I have a scrambler 400 and during hard accelleration there is a multiple clunking noise and as soon as I back off it stops.
in reverse there is no issue it lights em up even does good in Fwd until you hit hard or use dry pavement.

here is what I have done so far.
shift linkage was loose when I picked it up, I tighten it, the nut on the shift arm was what was loose.
new/check drive chain and sprockets. rear spocket and chain were in spec, trans output sprocket was replaced
new belt
new secondary clutch buttons " they were shot"
checked the freeplay on the trans chain "hardly any"

 

I remember your last post on the subject.

Like i said I think the chain slaps the bottom of the swing arm at times.
There is a wear pad that the chain rides on at times.


Jim

 

Have the same problem on the Boss. Just lube your chain up real good when it happens.

 

I been told on some forums the trans chain could be the problem. SO I DID THIS TEST
I put the bumper up against the side of the garage, put in foward and hit the gas, NO NOISE
just 2 big holes where the Lawn used to be. Could it still be the trans chain? seems under that kind of load it would have certainly skipped.
I do have a aluminum Skid plate on the swing arm.
trans oil was changed and no metal was found.

 

Before you do anything just try doing what I said. Totally cover your chain in lube. It worked for my Boss. It can't hurt to try it on yours right?[img]i/expressions/face-icon-small-wink.gif[/img]

 

I think its in the tranny , either a drive dog or the chain, I have the cover off both side to see whats going on and the final drive chain is fine.
no metal in the trans oil.
I can pull a wheelie and soon as it starts coming up I heard this grrr and I seem to loose my wheelie, front end comes down noise goes away
and it takes off quickly

 

It did the same thing on my Sport 400. It was the silent chain in the tranny. It was about $30 and i did it myself. Not to hard of a job but it fixed the problem.

Good luck.

 

You might want to check rear spocket, even though you said it was within spec if teeth are worn on tips in one direction chain could jump going forward and not backward. I had this problem on my explorer and changed both sprockets and chain and added chain guard to guide chain along the swingarm. Also might want to check swingarm bushings.

 

i think its the swing arm bushings lift the quad off the ground and see if the rear swings from side to side if it does then your swing arm is shifting to one side under acceleration and letting your chain grind the teeth on your sprocket...

 

thanks guys for the advice , I pulled the tranny and the chain is whooped, after changing the fluid a week ago , the magnet was already covered with fillings, upper gear might need replacement too.
thanks for all the help,