Help needed: YZF 426 surging in 4th and 5th

I am the original owner on a YZF426 02', and I am having problems. If you notice my older posts, quit laughing. I didn't mean to or want to drop my bike in the water and hydrolock it. I have been riding all my life, and I can't believe I did that. I didn't even have any beer with me.

With that said I done, before I bent the rod I noticed that I was having clutch problems. I was getting this heavy surge in the higher gears under heavy load. I ride Glamis frequently and I figured that the clutch was just going from the load. So replaced the clutch and put some heavy duty springs in. I thought that was the problem. Well two clutches later (one I installed and one the dealer installed), I still have this weird surge in the upper end of 4th and 5th. The dealer said it was the clutch so they put another one in. Well its still here. I am worried that I have tranny issues now. I told them to rip it down the street but they said they couldn't. I know I know, I was probably hosed on the whole deal but every once in a while I go to the dealer to give myself a gut check to remember why I do my own maintenance.

Anyone have any experience with this or have heard of something like this happening? I would think that if I was skipping gears it wouldn't be a good noise. Its weird because it just feels like I am clutching it real fast.

I'll trade a cube of chrome for some knowledge!

Does it have the feel of something like gears slipping over one another and grabbing again? Does it happen only in one or more particular gears?

Honestly it feels like I was fingering the clutch real fast and very consistent when on power. I originally thought it was clutch then went to gears but the shop said it wouldn't happen. He was kind of a derelict so maybe the info was wrong.

If I get on in in 4th its fine until about mid speed in 4th when I am on it hard its start to surge almost like its 3 to 4 to 3 to 4 then when in 5th its really bad and I really can't even ride in 5th anymore. I went out to the desert last weekend and even across the dry lake bed it was doing it. It must be the gears. I don't know too much about the tranny.

Sounds like worn locking lugs on the gears involved, along with worn or bent shift forks.

Is this normal? What would you suggest in replacing these parts? I will have to consult Mr. Manual. Just bummed that I didn't do this when I had the whole thing apart. Probably by the parts here on thumpertalk. Is it wise to just replace all the gears... Whats the norm in doing a job like this?

I really appreciate and thank you for your help.



it is a bummer. I have the same problem with my '04, just slipping out of 4th. I thought it was the clutch, so I replaced the clutch--still jerking!

On Grayracer's advice I am tearing it down. I was going to change the piston this week, but a tranny inspection is a little more than I expected. I completed 75% of the disassembly in a couple hours last night. It is fairly easy and few special tools are required (flywheel puller and case splitter is all I can tell). I will have the engine out as soon as my wife gets home with the 30mm socket for the clutch boss nut.

There are a couple gaskets and a half dozen o-rings to replace in addition to any bad tranny parts.

I was bummed because I just finished a crankshaft replacement in my sons YZ85 and thought I was free from intense maintenance for a little while.


Mr. Manual will have a picture in it something like the one below.

Item 1 is the main shaft, alternatively called the input shaft or the main axle. The gears in this shaft are called the pinions, because they are the driving member of each pair. The second half of each gear pair is on the counter shaft (output shaft, drive axle), and these are called wheels.

Items 3, 6, & 7 are the 5th, 3rd, and 4th pinions, respectively. The way this trans operates is that all 5 gear pairs are always in mesh with each other so that there can never be any grinding together of the actual wearing, load bearing tooth surface when shifted. Of course, the trans cannot be in any more than one gear at a time (it would lock up otherwise), so one of the two gears in each pair (like the 1st gear pair, the 2nd gear pair, etc.) is splined to the shaft it rides on, and the other half of the pair spins free.

To engage, for example, 5th, the splined to the shaft 3rd gear pinion slides over and engages three lugs protruding from the side of the gear into three matching slots in the side of the free spinning 5th gear. You can sort of see them in the picture. This locks the free half of the 5th pair to the mainshaft, and the power then flows from the shaft to the 3rd pinion through the splines, to the 5th pinion via the locking lugs, to the countershaft via the splines in the 5th wheel gear, and out. To make a 5-4 down shift, we move the 3rd pinion away from 5th along its splines and over against the 4th pinion, locking it the same way.

The locking lugs and slots look like they are perfectly square with the sides of the gears, sticking out at exactly 90 degrees, but they aren't. They are very slightly undercut, "dovetailed" if you will, so that once they engage, any load placed on them holds them together. The trouble starts when they begin to round over at the edge, and their under cut wears away to the point where it's slightly over cut. Then the load begins to force them apart instead. The sift fork can't be moved to a neutral position as in a car with this problem because of the way the shift cam is made, so it flexes under the force of the two gears being forced out of engagement, then slams the two back together again. Needless to say, this is not good for the fork.

So, in inspecting the trans, look at the edges of the locking lugs and slots and look for signs of rounding, chipping, and wear. If 5th gear skips, that implicates the 3rd and 5th pinions, but does not mean there is anything necessarily wrong with the wheel gears in either pair. Do inspect all of them, nevertheless, since those gears may be involved with another shift. The 5th wheel (#15), for example, is responsible for engaging 1st and 3rd gears.


Great Advice GrayRacer. That actually makes sense. Now I know how the system works. I have to do more checking on how that shift fork works because it shifts both the bottom section and the top section. Amazing stuff that people figure out.

I will be looking at Mr. Manual and hopefully start pulling the thing apart soon. One question, normally if someone has this problem, is it better to just replace the whole thing? Obviously it sounds like I should replace the shift fork and the 5th and 4th gear along with the locking lug gear the 3rd... well actually I am asking since I really don't know, nor have I opened it up. The main shaft should be fine though. Sounds like just the gears and locking rings, which has probably done damage to the shift fork. What, in your experience, should I replace according to the numbers on the chart? I will do all the checking so see the damage myself, but I was just wondering what is the norm for this. Probably even post some pictures when I have it apart to get a second opinion.

I only ask what usually is replaced in order to gauge how much money it will cost. Might just want to hand it off to another in order to buy a street legal bike enduro.

I really appreciate your help. Forums are tough and all that writing you did had to take some time. With the description of that diagram, I now can see why this might happen cause I do bump shift while I am at the track and when I just need to under the challenge of another. Might have to curb that habit. Comes from the old 80 and 125 days.

Yours, if it's the trans acting up, will need 3rd, 4th, and 5th pinions, and the associated shift fork. Inspect the rest carefully.


I found the condition you describe. The fork is bent and the lugs are worn/rounded. The manual directs replacing the fork and the two adjacent gears. Thanks for the great help with these posts.


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