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John Deere 670a Transmission issue

JAAZ

Member
Joined
Jan 1, 2023
Messages
5
Location
New Hampshire
Hello, I have a 1982 John Deere 670A I have run and maintained for 12+ years. The machine transmission always operated well despite the lube pressure always ran a little on the low side according to the gauge. This spring I drove it across town and lost drive in all speeds in forward and reverse. It seemed for a while the hydraulics continued to work but eventually would quit. I never lost steering. After shutting the machine off for a few minutes I could start it up and drive a few hundred feet then again quit driving. Before losing drive power, I would witness the lube gauge lose pressure then 10-20 seconds later the transmission pressure gauge would drop off prior to losing the drive.

I have changed the filters and screen in the transmission as well as checked all relief valves for broken springs and o-rings. Nothing jumped out at me. There was some evidence of clutch material but not very much. I would like to note in recent years it would slip a little under load but infrequently.

At this point I am suspecting an internal leak or possible bad transmission pump. I have read a couple others have the same symptom online however I have never read of a resolution. It seems this may have been a common problem as these machines as they age and was curious if somebody out there would know where I should tear into.

Other than constantly blowing an Oring in the left blade lift cylinder poppet valve which I have never been able to solve, this is a very tight machine that is worth fixing if possible.

Thanks for any help.
 

mg2361

Senior Member
Joined
Jul 5, 2016
Messages
5,310
Location
Pennsylvania
Occupation
Equipment Mechanic
Did anyone mess with the engine disconnect clutch linkage? Maybe the linkage is seized and the disconnect clutch is not fully engaged.
 

JAAZ

Member
Joined
Jan 1, 2023
Messages
5
Location
New Hampshire
Hello, thanks for the response… nobody has played with that linkage. Would that either make it move or not? I’m not sure how it functions but is there anyway that disconnect could get out of adjustment to make it only drive short distances before losing drive power? I’m confused as to why shutting the engine down for a few minutes allows it to regain drive power for a short time.
 

mg2361

Senior Member
Joined
Jul 5, 2016
Messages
5,310
Location
Pennsylvania
Occupation
Equipment Mechanic
I was just reaching for something easy. No, restarting wouldn't make a difference with the disconnect. Transmission pressure checks with gauges would be next (not the dash gauge).
 
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