Manual transmission fluid for M5R1 | Ford Explorer Forums - Serious Explorations

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Manual transmission fluid for M5R1


Explorer Addict
October 22, 2006
Reaction score
City, State
Huntington Beach, CA
Year, Model & Trim Level
98 XLT, OHV, 4D, 4x4, 5M
Just wanted to share this. I've been trying to improve the shift quality of my M5R1 transmission since I got the truck in 2006. Always has been notchy and quite stiff when cold. Tried Mercon, Mercon V, Mobil 1 ATF, 0w-20 synthetic, synchromesh. Nothing seemed to really make any difference.

I tore down the trans and rebuilt it with new bearings, synchros, and seals. Filled with Mercon V. Still notchy. Haven't tried it when cold yet.

I discovered this stuff - "GM Manual transmission fluid" - which seemed like a promising upgrade. Same viscosity as Mercon but with additives specifically for manual transmissions. The base stock is Dexron III. So far I am very happy with the shift quality although I haven't tried it in cold temperatures yet. Just thought i'd share if anyone else wanted to give it a shot. Right now its $6.59 a quart with free shipping (trans takes 2.8 quarts).


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Original Mercon is the spec fluid, and the generic DexIII/Merc fluids work fine. Merc V does not have the right friction properties for the M5R1, despite some of the later indications to just use it. You could also try XL12 Transfer Case fluid, which is just original spec Mercon with a higher price tag.

"notchy and quite stiff when cold" usually comes from a clutch issue on this setup. You also might want to throw a shifter kit (the wear parts where the shifter enters the top cover) if yours are worn.

So would this be ok to add to a transmission that I seriously doubt has seen much maintenance since warranty? (300000km ok her)

So would this be ok to add to a transmission that I seriously doubt has seen much maintenance since warranty? (300000km ok her)

Best to drain out what's in there, then refill with this stuff, or just atf.

That's what I mean by adding to, because as I've read only a fraction comes out during draining. I've got the m5od and noticed there isnt a dip stick so how does one fully flush besides the pan or dropping the whole thing? Just do the several fill,drain, drive cycles?

The m5od doesn't have a pan. It has a drain plug, and that will drain 99% of the fluid (except for what clings to the innards). It also has a fill plug where you fill it back up. Both are clearly labelled right there on the left side. Drain it out, refill it, and call it done.

What rb said. ^^
It's the auto trans that has a pan and doesn't drain fully.

Ahhh, it's the little things. Lol. So does that mean there is no filter? Making fluid changes that much more important?

No filter. The gears are just rotating in a bath of oil.

Alright, after reading this and a few threads at BITOG I put this stuff in my M50D and I have noticeable shift in improvement.

Can you elaborate on the improvement? Interested in maybe trying it...

Can you elaborate on the improvement? Interested in maybe trying it...

Ok, with the mercon, I would have shifts from first to second that were not smooth. Sometimes I had to bounce it in etc... Also at full stop same condition existed when putting it into first. They are not eliminated completely, but those shifts are much improved and first to second has almost entirely been eliminated. It's happened a couple of times on the really hot days, when it was over 110 degrees.

I was thinking about adding some Lucas Transmission Fix to my tranny fluid in the m5r1 to improve shifting. Has anyone tried this yet?