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2000 400EX 3rd gear problem

859 Views 19 Replies 2 Participants Last post by  Here 2 help
I have a 2000 400EX that runs great but will not go into third gear. Its been like this since I bought it a few months ago. All other gears work fine, chain and sprockets are in good shape and adjusted per the manual. I've tried some clutch adjustment but it makes no difference.

When I shift from second to third I let off the throttle, pull the clutch in, lift my foot on the shifter and hold, and let the clutch out. As soon as I let the clutch lever out, even if I do it slow, the shift lever pops down on my foot and it sounds like it goes into neutral then back into second gear.

I've done some research and it seems like either the fork is bent or the third gear dogs on the gear are worn/ damaged. I was going to pull the side cover and inspect the clutch and the star behind the clutch for damage. I've read that these can cause the problem too but I'm doubtful. If I remove the side cover will I need to replace the gasket? Use honda only gasket?

If I pull the engine and split the case, what will I need minimum to change regardless of what I find wrong with the transmission?

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Minimum 8 and 12 in the first breakdown and 3 in the second pic - it's possible the shift drum will be damaged also (# 5) - You will be best off to get a complete used engine if you can get one in good condition.

Product Font Auto part Diagram Engineering

Font Auto part Art Line art Drawing

HO24231-KCY-670 fork, l. gearshift 74.07222.21
no return
HO24300-HN1-000 DISCONTINUED: drum, gearshift 00.00
no return
HO23451-HN1-000 gear (28t) 88.9388.93
no return
HO23471-HN1-000 DISCONTINUED: gear (26t) 00.00
no return
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Thanks for the reply, I have a few of your post saved explaining how the trans works with every gear and the part numbers for each. Looks like a complete honda gasket set is about $50 + what ever I find bad in the trans.

I read somewhere about having the dogs machined if they are just rounded off. Is that possible?
Yes, a good machinist can renew the surface of the dogs if they are rounded from improper shifting and poor engagement - typically the dogs only engage about 30% of their total depth - renewing the engagement surface will weaken the gear slightly and increase backlash, but it will salvage the part and extend the serviceable life of the vehicle.
Finally got time to dig into it. Here is a picture of the gear, is that considered rounded?


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Yes, that is rounded and the shift fork is most likely damaged also - in severe cases the shift drum is damaged also.
I'll get pics of the fork this afternoon. I might see if a machine shop can fix the gears. Is worth asking if they can under cut them a few degrees? I only trail ride and the engine is stock.
We used to under cut the gears in Kawasaki 900 drag race motors so they would pull themselves into gear, but it was at the cost of making the gears a bit more difficult to up shift, so we used air powered shifters and shifted with a push button. I suggest cutting only the engagement face on both gears and only to the extent of removing the rounding (probably .020 to .040 inch - machinist will be the final judge of that)
Is there a way to get the dogs to engage more then 30%?
Is there a way to get the dogs to engage more then 30%?
Have the shift drum slot welded up and the slot re-machined to move the shift fork the desired distance for the depth of engagement.
Fork is shot, other two look perfect, no marks. Lucky the fork is still available.

Hand tool Tool Wood Handgun holster Knife

Wood Hardwood Wood stain Font Metal
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The fork is worn like that from the fork trying to hold the two gears in engagement while the rounded edges of the dogs were trying to push apart and applying pressure to the fork.
I'm going to check the bushings and snap rings tonight and then order a new fork and see if I can get the gears machined, if not I'll have to try and find good used gears.
I installed everything back into the case half.
Crankset Automotive tire Gear Bicycle part Bottle

I'm surprised it doesn't work... looks like more than 30% engagement.
Product Automotive tire Black Font Engineering
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How much movement is in the gear and shift fork? In the pic, everything is at the engagement extreme - what is the position of the parts at the opposite extreme? Remember, the transmission does not operate on it's side and there is play in in the shift drum, shift fork, gear and the shaft's the gears are carried on. A bad bearing in the engine case will contribute to jumping out of gear.
I had the same thought last night and started checking the engine case bearings and the fork shaft. They all seem ok, even the shift drum seem ok. Last night I ordered a new honda shift fork and the number 10 bushing that goes into the number 8 gear just in case the bushing is worn. I'm dropping the gears off at the machine shop today to have the dogs machined.

While holding the two gears in my hands and turning them in the direction that the dogs are rounded off I could easly get them to slip. I then turned them the opposite way in the direction that the dogs are still square and they hold. Granted this is me just holding the gears but I could see how that little bit of rounding really makes it easier to slip.
Sounds like you have a pretty good grasp on how the transmission works - I think you will get it repaired satisfactorily.
Update: The machine shop is backed up and can't get me my gears for a while so I bought some used ones. I cleaned everything and installed the used gears and new fork and bushing. I've only driven around the yard for a few minutes and it seems fine, goes into all the gears and is smooth. While I had it apart I cleaned and lapped the valves and add new stem seals. I also did a light hone on the cylinder, everything else checked out. I changed all the gaskets and oil seals, replaced the swing arm bolt and bearings too. Hopefully going for the first ride of the season this weekend, thanks for the help.
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