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JD 8400 powershift transmission

Robyn Richards JD 8400 tractor: In road gear (16) travelling with no load at 1500 rpm. Transmission locked up, back wheels skidded and engine stalled. "Declutching", disengaging gears engine restarted easily. After some time idling, failing to find anything wrong was able to resume. Symptom remaining is an "oil noise" somewhere under the cab.
Notes: Tractor is 9500 hours; Had been sitting for weeks with heavy mouse infestation. Oil could have been overfull.
Serious problem. Any ideas welcomed. Thanks.

ross Did the transmission lock up or did the park brake come on? I would drain the oil out of it and cut the filter apart and see if any metal shavings are present in the oil. Good Luck.
RR Thanks for the suggestion.
Recalling the incident now at first I did wonder about the brake coming on but didn't know how that was possible - in fact I don't know how the brake works. But I'll look into it, and check the filter.
The powershift box had worked without fault till this happened - and has worked since. Not sure I should be using it but still can't detect damage has occurred.
Any idea how the brake could come on with the lever in gear?

Robyn Apparently you were right Ross. It was the brake coming on - I wouldn't have thought it possible, but it did. Paying careful attention to the wiring under the armrest now to try to determine how it happened.
ross The park brake is spring engaged and hydraulicly disengaged. If the sender for the park brake is getting bad or shorting out then the park brake will come on with the lever in gear. The park brake switch is on the top left hand side of the transmission. To get to it, remove the battery box and the left hand engine side shield. There will be a DR port inline with the switch to check hydraulic pressure. I have seen the connector on the switch get oil in them.
Robyn I've been in the online parts catalogue, trying to find out how the park brake works, and the problem is to get a picture of more than an isolated few parts so's to make sense of it all.. I've had this tractor about 400 hours and I'm still doing urgent work with it, trusting to luck on the problem.
The specific information you've supplied is extremely useful. I knew the clutches on big JD -manual - boxes worked with an external spring pulling the clutch on as I'd broken one once. That the brake works that way on this 8400 is a thing I hadn't known about. I've got some information to work with now .. as soon as this boomspraying job finishes.

brandon eads i had the same thing happen on a john deere 8300. sent it to john deere, they changed the sensor under the seat cushion, and it fixed the problem. hope that helps.
simon b Your park brake should not engage over about 4km/h 3mph, the ground driven pump should stop the park brake applyin, when u check ur oil take off the belly plate and remove and inspect the strainer in the bottom of the transmission and also the strainer for the charge pumps. U should b able to find these in the owners manual. It is also common to see the transmission wiring harness wiring harness falling apart especially if the tractor has not been kept clean. That may be another place to look

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