[Here 2 help]

It's nearly impossible to identify which gear it's off of without taking the transmission apart, but gear #4 (mainshaft 2nd gear) is the most frequently damaged and failed gear in the entire tranny. If a replacement is found, gear #5 needs to be replaced also.

All the parts with $0.00 prices are no longer available

REF. NO.​	PART NO. / DESCRIPTION​	dealerorders.com's PRICE​	TRX400EX A9 A​
​

1​	23211-HN1-000 MAINSHAFT, TRANSMISSION (12T) ​	137.38​	1​
​

2​	23220-HN1-000 COUNTERSHAFT, TRANSMISSION ​	0.00​	1​
​

3​	23411-HN1-000 GEAR, COUNTERSHAFT LOW (35T) ​	0.00​	1​
​

4​	23421-HN1-000 GEAR, MAINSHAFT SECOND (16T) ​	0.00​	1​
​

5​	23431-HN1-000 GEAR, COUNTERSHAFT SECOND (31T) ​	0.00​	1​
​

6​	23432-HM3-670 BUSH (22X25X10) ​	11.04​	1​
​

7​	23441-HN1-000 GEAR, MAINSHAFT THIRD (19T) ​	0.00​	1​
​

8​	23451-HN1-000 GEAR, COUNTERSHAFT THIRD (28T) ​	0.00​	1​
​

9​	23452-HC0-000 BUSH, COUNTERSHAFT THIRD ​	17.78​	1​
​

10​	23452-KCY-670 BUSH, COUNTERSHAFT THIRD ​	14.09​	1​
​

11​	23461-HN1-000 GEAR, MAINSHAFT FOURTH (22T) ​	78.74​	1​
​

12​	23471-HN1-000 GEAR, COUNTERSHAFT FOURTH (26T) ​	0.00​	1​
​

13​	23481-HN1-000 GEAR, MAINSHAFT FIFTH (26T) ​	0.00​	1​
​

14​	23491-HN1-000 GEAR, COUNTERSHAFT FIFTH (26T) ​	0.00​	1​
​

15​	23502-KA2-000 BUSH (20MM) ​	25.38​	1​
​

16​	23512-KEA-000 COLLAR, SPLINE (22X14) ​	19.16​	1​
​

17​	23521-KCY-670 PLATE, BEARING SETTING ​	12.31​	1​
​

18​	23801-HN1-000 SPROCKET, DRIVE (15T) ​	0.00​	1​
​

19​	23802-KAE-870 PLATE, FIXING ​	4.62​	1​
​

20​	90001-MA2-770 BOLT, SOCKET (6X16) ​	3.31​	2​
​

21​	90118-958-003 BOLT, FLANGE (6X12) ​	3.22​	2​
​

22​	90451-KY1-000 WASHER, SPLINE (22MM) ​	3.80​	2​
​

23​	90451-KY2-000 WASHER, SPLINE (25X31X1.5) ​	3.80​	1​
​

24​	90454-KF0-000 WASHER, THRUST (17MM) ​	4.36​	2​
​

25​	90454-428-000 WASHER, THRUST (20MM) ​	2.40​	1​
​

26​	90455-ML7-000 WASHER B, THRUST (22MM) (BLUE) ​	4.84​	1​
​

27​	90456-MA6-000 WASHER, THRUST (25MM) ​	2.40​	3​
​

28​	90601-107-000 CIRCLIP (25MM) ​	3.71​	1​
​

29​	90601-329-000 CIRCLIP (22MM) ​	2.42​	2​
​

30​	91003-KCY-671 BEARING, BALL (25X52X13) ​	0.00​	1​
​

31​	91004-KN5-671 BEARING, RADIAL BALL (17X44X12) ​	0.00​	1​
​

32​	91005-KF0-008 BEARING, RADIAL BALL (62/22) ​	38.87​	1​
​

32​	91005-KS4-003 BEARING, RADIAL BALL (62/22) ​	38.87​	1​
​

33​	91008-KN5-671 BEARING (6203) ​	0.00​	1​
​

33​	91053-HB3-771 BEARING, RADIAL BALL (6203) ​	0.00​	1​
​

34​	91203-KCY-671 OIL SEAL (25X35X5) ​	7.11​	1​
​

35​

91204-HN1-003 OIL SEAL (17X34X4.5) ​

4.22​

1​

Also, how bad would it be to take it on one trail ride before fixing?
The worst that can happen is it will break and lock up the transmission, but it's not fixable if you take it apart, so take your chances - it's junk either way.

 

[Here 2 help]

Yes and used parts are almost gone too - the 99-04 TRX400EX is a relic - if you take it apart and can't get the parts you need, you can try to part it out, but don't expect much. Try to sell it as is and let the next guy find out what problem it has. If you are lucky a noob will buy it for 2 grand and you can get an o6 or newer, they will still be around for awhile. If it's special to you because of mods and performance parts, get a newer one and swap the special parts then sell the relic.

The truth hurts, but like Windows ME, XP and 7, the 99-04 TRX400EX is no longer supported by Honda and it's time to upgrade.

 

[Here 2 help]

Just be cautious of the used trannys - I have one - it's missing #4 - I sold #4 for $150 and it was perfect - I would sell the rest of the transmission for $100 - if you take it apart, maybe you will get lucky and it will not be $4