Wednesday, July 22, 2015

DIY Changing Front & Rear Differential Fluids

The AWD Q50 has 4 additional mechanical fluids other than the engine oil that need attention. The rear differential (same as only RWD Q50) as well as Front differential oil, transfer case and transmission fluid. 

Historically, I have found that the differential fluids have usually got a specific mileage at which they must be changes, however for the Q50, the only recommended maintenance is to Inspect the fluid every 10,000 miles or 12 months, unless towing a trailer, or driving in rough conditions in which case it is recommended to change every 24 months of 20,000 miles.

I found this rather bizarre for two reasons - 1. not really sure how one can “inspect” the oil without draining it, unless Infiniti consider a finger drip in to the differential will reveal much and 2. most of the mechanical wear on differentials like any other metal to metal parts will happen during the initial mileage and wear in. I have used this theory for all my cars and it has never set me astray, especially for the low cost of the fluids.

The Q50 much like most other AWD vehicles takes conventional 80W90 in the front and Synthetic 75W90 fluid in the rear differentials respectively, specifically:

  1. Front Differential: Genuine NISSAN Differential Oil Hypoid Super GL-5 80W-90 or API GL-5, Viscosity SAE 80W90. 1 3/8 US pt or  0.65L. I choose Penzoil as that is what my local Nissan dealership uses. I bought 1 QT of this.
  2. Rear Differentail - API GL-5, Synthetic Gear Oil, Viscosity SAE 75W-90. 2 1/4 US pt or 1.05L. I bought 2 quarts of Mobil 1 Synthetic 75W90 LSD Oil.
The other specific tools needed for the job are:

Gear Oil pump, plunger or syringe. I have a Mac Tools specific one that cannot be bought retail, however local auto shops and also have ones that will do the job well. There is simply not enough clearance to use the nozzle of the gear oil container to get the job done and not make a huge mess and waste.

The other is a 3/8in drive 10mm HEX socket and socket wrench. Do not use a Torx screwdriver or socket in the smaller hole in the plugs, chances are that that will either strip the plug or snap inside the plug. A smaller 3/8inch drive torque wrench is also very highly recommended as the components are cast aluminum and over torquing can mean a brand new differential which can result in thousands of dollars of damage. 

For this reason, no need for impact wrenches, rather GENTLE taps from a rubber mallet on a smaller wrench are better.

While mentioned not to do so, I have been told otherwise by techs and I have never replaced the gaskets. If you have the inclination to get some gaskets, then the local dealership parts department can supply those.

Rags for cleanup, low profile oil pan for draining, jack, safety stands, sockets, etc.

The car does not need to be warmed up unless it is a very cold day < 40F. It was a nice 75F day, so I did not bother warming up the car and it actually drains quicker when the car has been sitting overnight and all the oil has collected to the bottom.

A couple of important notes:
  1. Rather than opening the drain plug first, open the filler plug first! It would be a shame if one managed to drain the oil and realized that the filler plug will not come open. The care would be immobilized.
  2. When the filling is done it must be done with the vehicle LEVEL. This means that for home DIY-ers such as myself who do not have a 4-post jack, after filling is done, the car must be brought back to level surface to allow for the excess to drain out and achieve the proper level.
Procedure for Front Differential:

Follow the instructions in the Oil change post to up to step 4 ( to gain access to the front differential.

The front differential looks like this.

Note the filler and drain plugs.

Using a Hex socket and wrench loosed and remove the FILLER plug FIRST! Do not lose the gasket/washer. It maybe stuck to the differential, simply pluck it off and put it back on the plug.

To avoid a big mess to clean up gear oil from suspension components, I used a piece of cardboard and cut it in the shape of a channel to allow the gear oil to drain forward and wedged it just below the front differential (see pic a few down).

Next loosen the drain plug and remove it to allow the fluid to drain out into a capture container.
Because jacking up one side of the car will not allow for the drain to happen fully, I lowered the car on a low profile drain pan and waited 10-15 minutes to allows for all the draining to happen. While that is happening tine to remove the metal shavings of magnetic drain plug.

Note that the fluid is light golden brown, which means all the black stuff is metal shavings.

Clean the drain plug with rags/towels, and replace the gasket.

After the fluid is done draining, and it will never stop slow dripping, jack the car up again to gain access again, clean off the area near the drain plug  and replace the drain plug. Torque it to 35N-m or 26 in-lb (NOT ft-lb!).

DO NOT Remove the fashioned cardboard deflector. 
Using A CLEAN oil syringe, pump, etc suction up 1 full serving of 80W90 gear oil and inject into the filler hole. Repeat noting that it will take ~ 0.6L (about 60-70%) of the oil in a quart before it start overflowing.

Now lower the car and let it level allowing the excess to drain from the filler plug. When it stops dripping. Then it is at the right level. 
I found it better to jack up the car from the front passengers side to avoid the tilting of car to drain any excess.
Replace the Filler plug and washer/gasket and torque to 35N-m or 26 in-lb (NOT ft-lb!).
Now, remove the fashioned cardboard deflector, clean up the area of any drips, drops and spills. Clean the areas around the filler plug and drain plug.
Replace the shields and lower the car.

Procedure for Rear Differential:

First find the filler plug and drain plug of the rear differential. The filler plug is on the side, facing the passenger side rear wheel rather than straight back like the drain plug.

Jack up the rear passengers side using the proper jack point and place proper jack/safety stands.
This will allow for more room to access the filler plug.

Once again, open the FILLER plug FIRST, then the DRAIN plug and drain out the rear differential fluid:

Lower the car to allow for all the fluid to drain properly. The rear differential fluid was notably darker than the front fluid.
While the oil is draining, clean up the magnet on the drain plug, and put the gasket back on.

If you replaced the front differential fluid (AWD owners) now would be a good time to clean the oil syringe/pump. Do not use any chemicals - degreasers, petroleum based products, etc. If any contamination occurs it can break down the fluid and ruin the differential. Simply use lots of rags, shop towels.

Raise up the ear of the car again, clean off area and replace the drain plug. Torque to 35N-m or 26 in-lb (NOT ft-lb!).

Using the oil syringe/pump suction some 75W90 fluid. Direct the tube into the filler hole. I found it easiest to get in from behind the rear tires between the suspension part rather than at a 90 degree angle from the rear.

The rear differential will take just over 1 1/4 quarts before it starts overflowing. Lower the car and let the overflow drain out from the filler plug.  Once the draining stops, raise the car again, this should not cause it to drain any more if done from passengers side rear wheel area.
Replace the filler plug and gasket, torque to 35N-m or 26 in-lb (NOT ft-lb!). Clean up the area around the rear differential.

Lower the car and cleanup! Dispose of the collected gear oil at a proper facility.
I noticed that the overall drive is generally a little soother after the oil changes to the front and rear differentials.The best part is since the majority of break-in shavings from differentials have been removed early, the differentials should be maintenance free for the next 50-60K miles with normal driving.