I tried to research this issue but got even more confused. On my other car I know there are separate fluid changes for rear differential, transfer case, front differential and transmission. On my '99 RX I am fairly certain that I have only had the rear differential and transfer case fluid changed with the belief the front diff is somehow connected to the transmission and share fluids (I also thought the maintenance schedule only mentioned inspection of transfer case and rear differential fluids but I can't find the book). After my last oil change the Toyota service adviser stated the mechanic recommended a front differential fluid change as the fluid was dark. I have an ATF drain/refill planned for the next oil change as I have that done every three oil changes. So the $64,000 question is whether there is a separate drain/fill for the front differential. Thank you in advance.

 

Front diff shares fluid with the tranny. There are two plugs to remove when you do a drain and fill, one is the tranny pan, the other is the front diff. I'll direct you to some pics in a second.

 

This should help:





The first pic shows fluid draining from the tranny pan and a hex wrench in the front diff plug. The second shows the front diff draining.

 

This is the transfer case, it takes gear oil.

 

Now that's an answer! Thanks Carguy!

 

but now i have a question. Why the rear diff is 75w90 and the front is atf typ4 iv . question . the viscosity is the same ?

 

The rear differential and transfer case take 75w90 gear oil.

The front differential shares ATF with the transmission, hence the term transaxle.

EDIT: It seems I misunderstood your question, Salim has the answer!

 

Very very different oils.

The choice of oil has to do with environment, gaps between rolling objects, pressure formed to squeeze out the oil by rotating parts, emulsion/cleaners needed to move out debris etc. Another important factor is the loss of energy which is carried by the oil.

There is no pump in the rear diff. The gears sit in a bath of oil and viscous oil moves around by rotating gears.

There are other secondary effects like types of seals (how they react to oil) and outside (mud/air) exposure of the seals.

Salim

 

killed the doubt

 

You had the transfer case and differential backward. Differential takes gear oil, transfer case takes trans fluid.

 

the one share trans fluid is the transfer case, not differential. The differential connects to the drive shaft to the rear wheels. Any DIY for changing the oil for the front diff.?

 

This is my best understanding:
The transaxle in RX has the transmission and the front differential .. all enclosed in one casing. It couples the engine to the front two wheels. It has two low points for draining and one fill point through the transmission dip stick.

For AWD you will have a rear diff at the back.

Please correct me if I am wrong.

Salim

 

For what I've learned, transfer case usually attached to the transmission and commonly uses transmission ATF fluid. In the other hand, CV axles or axle shaft attached to the differential for spinning the wheels. Differential mostly uses gear oil not ATF fluid. Therefore, in the RX300, the unit attached to the transmission is the transfer case. I haven't seen a transfer uses gear oil. Transfer case only uses ATF fluid or special formulated fluid.

 

Your statement [in bold] is correct for rear differential in RX [AWD model]. The front diff (which is part of the transaxle) uses ATF which is shared with the ATF of the transmission for both AWD and FWD models.

Salim