Nomad Transmission Issue

[Woolfman]

I have a 2009 Nomad with 19,000 miles and have started having a problem when I am hard on the throttle in 2nd gear. When it gets above 40 mph (don't have a tach) it will give a heavy jerk as if the belt has jumped a cog. If I drive it normally with moderate or light acceleration, there is no problem. Never notice this in any other gear except 2nd. Belt is to spec, and bike is up to date on all maintenance.

Any suggestions??

[ringadingh]

Take a good look at the belt and sprockets perhaps a cog is missing.

[redjay]

Make sure the front pulley is tight on the transmission shaft and the nut holding it on is properly tabbed with a locking tab washer.

[RACNRAY]

Originally Posted by Woolfman

I have a 2009 Nomad with 19,000 miles and have started having a problem when I am hard on the throttle in 2nd gear. When it gets above 40 mph (don't have a tach) it will give a heavy jerk as if the belt has jumped a cog. If I drive it normally with moderate or light acceleration, there is no problem. Never notice this in any other gear except 2nd. Belt is to spec, and bike is up to date on all maintenance.

Any suggestions??

The most important aspect of your complaint is the "jerk" only happens in 2nd gear. If that is the case than issues with the belt and pulleys can be ruled out. But what has been mentioned should be checked anyways.

Unfortunately what you have is the most common failure of m/c transmissions, and it is due to the design. M/C use what are called "constant mesh" trannys. On the 1700's there are 2 tranny shafts, each with 6 gears. ALL GEARS are in tooth mesh, that is each gear and it's teeth are in constant meshing with it's matching gear on the other shaft, hence the name "constant mesh". Some gears "float" on their shaft (i.e. are not splined to the shaft), some gears are splined to their shaft. The reason for this "constant mesh" design vs what is found on most automotive manual trannys is that it can be packaged into a much smaller encosure, thus it's widespread use on skoots.

For each gear selected the individual gears are meshed via a combination of protrusions
(called "dogs") and/or slots on the SIDES of the gears. Torque is transferred from one gear to another via the engagement of the dogs/slots. This engagement is accomplished by sliding one gear sideways towards it's neghboring gear so the above is accomplished. The sliding gear is moved via the shift linkage acting on the shift drum which moves "shift forks" that are engaged into slots machined into the circumference of the sliding gears.

Over time, miles, incomplete shifting practices, poor design (I have seen inadequate dog to dog or dog to slot engagement), the surfaces of the dogs/slots will wear, will become rounded off. This reduces the contact areas which increases the load on those reduced areas DECREASING their ability to transfer torque thru that gear set, especially on acceleration. One gear of this engagement process is fixed in one position, the gear that was slid over to make engagement ends up being, well "spit" out of engagement. That gear is held in place by the shift fork(which does not move unless the gear shifter is moved), so the shift fork acts as a "spring' pushing the slidine gear back into engagement.

The result as we feel it is the jerk, a "skip" during acceleration. Depending on how bad the dogs/slots are worn dictates how bad the skipping will be. There is also collateral damage. The shift fork is bending every time the gear jumps out of engagement, so the shift fork may become bent. The hard chrome wear surfaces on the fork tips that make contact with the groove of the sliding gear may become damaged/worn, and the actual teeth of the gear may grind into the fork. Any one of these necessitates fork replacment. Since the fork is "pinned" into the shift drum, the groove of the drum may be damaged. There may be abnormal wear, or what I mostly see is material chipped off due to the drums being made from cast iron.

The repair is of course engine removal/disassembly to access the tranny. Most of the time the gears will have to be replaced along with the fork and drum. I also always "undercut" at least 2nd gear, and if the owner can afford to undercut the entire tranny this machining process goes A LONG WAY to preventing this failure again. Undercutting establishes an angle on the load bearing surfaces of the dogs/slots which helps to "lock" the gears together.

My recommendation is to NOT ride in a manner that incuces the skip, this may minimize the need to replace the shift drum, but there is the possibility it is alrady FUBAR.

If you have any questions call me at my shop...954-455-9665 Fla time.

RACNRAY

[Woolfman]

Thanks all for the comments.

Ray, I was afraid it might be something expensive sounding. Thanks for your detailed explanation. All seems well as long as I don't accelerate hard in second gear and it has been doing this since the end of the riding season last year. Just about ready to put it up for the winter now so may postpone this expense until next spring.