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

MLC LS1 said:
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.
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Yea, I am not convinced on filling the diff to the fill hole. Exact same known issue on Chevy 1/2 ton diffs. 2002 is mine for example. The fill hole is above the pinion seal and if you fill it to the hole it increases the chance of puking that seal. Seal is happy holding back splash oil, but not oil 24/7/365. Book says 5/8" to 1-5/8" inch below the hole. I do 3/4 which is a perfect 2.0 qts. To the hole is 2.5-2.8 qts. If your saying the fill hole is above the axle seals then I might stop at .5 ish and just do more often. 16oz is a pathetic amt of oil for a diff though, wow
 
Rule #1 for draining any gear box....loosen the fill plug before your remove the drain plug. If the fill plug is stuck and you can't get the fill plug out, don't drain the oil out.

Red Line 75W85 is my choice of gear oil for these jobs. I use the recommended amounts.

The plugs need good gaskets on them. Possible for a sealant would be plumber's thread sealant paste...it doesn't harden and it seals liquids. Teflon tape isn't a good choice...some of the tape remains on the internal threads the next time you the do the change, and shreds of the tape could be pushed into the machinery when the plug is reinstalled next time.
 
Does the 2016+ CX-9’s have one or two differentials? I assumed that since mine is AWD, it has both a front and rear differential.
 
shawnee said:
Does the 2016+ CX-9’s have one or two differentials? I assumed that since mine is AWD, it has both a front and rear differential.
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If you read through the previous posts in this thread, there's two places where oil is changed, the rear differential in the middle of the rear wheels, and the "transfer case" in the front.

The "second differential" is actually inside the transmission or something like that which you don't have to worry about. It's the transfer case in front and the rear differential in back that need oil servicing.
 
How critical is it for the vehicle to be level while filling? I ask because I can only get under there while up on ramps and the vehicle is not level. I realize that filling until it comes out the fill hole could depend on angle depending on the location of the fill plug.
 
Silly Wabbit said:
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
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I was under the impression my 2018 cx 9 does not have drain plugs for the transfer case or differential
 
When someone next pulls out the plugs, please post the diameter of the threads. Gaskets for drain plugs are available in auto parts stores. Aluminum, nylon, fiber, or copper are all available. Which material is the original gasket...or washer as they call it? 12mm, 14, 16, 18mm gaskets are commonly available.
 
Using the torque wrench to loosen the drain plugs?...may be OK, but I'd rather not. I don't know where one would get a torque wrench recalibrated, and I really don't want to damage mine.

The 'sludge' he finds on the drain plug magnet is bits of steel and iron, and a small amount is normal. On a crankcase magnetic drain plug the ferrous bits are too fine to be caught by the oil filter media but still abrasive.

He fills the gear box to the overflow point. I'll only fill mine the specified quantity, about what he drained out. We don't know why the fill hole is where it is, maybe to be accessible to a wrench, maybe to miss stiffeners on the housing casting. Sometimes more is not better.

If you're removing the plastic rivets that hold plastic pieces in place, if they aren't easy to get out, you're not doing it right. With a small screwdriver pop the center part half way out, then remove the whole rivet. If the center comes all the way out, OK, but not necessary. To replace, with the center halfway into the outer part, put the rivet all the way in place, then lock it by popping the center in flush.

Take a drive before changing the gear oil. It'll drain more completely when it is warm. Slightly warm the new oil, put it in the sun, or in winter in a pan of hot tap water so it'll flow more easily. By the way, the viscosity grades for motor oil and gear oil are on a different scale. SAE 40 vg (wt.) engine oil and SAE 90 vg. gear oil are about the same actual viscosity, ditto for 30 vg engine oil and 75 vg gear oil. Any viscosity grade 75 vg & above identifies the product as gear oil.

Is it still Lefty-Loosey south of the equator?

Does the Mrs. know where her green salad bowl is?

I don't think my Mrs. would get under a car if I was already there having a heart attack.

Oil drain plug magnetic removal tool (after first loosening), under $10, (won't work on a nonmagnetic stainless plug with a magnet pressed in to catch the wear bits):
1718218484656.png
 
PTguy said:
Rule #1 for draining any gear box....loosen the fill plug before your remove the drain plug. If the fill plug is stuck and you can't get the fill plug out, don't drain the oil out.

Red Line 75W85 is my choice of gear oil for these jobs. I use the recommended amounts.

The plugs need good gaskets on them. Possible for a sealant would be plumber's thread sealant paste...it doesn't harden and it seals liquids. Teflon tape isn't a good choice...some of the tape remains on the internal threads the next time you the do the change, and shreds of the tape could be pushed into the machinery when the plug is reinstalled next time.
Click to expand...
I am about to do the service on my 2018 cx9. Was going to buy the mazda 75w85 oil from the dealer but thankfully the partsman informed me that 1 litre is almost $80.00/L CND and that they have started using only bulk 75w85 from Petro Canada?
 
PTguy said:
Using the torque wrench to loosen the drain plugs?...may be OK, but I'd rather not. I don't know where one would get a torque wrench recalibrated, and I really don't want to damage mine.

The 'sludge' he finds on the drain plug magnet is bits of steel and iron, and a small amount is normal. On a crankcase magnetic drain plug the ferrous bits are too fine to be caught by the oil filter media but still abrasive.

He fills the gear box to the overflow point. I'll only fill mine the specified quantity, about what he drained out. We don't know why the fill hole is where it is, maybe to be accessible to a wrench, maybe to miss stiffeners on the housing casting. Sometimes more is not better.

If you're removing the plastic rivets that hold plastic pieces in place, if they aren't easy to get out, you're not doing it right. With a small screwdriver pop the center part half way out, then remove the whole rivet. If the center comes all the way out, OK, but not necessary. To replace, with the center halfway into the outer part, put the rivet all the way in place, then lock it by popping the center in flush.

Take a drive before changing the gear oil. It'll drain more completely when it is warm. Slightly warm the new oil, put it in the sun, or in winter in a pan of hot tap water so it'll flow more easily. By the way, the viscosity grades for motor oil and gear oil are on a different scale. SAE 40 vg (wt.) engine oil and SAE 90 vg. gear oil are about the same actual viscosity, ditto for 30 vg engine oil and 75 vg gear oil. Any viscosity grade 75 vg & above identifies the product as gear oil.

Is it still Lefty-Loosey south of the equator?

Does the Mrs. know where her green salad bowl is?

I don't think my Mrs. would get under a car if I was already there having a heart attack.

Oil drain plug magnetic removal tool (after first loosening), under $10, (won't work on a nonmagnetic stainless plug with a magnet pressed in to catch the wear bits):
View attachment 329037
Click to expand...
Thanks you so much for this info. Will help me in the future and aid me in passing on the correct information to others.

I ending up using 1.1L of oil… there was about 20ml in the pump.. so that left 90ml that was used… so hopefully not far off spec 0.45L for each diff. Was such an easy job when not messing with cameras lol.. so might do it again, as the new oil might have clearned some old laying in the bottom?

I was going use 75 Penrite gear oil which was advised by other mechanics on other forums… but when I found the Mazda oil wasn’t that expensive, I just went for the genuine bottle.

My wife ad I love working on cars together.. stripped down our problematic Audi Q7 a few times, mainly because the job was so big, even Euro mechanics wouldn’t take it on… and there was no way I was paying deal prices…would have cost more than the car. However, we have done fun stuff on cars, loved wrapping the Golf R in satin metallic purple (wife’s favourite colour).

Lefty Loosey lol… thinking out aloud lol.. my wife and I got quite good content with me using the gravy jug AKA oil jug lol… and wearing my slippers.. but it didn’t record!! Defo would have made good content lol.

Anyway, thank you for you super help and advice. I am new to Mazda, so will be reaching out for more in the future maybe. Have a great weekend
 
PTguy said:
If you're removing the plastic rivets that hold plastic pieces in place, if they aren't easy to get out, you're not doing it right. With a small screwdriver pop the center part half way out, then remove the whole rivet. If the center comes all the way out, OK, but not necessary. To replace, with the center halfway into the outer part, put the rivet all the way in place, then lock it by popping the center in flush.
Click to expand...

Those plastic fasteners can be a pain. They come out very easily in covered areas like under the hood. But the underbody shields, wheel well trim and liners are subject to dirt, debris, and salt that can get in the fastener and cause them to jam up enough to not want to come out as easily. I should remember to bring a can of WD-40 or silicone lubricant to reduce the chance of accidentally snapping the fasteners in half when I do my gear oil change.

They also make plastic fastener removal kits that come with extra fasteners of different sizes. Found this one locally, but I'm sure places like Harbor Freight also carry kits like these.
 
MIMazdaowner said:
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.
Click to expand...
Wouldn't it be easier to measure what was drained out and then put the exact amount back in?
 
What did your fluid look like after draining? I did the transfer case yesterday. Fluid was a caramel colour, tiny bit of sludge on the drain plug, and some fine metallic particles settled at the bottom.

Drained 13.5-14oz from the transfer case. Filled to the bottom of the fill hole.
 
After 135K usage the oil still looked fine. Similar to how you described its color. I drained 450 ml and refilled with same amount. Moving forward my plan is to drain both differential and transfer case every 100K.
 
Ok, I'm having a hard time with the rear diff. Only because I can't seem to get my socket and ratchet to fit on the fill plug! I'm using what I think are shallow sockets, they're about 40mm tall. And a 1/2" ratchet as the only 23 and 24mm sockets I could find locally were all 1/2" drive. Are my sockets not actually shallow? Am I maybe using the wrong tools? I can't get the socket on the bolt because the crossmember is in the way.

I feel stupid lol. I'm about to return these sockets and buy a couple of 23mm and 24mm wrenches instead. Hopefully those will work. Pic attached below.
 
If necessary a socket can be ground down so it has less length, just enough to engage the hex head, and you have more clearance.
 
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