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I have a 2016 Mazda6 Touring, stick-shift, with 36,000 miles. Sold originally in March, 2016 and I bought it as Certified Pre-Owned car with 14,000 miles in December, 2016. I've gotten snow tires, replaced the OEM junk tires, and done oil changes at independent shops. Hasn't really needed any other maintenance.

As winter has arrived, I've felt it occasionally shifts awkwardly, especially when cold. Like it's not happy to go into the gear shift gate. I'm pretty careful about rev-matching, etc., and this trouble is mostly up-shifting, especially 2-3. It's getting annoying and I'd like to fix it.

Anyone replace the OEM transmission fluid with a good synthetic like Redline or Amsoil?
Any other suggestions? (Might be time to flush the clutch and brake lines with new fluid, too.)

Thanks for sharing your wisdom...
 

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I'm not sure what fluid the MTX takes, but the AT takes this.

Head over to Redlines website and see what they recommend.


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Redline MTL is what I have in mine. It made quite a difference in shift quality and I've changed it a couple of times since (I'm right near 200k miles now).;)

Still 75w80, and I would NOT go thicker; that will make the notchiness much worse when cold. It's still somewhat of a PITA when I'm in below-freezing temperatures by a lot until I get it moving for a few minutes, but I don't do that often.

The spec is 75w80 GL-4. DO NOT use a GL-5 lube no matter what else is on the label (even if GL-4 is ALSO there); ALL GL-5s will eat the synchros in a gearbox designed for a GL-4 fluid.
 

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Our last Mazda with a stick was a first-year Mazda 5 (GREAT car!). I ran Red Line's MTL in it for nearly its whole life with us, and was very pleased. I believe the latest-gen 6's manual transmission specified the same or essentially the same thing as that 5 did, so I'd run Red Line MTL. That's what Red Line recommends, too. (-:

I notice that Amsoil does not have a manual transmission fluid they recommend.

The first reply here recommended the wrong viscosity fluid for the automatic transmission, but you don't have an automatic transmission, so hopefully you'll ignore that post. (-:
 

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I'm not sure what fluid the MTX takes, but the AT takes this.

Head over to Redlines website and see what they recommend.
Besides the fact that the poster has a manual transmission; this fluid is NOT recommended for the SkyActiv-Drive that his car would have, and their website reflects that
 

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Besides the fact that the poster has a manual transmission; this fluid is NOT recommended for the SkyActiv-Drive that his car would have, and their website reflects that
You're more likely to destroy an ATX by doing silly drain and fills at high mileage or neglecting the gearbox all together than using top notch ATF fluid though.

Safest bet is to use Mazda fluid, but once you see your local transmission shop pouring the exact same ATF fluid into every single car that pulls up to the shop without any issues you wont worry nearly as much.
 

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I have a 2016 Mazda6 Touring, stick-shift, with 36,000 miles. Sold originally in March, 2016 and I bought it as Certified Pre-Owned car with 14,000 miles in December, 2016. I've gotten snow tires, replaced the OEM junk tires, and done oil changes at independent shops. Hasn't really needed any other maintenance.

As winter has arrived, I've felt it occasionally shifts awkwardly, especially when cold. Like it's not happy to go into the gear shift gate. I'm pretty careful about rev-matching, etc., and this trouble is mostly up-shifting, especially 2-3. It's getting annoying and I'd like to fix it.

Anyone replace the OEM transmission fluid with a good synthetic like Redline or Amsoil?
Any other suggestions? (Might be time to flush the clutch and brake lines with new fluid, too.)

Thanks for sharing your wisdom...
I don't think any of those maintenance items are necessary at such a mileage, to be honest.

If you're bored of the stock shifter fee try throwing in one of those metal short throw knobs, they are great.
 

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There are a number of things you can do to deal with this:
  • First, ensure that the transaxle is, in fact, full. Some apparently were shipped with not-full 'boxes!
  • Drain fluid hot and try Redline MTL which is the correct 75W-80 GL-4. Many folks have found that this product has improved notchy shift action but also be aware that some folks have found that it "centrifuges-out" some of the additives, leaving a pastey residue, with the fluid-proper being deficient in wear protection (and with ensuing gear face and rolling element wear occurring). YMMV. Others?
  • Do the shift cable neutralization TSB (05-007/13 - applicable to Mazda3's and Mazda6's)). If you want more info on this - including how to access the shifter - let me know.
  • Realize that all gearboxes (at least every last one I've driven) DO feel "crotchety" when cold. For me it's a fact of life. I recommend you accept it and "nurse" the box to operating temp. Either start off your drive on a down-gradient, in 2nd gear, and shift-up at low rpm, slowly and deliberately... 'til up to temp.
  • The choice of the best manual transmission/transaxle lubricant is a study in competing priorities. A bit higher viscosity may give a bit more gear tooth/flank wear protection (though additives modify this... ) at the expense of cold shifting feel and possibly shift smoothness at normal temps too. Don't choose based solely on shift feel.
  • You can experiment with shifter height, shift knob weight, short-throw shift plate fitment, and finally shift-pivot/rod/vertical gearbox shaft "pendulum" weights.
Lotsa stuff to potentially try...

Finally, don't expect a miracle. There are a fair number of folks complaining about this C66M-R box. It's not perfect...
 

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One other item to add: The C66M-R transaxle (SkyActiv-MT) has the speed-gears (e.g. 1st gear, 2nd gear, etc.) running on a spline on the shafting... oil-fed with an oil funnel-type shaft pumping system. Contrast that with, say, my Toyota Aisin-Warner transaxle... with each speed-gear running on two half-shell caged needle bearings. The oil viscosity it seems to me is critical particularly for the Mazda design lest an inadequate amount of oil be pumped and delivered to the radially drilled spline oil supply holes.

That's why I say stay with 75W-80 synthetic lubricant, GL-4. Don't go heavier by way of viscosity. Also, don't go lighter either... sacrificing gear tooth and rolling element life expectancy for better synchro feel.
 

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One other item to add: The C66M-R transaxle (SkyActiv-MT) has the speed-gears (e.g. 1st gear, 2nd gear, etc.) running on a spline on the shafting... oil-fed with an oil funnel-type shaft pumping system. Contrast that with, say, my Toyota Aisin-Warner transaxle... with each speed-gear running on two half-shell caged needle bearings. The oil viscosity it seems to me is critical particularly for the Mazda design lest an inadequate amount of oil be pumped and delivered to the radially drilled spline oil supply holes.

That's why I say stay with 75W-80 synthetic lubricant, GL-4. Don't go heavier by way of viscosity. Also, don't go lighter either... sacrificing gear tooth and rolling element life expectancy for better synchro feel.
So basically speaking, what does this mean? what is the difference between the two gearboxes?

adding some Synchromesh fluid into the gearbox along with the regular MTL fluid during a fluid change. It will help with the notchiness.
 

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I have seen exactly ZERO issues with running Redline MTL and I'm right near 200k miles at this point. The OE oil was dumped at ~50k and I change it approximately every 50k miles (which means I'm coming up on being due for it again.)

The OE fluid came out fairly decent-looking and so have all the other drains. Could I go longer? Yes, but why? The oil is cheap and the change is easy, so..... yep.
 

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Here is the drill, re shift cable neutralization.

The ambient temperature (really, the temperature within the car interior) might have a bearing on when you would want to do this procedure. Hot is best because: i) you are using an interior trim removal tool to liberate some rather stoutly-affixed interior trim clips... and the hotter it is, it seems, the less brittle they will be; and ii) you will be engaging 4th gear and shaking the shifter left and right five times... and waiting 30 seconds to see if any changes in shifter setting occurs. As the shift cables pass through (likely) teflon lined casings (and I'm not sure what kind of lubricant is used) - when it is hotter, the gliding of said cables through their casings is likely more evident.

Here is the TSB: http://australiancar.reviews/_pdfs/SB-10059728-0335.pdf It applies equally to the Mazda3 and the Mazda6 - and beyond the years indicated.

Re the following link, at the 1:35 mark, there is some YouTube footage (from one of our Members) that shows him removing the upper console (though if memory serves, he does not talk about removal first of the screw under the rearmost cup holder in the upper console). You can glean good info from i) the interior trim removal tool he uses; and ii) the types of clips that are used (use freeze-frame to study those):

Please see the titles for the following graphics, to view things in the correct order. I will have to add a second post to be able to add-in all of the graphics...

I have tested-out the graphics... and I see that the bottoms get cut off. To see the whole graphic, and the instructions / text that is often at the bottom... you need to open the images "in a new tab"... to see this stuff (or in full-screen, I later found out)!

I would suggest you view all of the graphics before you do the work... as some detail is evident later-on in the stream of graphics.
 

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Here is the drill, re shift cable neutralization.

The ambient temperature (really, the temperature within the car interior) might have a bearing on when you would want to do this procedure. Hot is best because: i) you are using an interior trim removal tool to liberate some rather stoutly-affixed interior trim clips... and the hotter it is, it seems, the less brittle they will be; and ii) you will be engaging 4th gear and shaking the shifter left and right five times... and waiting 30 seconds to see if any changes in shifter setting occurs. As the shift cables pass through (likely) teflon lined casings (and I'm not sure what kind of lubricant is used) - when it is hotter, the gliding of said cables through their casings is likely more evident.

Here is the TSB: http://australiancar.reviews/_pdfs/SB-10059728-0335.pdf It applies equally to the Mazda3 and the Mazda6 - and beyond the years indicated.

Re the following link, at the 1:35 mark, there is some YouTube footage (from one of our Members) that shows him removing the upper console (though if memory serves, he does not talk about removal first of the screw under the rearmost cup holder in the upper console). You can glean good info from i) the interior trim removal tool he uses; and ii) the types of clips that are used (use freeze-frame to study those):

Please see the titles for the following graphics, to view things in the correct order. I will have to add a second post to be able to add-in all of the graphics...

I have tested-out the graphics... and I see that the bottoms get cut off. To see the whole graphic, and the instructions / text that is often at the bottom... you need to open the images "in a new tab"... to see this stuff (or in full-screen, I later found out)!

I would suggest you view all of the graphics before you do the work... as some detail is evident later-on in the stream of graphics.
Wow dude, many thanks for taking the time to put this together. I am really hoping at least a couple different MTX users will find this useful. I would repost this as it's own seperate thread so that more people see.
 
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