Guide: 2016~2021 CX-9 DIY Transfer Case + Rear Differential Fluid Drain and Fill

:
Mazda CX-9 Signature
Items needed:
1) 2 quarts of LONG LIFE HYPOID GEAR OIL - SG1 - Mazda (0000-77-SG1-QT)
2) 23MM shallow socket for fill plug
3) 24MM shallow socket for drain plug
4) 4 pieces of drain plug gasket (9956-41-800)
5) Fluid pump

Please note owner's manual states approx 0.45qt (15oz) for transfer case and approx 0.45qt (15oz) for rear diff. However, do pick up 2qt of oil because rear diff was under-filled quite a bit.
Always crack open the fill plug before draining the fluid. Replace all washers. Torque them 35ft/lb. 1 quart = 32oz

I drained 14oz from rear diff and filled approx 22oz
I drained 16oz from transfer case and filled approx 18oz
 

Attachments

  • 20200820_102134.webp
    20200820_102134.webp
    215.6 KB · Views: 1,513
  • 20200820_102628.webp
    20200820_102628.webp
    193.7 KB · Views: 1,308
  • 20200820_104419.webp
    20200820_104419.webp
    240.4 KB · Views: 1,111
  • 20200820_105724.webp
    20200820_105724.webp
    200.6 KB · Views: 1,049
  • 20200821_094157.webp
    20200821_094157.webp
    468.7 KB · Views: 1,165
  • 20200821_095224.webp
    20200821_095224.webp
    342.7 KB · Views: 1,394
Thanks for writing this guide. It's really helpful to know what you are getting into before starting a job. Do you have to remove much of the under car plastic to get to the transfer case? Most of the underside of the front of the car seems to be covered.

Also, have you investigated doing any transmission fluid maintenance? I don't see a dipstick in the engine compartment, so this vehicle may be one of those where you pump the transmission fluid in via the drain.
 
I have yet to tackle this, my bathroom renovation took some interesting twists so I'm behind on what I wanted to complete and write up. I would like to add some snapshots from the manual for drain and fill locations for those who will use this guide.

Transfer case Drain bolt location: to get to these locations you need to remove the large undercover.
both torque settings are 30-42 ft/lbs (40-58 Nm)
transfer case drain.jpg

Transfer case fill location:
Trasfer case fill.jpg


Differential drain and fill locations: both torque settings are 30-39 ft/lbs. (40-53 Nm)
rear diff. plug locations.jpg


I plan on replacing both fluids this fall, I have to get done with my remodel project and make room.
 
I have yet to tackle this, my bathroom renovation took some interesting twists so I'm behind on what I wanted to complete and write up.
I would like to add some snapshots from the manual for drain and fill locations for those who will use this guide.

Transfer case Drain bolt location: to get to these locations you need to remove the large undercover.
both torque settings are 30-42 ft/lbs
View attachment 226672
Transfer case fill location:
View attachment 226673

Differential drain and fill locations: both torque settings are 30-39 ft/lbs.
View attachment 226674

I plan on replacing both fluids this fall, I have to get done with my remodel project and make room.

Thanks for this!!
 
Items needed:
1) 2 quarts of LONG LIFE HYPOID GEAR OIL - SG1 - Mazda (0000-77-SG1-QT)
2) 23MM shallow socket for fill plug
3) 24MM shallow socket for drain plug
4) 4 pieces of drain plug gasket (9956-41-800)
5) Fluid pump

Please note owner's manual states approx 0.45qt (15oz) for transfer case and approx 0.45qt (15oz) for rear diff. However, do pick up 2qt of oil because rear diff was under-filled quite a bit.
Always crack open the fill plug before draining the fluid. Replace all washers. Torque them 35ft/lb. 1 quart = 32oz

I drained 14oz from rear diff and filled approx 22oz
I drained 16oz from transfer case and filled approx 18oz

Hey! Thanks for this! Just wondering, it is the same process for the 2016 CX5? Also, I see that you can check the transfer case oil level by putting a finger in, but can you do the same with the rear diff? I understand that I have to put more oil than what Mazda says. Is there such thing as a transfer case and rear diff overfill? My CX5 has 55k KMS on it, but its a 2016, so I was starting to think about that maintenance. Thanks!
 
Items needed:
1) 2 quarts of LONG LIFE HYPOID GEAR OIL - SG1 - Mazda (0000-77-SG1-QT)
2) 23MM shallow socket for fill plug
3) 24MM shallow socket for drain plug
4) 4 pieces of drain plug gasket (9956-41-800)
5) Fluid pump

Please note owner's manual states approx 0.45qt (15oz) for transfer case and approx 0.45qt (15oz) for rear diff. However, do pick up 2qt of oil because rear diff was under-filled quite a bit.
Always crack open the fill plug before draining the fluid. Replace all washers. Torque them 35ft/lb. 1 quart = 32oz

I drained 14oz from rear diff and filled approx 22oz
I drained 16oz from transfer case and filled approx 18oz
Thanks for the info, but Did you fill until it comes out of the fill hole?
 
Dumb question here, but for the transfer case do you fill it until fluid comes out the fill hole or is there some other procedure for determining the proper fluid level? Reason I ask is I filled it until it leaked out but the axle seal is lower than the fill hole and I'd hate to put too much in and cause that axle seal to leak. If anyone can let me know so I can drain as needed I'd appreciate it. I can't find any info anywhere else on the subject.

Edit: I see 2 posts above says it should be filled to the top but want to confirm 100% you are talking about the transfer case too. Replacing that seal will be a b***h if it pukes.
 
Last edited:
Edit: I see 2 posts above says it should be filled to the top but want to confirm 100% you are talking about the transfer case too. Replacing that seal will be a b***h if it pukes.
Yes, fill to the fill hole in the picture I posted in post #5.
Drain using the fill hole and fill using the fill hole until it weeps out. If you're so inclined you can also replace the drain plugs with magnetic drain plugs for additional fluid cleanliness since there are no filters for the diff or transfer case. These two locations have a lot of metal on metal contact. A magnetic drain plug is just additional insurance.
 
Yes, fill to the fill hole in the picture I posted in post #5.
Drain using the fill hole and fill using the fill hole until it weeps out. If you're so inclined you can also replace the drain plugs with magnetic drain plugs for additional fluid cleanliness since there are no filters for the diff or transfer case. These two locations have a lot of metal on metal contact. A magnetic drain plug is just additional insurance.
Thanks! I just reinstalled with the stock fill plug as is but I can see how an extra magnet would be of benefit. There was A LOT of fine metal on the lower magnet. Car has 66k on it. Not enough metal to make me nervous, I suspect alot of break in has occurred over time and I'm glad I swapped the fluid.
 
Hey all, is it recommended to apply some sort of anti-seize compound or sealant on the bolt threads when reinstalling them or is it not necessary? I'm coming up on 30,000 miles on my 2018 CX-9 and will be replacing the oil in the transfer case and rear differential soon so just want to make sure. I plan on doing it again at 60,000 miles and every 30k miles afterwards.
 
Last edited:
I have a 2016 CX-9 and I’m at 67300 miles. Would you guys recommend me changing my diff fluids?
 
I have a 2016 CX-9 and I’m at 67300 miles. Would you guys recommend me changing my diff fluids?
Yes, especially if you plan on keeping it long term and want to avoid problems with the AWD system down the line.

When Mazda says it's "lifetime" fluid, lifetime in their sense is the warranty period which isn't very long. I think in 2016 models and on, Mazda started saying the transfer case and differential have "lifetime" fluid. In prior model year CX-9's, the maintenance schedules for those recommended the fluid be replaced every 30k miles I believe.

Might want to think about doing a transmission fluid drain and fill since you're at 67k miles already. I'm going to do mine at 50k miles and every 50k after.
 
I just completed this maintenance today and thought I'd share my experience. My CX-9 is just shy of 32k miles and the oil in the rear differential was still in very good condition with a light brown color. When I removed the fill bolt on the rear differential nothing dripped out. The amount drained filled an empty 16oz Kirkland water bottle between 1/2 and 3/4 full.

The transfer case oil was a little darker brown in color, but still not bad in condition. No oil dripped out again when removing the fill bolt. The amount drained filled the same 16oz Kirkland water bottle to about 3/4 full. The drain bolt magnets on both had a glob of metallic particles on them, but nothing out of the ordinary.

Knowing now that the factory oil was still in good condition, I think I could've put this maintenance off to 40k miles. But hey, that's what preventative maintenance is for, right? I'll also note that I'm not an aggressive driver and don't run the CX-9 hard. I like to get good gas mileage, so no jack rabbit starts or anything like that where I'd be putting more wear and tear on things and getting crap MPG. Just normal boring city/freeway driving, so take that into consideration if you're wanting to put off changing your differential/transfer case oil.

Drove the car around for awhile afterwards to make sure I had no leaks and to just test her out and could immediately notice just an overall smoother/lighter ride.
 
To add to this thread, did the differential and transfer case change on my 2019 CX5 GTR (same powertrain as CX9). Car has 45k miles.

Transfer case: Easy, no fluid dripped out when cracking the fill bolt, fluid was a bit brown but in decent condition. Some metallic shavings on magnetic but nothing out of the ordinary. Pumped in new fluid while on ramps until dripped out. Sealed and drove. Added more fluid while car was off ramps (level), only needed a few more pumps, not sure if it's worth it to add more fluid a second time.

Differential: Harder due to the constraints on the space. Would recommend getting ratchet wrenchs vs socket wrenchs. I had a 24mm socket that just barely fit. I had to use a low profile wrench with a 23mm socket to get the fill bolt. No fluid dripped out when opening the fill bolt. Fluid was dirtier than the transfer case which was suprising. There was also more metallic shavings on the magnetic vs. the transfer case. Filled and drove. Again not sure if it was worth it to do another fill after driving. Only got in a few pumps.

Overall easy job. I wish mazda added wholes in the crossmember for the differential like Honda does to access the bolts. To change the differential on the older pilots you just need a 3/8 inch drive, it goes through two holes in the crossmember put there specifically for serving the differential. You do need to drop the spare tire on the Pilot though, so I guess pretty much a wash?

You absolutely do need 2 quarts of fluid. Do not think you can get by with 1 quart.
 
Back