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Transmission overview

by Kerry Wood


This past weekend I tore into the 78E that I'm going to sell to fix what was a bad first gear problem. When I bought the bike I knew there was a transmission problem due to the fact that the bike didn't seem to want to slide into first gear. My first thought was that the shift fork was bent or damaged in some way.

Sure enough, once I pulled the counter shaft out of the bike it became obvious what the problem was. The dogs on the 4th pinion gear and slots on the 1st wheel gear were worn quite significantly and the number 3 shift fork was showing very extensive damage to its side and also corresponding damage on the gear slot where shift fork number 3 resides. From examining the damage, it became clear to me that the bike had been slipping out of first gear and the previous rider had been holding his foot down on the shift lever during acceleration to keep the bike in first gear. Therefore, damage to the sift fork itself was obviously the end result.

During the process of sorting through my spare transmissions I had four complete counter shaft assemblies that I could pick and choose from to get a good solid transmission together. Out of the four assembies all were showing significant damage to the first gear and only slight damage to the infamous second gear. Finally, I tore into the bottom end of my parts bike and found a almost perfect first gear and a bad second. So, I was able to put together a really good tranmission out of my parts bin.

Now, here is where things get somewhat interesting. My thoughts turned to wondering why out of four counter shafts all were showing signs of severe wear on the first gear and various wear on the 2nd. In addition, why was my parts bike showing a good first gear but a really hammered second gear. So, I took one of my primary shafts, counter shafts and shift forks and placed them in V-Blocks so that I could study the transmission design and function to try and come up with some ideas. I simulated on my bench the shifting process of the transmission so that I could understand how the gears all functioned together and if there was anything in my shifting style that I could do to minimize damage occuring in any of my bikes. Here are some of the things that I came up with and possible solutions.

  • If your bike is jumping out of gear don't hold down (or up) the shift lever to keep the bike in gear. By doing this, you are actually doing more damage and compounding your problem. If your bike is jumping out of gear fix it and don't continue to ride it until the fix is done. This was evident by the transmission I just fixed.
  • The primary shaft in these bikes appears to be rather bullet proof and I haven't noticed any damage to any of the primary shafts and gears I've looked at. It is a good thing, since the primary shaft is buried in the engine and the only way to remove it is to split the cases.
  • 2nd into 3rd gear and 4th into 5th gear seem to have the smoothest shift transitions. I first noticed this on the bench and proved it later on a test ride. My bike seems to shift so smooth that I hardly notice the sound of the transitions between these gears. The other transitions (Neutral to 1st at standing, 2nd to 1st, 1st to 2nd, and 3rd into 4th) seem to offer the most hard shifts and the most problematic area of the transmission.
  • My thoughts then turned to understanding at what point 1st and 2nd gear were under the most stress. The dogs on 1st gear appear to get worn the most during shifts from neutral to first at a standing position and during 2nd to 1st gear during deceleration when the shift occurs at too fast of a speed. Solution to minimize first gear wear? Well, rather than shifting to neutral as you roll to a stop, try shifting the bike into first gear when you slow to about < 5 miles per hour prior to your stop. Use your clutch lever at a stop light rather than letting the bike idle in neutral. This way, you aren't having to jam the bike into first gear at every intersection you come to. We are all familiar with the famous XS 750/850/1100 chatter/clunk that occurs when shifting from neutral to first. On a test ride last night, I found that shifting into first just prior to my stop made my bike much happier.
  • It seems logical to me that 1st and 2nd are the gears that are hammered the most during hard acceleration when the motor is applying max torque through the countershaft. Therefore, they are bound to show the most wear in most applications. Depending on your riding style, you can affect wear and tear on the transmission. Hard shifting at higher RPMs will cause more wear than shifting at an RPM that the transmission is more comfortable with. Therefore, I've modified my riding style to enjoy more of the roll on power of the XS11 as opposed to seeing how fast I can get to 5th gear. Becoming more familiar with the RPMs at each shift your transmission is comfortable with will help a great deal. After much practice, I've finally arrived at a point where I've found the most "natural" shift points.
  • When sitting at idle with the bike in neutral and the clutch lever out the primary shaft is always spinning as is the 1st wheel on the countershaft. Upon shifting into first, the 4th pinion gear on the countershaft slides to the left allowing the dogs on the forth pinion to mate with the first wheel slots and thus enguaging the "1st" gear of the transmission. When pulling in the clutch it disconnects power from the primary drive shaft (the shaft that the primary drive chain is connected to) to the primary shaft of the transmission. Under ideal conditions, the primary shaft of the transmission would stop spinning and therefore first gear would enguage with no clunk. However, it appears (although I can't prove it since I don't have a see through oil pan) that the primary shaft continues to spin due to the slight drag on the clutch plates. The act of shifting into 1st causes the primary shaft of the transmission to come to a complete halt. The chatter sound just prior to the 1st gear enguagement is caused by the 1st wheel on the countershaft slowing down to meet the 4th wheel pinion which is not spinning. The problem is also compounded by the fact that since these bikes are shaft drive they don't have chain slop to absorb some of the shock that occurs when the counter shaft is jerked. Look at a chain driven bike sometime and notice what happens when it is shifted into first while sitting still, the chain will jump up and down abosorbing this shock. Therefore, it is never telegraphed to the rear wheel like it is on a shaft drive bike. So, the best thing to do when shifting into first from a dead stop is to pull in the clutch and wait 5 seconds or so so that the primary transmission shaft can slow down somewhat. This seemed to make a noticeable difference when I did this with my XS1100.
  • When decelerating down from 5th approaching a stop light. It appears that letting the brakes stop you instead of the transmission will help also. Brake pads are cheaper to replace than gears are. I would rather the wear of slowing down appear in worn out pads than worn out gears. Shifting down as you slow and letting the clutch out just long enough to allow the next higher gear to engauge will help as you approach first gear and the stop light. Shifting down should be a transition like up shifting where all shifts occur at a different speeds. So, don't try and jam the bike into 2nd gear when you are still going 45 mph. Shifting down is very important though, have you ever tried had the bike in 5th gear at a stop light and tried to put it into 1st. It ain't easy brother!
  • If pressing the shift lever you find that the bike doesn't want to go into a gear don't jam your foot on the pedel. At that point, all you are doing is bending shift forks. Rather, let out your clutch and pull it back in long enough for the primary shaft to change positions or roll the bike backward and forward enough to rotate the countershaft slightly. The bike should then be able to drop into gear.

Gang, I'm sorry that this is so long. I guess it is my analytical left brain that tends to take over in these cases. It was fun studying the transmission and now I have a better appreciation for why this transmission acts the way it does. It all seemed rather obvious once I began looking at it. These things have helped me out in understanding how to operate my XS1100 a little better. I'm rather confident if I follow my own rules that my transmission will last longer and give me better service.

Kerry Wood
 

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