Manual Trans fluid recommendations

So it's time to continue baselining my GF's car and the next order of business is the manual transmission. What is the hive consensus on type/viscosity? Does it have to be GL-4 or GL-5? 75W90 or ??

In the past my "GO TO" fluid has been RedLine MTL which is the perfect cure for an early Miata "notchy" transmission.
 

pcb

The Diagram Dude
:
2002 MP5
I went with syndromesh oil because my gears would grind for 20 minutes every day in the winter.

My gears don't grind anymore.
(It's always warm where you are though, so there's probably better options for you.)
 
I went with syndromesh oil because my gears would grind for 20 minutes every day in the winter.

My gears don't grind anymore.
(It's always warm where you are though, so there's probably better options for you.)
We don't have that problem here; ours is the fluid getting thin from the heat. :)
 

pcb

The Diagram Dude
:
2002 MP5
I remember a lot of guys use Redline.

I remember too that our gearboxes don't have hypoid gears so we don't need the special additives (like sulfur) in the oil.

GL-4 and GL-5 have stinky toxic additives.


Actually, I lied when I said I'm using synchromesh oil.
That stuff was $17 a liter.

I remembered my 83' GLC said you can use ATF type F in a manual transmission at cold temperatures.
(Apparently, the F stands for either Friction modified or Ford, who used it in their automatic transmissions.)

So I used it ($7 a liter) with a liter of Lucas Oil. Lol

It's my own recipe and has been in there for almost 10 years.

(I drive very smoothly though and never slam gears. )
 
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Correct. Type "F" is Ford spec.

Just curious, is the differential on its own case or does it share the case with the transmission?

Hypoid gears require GL-5 fluid.
In order for the synchros to have the correct amount of "grippy" you need GL-4

In the Miata world, some people are swearing by [and at] the fancy German fluid that Ford specs for the Mustang transmissions, it's almost as thin as ATF . That stuff is crazy expensive at between US$17-$20 a quart -and you need two. Personally I stay with MTL.
 

pcb

The Diagram Dude
:
2002 MP5
Just curious, is the differential on its own case or does it share the case with the transmission?

I assume it's a shared case because there's only one oil to change.


In order for the synchros to have the correct amount of "grippy" you need GL-4
I figured that the Friction modified ATF made it grippy enough.
And the Lucas Oil made it clingy. Lol

In the Miata world, some people are swearing by [and at] the fancy German fluid that Ford specs for the Mustang transmissions, it's almost as thin as ATF. That stuff is crazy expensive at between US$17-$20 a quart -and you need two. Personally I stay with MTL.
The synchromesh oil is the same price.








 
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02 Protege LX, 03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
So it's time to continue baselining my GF's car and the next order of business is the manual transmission. What is the hive consensus on type/viscosity? Does it have to be GL-4 or GL-5? 75W90 or ??

In the past my "GO TO" fluid has been RedLine MTL which is the perfect cure for an early Miata "notchy" transmission.
1) P5 manual transmission calls for same spec fluid as my NC Miata.
2) People on miata.net swear by Motorcraft MTX-75
3) I did have some 2nd gear grind in one of my P5s and using the above fluid got rid of the grind.
4) Cheapest I have found it...
 
1) P5 manual transmission calls for same spec fluid as my NC Miata.
2) People on miata.net swear by Motorcraft MTX-75
3) I did have some 2nd gear grind in one of my P5s and using the above fluid got rid of the grind.
4) Cheapest I have found it...
Yep, and as there are stories like yours where the unicorn tears fixed a transmission, there are equal number of ones where it royally F-them up.
About 99% of the cases where there was some perceived improvement it was due to replacement of 100 K miles original fluid with something fresh.

The transmissions that best benefit from the Ford stuff are NAs [probably due to age], 5 Sp NBs, [does nothing for the 6 Sp]. The NC 6 Sp gear box is one of the best Mazda has put in Miatas. It's even superior -stronger- to the ones in the ND1. There is a adapter kit to mate the NC box to the ND1 motor.

That said, the transmission in our ND2 ['19 30AE] is one of the best shifting boxes I've ever used. I do just fingertip shifting.....
 
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02 Protege LX, 03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
Yep, and as there are stories like yours where the unicorn tears fixed a transmission, there are equal number of ones where it royally F-them up.
About 99% of the cases where there was some perceived improvement it was due to replacement of 100 K miles original fluid with something fresh.
AFAIK this is the Ford stuff is the original MT fluid put in at the factory. Not sure how that could mess a trans up.
Mine was not 'perceived' improvement. I had previously used mobile 1 synthetic fluid that met the specs in the owners manual. 2nd gear started grinding around 20 or 25k later. Next change at 30k I used the Ford stuff. No more problems.

I am sure a cheaper brand will work fine most of the time. But for me the Ford stuff worked better, so I use it from now on (in both my P5 and NC2).
 

pcb

The Diagram Dude
:
2002 MP5
What year/car? Auto/manual?

I was thinking he had his dipstick stolen, lost, or broke it. Lol







PS. If you have a manual transmission, remove the oil fill bolt first.

If you remove the drain bolt first then can't get the fill bolt off, you're in for a world of hurt. Lol
 
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pcb

The Diagram Dude
:
2002 MP5
Getting the oil into the transmission is a PITA.

You can barely hold the bottle of oil horizontal and you're lucky if you can squirt half of the bottle in.


I bought an oil pump to do it.
Something like this..



 
Getting the oil into the transmission is a PITA.
One trick we use in Miatas is to get a pipe thread to hose barb fitting, screw it in place of the plug, slide a length of clear tubing on it, bring the other end to the top of the engine compartment, place a small funnel on the tubing and pour the fluid slowly, watching the clear tubing where it meets the barb at the transmission. Once you see fluid backing up you stop. Replace it all with the plug and you're good to go. Worst case scenario you'll lose maybe a couple of tablespoons of fluid.

Been doing it this way for years.
 
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