Rear Shock Issues

[nate450x]

Well, my wife has always told me i am hard on stuff but this is rediculous. Went riding sunday at my buddies mx track like i do every weekend (unless there's a race) took a few wam up laps to get loose and then hit it hard. On the second lap i came around and cleared the 70' table top but when i landed i noticed something was very wrong. Looked back and my rear tires were against the fenders. Come to find out i had busted the shock shaft in half!!!! So when it landed and bottomed out (broke the shaft) it also took out my air box, bent my brand new (one week old) Motoworks Full Exhaust, busted out the battery box, bent the axle and the sub frame!!!! Im not sure but my dealer is doing everything they can to get it warranteed since i have the extended service but we will see. Has anyone else heard of this or am i the only one? What a crazy day!!!! will have some pics soon!!!

[ratsracung6]

Austin Wilson was telling us about this the shock hits the frame
when you bottom out completely. You have to file down the frame
a little to avoid it. Its pretty easy to do take a ratchet strap and
compress the shock all the way down, and you will see were it
hits file it down there a little at a time untill it dont hit any more.
We did ours have not had any problems with it.

[craigmacphee]

just so I got this right.....file down the frame at the top of the rear shock? I am a heavier rider and bottom out quite a bit. I certainly do NOT want this sort of thing to happen to me. Thanks in advance for your reply. Craig

[ratsracung6]

Well he told us some of the riders were breaking shocks in half
so we looked at ours and it was hitting so we filed it down.
I dont know if its a problem on all of them, it would probably be
a good idea to check it anyway.


Scott

[X400EX]

I'm not sure to understand, do you have any pics?

[Aussie_YFZ450]

Nate, is this on an 08 or 09MX?

The 08's had a very small shaft, which is quite a bit weaker than the 09

[ratsracung6]

Originally posted by X400EX
I'm not sure to understand, do you have any pics?



I dont have any pics Ill see if I can get some if I can get a camera
in there to take a pic.

[nate450x]

Yes Aussie it is an 08' and it has been a great quad until this happened. Do you know if all of the 09's have lager shafts or is it just the MX version. I have really been considering selling my 08'X so i can buy the new 450MX but i will probably lose my a** trying to get rid of it. I want to race this year but if things like this keep happening i won't be doing anything!!!!

[Aussie_YFZ450]

Its only the MX that has the larger shock, but if you can pick up a shock it will fit straight into your 08....

[yfzracer14]

hit about a 70' tripple at a race yesterday, broke my shaft in half also

[blaster99]

Someone need to post pictures on where to grind down the frame.

[mhill157]

Guys just take a ratchet strap and wrap it around your swing arm and your grab bar and start ratcheting you will see where it hits. I have the '09 mx shock and it barely hits but it does. Tried to take a picture but it is in a horrible place. When I get my motor out I will try to get better pictures.

[TNT]

I really don’t think the grinding is what is causing the shafts to break on 08’s. The only way that can happen is if it somehow restricts or binds shock rotation. Sounds like for the 08’s the shock shaft is under sized and it’s only a matter of time before they fail. The upper shock body grinding on the frame is not good for the shock, but in this application it would not cause the shaft to fail since it is right next to a pin and clevis or upper shock bolt that takes a lot of load. It could impose a small bending moment on the shock shaft from this location when fully compressed but probably not enough to break it. What’s happening is a larger bending moment is occurring in the middle of the shaft when it is extended as the swing arm travels up there is a component force from the tires that gets reacted into the swing arm bolt and frame, a portion of this load travels up the shock shaft to be dampened out. Well someone screwed up when they sized the diameter or cross-section of the steel shaft to take this load so it fails in shear, in 09 they sized it up. MX sees larger travel and greater bending moments than XC so it's larger shaft; in XC we see more fatigue and cyclic loading.

We run PEPs, an after market shock for heavy MX is probably good and be sure the shock is valved and set up correctly for your weight.

[jlrenken]

well i found y my 08 shock bent. and i suppose it could have broke but i got lucky. u need to check where the linkage where there are two grease zerks and the only place that doesnt have one is where the bottom of the shock goes and i was told u need to clean it once and awhile. when i took it apart it was pretty rusty. i would say that migt have been the prob. let us know
thanks

[Foxstar45]

I have an '08 DS with an '09 MX shock set up. Does all this affect me?

[Aussie_YFZ450]

no, the 09 has a thicker 16mm shaft...its alot stronger