GasGas 04 TXT280 Pro Transmission Problem

I lost my chain today(no Excuse for this) as I bottomed the suspension in the dip at the bottom of the incline. The engine reved a bit as I heard some unpleasant noises when the chain was wrapping the front sprocket then it instantly killed the engine. We dislodged the chain by removing the flywheel cover- no external case damage. Reinstalled the chain, cranked the motor, there is now a noise that sounds like a piece of metal bouncing around inside the cases. It will shift into 1st but I shut it down due to the pinging sound. I have not started taking it apart yet & have heard these motors are "different",until now I have never had any other major issues with this bike If anyone has any tips on what I could expect, I would appreciate it,thank you

this sounds vaugly familiar... slightly diffrent cause of the chain jam, same end result. sorry dude, but your gonna have to split the cases. for me, stripped half the teeth off first gear. catch is first gear on the side i stripped is part of the main shaft. was north of 3 franklins. Now, sounds like u didn't go as far as i did with it, it locked my engine, but my guess is you broke some teeth off.

As to them being diffrent, the beta was fine to tear apart. just take your time and pay attention.

Start out by taking the clutch cover off, and then removing the clutch assembly and it's basket. At that point you may be able to see if there's any metal fragments on that side of the engine.

In any case, it sounds as though you're going to be splitting the cases. No use trying to find a way around it, something isn't right. Trying to find the easy way out will likely only cost you more $$$ due to continuous damage from something floating around inside the transmission.

If you or a friend have a decent technical background, it's not that big a deal. Just takes notes as you slowly dissasemble the engine, better yet, take pictures as a reference. You will need to obtain the torque specs for a number of items for reassembly. Also, clean everything 110% before reasssembly. It makes it a lot easier to work on something when it's not covered with a film of dirty oil.

Just another note....not sure how many hours are on your bikes engine. While you have it apart, you may want to treat the engine to a fresh set of crankhaft end bearings and seals. If $$$ is an issue (when isn't it) you don't necessarily have to do this, it's just worthwhile since you're that far into it.....

Will the bike shift through the gears when just sitting on the stand? - note- you have to lightly rotate the rear tire as you try to shift it.

If the bike shifts OK - check top end. (I wasnt clear from your description this was definate a tranny noise)

If the bike doesnt shift through ALL 6 gears and back like it should, you may have damaged the internals (gears/forks/rollers) OR maybe as simple as just broke the fused link on the end of the shift shaft (under the clutch ) - see video for clarity.

Here's a link that has videos of how to repair your transmission. Commit them to memory - as they are invaluable. The pro is actually very easy to work on, so if your mechanical, you'll do fine with the aid of the video. Word of advice, Nothing needs to be forced - Ever!

I seem to remember reading that there was a fairly common transmission issue specifically with the early pros, but when you get inside the cases of any of the modern bikes it's amazing how small everything in the gearbox is.

You might want to call Lewisport and see if he might be of some help.


Common problem with early Pro's...You have a bent shift shaft/shift fork assembly. Miike @ the tryals shop can repair it . I have done many of these and the process is easy but you need a good knowledge of the bike and its special features to repair.......Good Luck

I know a guy who's '04 has two 3rd gears and no 4th. Fun fact of the day!

I know a guy who's '04 has two 3rd gears and no 4th. Fun fact of the day!

how does that work? if the trans is anything like the beta, some of the gears are sorta a two in one deal, and fitting something like that wouldn't happen.

I have no clue, but he wins almost every NE event that he enters.

I have no clue, but he wins almost every NE event that he enters.

wow! did it come from the factory that way as a screw up or did he do it?

Don't know if it was the factory or the friend that he bought it from, but it definitely wasn't him....

kinda a funny thing to do... just goes to show it's all about the rider, not the bike.

Yep, this is the same guy that competes in jeans, workboots, and a bicycle helmet...

bicycle helmet? they allow that?

Fine, I don't remember if he competed in it. But that's all he practices in.

wow... They say with like motocross and whatnot it's 90% rider 10% bike, i think with trials it's closer to 99%... that 1% bike won't really matter.

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