Which Transmission Fluid is best?

[MADMODDER]

Sorry for my lag everybody. Been busy few days.
And there is a wealth of information. I'm gonna need a minute to digest it all.

I'm coming up on my 21st hr.

I'm likely have to re-read this a few times.

But I'll give it a go now. Let me know if I'm wrong and/or missed anything.

"Synthetic is bad" is BS. Ya? Thanks for the break down on that @gw33gp.

75w140 for the differential. Could use it in both but I dont do the 4x4 thing. I've only used 4WD like once or twice in the 3 years I've owned it. So use 80 or 90 because it cheaper. BUT to use the 75w140 as transmission fluid too. Ya?

Redline synthetic 75w140 matches for oem spec of M2C192A.

And as for the transfer case, just whatever oem fluid I can get from the dealer. Ya?


What a rabbit hole.

 

[Dirtman]

Ummm for the love of god don't put 75w140 or any gear oil in your transmission...

 

[MADMODDER]

What did I miss?

4x4junkie said his books say to use gear oil. He said M2C192A was the specification for the synthetic.

 

[19Walt93]

The transfercase uses Mercon III spec fluid, Ford's transfercase fluid is Mercon III for 3 times the money.
I've only heard of synthetic fluids causing problems for 2 things: T5 transmission syncros don't like synthetic fluid because it's too slippery for the blocker rings to grip properly and Auburn gear told me not to use synthetic gear oil with my Auburn Pro because it would make noise. Auburn limited slips shed metal particles into the fluid so the fluid needs to be changed regularly and the particles will eventually ruin the bearings. I bought a Yukon clutch type diff to replace the Auburn.

 

[Josh B]

Is Mercon III equal to Dex/Merc ?

 

[Dirtman]

No. Regular mercon is dex/merc

 

[Dirtman]

What did I miss?

4x4junkie said his books say to use gear oil. He said M2C192A was the specification for the synthetic.

He was high or you miss-read. M5od takes mercon 5. In no way shape or form gear oil...

 

[Josh B]

Early M50D uses Mercon(Including my 93), later(I'm not sure which exact years) uses Mercon V

 

[Dirtman]

Early M50D uses Mercon(Including my 93), later(I'm not sure which exact years) uses Mercon V

I wont get into the mercon V superseding mercon debate... still FAR from gear oil in either case.

 

[MADMODDER]

Idk if there is conflicting opinions here or if I'm confusing myself.

Redline website says my transmission is the M5R1HD but I'm being told here that I have an M5ODHD.

I'm going to assume that redline is wrong. From my experience with euros, websites selling aftermarket options are more wrong than not.

Would that be a fair assumption in this case too?

So, assuming that is the case, I want the Mercon V for the trans, merc 3 for the transfer case and 75W140 for the Diffs.

Have I got that right?

 

[Dirtman]

You have an M5OD the "R" part is just what revision it is and really doesn't matter because it's still the same transmission. "HD" is heavy duty and again, doesn't matter. Still the same transmission no matter what revision or if its HD or not.

If it matters, you most likely have the M5OD-R1HD since you have the 4.0. (Mazda 5 speed Over Drive, Revision #1, Heavy Duty)

The last part is right... Mercon V for the trans, Mercon 3 (now called transfer case fluid) for the transfer case, 75w140 in the diffs.

 

[MADMODDER]

Ok. I see. Thank Dirtman. Any input on the diff covers?

 

[Dirtman]

Unless your rock crawling stock is the best. The stock covers provide the best oil flow.

 

[Josh B]

I think maybe it's transmission dealers and rebuilders who turned the M50D R1 R2 etc into M5R1 M5R2 etc, probly cause they refer to them a lot around the shop and such, and apparently their name for it could not be easily confused with any other brands/models(and they deal with many brands, makes, and models)

I recently did some substantial research into new and rebuilt trannys while looking for a replacement for mine, and those places are where i was introduced to those numbers (as opposed to Ford dealers and parts stores, where you mostly use the original ones)

When the M50D(which I use for the number on mine, which is what the Ford manual, and most parts stores and Ford dealers use) first appeared, there were no R1 R2 etc, only an M50D. An updated M50D became the M50D R2 when it first appeared, etc, effectively then rendering the original M50D into becoming the M50D R1

I have no hard factual evidence of any of this actually, it's just that at this time, it's the very best supposition I can offer

 

[Dirtman]

I say the exact same thing about that dude with the one milky eye who hangs out behind the wawa...