Clunking in driveline under acceleration!!!

[hookedonblue]

Hey everyone, HAPPY NEW YEAR!!! Hope everyone has a great 2017 ****************
I'm asking this question for a buddy of mine
His 2009 Venture Miltipurpose has a severe clunking noise while accelerating forward under strain. I don't think it occurres on light to moderate throttle.
When he places the back of the machine on a hoist, and accelerates sled up to speed, there is no noise or clunking noticeable at all...
I'm sure someone has experienced this before and there's likely a post on this topic somewhere but I was unable to find it.
Any help or direction will be greatly appreciated...thanks guys
Hookedonblue

 

[maim]

is it from a dead stop?

 

[hookedonblue]

is it from a dead stop?

Yes it is. It's like a gear clunk. As though it's in and out of gear. But when rear of sled is hoisted up, I can spin the track up to any speed and no clunk. So it's only happening under strain.

 

[Mooseman]

Does reverse work? Reason I ask is because this possibly is a problem with the reverse gear box. My son's 09 Phazer had the same issue. It almost sounds like an impact gun. It's a very distinct type of noise. The dog gears inside weren't engaging properly and it wasn't the servo. It got so bad it would hardly move. We wound up replacing the gear box.

 

[hookedonblue]

Does reverse work? Reason I ask is because this possibly is a problem with the reverse gear box. My son's 09 Phazer had the same issue. It almost sounds like an impact gun. It's a very distinct type of noise. The dog gears inside weren't engaging properly and it wasn't the servo. It got so bad it would hardly move. We wound up replacing the gear box.

Yes it goes in reverse fine.

 

[Mooseman]

Did you check the drive chain adjustment? Check for metal in the oil.