6400 jerky clutch

stoneridgemb · Feb 6, 2020

this is a JD 6400 fwa, power quad with right hand reverser. Just as the clutch is about to engage, the tractor jerks forward. it had a broken spring in the modulation valve and I also changed the piston but it did not solve the problem. If I quickly release the clutch the tractor pulls away smoothly. what do I look at next? Tractor has 12000 hrs, is clean and works everyday

jd110 · Feb 6, 2020

Does tractor shift forward to reverse and reverse to forward smoothly without using the clutch? If so, I suspect the clutch valve may be sticking in the bore. you need to remove the front cover on the transmission to inspect it. I had one that link 49 was worn crooked and was binding on guide 31. Replacing the link and attaching pins 27 and 30 cured the problem.

stoneridgemb · Feb 6, 2020

It usually shifts smoothly but once in a while it is choppy. Seems better since I changed the spring+valve. I'll try checking the items you mentioned. do I need to drop the oil in tranny?

stoneridgemb · Feb 6, 2020

TRANSMISSION FRONT COVER - ST237081 is where I'm looking at JD parts.com. Is the linkage external?

DJ54 · Feb 7, 2020

A buddy of mine had the same problem on his 5400 2wd 4-5 years ago. After contacting the local independent JD mechanic, he told him it was more than likely the clutch pack needing replaced. Not from wear, but from rust/corrosion in the clutch pack not letting all the plates and disc's release evenly, causing the tractor jerk, when releasing the clutch pedal. As I understand, your not able to rebuild the clutch pack, so a new unit is required.

Being my buddy was working a lot of overtime at that time, he decided to let that mechanic do the work. I don't recall the total bill, but remember the clutch pack was around $650 at the time.

Zebrafive · Feb 7, 2020

Looking at JD parts catalog, it looks like you have to remove the front cover to get to the parts he mentioned (27, 30, 31, 49). I would say you have to drain the transmission.
I am not sure what you mean by is linkage external. It looks like arm 20 to shaft 22 to internal part 23 which connects to link 49. Arm is external rest are internal. I assume clutch cable connects to arm 20.

stoneridgemb · Feb 7, 2020

If I pull off the front cover can I expect anything to come apart? any springs or valves that will be between the cover and rest of tranny or are they secure?

Tx Jim · Feb 10, 2020

DJ54 said:
A buddy of mine had the same problem on his 5400 2wd 4-5 years ago. After contacting the local independent JD mechanic, he told him it was more than likely the clutch pack needing replaced. Not from wear, but from rust/corrosion in the clutch pack not letting all the plates and disc's release evenly, causing the tractor jerk, when releasing the clutch pedal. As I understand, your not able to rebuild the clutch pack, so a new unit is required.

Being my buddy was working a lot of overtime at that time, he decided to let that mechanic do the work. I don't recall the total bill, but remember the clutch pack was around $650 at the time.

JD 5400 has a dry clutch while 6400 has a wet(hyd operated) clutch. Comparing operation of each type clutch is similar to comparing "apples to oranges".

Zebrafive · Feb 10, 2020

stoneridgemb said:
If I pull off the front cover can I expect anything to come apart? any springs or valves that will be between the cover and rest of tranny or are they secure?

I have NOT done this job, BUT looking at JD parts it only looks like there is plate with gaskets both sides behind the front cover.

IIRC the cap screws that hold the drive shaft in (4 front, 4 rear) are "one time use". They have serrations on the under side of the head.
Key 10 and 11 in the drawing.

stoneridgemb · Feb 26, 2020

Been running tractor waiting for a local tech to make time to look at the clutch valve, noticed the tractor does not jerk when it's in reverse. I can back up smoothly to hook up implements etc.. but when I go fwd it jerks on takeoff. Is this still likely the clutch valve?