B7100 3 point hydraulics drift down.

[AdamB7100]

Hello,
I recently purchased an old B7100 gear drive and am in the process of getting it back in shape. The rear 3 point hydraulics will lift but then will drift right back down. Any thoughts on where i should start looking?
Thanks!

 

[Dave_eng]

Hello,
I recently purchased an old B7100 gear drive and am in the process of getting it back in shape. The rear 3 point hydraulics will lift but then will drift right back down. Any thoughts on where i should start looking?
Thanks!

A suggestion to narrow down where the leakage is occurring.

Adjust the Lowering Speed Adjustment to the slowest setting which likely will be to lock the lift arms up.

If the arms still leak down at too fast a rate then the piston seal is the problem.

A useeful WSM can be found at this site.

Look for the 3 part manual covering B5100-6100 7100

Kubotabooks.com

Daave

 

[AdamB7100]

Thanks for the reply. I did try that already and the 3 point still dropped down right away. I removed the control valve and inspected. It looks good as far as scratches or wear but there is no O-ring present on the spool. Should there be?

 

[Dave_eng]

Thanks for the reply. I did try that already and the 3 point still dropped down right away. I removed the control valve and inspected. It looks good as far as scratches or wear but there is no O-ring present on the spool. Should there be?

If the arms still dropped with the lowering speed adjustment all the way, then you can rule out the valve.

O rings seals on the lift piston are likely old and cracked from old age.

Read the caution in the Fig 102 paragraph about some models only having an o ring but others also have a sealing ring.

Dave

 

[AdamB7100]

The spool that I took apart is linked to the lift/lower lever. It is not shown in the photo you sent. Is the one you show in the picture something I should look at as well? I have the diverter valve style at the top of your picture. Thanks!

 

[AdamB7100]

Oops! I see you are showing me the lift piston in the photo. Disregard previous comment. I will tackle the lift piston next. Any idea if these parts are available from Kubota?

 

[Dave_eng]

The spool that I took apart is linked to the lift/lower lever. It is not shown in the photo you sent. Is the one you show in the picture something I should look at as well? I have the diverter valve style at the top of your picture. Thanks!

Somehow I am not making myself clear for you. This is my issue not yours!

I do not think the valves you are focusing on are causing your problem.

You do not have any external cylinders connected so the selector valve under the seat is doing nothing.

Most hydraulic control valves do not rely on seals, (O rings etc), to seal the moving spool to its bore. Instead, the clearance between these parts is manufactured to tolerances so close that an ordinary mechanic cannot measure them. These tight clearances use the viscosity of the fluid to achieve minimal to zero leakage. The control valve for the 3 pt hitch would be manufactured with this design philosophy.

Clearance between the valve spool and its bore would be around 0.0002" ! You need to count the zero's to realize just how tight the clearance is.

It is the seal between the piston #59 and its cylinder where the problem usually is happening because that seal relies on O ring(s).

Dave

 

[AdamB7100]

Somehow I am not making myself clear for you. This is my issue not yours!

I do not think the valves you are focusing on are causing your problem.

You do not have any external cylinders connected so the selector valve under the seat is doing nothing.

Most hydraulic control valves do not rely on seals, (O rings etc), to seal the moving spool to its bore. Instead, the clearance between these parts is manufactured to tolerances so close that an ordinary mechanic cannot measure them. These tight clearances use the viscosity of the fluid to achieve minimal to zero leakage. The control valve for the 3 pt hitch would be manufactured with this design philosophy.

Clearance between the valve spool and its bore would be around 0.0002" ! You need to count the zero's to realize just how tight the clearance is.

It is the seal between the piston #59 and its cylinder where the problem usually is happening because that seal relies on O ring(s).

Dave

Copy that! I removed the piston and the o ring seal looks distorted/worn. I will replace it and let you know the outcome. Thank you