Changing Diff/Trans Fluid.
I added a pic of the transmission because it almost the same procedure.

Tools Used
10mm Allen Wrench
Drain pan
Floor jack
Four jack stands or a lift.
Suction Pump/Gun. I bought mine from Advanced Auto for $10.
Harbor Freight has one for $4.99.

Rags
Replacement oil 75W90 about 2 quarts. About 4 quarts for transmission.
Two replacement crush washers.

Update:
Adding the requirements as stated in the 2003 Service Manual
Transmission API GL-4,Viscosity SAE 75W-85
Differential API GL-5, Viscosity SAE 80W-90


Procedure
1. Make sure wheels are blocked.
2. Raise and support car making sure that it is as level as possible.
NOTE: It is better to drain the fluid when it is warm so it flows easier.
3. Use 10mm allen wrench to loosen fill plug (to ensure you can refill the differential before draining old oil).
4. Using 10mm allen wrench, loosen drain plug and allow diff to drain.
5. Wipe off excess oil from drain plug along with fine metal shavings. Remove old crush washer and install new washer.
6. After diff/trans is drained, reinstall drain plug. 23 - 28 ft-lbs for transmission; 55 - 61 ft-lbs for rear diff.
7. Use 10mm allen wrench to remove fill plug.
8. Remove old crush washer and install new washer onto the fill plug.
NOTE: To fill suction gun, I took off the top, pulled handle out of the gun and poured the oil into it. You could stick the hose into the bottle and suction it out but it wont pick up as much.

9. Using suction gun, fill diff/trans to lower level of fill plug and allow overflow of fluid to drain off.
10. Reinstall fill plug. 23 - 28 ft-lbs for transmission; 55 - 61 ft-lbs for rear diff.
11. Double-check all plugs for correct torque (DO NOT OVERTIGHTEN) and wipe off any excess oil.
12. Lower the car.

NOTE: Since you have the car raised it is a good time to change the engine oil, check your tires for feathering, check your exhaust for leaks and bottoming, check your fuel lines for damage and anything else that may look unusual under your car.

 

Is it really necessary to lift the car?

I haven't climbed under the back of my G yet except to install my splash guards, so I'm not really sure how much clearance there is under there.... but when I used to change the differential fluid on my 240SX, I never needed to lift it.

Also... did you go with synthetic gear oil?

 

I just changed my differential fluid with Mobile 1 synthetic 75w90, and it isn't necessary to lift all 4 sides, just the back. I presume that Monsta lifted all 4 sides in order to make it easier to change all fluids without having to lift the back and front separately. Overall, the fluid changing was easy and could be done by anyone with a small amount of knowledge. Props to Monsta, you made it much easier for me. Thanks!

-Eric

 

The reason you should lift all 4 sides is because the car is supposed to be level when filling up the diff fluid. When the fluid dribbles out of diff fill hole up top, you want it to be level, otherwise, if you lift only the rear--assuming th car is not level to gravity--you'll be overfilling as you let the fluid dribble out; because the diff is at an angle forward. hope that helps

 

Thank you.
I lifted it to change the trans fluid too. Like jinsei says, it has to be leveled to properly fill the diff. You don’t really have to be a mechanic to do this. Just common sense.
I used Amsol synthetic.

 

silly question...

did you use synthetic 75w90 both in tranny and differential?

and did you get the crush washers from your dealership?

 

Yes
It’s the same weight in the diff and the MANUAL trans. Automatic transmissions use a different oil.
I went to an auto parts store and they didn't have the same size crush washer so I checked Nissan and they had to order them. I wound up using the same ones w/ no leaking. If you want to use new ones, order them from the dealer before you start the procedure.

 

It's the same weight but NOT the same API Service rating. You need GL-4 for the manual tranny and GL-5 for the rear diff. Some lubes do meet both specs.

Also, always loosen fill plugs prior to draining out fluid from the tranny and rear diff. What would you do if the fill plugs were frozen and you could not get them loose??

 

Whats the difference between GL-4 and GL-5? isn't the GL-5 just a newer spec.?

 

Try this out:
http://api-ec.api.org/filelibrary/glchart.pdf

 

Thanks for the link. Sounds like the GL-5 is interchangable with the GL-4. The GL-5 spec may be better with higher loads as well.

 

Some metals used in some transmissions are not compatible with the GL-5 lubes. GL-5 also has additives for the LSD. I am using a lube that Amsoil sold a couple of years ago which specifically stated that it met both standards. You need to be certain of this if you are still in warranty period.

 

I used the Mobil 1 75-90. It is a GL-5 spec. Do you think this will do any damage to the transmission? I have about 200 miles and it seems to shift fine. I do notice that it shifts better after it gets warmed up and is still a little notchie when cold.

Thanks

 

Here is the spec sheet for the Mobil 1 you are using:
http://www.mobil.com/USA-English/Lub..._LS_75W-90.asp

It is curious in the notes at the bottom that it can 'also be used in rear axles where GL-4 is specified. No mention of transmissions requiring GL-4.
I would send an email to their tech dept asking about use in our MT.

 

Okay I just got off the phone with the Mobil folks. They informed me that the GL-5 rated Mobile1 Synthetic gear lub LS 75W-90 is not suitable as a replacement GL-4 lubricant. Seems Mobil only has an 80W-90 gear lube that meets both GL-3 & 4 called SHC350. I know the Nissan manual calls out 75W-85 API GL-4 so I guess I'll find some and use it.

Thanks for the help Z'd!

 

I just picked up 6 bottles of Amsoil 75W90 GL-5, the guy at the store told these are fine for both the trans and the diff.
Z'd, do you have a pic of the Amsoil gear fluid you picked up?

 

No pic handy but I can probably dig out a quart and take a pic if you need.
It is (was) called Series 2000 "TGR" and was rated for GL-1 through 5.
Here is the email response I got from the Amsoil Tech when I asked about suitability:

"Absolutely. TGR can safely be used in both applications and is actually an excellent choice.

Thank you,

Ed Kellerman
Manager, Amsoil Tech Services"

If you look to purchase a current Amsoil product, it would be this one:
http://www.amsoil.com/StoreFront/mtg.aspx

 

Nissan calls for GL-4 only, no GL-5 in transmission. I read somewhere that some extra additives in GL-5 grade (sulphur??) are corrosive to some of the internal metals in the transmission, but GL-4 is safe for the Z transmission, hence Nissan manual calls for GL-4 only. I just changed all my fluids today. Amsoil 5W30 in engine. Amsoil Gear Lube 80W90 GL-5 for differential. Redline MT-90 75W90 GL-4 in transmission. Amsoil oil filter (SDF13). I wanted to use Amsoil manual transmission gearlube 75W90 GL-4, but store I purchased from was out of stock, so I went with Redline.

Anyone know for sure about GL-5 being corrosive to some metals in transmission??

 

Conventional gear lube with GL-5 rating can reportedly do damage.
Synthetic products, however, are not in the same boat. They could not be rated for both GL-4 and GL-5 unless they could handle both applications properly.
Most syn producers have moved towards specific lubes for each purpose now.

 

API GL-5 gear oil designates service of hypoid and other types of gears commonly found in rear axles. A GL-4 oil may be employed in certain manual transmissions.

These differences are mainly distinguished by the level of active additives employed in the product. Different applications require different additive levels and different component materials can be affected by the levels of additives present in the lubricant.

Having said that GL-4 and GL-5 gear oils are not compatible and manufacturer's recommendations should be adhered to. They cannot meet the same specifications and the product performance and tests are different.

Typically, a GL-5 gear oil will have about 2 times the active additive level of a GL-4 product. This additional additive can cause problems with yellow metals like brass or bronze.

This information came from the Castrol tech line.