763 ,persistent main seal failure on the drive motor

[tecarr]

My 763 stopped moving because the hydraulic reservoir emptied into the chain case via a failed main seal on the drive motor. I installed a washer and seal kit on the hydraulic control unit (all 2 thousand pieces) and then replaced both main drive motor seals. After a few minutes of operation, the hydraulic reservoir was empty again, and one of the drive motor seals was blown out. Next, I replaced the main relief valve, and a port relief valve in hopes that would fix what I perceive to be an excess amount of pressure on the drive motor seal. Still no luck, the seal blew out again. Any suggestions?

 

[cnord]

Check your drive motor case drain filters.

 

[Tazza]

Check your drive motor case drain filters.

Exactly as Cnord said, check the case drain filters, they look like a alloy can about 3" long and 1.5" diameter that go on the drive motor case drain hoses (the little ones). They essentially filter out any particles caused by motor wear before they enter the main reserve tank. Thses line should have little to no pressure in them, when they clog up they cause a back pressure and blow out seals like is happening to you. There should be two filters, one will possible mounted under the hydraulic tank the other will be closer to the other drive motor, they are easy to spot.
The motors have a small amount of internal leakage to lubricate them, so there will alwasy be case drain flow but its not meant to be restricted.

 

[tecarr]

Check your drive motor case drain filters.

Thanks. Filters did it

 

[tecarr]

Check your drive motor case drain filters.

More trouble. The main seals are working fine, but now the lift arm, bucket tilt, and 4 in 1 cylinders are much slower and less powerful than before ( about 50% ). Also, the hydraulic fluid in the reservoir is a milky yellow in color, though I can't see any bubbles. Could the relief valves I just replaced be a factor? Note- the drive power seems just fine with respect to speed and power.

 

[Tazza]

More trouble. The main seals are working fine, but now the lift arm, bucket tilt, and 4 in 1 cylinders are much slower and less powerful than before ( about 50% ). Also, the hydraulic fluid in the reservoir is a milky yellow in color, though I can't see any bubbles. Could the relief valves I just replaced be a factor? Note- the drive power seems just fine with respect to speed and power.

Check your other thread, hopeflly its just air that will self purge.