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jratcliffe3

2009 YZ450 - Strange Gearbox Issue

16 posts in this topic

Hi,

When riding yesterday, I was getting a false neutral when going down gears between 3rd and 2nd gear. Oil is changed every couple of hours. Any ideas what this may be? I was wondering if a selector fork may be bent?

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Most likely just not shifting firm enough. Between each gear there is neutral. If not shifted firmly enough the stopper leaver that rides on the shift star on the shift drum can actually hang up between gears.

I wish someone would come out with a stonger stopper leaver spring so as to allow the shift drum to be forced into a positive shift with stronger force.

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Most likely just not shifting firm enough. Between each gear there is neutral. If not shifted firmly enough the stopper leaver that rides on the shift star on the shift drum can actually hang up between gears.

I wish someone would come out with a stonger stopper leaver spring so as to allow the shift drum to be forced into a positive shift with stronger force.

Don't think I am shifting any less firm than usual, I have had the bike from new. It has always been possible when power shifting up the box to miss a gear if you dont shift firm enough, but have never had this issue going down gears before.

Is it possible the stopper lever or shift star are slightly worn, causing them to stick between gears more easily?

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Maybe your spring is getting soft. Yamaha part # 90508-26021-00 , it's about a $5 part. I have never seen a worn stopper leaver or shift star (segment) but anything is possible!

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I got same kind of problems my 2011 450yzf. Belive me or not i was using most expencive racing oil made specially for 4stroke mx bikes and i got this shifting issue. I change oil for normal mineral oil 20/40 didnt have problems after.

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I got same kind of problems my 2011 450yzf. Belive me or not i was using most expencive racing oil made specially for 4stroke mx bikes and i got this shifting issue. I change oil for normal mineral oil 20/40 didnt have problems after.

Might be worth a try, I too use expensive racing oil in my bike.

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Maybe your spring is getting soft. Yamaha part # 90508-26021-00 , it's about a $5 part. I have never seen a worn stopper leaver or shift star (segment) but anything is possible!

This is what it sounds like, like you said if the spring is too soft/worn, the star may not engage full movement of the shift fork from gear to gear.

I've seen stoppers hanging by literally two threads of the bolt that holds it in place, just about ready to come right out. Things like this will show up as shifting issues.

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Thanks. Having never had the need to look into the bottom end of my Yam too far, is this spring on the clutch side or do you have to split the cases to change it?

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Thanks, thats what I suspected (was just checking that I didn't need to split the gearbox). I'll get a new spring ordered and fitted, and inspect the stopper lever and segment whilst I am at it.

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Changed the stopper lever spring, same issue. When changing it though, I noticed the segment is broken slightly between 2nd and neutral, with a small part of the detent broken off. I have ordered a new segment, pawls and stopper lever, will fit them and hopefully the problem will be cured.

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... I noticed the segment is broken slightly between 2nd and neutral, with a small part of the detent broken off.

Can you post a picture of that? I can't imagine anything breaking the segment. The segment has 5 lobes, with the low spots between them serving to hold the indexing roller. The peak of the lobe between first and second is ground out to enable the roller to hold the trans in neutral at that point. If that's what you meant, it's made that way, and it's normal.

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I'll post a picture. There are two peaks between 1st and 2nd - so the roller sits between the two in neutral. The one closest to 2nd is broken, I noticed this much when changing the spring. Cannot say how much wear is on the segment and pawls yet till i strip it down again once the parts arrive.

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This might be a silly question.......

If I remove the shift shaft with the bike on its left hand side, will the oil come out of the shift shaft hole on the left side of the case?

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Doesn't if you have the bike at about 30 degrees. The bit broken off the segment is probably too small to see on a photo, but there is definitely something missing off the top part of the neutral detent.

The main problem is though that the tab is broken off the guide plate. The only thing I can imagine caused this is I broke a drive chain, which in turn bent the shift shaft (which I changed out straight away). This may have overstressed the guide plate, causing it to prematurely fatigue. Either that or I just got a bad one.

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