atf in the t-case?

[sw]

had a look in the book for the patrol and like pathys there is supposed to be atf in the t-case. does any know why this is so?

 

i really dont get it. atf is a thin hydraulic type oil. yet a gear type oil (i.e. say 80-90 gear oil) is thicker.

 

now our t-cases are just a big box with 3 or 4 gears and one very very thick chain, well d21 pathy & patrol anyway. so based on its simplicity i would tend to assume just a basic gear oil is the go.

 

i always ran 80-90 in the pathy t-case & i know for a fact that the patrol has 80-90 in it now (easy to tell due to viscosity, color and smell). never had any trouble at all with the pathy t-case & the patrol t-case seems exactly the same - runs great smooth, no noises etc. do i leave it?

 

:confused:

Edited September 28, 2006 by sw

[mws]

Engineer steps into the room....

 

Please use what the original engineer spec'd, please. Unless you know for a fact what they spec'd is a mistake or a stupid marketing/accounting decision.

 

ATF originally was basically just hydraulic oil, but it has evolved to also be a very good lubricant that has much less viscosity and resulting frictional losses than gear oil. Same concept as when designing engines to use 5W30 instead of 20W50. Thinner oil, less friction, better mpg.

 

And you're right, the gear oil will be every bit as effective at lubing gears and chain. BUT, there are also bearings on either end of the shafts.

 

And when designing for a lower viscosity lubricant, bearing clearances MUST be dramatically reduced to allow the oil to do its job. Which means if you put 90 wt gear oil in a gear box designed with very tight clearances for ATF, the thicker oil will most likely NOT be able to fit in the bearing and do its job.

 

The 5 speed manual transmission in my BMW specifies ATF. They are known to last at least 500K to a million miles...

 

So use a good ATF and enjoy the mpg! I like Redline....

[94extreme]

on some of the earlier years nissan calls for gear oil.... in later for ATF.. not sure when the changeover was.. i have a MT on my truck and due to that fact i have no atf fluids other then the T-case.. so i switched.. i have had gear oil in mine for 15kmi and i have used 4x4 quite a bit.. i have wheeled rather hard numerous times and i haven't noticed any problems at all.

[89_trailboss]

use what ever is in transmission. the point to the ATF is so that if your seal is gone, you wont get gear oil into your trans.

[88pathoffroad]

I don't think that's so, but it seems like rational reasoning. My t-case calls for 80W-90(per my FSM) and I have an automatic, so draw your own conclusions. I really doubt that the trans/t-case seals will allow fluid exchange like that. I'll take a look at the separated t-case/trans in my garage and get back to you on whether or not it *looks* like it might do that or not.

[89_trailboss]

unno. I called nissan here and the guy there said thats why. and the guys at AC also said so. unno. at anyrate Im running ATF in mine. works fine.

[88pathoffroad]

OK, I officially call BS on that idea. I went out and looked. There are two drain slots at the joint between the trans and t-case that will allow fluid to drain out if either the output seal on the trans or the input seal on the t-case start to leak. It's not possible if you take a look. The two just aren't sealed together like that.

[sw]

well small update

 

with the october long weekend (australia) just passed i went with a 4wd club along the boarder track in s.a.

 

now before i went i did all my pre trip checks etc. this included greasing the front drive shaft. now as ive only had the car 3 months or so this was the first time its has been done by me. soon as i got on to the freeway and got up to freeway speed i could hear my stupid auto hubs clunking in and out.......

 

obviously the freshly greased shaft is now alot free'r and was free spinning up at high way speed, then the stupid auto hubs would see this and engauge. they continued to bang in & out until i stopped and tied up the front drive shaft.

 

clearly the auto hubs have to go, no argument there.

 

however the thicker gear oil maybe causing the front shaft to free spin up at highway speed.

 

i think i will try the atf.

[mws]

I agree with your diagnosis and plan. Let us know how it turns out!