see the sequence of photos to jog my memory.

The last time I saw the insides of a bike transmission was back in 1980 when I helped my Brother-in-Law rebuild the transmission on his Yamaha RD-400!
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greywolf
Male Moderator
1484 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 01/08/2013 :  4:42 PM
Maybe people can better understand what happens in an emergency braking action that ends up being stopped in 5th. Some motion normally needs to be imparted to the shafts to do gear changes after such an event. Rocking the bike or letting the clutch out a little, just enough to get a little movement, will help each gear change.
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scottrnelson
Advanced Member
6960 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 01/08/2013 :  5:37 PM
quote:
Originally posted by greywolf

Maybe people can better understand what happens in an emergency braking action that ends up being stopped in 5th. Some motion normally needs to be imparted to the shafts to do gear changes after such an event. Rocking the bike or letting the clutch out a little, just enough to get a little movement, will help each gear change.

You can get a good understanding of that in your own garage with the bike off. Just shift all the way up to top gear, then all the way back to first a few times. When it doesn't want to shift, rock it back and forth an inch or two to see what it takes to get things to line up.

Anybody who hasn't tried that should go do it right now. Even if your bike has been put away for the winter, you can learn how it shifts when not moving and the engine is off.

Knowing how to shift multiple gears when stopped might come in useful someday out on the road.
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twc
Male Advanced Member
836 Posts
[Mentor]


Fort Collins, CO
USA

Harley-Davidson

Electra Glide Ultra

Posted - 01/08/2013 :  6:01 PM
quote:
Originally posted by scottrnelson

When it doesn't want to shift, rock it back and forth an inch or two to see what it takes to get things to line up.

But first, read the label to see if it's a Kawasaki. That trick doesn't work on a motorcycle with a positive neutral.
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greywolf
Male Moderator
1484 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 01/08/2013 :  8:20 PM
I prefer pre loading the shifter and feeding a little clutch to rocking.
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jilp
Male Junior Member
84 Posts


Mexico, Mexico
Mexico

BMW

R1200GS

Posted - 01/09/2013 :  6:50 PM
I preload the up shifts well, but when I thought the same applies to downshifting my bad surprise is that it downshifted with no clutch pulling. Why it works up but not down? Does it damage my trans? I only did it once by misknowledge.

Is the clutch to stop spinning the countershaft (higher shaft) prior to shifting? or to align the lockers with the holes in his neighbour?

Thank you
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scottrnelson
Advanced Member
6960 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 01/09/2013 :  7:02 PM
quote:
Originally posted by jilp

I preload the up shifts well, but when I thought the same applies to downshifting my bad surprise is that it downshifted with no clutch pulling. Why it works up but not down? Does it damage my trans? I only did it once by misknowledge.

Is the clutch to stop spinning the countershaft (higher shaft) prior to shifting? or to align the lockers with the holes in his neighbour?

When accelerating, the engine is applying significantly more force on the gears than when decelerating, which is the most likely reason why pressure didn't cause a shift up, but did for a down shift.

The clutch doesn't stop spinning, it just reduces the forces on the gear dogs so that you can slide them out of engagement with the current gear and slip them into position for the next gear.

As I understand it, there are two things you can do to damage your transmission by improper shifting: 1) it can round off the corners of the dogs so that they are more likely to slip back out, and 2) if the forces are strong enough and often enough, you can crack and break the dogs.

I like to be sure that I can shift without a clutch for the rare case where I break a clutch cable, clutch lever, or have issues with a hydraulic clutch slave. I've done all of those at least once. But otherwise I use the clutch to reduce forces on the gears when I'm shifting, because I don't want to deal with transmission problems at some point in the future.
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greywolf
Male Moderator
1484 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 01/10/2013 :  8:55 AM
A small change allows unloading forces on an upshift. Preload the shifter and cut the throttle and you'll change gears without touching the clutch. A downshift is the opposite. Cut the throttle and the pressure on the downshift side increases.
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scottrnelson
Advanced Member
6960 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 01/10/2013 :  10:02 AM
quote:
Originally posted by greywolf

A small change allows unloading forces on an upshift. Preload the shifter and cut the throttle and you'll change gears without touching the clutch. A downshift is the opposite. Cut the throttle and the pressure on the downshift side increases.

I don't follow your argument here.

The first thing that has to happen is for the gear dogs to be pulled out of the slots regardless of whether you're shifting up or down. How is the pressure any different on a down shift than on an upshift?
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kacinpa
Male Advanced Member
802 Posts
[Mentor]


Lansdale, PA
USA

Triumph

Sprint GT

Posted - 01/10/2013 :  11:00 AM
quote:
Originally posted by scottrnelson

quote:
Originally posted by greywolf

A small change allows unloading forces on an upshift. Preload the shifter and cut the throttle and you'll change gears without touching the clutch. A downshift is the opposite. Cut the throttle and the pressure on the downshift side increases.

I don't follow your argument here.

The first thing that has to happen is for the gear dogs to be pulled out of the slots regardless of whether you're shifting up or down. How is the pressure any different on a down shift than on an upshift?



The difference is how you handle the throttle in combination with the shift. On an upshift with slight pre-load the shift will happen easily if you let up on the throttle ever so slightly, which is natural before shifting and takes the drive load off of the dogs. When you down shift, if you pre-load and back off of the throttle the force is increased on the dogs and the shift won't take place without significant force on the shift lever. If you hold the throttle steady or ever so slightly open the throttle the shift will also happen easily. It is more of a tendency, however, to cut the throttle when slowing so also more likely that the forces on the dogs will make the downshift feel more difficult than the upshift.

At least that is my interpretation of what Greywolf is saying, based on my experience. It took me some thinking to describe as when I shift "clutchlessly" it is more instinctive and I don't really think about it. Like many things, if I think about it too much, I mess it up!
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jilp
Male Junior Member
84 Posts


Mexico, Mexico
Mexico

BMW

R1200GS

Posted - 01/10/2013 :  12:35 PM

quote:
Originally posted by kacinpa

If you hold the throttle steady or ever so slightly open the throttle the shift will also happen easily


That is what happened when I downshifted and it was very easily, but I do not do it as a habit. I allways use the clutch.

But now I do not get it when downshifting when the blipping should take place, do you have to easy of the throttle and then blipping, or what is the sequence? (not racing related)
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greywolf
Male Moderator
1484 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 01/10/2013 :  12:38 PM
One set of dogs needs to release and another set simultaneously engage. It isn't just a release involved.

Try clutchless shifting at speed. Upshifts are easy but downshifts are not until you get below about 20mph on most bikes to reduce the power enough to make the downshift.

On an upshift, backing off the throttle eases the pressure on the dogs and puts the throttle in the proper position for the higher gear. Less rpm is needed to hold the same speed in a higher gear. It's exactly the needed combination of events.

On a downshift, backing off the throttle eases the pressure on the disengaging dogs but the throttle position went the wrong way for the engaging dogs. More rpm is needed to hold the same speed in a lower gear. The forks moving the gears to engage the dogs are driven by the same drum and the gear that needs to increase speed to engage its dogs to engage is slowing, applying too much pressure for the fork to move it. If throttle is added to accommodate the engaging gears, the load on the gears that need to disengage is too great to allow it. The combination of events is at cross purposes.
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scottrnelson
Advanced Member
6960 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 01/10/2013 :  12:49 PM
I guess I forgot that you're not going to have the same acceleration forces when downshifting, since you're not likely to be trying to speed up when you do it. I guess a few slight misunderstandings actually help get better answers as everyone tries to straigten things out.

Next question:
quote:
Originally posted by jilp

But now I do not get it when downshifting when the blipping should take place, do you have to ease off the throttle and then blipping, or what is the sequence? (not racing related)
I've found that the best thing is neutral throttle, whether or not you're using the clutch to downshift. You want just enough throttle that if you pull in the clutch, the engine doesn't change speed.

And the lower the speed of the engine at the time of the shift, the easier it is, since lower forces are involved. It's also less likely to damage something.
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