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M939 What Fluid for Trans/Pwr Stg?

Gunzy

Well-known member
1,769
65
48
Location
Roy, Utah
Do what you feel is right for YOUR truck. As for me, 15W40 in engine, P/S fluid in P/S, 10wt in trans and PTO hydro, 80w90 in diffs and T-case. This should never cause any problems due to fluids. I found that 10wt is a lot less money than Dex III. Besides, if it was good enough for the military and has proven itself why change and possibly open a new bucket of worms. JMHO
 

aheilmann68

Member
228
1
18
Location
North NJ
I used tractor supply hydrostatic/hydraulic fluid. They are essentially all the same specs. Allison is looking for C4 certified IIRC which most universal hydraulic fluid is. The transmission takes pretty much 5 gals
 

Natron

New member
13
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0
Location
Buffalo, NY
My fault, when I googled this topic for my hmmwv it popped me right into the last page of this post, I didn't see the heading, sorry bout that.
 

SCM35A2

Well-known member
Steel Soldiers Supporter
2,015
2,812
113
Location
Florence, SC
Do what you feel is right for YOUR truck. As for me, 15W40 in engine, P/S fluid in P/S, 10wt in trans and PTO hydro, 80w90 in diffs and T-case. This should never cause any problems due to fluids. I found that 10wt is a lot less money than Dex III. Besides, if it was good enough for the military and has proven itself why change and possibly open a new bucket of worms. JMHO
I'm about to do some fluid changes in my 5ton/923A2 truck & I'm going with what Gunzy posted.
 

th3v3rn

New member
8
2
3
Location
Utah
So bought a used truck and have no idea how long it was sitting so changing fluids and filters. Got to the transmission and draining that it looks way thinner than motor oil which I've heard is usually what's in these. It's not as dark or black as the motor oil when I drained that and as an aside I don't think the motor oil has been changed since 2012 given the date on the filter.
You transmission oil looked pretty good coming out but is motor oil colored with just a little bit of mileage on it but is significantly thinner and almost has a red hue to it. Is this the dexron? I was talking to a friend that is a diesel mechanic and he says that it's likely hydraulic fluid?
 
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