D8K Tansmission mystery

Billy, change and cut open the trans filter and check the mag screen, then you need to do a complete trans perssure test.
Your symptom of"works good untill it warms up" tell me there is an oil leak some place. A trans system needs lots of flow to cool properly but you may have other problems. Maybe check the oil left in the torque housing when it acts up. Come on back with what you find.
Later Bob

I checked the mag screen and replaced the filters and oil 20 hrs ago. The filters and oil had not been changed in a while. The Filter bowl had sediment in the bottom and both filters were in poor shape and appeared to be restricted if not plugged. The Mag screen had no chunks on it however it did have a quantity of black magnetic goop. I replaced the filters again 5 hrs ago and found some sediment. Mag screen had some goop on it as well. I did not check scavenger pump mag screen as I am unsure of its location.

Hi Team,
suggest you run machine until symptoms just start to occur.
Then run the main engine at low idle for short cool down time and then stop the engine.
Being careful of the hot oil in the T/C housing, drain off the T/C housing from the plug at the bottom of the flywheel-T/C housing.
You should get no more than 1.5 to 2 gallons of oil out--be ready for more if the scav. pump is at fault or the T/C seal rings are shot and the scav. pump cannot keep up.
It is not unknown for scav pump shafts to be bent when people remove-refit the T/C without removing the pump first or installing last, along with a couple of gallons of oil added to the T/C housing for the scav. pump to pump until the T/C leaks enough oil for it to pickup. If this oil is not added then the scav. pump can chew itself up so it is ineffective when hot oil is to be pumped.

Problem seems more like leaks at the tube "O" rings that take oil into the control valves and/or to the packs from the valve, or stuck pressure control valve spools inside the trans. or the clutch pack seal rings.
The sequence valve at the rear of the trans. supplies oil to the steering and brakes first for safety reasons as this circuit works OK it proves the trans./steer. supply pump is OK.

Seems to be a couple of D8H/K's with similar problems at this time.

Hope this helps--getting too far back since I worked on these.
Cheers,
Eddie B.

I would start with the sump oil drop test at the converter frist, 2gals max in converter sump ,like was said before , But I am wondering if you have more than one problem .as you saying there;s no nuetral when hot . The safty valve should kick the shift lever into neutral when Low oil pressure occurs at the transmission control valve If thats not happening ,its sounding like the safty valve is hanging up in the control valve ,and possibably others as well .Also a big problem with all those power shift 8's was the sealing rings at the supply tubes inside the trans from inside the trans case to the control valve .I would susject removing the control valve dissembling the control valve wash and inspect the valves in the contol valve and reseal it and the suppy tubes. I have seen some D8's were the torque converter transmission ,and bevel gear case was so comtimated with fine metal that the whole system from torque converter to steering clutch case to oil cooler had to be dismantled washed out and resealed .

Thanks everybody for all of the great advice.
I will do the tests as outlined in the posts and communicate the results as soon as I am able to do so.
Cheers