ATF-type A equivalent?

[Clipper4730]

Hey just a quick question, what is the best equivalent to type A automatic transmission fluid. Our manual says type A but it is pretty hard to find. Some yanmar dealers have said to use Dexron III, but others have said SAE30w or type F. Think we will go with the Dexron but wanted to get your thoughts.

Thanks
Will

[Hope_I_Float]

Clipper,

Did you ever find the info you were looking for on the ATF-A replacement?

My 85 C-30 manual recommends ATF-A or Dexron-II, understandably both out-of-date specs.

Like you, I'm also looking for some definitive answers on what the best replacement transmission oil would be for those outdated specs (ie currently available, preferably in Canada for me, and fully compatible with my Hurth Transmission).

I know not to get anything with molybdenum disulphide in it but beyond that haven't come across some solid references on on replacement fluids.

Thx

[Crew of Turning]

The topic has been covered in earlier postings filed under propulsion. The comments indicate that ATF A or Dextron is backword compatible. We use it in a 40 year old Kanzaki KBW10. We change it out every 2nd year.

[a64pilot]

I use the newer synthetic transmission fluid that seems to replace everything.
Overkill certainly
Mobil 1â„¢ Synthetic ATF Â*

Do NOT use motor oil

Type A I believe was Dexron, before there was Dexron. Dexron is a GM brand of course.
Type F differs slightly in that is is not quite as slippery, way back when we used to run type F in our GM and Mopar transmissions to make them shift more firmly, less slip. There really is not all that much difference between transmission fluids, and just simple wet clutch systems like we have I'd bet it doesn't matter.
As a point of interest the original type A trans fluid used sperm whale oil, and the endangered species act is why there is no (real) type A anymore, I assume if you can buy specialty type A, your buying Dexron that meets type A specs and is labeled as such
https://en.wikipedia.org/wiki/DEXRON

[Hope_I_Float]

RESULTS OF SOME RESEARCH SO FAR:

Digging online I found this recommendation from Foley Engines (their website suggests a knowledgeable outfit):

"Which Fluid? The ZF/Hurth Workshop Manual indicates that automatic transmission fluid or ATF is to be used in these mechanical gears. ATF, commonly known as Dextron II or III, is far preferable to the thicker SAE 90 hydraulic gear oil. However, given that these small gears are essentially oil cooled and that they contain very little fluid, we strongly recommend that you upgrade to Red Line synthetic ATF or, better, our Foley Hytork Fluid. Both will allow the transmission to run cooler. Cool transmissions are happy transmissions because heat is the enemy of all marine gears."

Hurth Marine Transmissions: The Ins and Outs of Basic Service | Foley Engines

One of the distributors of Red Line shows a product write-up for the Red Line D4 Synthetic ATF claiming to be compatible with Dexron II (and other older specs):

https://performanceimprovements.com/...roducts/d4-atf

The transmission fluid spec for the Hurth-equipped Universal M-25 on my boat is here (consistent with the original user manual which came with the boat):

Universal Diesel Engine Owners Manual - Sea Water Impeller Replacement - Marine Diesel Direct / TOAD Marine Supply

Alan Wheeler, a very experienced fellow forum poster, posted on this subject back in 2008:

Originally Posted by Alan Wheeler

I am using Amsoil synthetic ATF in my BWVelvet Drive. The heat reduction has been quite significant. With hydraulic boxes, heat is a killer to them. The cooler you can keep the oil, the more miles the thing will run for.

RAM, another experienced forum user replied:

Originally Posted by Ram

I also run Synthi in everything, but not the Herth, I have a trawler that has a hurth in it , that slips if i use Synth in it ,so I only use reg ATF in it ,

There are however several threads on the internet about NOT using synthetic ATF in Hurst Transmissions (I note that Mr. Wheeler's post refers to him having a BWVelvet Drive)

As I was reading online, adding to this thread, Crew of Turning and A64Pilot wrote in (thank you) to provide input.

I've now read hours worth of info online about the history of the various ATF/Dexron specs, how their licensing works, current replacement specs, etc..

Among many interesting articles, this one made reference to some comparative testing:

"We tested DexronVI against DexronIII and Mobil1 ATF and Amsoil ATf in our lab. The DexronVI outlasted all of them on bearing and gear heat and radial overload testing. I would use the Dexron VI. Mobil1 would be my second choice."

https://bobistheoilguy.com/forums/ub...opics/825873/1

Some of the posters on that forum seemed to have some technical background in this area ... see page 2 (notably Whitewolf ... whose considered opinion I read about on numerous forums ... he provides an SAE test paper reference on the superior properties of Dexron VI vs III ... not surprising given the relative age of those specs.

Additional info on the various formulations (ie blends) available for Dexron VI here:

https://bobistheoilguy.com/forums/ub...pics/3008186/3

In summary:

What different manufacturers call 'synthetic' varies and the regulations aren't specific. The above links provide the details.

To meet a Dexron VI spec, manufacturers require at least some synthetic base. Different manufacturers use different combinations of base oils and additives to meet the Dexron VI spec (presumably same need for other ATF specs as well).

Sifting through a lot of material, which includes a lot biased partially-informed opinions on 'what's better', I haven't found anything so far in hours of reading (it could be there; just haven't run across it yet) which suggests a Dexron VI or 'Synthetic ATF' (this is really more of a catch term than anything) shouldn't be used in a mid 80s vintage Hurth HBW marine transmission although some posters, as noted above and elsewhere, have reported slippage with 'synthetics' ... which as per the above references could mean anything!

Happy to review contrary information.

[Scot McPherson]

You want to use the newest oil in that group or class of oils. It's the same with engine oil. My manual says to use SAE30 C or D, but today's oils are I think up to J already? shoot I just bought some a month ago...ah well..anyway....


Believe it or not, sticking with ATF-A probably causes more wear than if you started using one of the newer ATF specs. Make sure you are using the right _kind_ of oil, but use the latest technology and spec of that kind that you can.

[a64pilot]

Bobistheoilguy is usually a very good source, however it is a forum, so trust, but verify.

If I were getting slippage with a transmission that spec'd Dexron, I'd switch to type F fluid. Slippage will kill the hard plates in a wet type of clutch disk pretty quick, they warp from heat.

[Diesel Bill]

Originally Posted by a64pilot

Type A I believe was Dexron, before there was Dexron. Dexron is a GM brand of course.
Type F differs slightly in that is is not quite as slippery, way back when we used to run type F in our GM and Mopar transmissions to make them shift more firmly, less slip. There really is not all that much difference between transmission fluids, and just simple wet clutch systems like we have I'd bet it doesn't matter.
As a point of interest the original type A trans fluid used sperm whale oil, and the endangered species act is why there is no (real) type A anymore, I assume if you can buy specialty type A, your buying Dexron that meets type A specs and is labeled as such
https://en.wikipedia.org/wiki/DEXRON

Right you are. Back in the mid 1960s I worked in an automatic transmission shop and we only had 55 gallon drums of type A, and type F. I don't remember Dexron until a few years later. I used to run type F in my G.M. hot rod Fire Bird with built Turbo 350 with shift kit and B&M Street Master torque converter.
My grandson has a Toyota that uses a Toyota specific trans oil and it's over
$12.00 per quart in the auto parts house, and not even a synthetic or blended synthetic. Supposed to be the only thing to use.
I wonder if all the newer spec oils are really necessary for the transmissions or if they are specified for profit motive.

[Northbound44]

In my old Hurth transmission, the specifications said Dextron A, I always used Dextron 3 as recommended by Foley engines. Synthetic ATF is considered superior but it stinks so I don't use it.

[a64pilot]

Originally Posted by Diesel Bill

I wonder if all the newer spec oils are really necessary for the transmissions or if they are specified for profit motive.

Awfully sure there is no Magic there, its profit related.
last several years it seems business has become more about being a thief and getting away with what you can.
It really did I believe used to be about manufacturing the absolute best product possible, and the belief was if you did, then John Q. Public would beat a path to your door wanting to buy and would pay a good price too.
Now its about cutting corners, buying part as cheap as possible, not the best quality and beating up your suppliers to get cheaper, not better.

Business it seems has forgotten what Deming taught them, or maybe what I just thought he taught

[Hope_I_Float]

Thanks for the feedback folks.

Northbound ... thanks for that ... I hadn't considered smell as it relates to the ATF and this is the first I hear on the use of synthetic ATF generating a foul odor in these old Hurth HBW marine transmissions. Good to know. Wonder if others have experienced this smell related issue with synthetic ATFs.

This is making me lean towards the Dexron VI spec. I have yet to change the transmission oil out. Had to concentrate on other pre-lift-in projects and put this one aside until after lift-in.

It's tight getting in there to change out the transmission oil on a C30. I could suction it out as I do with my engine oil but I've been reluctant to do that for what is my first changeout since I don't know when it was last done and wanted to drain the current oil well so as to remove any accumulated particles which might have settled in the bottom of the transmission (i was going to try to flush with some extra ATF fluid prior to refill).

I was going to send the transmission oil out for analysis to establish a baseline and resend next season to see if there is any evidence of wear from the particle analysis.