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Deere 9420 hydraulic oil transfer between reservoir tank and transmission
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Posted 7/10/2024 08:45 (#10805198)
Subject: Deere 9420 hydraulic oil transfer between reservoir tank and transmission

I’ve got a 9420 that’s transferring oil from the upper reservoir under the hood down to the trans/axles. I’ve dealt with this before and usually the cause is worn brakes allowing the piston to push out too far and let oil escape past the orings. Doesn’t seem to be the case here. This is a list of what I’ve done so far.

Pressurized front and rear axle brakes separately to 600 psi, no leak down in 2 hours.

Removed rear axle to check brakes just for fun at the customers request, no visible issues and replaced all brake parts and orings anyway and reinstalled.

Removed and examined check valves in the front hydraulic filter housing and in the brass fitting underneath the reservoir, no issues.

Removed axle lube pump and performed seal upgrade (Dtac solution) calls for installling new seal on shaft flipped opposite of the original so lips face charge pump with a washer behind the seal to space it.

Removed hydraulic pump to check seal, looked fine but replaced it anyway.

Brake and diff lock lines were hooked up correctly but now diff lock lines are removed and capped as diff was having issues and customer doesn’t normally use it.

Also checked pump case pressure which was like 13 psi, slightly below high end of spec while deadheading scvs/loop hose etc.

I’ve exhausted all possibilities I know of. What else is there I may be overlooking?

Edited by Deeregreen802 7/10/2024 12:18
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