Letting go of drive at full power

[Mossbo]

On my 2019 Thundercat there is a strange thing happening.
It feels like someone is putting it into neutral gear, it happens absolutely nothing. Like loosing the belt but no mess.
No bad sound from anything, jut lets go.
After stopping and restart it is fine again!
Happens when pushing really hard, at full throttle and not at short pulls but when you have been very aggressive for some miles.
Sled is tuned and is working perfect otherwise, but has rather bad clutching, with too high rpms at wot.

What can cause this strange behaviour?

I have info from previous owner that it has happened earlier as well a couple of times, but I am using it to the full and putting a bit more pressure on things perhaps...

 

[1nc 2000]

Top gear bushing in chaincase is shot.
Lots of reading on here about it.
The aftermarket has a fix for it.

 

[sideshowBob]

As stated it sounds like the top gear bushing issue or assembly problem in the chaincase.
Otherwise we will need more information.
-what companies tune does the sled have
-are you using a stock belt
-is the belt new and in good shape.
-when you say its letting go does the engine quit running or does it just free rev suddenly
-what clutching components and setup are you using
-have you removed the primary clutch and reinstall ensuring it is tightened/torqued to factory specs

 

[Fords4life]

I would look into the chaincase, had this happen to me some years back, bushing out of upper gear, this causes fork pads to break ect.. amoung other things getting destroid.

 

[Mossbo]

As stated it sounds like the top gear bushing issue or assembly problem in the chaincase.
Otherwise we will need more information.
-what companies tune does the sled have
-are you using a stock belt
-is the belt new and in good shape.
-when you say its letting go does the engine quit running or does it just free rev suddenly
-what clutching components and setup are you using
-have you removed the primary clutch and reinstall ensuring it is tightened/torqued to factory specs

It has Maptune with 275hp, hoses, bov, muffler, intake etc, stock belt, stock gears etc., and sled has only 2000km on it and is in new condition otherwise.
Clutch setup is not perfect at all, way too mild setup for the power it makes. Ordered some upgraded stuff for both clutches.
Primary is probably never removed, and it still has stock weights it seems...and a soft spring.

Engine is just free rev all of a sudden, no problems, just does not grip the track at all. Like neutral came in if there were any.
After restart your good to go again!
Feels like chain case but I have been around on other sleds, and normally you hear or feel something is bad.

 

[Mossbo]

I would look into the chaincase, had this happen to me some years back, bushing out of upper gear, this causes fork pads to break ect.. amoung other things getting destroid.

Should the reverse and normal drive work after this braking? I would think it should be a mess inside the chaincase!

 

[sideshowBob]

I would start with a chain case disassembly and inspection.
If everything in the chain case is good I would then inspect and properly calibrate your clutches for your tune.
I have seen where secondary clutches will open too far at full shift out and allow the belt to dop down too far in the clutch and lose its grip. That would only happen at very high speed when the clutches "over shift" and is not normally an issue with stock clutches

 

[Mossbo]

I would start with a chain case disassembly and inspection.
If everything in the chain case is good I would then inspect and properly calibrate your clutches for your tune.
I have seen where secondary clutches will open too far at full shift out and allow the belt to dop down too far in the clutch and lose its grip. That would only happen at very high speed when the clutches "over shift" and is not normally an issue with stock clutches

That can be the case here!, would explain why it goes back to normal after restarting at stand still.
I have in mind that the old 1100T Cat with Suzuki had some limiter on the movement in the secondary.

 

[DMCTurbo]

Top gear bushing

 

[Fords4life]

Reverse still worked excellant after having no forward drive, also no noise before hand, had to drive mine backwards for 16 miles back to trailer.

 

[REDLINE 1]

Reverse still worked excellant after having no forward drive, also no noise before hand, had to drive mine backwards for 16 miles back to trailer.

Wow that sucks! Nobody with a tow rope to tow u back?

 

[Fords4life]

Nope by myself end of season in the Big Horns, stood on running broards facing the rear of sled with arms behind me, was pretty twitchy could only go about 3mph so i stoped and pulled wear rods off which made it way better could then travel 10mph with out twitch...lol, dont care to do that again!!

 

[Fleecer]

Nope by myself end of season in the Big Horns, stood on running broards facing the rear of sled with arms behind me, was pretty twitchy could only go about 3mph so i stoped and pulled wear rods off which made it way better could then travel 10mph with out twitch...lol, dont care to do that again!!

Haha....happened to me too, first year on the winder, middle of the night at -15F. Drove for miles in reverse, got mired in a drift 1.5 miles from home. Had to walk.

Rented a sled the next day to rescue mine. Sank it outta sight trying to pull mine out of that drift.....walked home again. Got a shovel, walked back, dug them both out, and finally pulled it home. Once home and thoroughly pissed off, I got undressed, as I soaking wet from sweat.

Wife says, Hey.....that's quite a machine you bought there. By the end of winter.....you'll be in top physical condition!!

 

[Mossbo]

Top gear bushing

Would that be possible if the sled works just fine at all other times then when it is almost (or fully) outshifted clutches?, was thinking it must make some kind of noice or issues with changing back and forth into reverse? Only happens over 100mph.
Asking as I am in mountains without too much possibility to get spares soon...

 

[Fords4life]

Would that be possible if the sled works just fine at all other times then when it is almost (or fully) outshifted clutches?, was thinking it must make some kind of noice or issues with changing back and forth into reverse? Only happens over 100mph.
Asking as I am in mountains without too much possibility to get spares soon...

Not hard at all to pull the chaincase cover and look gasket is reusable just dont use carb or brake cleaner on gasket ad it can cause it to swell, had my upper gear fail in lrss than 1200 miles.