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Discussion Starter · #1 ·
I have a 2003 400ex (only owner). I had a problem with my transmission, when in 3rd gear transmission slipped and was it was hard to change gear after.

I put a brand new clutch, I disassembled everything and I placed new forks, made sure i could shift through all the gears (engine removed) and then I put everything back.

Problem is still there, there was a little clicking sound in 1st and 2nd and then it stuck in 3rd. It is now not possible to change the gears, shifter is stiff, I have to remove the engine again.
Do you have an idea what could cause this and if I should replace pretty much every transmission component or just some of the parts.
Thank you for the help !
 

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The transmission, for all it's complexity is pretty simple, but precision is required during assembly.

First question: where did you get the gasket that goes between the crankcase halves? The thickness of the gasket is critical for proper clearances.

How well do you understand the operation of the transmission?

Using the two pics below let me explain a couple of things - in the first pic, it details the position and orientation of the shap rings and thrust washers. Correct assembly is critical.

The second pic is the actual breakdown of the transmission - continued bleow
Font Parallel Diagram Auto part Music


Product Font Auto part Diagram Engineering

#1 is low gear, #4 is second, #7 is third, #11 is fourth and #13 is fifth
1st is made by moving #12 into #3
2nd is made by moving #14 into #5
3rd is made by moving #12 into #8
4th is made by moving #7 into #11
5th is made by moving #7 into #13

If you notice; gear 1 (low gear) is cut directly into the input shaft - the gear it mates with is #3 - #3 is spinning freely on the output shaft - when gear #12 (splined to the output shaft) engages with #3, power is transmitted from 1 to 3 to 12 and the output shaft turns.
Second gear #4 is splined to the input shaft and is meshed with #5 on the output shaft - #5 is spinning freely - when gear #14 (splined to the output shaft) is moved into gear #5, power is transmitted from #4 to #5 to #14 and the output shaft turns.
Third gear is #7, splined to the input shaft and enmeshed with #8 (freewheeling on the output shaft) - when gear #12 (splined to the out put shaft) engages with #8, power is transmitted from #7 to #8 to #12 and the output shaft turns.

Since your problem is third and the shifter won't move, I'm going to skip 4th and 5th.

For the shifter to not want to move gear #12, the problem has to be on the output shaft - possibilities include the RH shift fork, shift fork shaft, the shift drum or gear #8. If the shim #23 is on the wrong side of gear #8 or the shim #27 is incorrectly positioned, or the RH shift fork is bent, or the shift fork shaft is bent or the shift drum is damaged (has a dent where the pin on the shift fork rides in the slot of the drum and does not want to come out of the indentation) or a remote possibility the shift shaft has a broken spring or another problem and is not engaging the shift drum.

Unfortunately, every possibility pretty much requires complete engine disassembly to correct.
 
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