Yanmar Powershift Will Not Shift

Yanmar PowerShift transmissions are extremely reliable but, just like anything mechanical, will eventually need service. The most common cause of failure is that the transmission will just not move when shifting or seems to go into the wrong gear. 

So what causes this problem? The most likely cause is also the easiest fix in this case. The shift linkage starts to wear over the years and starts to get a little sloppy. When you

combine sloppy linkage with a metal shift gate like Yanmar uses on most of their tractors, you can develop a situation where the shifter handle hits the shifter gate before the valve has fully switched into gear.  This is most obvious in reverse since you can not shift beyond the reverse position but can happen just as easily in the forward gears also.  To troubleshoot, try removing the shifter guide and see if the tractor shifts normally when you can move the lever a little farther.  If so, the fix involves removing the shifter linkages and replacing any wore out pins or bushings. You can also adjust or elongate the shift gates with a rotary grinder if you are in a hurry but that is not really a good fix. 

Another problem that can develop is the teflon seals on the main powershift shaft can start to leak. The common symptom of this failure is a transmission that feels like it is trying to go in two gears at once (binding) or starts to move in reverse when shifting forward or the other way around. Leaky teflon seals can often be the cause.

Your main powershift clutch shaft is a large shaft with several holes bored into it lengthwise and those holes terminate at different positions along the shaft. These holes direct pressurized oil into different clutch packs which cause different gears to engage. 

The front end of this shaft goes into a valve body where several (usually 5) teflon seals direct the oil into the correct passages depending on where your shifter handle is positioned. As those seals start to wear, they will start to spill that pressurized oil out into different passages which causes the wrong clutch packs to try to engage.

So what is the fix? Unfortunately, those teflon seals will need to be replaced. The job requires splitting the tractor just as you would a clutch replacement. The valve body is right there in the bellhousing and, actually, pretty easy to get to. New teflon rings will need to be installed and you should be good to go for another 40+ years. 

Feel free to contact us if you have any questions or problems! Our technical support is always free.