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Transmission shift issue

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Hello all,

I have a 2009 yz450f.  I had to buy new cases (used) because the crank bearing let go and took out the inner webbing.  I've changed all the bearings and seals so everything is brand new including the crank, rod, piston and cylinder. I'm having a problem down shifting, it will up shift fine.  I've split the cases again and have found nothing wrong.  I've checked fork wear, gear movement, and groves on the shift barrel for burrs or wear, everything seems to be ok.  Do the shafts have to go in at a certain position, like a timing thing or do they just go in?  From what I can see it appears to be the "r" fork that's on the "bump" of the shift barrel, looking at it with all the gears in the right side case it appears that the fork has to come up or out from the right side case because the shift fork pin is right on the "bump" of the barrel. The fork itself slides freely in the shaft bore so I don't think it's binding.  That's why I'm wondering if the gears have to be placed in a specific order to mesh properly like a timing thing.

TIA

Don

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1) Are you shifting "dry" or with the engine running?

2) Will it shift to first from neutral?

3) Will it shift all 5 gears up in order?

4) If you raise the lever some before trying to downshift, will it shift down?

5) When you attempt a downshift, does the lever move without doing anything, or does it jam, unable to be moved?

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Hello Grayracer513, thanks for the quick reply.

1)  Right now the cases are still split so yes, I'm shifting dry.  The first time I put the bike together we had the same problem, so I thought it might be because I'm not spinning the tranny fast enough but when I tried to run the bike it wouldn't down shift it upshifted  fine through all the gears.

2)  No, it will not shift to first, I can just barely get it into neutral.  The spring loaded roller won't sit perfectly in the neutral stop in the segment.

3)  Yes, it will shift through all 5 gears and then it jams.

4)  I'll try to raise the lever up after work today and let you know.

5)  When attempting to downshift the lever will not move.  When this is happening the only fork that looks like it should move is the "r" fork.  The reason I think this is because the other two fork pins in the shift barrel are in where the groove is straight so I believe they are not supposed to move anything at that position.  If I set it up in neutral so the roller is perfectly in the stop on the segment it still won't downshift but upshifts fine.

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The right side fork on the output shaft is the fork that operates 1st and 3rd gear by moving the 5th "wheel" (driven) gear. The fork at the left side of the output shaft shifts 2nd by moving the 4th wheel. The fork on the main shaft moves the 3rd "pinion" (driving) gear to shift 4th and 5th.

The first thing to do is to remove the shift segment (#17 in the picture) from the cam and verify that it is correctly indexed to the cam.  There is a small pin in the end of the cam, and a matching hole in the segment to align the segment correctly.  If this is assembled out of alignment, The segment will be out of sync with the correct cam position, and you can end up pushing the pin down flush and render it ineffective.  It might be possible to correct that by driving the pin through and out, then retrieve it from inside the cam barrel, but I'm not sure the hole is drilled through.

Once you have verified the segment indexing, assemble the segment and guide/retainer plate to the cam, leave the ratchet assembly off of the cam and see if you can rotate the cam through all 5 gears and back using a socket on the shift pin/bolt (10). 

Bear this in mind: You have the cases split.  The main shaft is located laterally by the clutch boss nut pulling it to the right up against the right side main shaft bearing.  The output shaft is located laterally by the front sprocket nut pulling it to the left against the left output shaft bearing.  With the cases split, that bearing isn't there, and the output shaft can drift to the right 5-6mm or more out of position.  You may want to mock up the assembled cases for the test.

If it passes this check, then assemble the ratchet assembly into the cam and check that the gearbox sits cleanly in neutral.  Then assemble the shift shaft to the thing and observe how it operates.  There my be something preventing it from correctly returning to a centered position.  The correctly centered shaft will position the ratchet pawls so that moving either way will catch the segment and turn it.

Good luck

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I've checked and double checked the assembly, I'm very certain the segment is in the right position, I've put the cases together thinking that if the shafts have no support, maybe that's the problem but it didn't help.  This bike has been together and running since the rebuild and it wouldn't downshift then, upshifts fine.  I've already done what you've asked and observed it's operation I can't see anything wrong it's driving me crazy!  It just doesn't want to even start to move in the downshift direction even with the segment nut in and trying to move it with a socket.

Edited by openbrain
punctuation

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Hey Grayracer513,  Did I say something to offend you?  I really appreciate your help and I know my last post sounded like I was bitching but that is not the case at all. It's just my frustration coming through.  Hope you will continue to help. Again, your help is greatly appreciated

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No, not at all.  Times are extraordinarily busy for me right now with selling the house and dealing with contractors who won't perform on their warranties and who knows what.  Then there's the fact that I frankly can't make anything out of the fact that your shift cam refuses to be rolled counterclockwise after you shift up even when you have the segment removed and are turning it with a socket.  There are assembly mistakes possible that would stop it from shifting the full range of gears, but if it will go from 1st to 5th, it should be able to go back. 

You say you have the cases together.  Set up enough hardware on the output shaft to be sure it stays left, and keep the main shaft pulled right as you try your shifts.  With just the socket, no segment, can you shift to second, then back to first?  To third and back?  Does it only refuse to downshift from 5th? 

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A remote possibility is damaged shift rail bores, particularly the bore for the forward, or center shift fork (fork 2 ) that shifts 4 and 5. 

When you say it shifts up and can't be shifted down, even with just the bare cam and no segment, what do you have to do to get it back out of 5th?

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You have to jiggle it around which I think changes the angle of the shift fork pin and the it will shift down.  I think it could be the bore as these cases where bought used.  I made sure before purchase that they were a matched set and was assured they were.  One of the bores was a little gouged so I cleaned that bore out with the back side of a drill (smaller than the bore diameter) and some very fine sand paper taped to it, that definitely helped and made the movement smooth.  The bore for the r shift fork doesn't show wear.  The bore is almost a through bore on the right side case so I'm going to try to tap the the shaft from there and see what happens.  I feel the same way you do, I don't understand why it will go up but not down.  I took many pics of the disassembly so I'm sure the assembly is correct.  The other theory I have is when the engine locked up I wonder if something happened to the transmission, although I gave it a thorough inspection and made sure all the gears slid easily on the shafts.  I think I've got it down to two possible problems either the r fork shaft is binding in the bore or the gear it moves is binding.  The problem is I can't separate them without moving them so I can see which one is the problem, as soon as I move anything it unlocks so I can't tell which one is binding.   Sorry for the novel but if I was trying to help someone fix a car I would like all the info I could get, hopefully it helps you, and doesn't make things worse, lol. 

 

I can post a couple a pics if you'd like, maybe you can see something in the pics I don't see.  Give me a couple of days though on my way to my son's college graduation for the weekend, don't know when I'll be back home, I'll send them as soon as I can.

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One of the problems with this type of assembly is that once it's together is a functional state, you can't really observe it very well.  Something to try to look for is any sort of significant excessive clearance between the two fork fingers and the diameter of the groove in the gear it fits on.  If there's too much, the fork may be able to rock, or pivot on its rail in response to the cam bearing against the follower pin, and that could cause some binding.

You keep mentioning the "R" fork.  I don't have any of the parts in front of me, and I don't recall how each of them are marked.  What markings do the other two have on them?

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Hey Grayracer513,

Here are the pics, let me know if you need different angles. I took a pic of the clutch side of the case don't know if that helps, there's really nothing to see there the ratchet is not installed. I haven't had time to do what you asked , hopefully you'll see something in these pics that can help me. Thanks again for your time it is greatly appreciated. By the way what is your name? 

Don

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OK, that's kind of what I thought.  The reference to the "R" fork is confusing.  The "R" fork is Fork 3 in the manual, and it shifts 1st and third gears.  In 5th, where the unit jams, it should be in a straight section of the rightmost groove in the cam.  The "C" fork is Fork 2, and that's the one that shifts 4th and 5th by shuffling the 3rd pinion to the left for 4th, then to the right for 5th, with the fork follower pin in roughly the position marked in the picture showing the underside of the cam.

I mentioned shaft end play before.  Once assembled, there should be no more than bearing end play in the output shaft.  Sitting in the case as shown, the output shaft will be out of position to the right by a significant amount.  The main shaft will have a little more play; bearing play plus a small amount of clearance between the clutch boss thrust washer and the clutch basket starter gear.  Maybe .015" or so.  The shift cam end play is controlled by the right side cam bearing.  The cam should be solidly clamped to that bearing by the segment when it's bolted in place.

The assembly looks correct from here otherwise. 

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ok, so there might be a little confusion, the trans upshifts fine but it not only jams in 5th it jams whenever you want to downshift if I shift from neutral to second it will not downshift. It will not downshift at all in any gear.  I'm going to install the trans into the left case and make sure the output shaft is in the proper position and try to down shift, I think this will isolate the cases. If it down shifts with the trans in the left side case I'll know it's the cases.  The thing I don't get is that this bike ran fine until it came apart. I'm just concerned the I bought a junk set of cases and that's the problem.

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It's never going to shift correctly stacked in one case only regardless which one it is.  There isn't enough support for the cam, the rails, or either shaft without both cases in place and the segment, clutch and front sprocket all in place. 

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I figured that, I'll have some time this weekend to put it together and try again.  I haven't had it together since I cleaned out one of the fork bores, hopefully that did it.  Are there any fork thickness specs I can get.  My other concern is what if one or more of the forks were bent/twisted when the thing came apart?  Is there anyway to tell?

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Found it, damn it!  So I decided to put the trans back in the old cases to see if it would shift in the old cases, it shifted up and down effortlessly.  I then stripped the cases down and compared them side by side to see if I may have put a bearing in wrong or not flush.  Everything was exactly like the original case.  So at that point I thought the cases I bought were bad.  Upon further inspection I found that one of the shift fork bores was not a through hole just like the original case.  Pics attached.  I drilled the bore out and voila it shifts.  I'm a little concerned that if that was different the what else could be different but at this point I'm going to put it back together and hope for the best, if it comes apart again I'll have to buy new cases, but I'm going to take a chance. 

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Thank you VERY much for all your help it was Greatly appreciated. I apologize for the frustration I gave you , but this was a good one.  Again thanks for your help.

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The only frustration was in not being able to come up with a solid answer for you.  This was one of those really oddball things that's much easier to put a finger on with the parts right in front of you, and in that sense, I was working somewhat blind.  Good find on your part.  It's probably an issue that resulted from the use of a pair of cases made for a different year model having a minor revision made to it, and having a differing part number in the last two or four digits only.  Shows you the kind of trouble you can get into by assuming look-alike parts will automatically interchange. 

Get it back together and have some fun with it.

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