Dexron II or Manual Transmission Oil??

[Grandpas_Truck]

Can someone please explain this to me?
I want to change the fluid in my 4 speed manual (3 forward gears plus one granny gear). and I found this in the manual and on ProDemand
"All manual transmissions except 4-speed (89mm), 5-speed (77mm) and those in the "S" series, use SAE 80W, GL-5 or SAE 80W-90 GL-5 multipurpose gear lubricant. The 4-speed (89mm), 5-speed (77mm) and all "S" series vehicles with manual transmissions use Dexron II automatic transmission fluid."

Is this correct? I have never heard of a manual transmission using AT fluid?? I can guarantee it doesn't have AT fluid in it right now. Truck is a 1986 GMC k2500

 

[dusterdude]

Drain it and see (1) if its thick or red,if its red,its atf.also see if it stinks,if it stinks,ots gear oil

 

[squaredeal91]

Smelling helps allot

 

[TotalyHucked]

Yep, lots of manuals use ATF. My current T56 does as did all the T5/T45s and 3650s I've had. Older ones like Muncies and Saginaw's probably used gear oil but I know old Porsche transaxles, we'd use ATF in them too. Just depends on what spec oil they need and what the tolerances are

 

[nvrenuf]

... (3 forward gears plus one granny gear)... Truck is a 1986 GMC k2500

This will be an SM465 transmission which used gear oil forever. It's possible the last few years had ATF spec'd for improved economy, the NP205 tcase was this way. I run gear oil in my SM465 (mixed years of parts plus aftermarket tailshaft).

 

[Keith Seymore]

They are referring to the New Process A833, which is the three forward gears plus overdrive trans. It uses auto trans fluid.

The M20 with the creeper gear uses gear oil.

K

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[Ricko1966]

One other thing you need to be aware of,if you use gear oil it make sure you are using the correct gear oil,verify what was suggested OEM some gear oils will damage syncro rings. A lot of people think it's okay to run gl5 in place of gl4,maybe with certain brands in certain transmissions. But I would verify what it called for originally before I used what the new lubrication guides say.

 

[Grandpas_Truck]

They are referring to the New Process A833, which is the three forward gears plus overdrive trans. It uses auto trans fluid.

The M20 with the creeper gear uses gear oil.

is the M20 and SM465 the same thing? Sounds like this is what's in my truck. my shift knob does not look like the one you pictured. (No Overdrive and the reverse is in the far right bottom)

 

[YakkoWarner]

I had a Ford truck with a 5 speed manual and it called for ATF as lubricant. I also have a British car with a 4 speed manual that specs 20-50 engine oil for the transmission. Only bring those up to point out that the lube spec can be all over the map - I would say it is important to find out exactly which tranmission you have and then you will know what it likes to drink.

 

[Keith Seymore]

Yes. M20 is the RPO code for the SM465.