Adding oil to freshly rebuilt transmission

[VA Mountain FJ40]

I just recently installed a fresh motor / transmission / transfer case in my 1968 FJ40. Still have the interior transmission hump cover out and shifter out. The renewed tranny and tcase were shipped dry by Valley Hybrids (with a big reminder tag to add lubricants before use).

I plan to add oil to the transmission and transfer case after I install the vacuum shifter pod I’ve been refitting. A buddy suggested I could put the recommended quantity of gear oil into the transmission directly via the gear shift orifice inside the FJ, since the cover and shifter are already off. (As opposed to pumping gear oil into the fill port underneath til overflow.)

I would still want to install fresh crush washers and carefully torque the drain/fill bolts from below.

Buddy also wondered if transmission and transfer case co-mingled oil. I think not… (why would they have separate drain and fill plugs) but would appreciate an authoritative response to pass on.

I plan on adding oil to the tcase from underneath the truck and will likely just pump in the fresh transmission oil while I’m there with new crush washers… but is the option to add tranny oil via the gearshift hole up top a real thing?

Thanks again for the help.

 

[Pighead]

but is the option to add tranny oil via the gearshift hole up top a real thing?

Yup, real deal.
Transmission and transfer case aren't supposed to share oil, but they do when the seal between the two goes bad

 

[charliemeyer007]

I don't think it matters how you get in the correct amount of correct oil. I just filled my 72's T/T with Valvoline Syncromesh. Tranny was was a little low and transfer was nearly empty. I know they mix, bad seal inside. Previously I had changed all the gear oil to Kendal 85-140 (1990's) because the local Toyota dealer told me too. Yea well the Kendel was fine for the differentials and transfer case - but wrong for the tranny. When I changed the tranny fluid I didn't see any brass chunks or glitter. Maybe I'll get lucky.

I bought the T/T bypass hose from shipmag - nice unit.

 

[pb4ugo]

Remove the trans fill plug and fill the tranny thru the shifter hole until lube comes out of the fill hole. As Pig mentioned, there is a seal between the trans and tcase to keep the oils separated. When that seal fails the tcase will pump its lube into the tranny and empty the tcase. Someone on this site sells a bypass hose that connects to both fill holes, so if the seal fails it will allow both cases to equalize to their proper oil levels. It's sort of insurance that the tcase wont run dry, if the seal fails. I think GL4 lube is recommended.

 

[VA Mountain FJ40]

Yup, real deal.
Transmission and transfer case aren't supposed to share oil, but they do when the seal between the two goes bad

Makes sense. With a new 0 hour trans and tcase build, should not be sharing now. Thanks Pighead!