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Has anyone out there tried this?


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OK you purists out there here's something to put your knickers in a twist. :D I'm 60 years old and been working on cars for 42 years professionally but still haven't figured it all out :confused:   I have had a few experiences though and I'm an old drag racer so I try things sometimes that make sense to me. LOL maybe it only makes sense to me? SO... what do you all think about this. I live in the mountains and commute to the valley to work every day. When its 17 degrees in the morning and you can't get your transmission in gear till it warms up it kind of sucks. Years ago when I was working on Toyota's the W-55 5 speeds were notorious for customer complaints of hard to shift cold. Toyota service reps had us putting 10w30 motor oil in the transmissions instead of the 80w90 gear oil, It solved the customers concern and I never had one come back in a pile so I guess they were OK. Later on I started seeing ATF in manual transmissions so I tried it in the W 55 and it worked great. Since then I've used it in Mitsubishi's, Mazda's and Nissans for the same reasons. Many newer cars and trucks call for it from the factory so I'm referring to those older applications that don't. Most recently I put it in my old 82 KC 4X4, It seems great. Right into gear cold, shifts smooth, no abnormal noises, better fuel mileage and its not leaking. So call me crazy but it seems to work. :hyper: Now here is my latest fit of crazy thinking. Many transfer cases of today are also using ATF, I know that most of them that do and I am acquainted with are chain drives and this Datsun of mine is gear to gear but after a quick look in the manual the transfer case does appear to be sporting synchronized helical gear sets.  Perhaps the ATF would do the same thing for the transfer case that it has done for the 5 speed? Less drag and smoother operation? Has anyone tried it in one of these old transfer cases like the one in my 82 KC?

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I don't know about the ATF but people on here have had really good luck with Syncromesh in datsun transmissions. Is there any risk to yellow metals from the ATF?

Great to hear because that's what I just bought on a whim of needing "manual transmission fluid" (No one had heard of that round here) and no one having anything but that.

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So. Im no expert, but here's what I think I know. You likely will benefit from oils with extreme pressure additives. ATF is not very good at high pressures, high torque situations. MTF is. The sulfur in ATF or GL4-5 is not good, but most active sulphur additives are deactivated first. They still do have higher potential to increase wear on brass parts. If you find something sulphur free, great. I bet you will be able to run with ATF for a long time if you don't ask much of it. But if you are driving this thing in high torque off-road, or off the line driving, you would be tempting fate.

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I recall that 80w90 gear oil and engine oil are not rated for their 'thickness' the same. 40W? engine is fairly close to 80w90? Something like this. My son's old FWD POS had the engine and transmission sharing the same 10W30 engine oil.


My Datsun FS5W71B was stiff the first few shifts in the morning and moderately stiff as it cot colder. The first shift to second would often clip a few teeth. Up shifting is fine down shifting was so much trouble (1dt and 2nd, hard push and a grind) I rarely did it. You could double clutch but it sounds retarded and rarely do you ever need to do this anyway. It was a 5 speed I found in a '79 zx, no idea of mileage, this was in the mid late '90s. My 620 transmission went out swapped it in there for 8-10 years heavily used. Now it's in my 710 and I've put about 10K on it.


Couple of years ago I filled it with the AC Delco Synchromesh Transmission oil. It's noticeably thin and orange yellow color. Unbelievable difference. Cold shifting stiffness, gone and I'm driving it even below freezing now this year. Shifting is faster, not that I always shift 'fast' but you can now where it was a bit of a push before. Down shifting compared to 80w90 is night and day. Just shove it in, hardly any resistance and never a grind.


It did wet the tail so I replaced the seal. After two years it may be wet again so this spring I'll replace it again, only $5. 

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Good articles, good points still I have questions. Nothing I've read seems to lend a definitive answer. I have questions because that is how we learn.


1. Many manufacturers are using ATF in late model manual transmissions. The ZF 5 speed in my old Ford F250 4x4 diesel has 300,000 miles of hauling in the extreme heat and cold yet it remains cherry. Of course we are talking about Mercon, 3 then 5 and now LV not Type F and it has been serviced regularly.


2. I would think that a thinner fluid bathing the counter gear would splash, penetrate and therefore lubricate more effectively especially in the extreme cold


3. I have a little bit of trouble with the idea that automatic transmissions do not have extreme pressure concerns when the holding and driving of essentially smaller sun, ring and planetary gear sets are concerned. Todays 6 speeds are using 3 planetary gear sets and they are all turning and reversing or holding their related components. Now factor in the heat that an automatic makes in comparison to a manual transmission and I think you have room for debate as to the abilities of todays ATF to do the job in the manual transmission of yesterday. At least in the small truck and automotive world.


4. As to the additives and there properties and how they might effect a manual transmission versus an automatic. Does a automatic not have brass, copper or bronze components? Do they not both drive helical gear sets? What is in a manual transmission that is not in an automatic. I can't really come up with anything that I see as a negative consequence. In reality would the automatic not suffer the same corrosion deterioration and metal failures as the manual? My point is that they don't.


5. My truck is a crazy project, its not worth much and I don't have much to lose. ATF is cheap, Royal Purple is expensive. This truck has 200,000 miles on it, do I really need to be worrying about what might happen in 50,000 miles? Still its all very interesting to this hopeless gear head.


6. I'm really considering trying it in the transfer case. I'm thinking less drag, less heat, better fuel mileage GOOD, possible inefficient lubrication or EP concerns BAD.  Unless someone has a definitive absolute and says NO "Don't do that because" What the Hell, I'm giving it a shot in the transfer case. I was thinking maybe add some Lucas to improve the EP?  :)

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I definately say go for it, flog it hard and report back.


I have zero idea if automatic transmissions use yellow metals, so I have no idea if atf is yellow metal safe. That's why I asked :)

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I tried it and after about 5000 miles of freeway commuting I have no ill effects that I can see. The benefits have been that the transfer case will shift from 2wd to 4wd high on the fly, It wouldn't before. The ATF has also done a great job of cleaning  the sludge from the inside of the transfer case. Fuel mileage is pretty much the same. Can't really speak for heat as I didn't  put the laser on it before so I don't have any data to compare to what I have now. I have had it on the lift and it does seem like its running cooler. I'm not to sure how much faith to put in the touchometer though :)

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