What auto trans fluid for 74 620

[agouge888]

Stock 74 auto tranny. Sat for years and wanted to change fluid. Book says Dexron, but what are u guys using these days? Hopefully it’s something I can pick up at the local parts house.

 

 

 

Thanks,

 

Blue71

[Stoffregen Motorsports]

Best auto trans fluid for a Datsun is a manual trans.

[datzenmike]

Don't listen to him. The correct ATF is DEXRON.This isn't gas where anything will do. Any brand you like but must be DEXRON.

[Stoffregen Motorsports]

I've had a crash course in ATF requirements over the past year. So many of my engine swaps are getting automatics these days (some new and some rebuilt) and a lot of them have different requirements. Just the other day I accidentally put about a quart of the wrong ATF into a brand new trans, and it had me freaked out, because I would have had to drain the 14qts I just put in it to get the wrong one out. I made a couple of calls, one to my trans rebuilder, one to a good friend who owns a repair shop, and one to AAMCO. They all had the same thing to say.

 

It essentially boils down to this:

- There are two basic groups of ATF - synthetic and non-synthetic.

- What makes the multitude of variants in each group different from each other is the content of gear oil in the mix.

- Starting with about Dexron III (I think, can't remember for sure), they were all very similar and for the most part, interchangeable. In other words, synthetic fluid types are all very similar and mostly interchangeable.

- I don't think this applies to non-synthetic ATF, but there are compatibilities between them. While the OEM may require a certain fluid, time may have shown that another type is better.

 

Apologies for the inevitable confusion that I may have just created, but this is the learning curve I am up against and I thought I'd share what I have been learning.

[datzenmike]

The later (after Ford type F) Mercon is similar to the Dexron but tends to improve the clutch grip. This might not be a good idea as this presumably will increase wear from hard shifting.

 

Why fuck around with something not specifically recommended by the vehicle maker, that may damage or shorten it's life, when the correct ATF is readily available?

[agouge888]

Thanks for the info. Is Dexron III acceptable these days? Or even Dexron IV? Can’t seem to find just Dexron.

 

thanks,

 

Andy

[datzenmike]

Some of the later ones may be synthetic. Read the label for compatibility.

[Figbuck]

My 4 speed was really hard to shift, up or down, and especially when it is cold. I thought the engagement dogs were toast a long time ago. I have been keeping a maintenance log for a long time. I thought I remembered changing transmission oil a bunch of times, but really it was 100K mi. ago. Whoops. I had a hard time getting filler plug out. What drained out was the most vile nasty roasted burnt oil I have ever seen. 

 

I went to CarQuest the close local auto part place. I ask the three old guys behind the counter what they thought about running synthetic to make it shift easier. They seem to think that was OK. At least not wrong. They argued for a while and agree on Castrol Transmax import Multi Vehicle ATF. The said it was a Dexron style. Dang, the transmission shifts really well now. I can't believe I've been living with burnt fucking peanut butter lubricating the trans. The only problem is a small bit of oil is leaking. I wiped it off to see, but it seems like it's better now. Maybe just over filled it a bit.  Maybe thinner oil is leaking past a seal...

[datzenmike]

ATF does not have a specific 'weight' like other transmission oils... but it's around 7w to 12w. I did some research into using ATF to replace the hydraulic oil in my sedan struts. ATF is a hydraulic oil and it also lubricates gears so it will work in a manual transmission. It has more anti foam and highly detergent than normal gear oil. I think you should be ok with a tiny L16 and I doubt you drive it that hard. I've used synthetic before and the seals leaked. Replaced and it was ok. My zx transmission has the General Motors Delco 'Friction Modified Synchromesh Transmission Oil' in it designed for the Corvette and Camaro use. It's like your ATF the shifting is immensely better... smoother faster and I can down shift now! The oil oil was a bit stiff for the first few cold shifts..that's gone.

 

When I was younger I bought a new '70 Dodge 340 Dart and within less than a year the transmission bearings were growling. I had a garage look and it was full of what looked like ATF in it.  I took it in under warranty and they replaced the bearings and it was quiet. Just for the hell of it I took it to the garage and they had put ATF back into it. I replaced with 80w90 and no more problems. The reason for the ATF was the cold winters. With 80w90 you had to shut it off for the night in neutral or you could not pull it out of gear in the morning and had to warm up with the clutch down for 10 min. This would be minus 15-20F and not at all like the PNW.

[datzenmike]

I see from other posts you tow trailers up and down mountains. That might be considered extreme use for a light weight oil.

[Stoffregen Motorsports]

On 3/29/2019 at 8:37 PM, agouge888 said:

Thanks for the info. Is Dexron III acceptable these days? Or even Dexron IV? Can’t seem to find just Dexron.

 

thanks,

 

Andy

As I mentioned earlier, starting with Dexron III, it was synthetic. So is anything after that.

 

Call your friendly AAMCO guy and ask what he would recommend.