Yz450f 1st gear to 2nd problem


12 replies to this topic
  • 2wheelers

Posted March 28, 2012 - 03:39 PM

#1

I got a 2008 yz 450f and when you try to shift from 1st to 2nd it goes into neutral. I am clicking it as high as the lever goes. all the other gears shift good. So when ever i go from 1st to 2nd i have to go 1st neutral then 2nd. I even tried it on the stand with my hands and it won't go into 2nd gear after 1st like it should. Is this a problem with this bike or is it normal. The bike runs good other than that. Thanks in advance!!

  • Yamaryder29

Posted March 28, 2012 - 06:42 PM

#2

Sounds like you may have a bent shift fork.

  • 2wheelers

Posted March 28, 2012 - 07:04 PM

#3

what does that mean. is that a serious problem?

  • grayracer513

Posted March 28, 2012 - 07:39 PM

#4

It would be a bit unusual for the cause to be a bent shift fork. The problem may be nothing more than the shifter is mounted too high. Try lowering it one notch and see how that works. If it really does have a problem, it's more likely to be a bent centering tab on the shift lever assembly, which can be both verified and repaired by removing the right side cover and the clutch.

Edited by grayracer513, March 29, 2012 - 08:20 AM.
reconsidered


  • Yamaryder29

Posted March 28, 2012 - 07:41 PM

#5

Well, if that's the case, the cases will have to be split to change it. It's rare that one bends, but I had it happen to my 250f and it cracked the case where the fork is held in place.
I would have a professional mechanic look at it. If its just a bent shift form, your major cost is labor. That's the only thing that I know from experience would cause it to shift like that.

  • mikedabike

Posted March 28, 2012 - 08:36 PM

#6

Hmmm. I have a 07 I bent the shift shaft on. It sometimes does this. Not too much but definately more than it use to. I have a new shift shaft and seal just have not gotten around to replacing it yet. I was hoping that would solve the issue and nothing else was causing the issue. I haven't replaced it yet because I have been riding every weekend and was waiting until I had a couple weeks off in case it was a bigger repair.

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  • grayracer513

Posted March 29, 2012 - 08:17 AM

#7

What you have to look for in a case like this, assuming it's not simply a matter of lever positioning and there's a real mechanical problem, is something that limits the ability of the shift linkage to rotate the shift cam completely into the second gear position. The problem is likely that the ratcheting assembly does not center correctly once placed in first gear and doesn't pick up the right notch to be able to roll the cam that far. When "dry shifting" on the stand with the engine off, going from 2nd to 1st and back to 2nd should feel much the same as going between any other two gears. If lever travel is different when downshifting to 1st from 2nd than it is from 3rd to 2nd, that could indicate an internal problem.

At this point, I'm going to back off of my earlier statement that it can't be a shift fork problem. I will say it's not likely, but if shift fork 2 were bent toward the right, it might be what limits the cam travel going to first, particularly if the other gears seem to work in a normal manner. If the cam doesn't rotate far enough when engaging 1st, it will be staged incorrectly to go all the way to second on the next upshift.

  • HRC

Posted March 29, 2012 - 10:07 AM

#8

Welcome to the Yamaha club !

Where gearboxes brake !

The only complains I got with Yamaha is the gearboxes

  • 2wheelers

Posted March 29, 2012 - 11:31 AM

#9

i repositioned my shift lever and tried on the stand and everything seems normal now. to go from first to second the rim has to spin all the way forward or backward not in between when in first. i can't explain it but this was on a stand and moving the lever helped. thank you for the help!

  • grayracer513

Posted March 29, 2012 - 12:06 PM

#10

The explanation for your difficulty in shifting without turning the wheel lies in how the gearbox operates. Each of the 5 gear ratios consists of two gears, one on the main shaft (these are called "pinions"), and the other on the output shaft (called "wheels"). In each case, one of the two is fixed to the shaft, usually on a set of splines, and the other is free to turn on the shaft. All of the gear teeth remain meshed at all times, but none of them can drive anything, since only one of the two is connected. When you decide to engage second gear, for example, the splined 4th wheel gear next to the free turning second wheel gear is moved over against 2nd and locks to it by means of 4 lugs sticking out from the sides of it, somewhat like lug nuts on a wheel. These lugs engage into slots in the target gear, or into a matching set of lugs, and this locks the free turning member of the one gear set to that shaft. Since both halves of second are now mechanically connected, you have second gear.

The reason the wheel must be rotated to shift on the stand is that there are only 4 positions in 360 degrees of the rotation of these two gears where they will line up with each other. Something usually need to be turning in order to arrive at that point, and ordinarily, it's the clutch and main shaft turning at a different speed than the output that does that. With the engine off, that doesn't happen.

  • 2wheelers

Posted March 29, 2012 - 12:29 PM

#11

So i guess my problem is normal.?.
I got a off topic question. Does the 08 yz450f have a oil filter spring because i never saw one and i just put in there no spring

  • grayracer513

Posted March 29, 2012 - 02:53 PM

#12

Does the 08 yz450f have a oil filter spring


No spring.

  • jratcliffe3

Posted March 31, 2012 - 02:27 PM

#13

It would be a bit unusual for the cause to be a bent shift fork. The problem may be nothing more than the shifter is mounted too high. Try lowering it one notch and see how that works. If it really does have a problem, it's more likely to be a bent centering tab on the shift lever assembly, which can be both verified and repaired by removing the right side cover and the clutch.


Had the tab on the guide plate break off in mine, some time after the shift shaft (which was replaced) had been bent by a snapped chain.

With the tab broken off, I was getting neutral a lot between first and second. On replacing it, I noticed that the detent in the segment for neutral was also very slightly chipped, so I changed the lot out - no more problems.





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