2014 Bennche 700 EFI crew reverse problem

[Lyonel Geary]

When I try to back up a hill, belt squeals and engine surges.  Will not back up.  Never have any problem going forward on the steepest hills.  Have seen this problem posted before but, never an answer. 

[Dan W.]

Did you ever figure your reverse problem? I have the same problem now one knows. Thanks Dan Wuchina.

[Dan W.]

On 6/20/2020 at 3:09 PM, Lyonel Geary said:

When I try to back up a hill, belt squeals and engine surges.  Will not back up.  Never have any problem going forward on the steepest hills.  Have seen this problem posted before but, never an answer. 

I have the same problem did you figure it out. No one can send anything that makes any sense.

[Lyonel Geary]

I have not solved this problem. I'm surprised no one has responded. 

[cliffyk]

My first thought when I read "belt squeals": is that the rubber band in the CVT is severely glazed-that's the only thing in there that can "squeal"--if the belts looks good I'd pull apart the variator (drive pulley--often and  quite incorrectly called the "primary clutch")) and torque multiplier (driven pulley--often an d quite incorrectly called the "secondary clutch") and make sure all components in same meet their specs (primarily the roller weights in the variator; and spring, torque cam and cam followers in the multiplier.

Though I really don't understand why such problems would be unique to reverse gear.

 

 

 

[cliffyk]

Just had a thought, reverse is generally a lower"gear"  (a numerically higher ratio) than any forward gear--that means for any given vehicle load less torque being transmitted through the CVT. That lower torque requirement could show itself if a jammed up movable pulley face in the torque multiplier is also present,

The spiral slots in the outer (movable) pulley hub are the Torque multiplier cams--the  pins (p/n 5) are the cam followers)

The torque spring (p/n 3) forces the pulley faces together, working against transmitted torque to keep the driven pulley effective diameter large and the variator (drive pulley) working diameter smaller (I.e. a "lower gear)--this happens while the variator centrifugal weights are also trying to make the variator pulley effective diameter larger. This battle between the two is part of what determines the overall CVT ratio.

However when torque needed to accelerate the vehicle reaches a certain level the belt slips on the inner (fixed) driven pulley face but not on the movable face causing the outer pulley half  to try rotate--if it can rotate  the torque multiplier cam and its followers work with the spring to force the driven pulley faces further together to further increase its effective diameter (if not already closed completely) and thereby forcing the variator face apart decreasing its effective diameter--temporarily forcing a lower yet over all ratio until yet another equilibrium is struck. when vehicle torque demand falls off. This is why the assembly is called the "torque multiplier".

If the outer multiplier pulley was jammed on its shaft unable to rotate and effect pitch diameter , a lower torque demand (as in reverse gear) could cause the belt to effectively loosen, slip in both sheaves ,  and squeal.

110% speculation, but its been 8-9 months, what else do we have?  And I would bet "dollars-to-donuts" it's a CVT issue.

Not sure I explained this fully or sufficiently clearly, if anyone has questions or comments let 'em fly...

 

[Dan W.]

Thank you