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Hot Rods ATF vs Gear oil

Discussion in 'The Hokey Ass Message Board' started by Boneyard51, Oct 8, 2018.

  1. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,871


    Ive wonder about this for a while and thought I might get some opinions an their use. A lot of manufacturers now recommend ATF in their non- automatic transmissions/ gear boxes.
    It’s my understanding that ATF has a different coefficient of friction, that is it’s not as “ oily” as gear oil. It is formulated that way so the clutches will hold. I get that, in an automatic transmission, because automatic transmissions have clutches. But wouldn’t you want the best lubricant you could get in a transmission with no clutches.
    I understand that synronizers need friction to work , but they used to work in oil. Then there’s the gearboxes that don’t have synronizers, and they still recommend ATF. Some also recommend it in the power steering.
    I would think a person would want the best lubricant you can get... and for a lot of places where it used , I don’t think ATF is the best.
    An opinions on this?

    chryslerfan55 likes this.
  2. I use ATF in my 5 speed transmission since the manufacture recommends it.HRP
    seb fontana and chryslerfan55 like this.
    Joined: Dec 14, 2009
    Posts: 1,536


    Had an O/T car a while back drained the trans of atf and put 80-90 in it
    Wouldn’t shift worth a shit untill it warmed up
    Switched back to atf and all is well with the world.

    The is a “ universal” lube TDH. Transmission, differential and hydraulic fluid. That’s used a lot in general industrial applications.

    There are times when an “improved” oil or fluid can make something run better. But most times the engineers had it right from the get go.
    chryslerfan55 likes this.
  4. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,291


    Back in the day racers would fill their trans and rear end with atf to cut back on the drag that 90wt created. Now days, they use atf to increase milage because there is less drag. The newer transmissions are designed to use atf and putting the thick stuff in them prevents them from getting adequate lube.
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  5. Are you wondering about OEM use, or 'retrofitting' it into older gearboxes? On new ones that came with ATF, the tolerances involved are such that using gear oil will starve some surfaces of proper lubrication. Gear oil is simply too 'thick' to get into/out of places to properly lube everything. My understanding is some modern gearboxes actually have 'oil pumps' in them to insure the ATF gets everywhere it needs to.

    On older boxes, it is possible to substitute ATF for gear oil. It has adequate load-carrying capabilities according to the 'experts' and is used by many race teams to reduce friction and free up power. I've actually tried it in a couple of 'early' gearboxes (both a T10 and a Toploader 4-speed) with no apparent harm and it actually quieted the Toploader somewhat. Shifting effort seemed to be slightly improved. But the issue is leaks....

    The T10 was used, the Toploader was a fresh rebuild. Both started leaking out of various places. Not badly, but enough that I 'spotted' anyplace I parked for more than a 1/2 hour. Usually only a few spots, but spots nonetheless. Enough that you had to add a small amount of ATF when checking the level at each oil change. No so much at the front/rear seals (although these showed a fair amount more than the usual amount of seeping), but at the shift forks and speedo drive. The T10 also tended to puke some out the case vent. I got tired of the mess, drained/flushed them and reinstalled conventional gear oil and the leaking stopped.
  6. Blues4U
    Joined: Oct 1, 2015
    Posts: 3,160

    from So Cal

    Hmmmmm, not sure what you mean here. What does "oily" mean? Do you mean "lubricity"?

    I may be wrong here, but I think you're referring to friction modifiers used in certain lubricants to increase the lubricity (make it more slippery). ATF does have a balanced blend of friction modifiers so that it provides a specific friction characteristic for the friction plates in a clutch pack, not to aggressive and not too slippery. Different ATF specifications can have different friction characteristics. I.e. the old F type ATF for Ford transmissions is more aggressive with less friction modifiers. But they all contain some amount of friction modifiers, some more than others. It depends on the type of ATF and the specification it is blended to.

    Beyond that there are other additives to consider as well as the viscosity.

    Versus gear oil, ATF DEX III is roughly about half the viscosity of a typical 80W-90 gear oil or SAE 50 grade engine oil (very common viscosity grade in manual shift tranny's). And ATF relies on anti-wear additives like ZDDP while gear oil often has extreme pressure additives (sulphur/phosphorus). Both AW and EP additives prevent wear by forming a "self-sacrificing" protective film, but EP additives provide a much harder, more durable layer over gear tooth surfaces, AW additives are more easily removed by contact; but EP additives actually require some contact & wear to occur in order to activate and plate out on the gear teeth, AW additives do not.

    In any case, the transmission manufacturer has designed their transmissions to work with specific lubricant types, so if they tell you to use ATF that is going to be the best lubricant to use. And as Vandenplas posted above, putting 80W90 in instead of ATF can cause problems.
    Hnstray, blowby and Truckdoctor Andy like this.
  7. Blues4U
    Joined: Oct 1, 2015
    Posts: 3,160

    from So Cal

    Your describing a very common Tractor Hydraulic fluid, used in about a bazzillion wheeled tractors all over the world. In the olden days farm tractors had a common sump for transmissions and rear differential. IH, Deere, Allis Chalmers, Case, etc, they all used that format. 1 sump for everything. When hydraulic hitches were added to tractors they simply used the same sump for hydraulic oil too. So a universal type of oil was developed. It's been around for decades and is still a very common oil used in agriculture and construction equipment all over the world. It's one of the most heavily additized and specialized fluids out there, capable of protecting transmissions as well as differentials as well as hydraulic systems, and brake systems too. But, you definitely want to use it in applications that were designed for it, don't just use it willy nilly. The friction modifiers in it will probably cause most automatic passenger car transmissions to slip badly. And it is not a GL-5 type fluid, so not good for hypoid differentials.
  8. dirty old man
    Joined: Feb 2, 2008
    Posts: 7,848

    dirty old man

    One thing no one has mentioned is that the manual transmissions that were built and intended to use 80/90 should use GL4, not GL5 or GL4/5, as the latter 2 have an EP additive intended for the EP requirements of hypoid gears and are to "slick", lubricity wise, to allow the cone surfaces in synchronized transmission to properly synchronize the meshing gears when shifting, up or down.
    banjeaux bob likes this.
  9. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,871


    Steve, the purpose of this post is a genuine interest in lubricants. As HRP mentioned,,manufacturers recommendions carry a lot of weight with me, but I never blindly follow the recommendations 100%. Sometimes they are given as a matter of convince or an attempt to accomplish something other than longevity, gas mileage or planned obsolescence ,are a few examples.
    I hoped Blues4U would chime in. His expertise is always appreciated, even though this country boy has trouble understanding some of it.
    Not trying to change any fluids, just trying to understand something that has bugged me for years.
    One is why some manufacturers recommend ATF or power steering fluid in their systems. Power steering fluid is different than ATF, closer to hydraulic fluid. I have changed out ATF fluid to power steering fluid in nosiy PS systems in the past and made the noise less. Wondered why the manufacturers didn’t put it in in the first place? Cost? Convince?
    Manufacturers recommendions can have hidden agendas.

    dirty old man likes this.
  10. The one gear lube I've been impressed with is the Royal Purple synthetic. While I haven't tried in in an automotive application, it appears to work very well in shaft-drive motorcycle final drives. It reduces running temps to where the drive will be cool enough to put your hand on it after a long run, where with conventional OEM-type gearlube it will be too hot to comfortably touch.

    Do the OEMs make selections based on cost? All the time....
    Boneyard51 likes this.
  11. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,871


    Thank you, Steve.
  12. KenC
    Joined: Sep 14, 2006
    Posts: 191


  13. KenC
    Joined: Sep 14, 2006
    Posts: 191


    ATF in manual trans recommendations go way back. I had a '65 Dart with the little 273 4bbl 4spd. Same trans that Mopar used in a 4 spd cars back then. ATF was the right lube. BTW, that is till my all time favorite 'newer' car. Shifted slicker than....anything.
  14. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 6,940


    It just does not seem right to use ATF in a manual trans after using 80/90 gear lube for so long,the T-5 in my 37 is supposed to have ATF but was wondering if 30 # oil would be better.
    Boneyard51 likes this.
  15. Scruffy49
    Joined: Sep 23, 2018
    Posts: 29


    I use a LOT of hydraulic fluid. And not just in the tractors.
    Power steering? Check.
    Manual steering gear box? Check, but 1/2 is prefilled white boat trailer hub grease. Seattle to Brighton TN with zero issues, towing a horse trailer, with well over 1000lbs in the truck bed.
    Slushboxes? Check. But only C6, 727 or Th400.

    Should I? Probably not. But so far so good.
  16. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,871


    Junkyard, that’s kinda what the purpose of this thread is. To me ATF is a comprise, in order to do two jobs in an automatic transmission. Works good for both, but not 100% for either. That’s my whole question.

    On a side note, on the ranch we have a 1030 Case tractor that calls for 10W motor oil in its gear boxes,according to manufacturers recommendions. It has gears bigger than most whole car transmissions. Never could do it. It got 30w motor oil or universal tractor fluid. It’s the main tractor on the place since the early seventies and had had no gearbox problems.
    But remember this thread is for opinions.

  17. blowby
    Joined: Dec 27, 2012
    Posts: 5,604

    from Nicasio Ca

    Some T5s have non-metal in the synchros..
  18. Kiwi 4d
    Joined: Sep 16, 2006
    Posts: 2,338

    Kiwi 4d

    I must be a simpleton , rather than ponder all the complexities of an oil I just use what the manufacturer recommends . That’s me “simple” .....
    Dick Stevens, clem and Hnstray like this.
  19. Mike VV
    Joined: Sep 28, 2010
    Posts: 1,320

    Mike VV

    Sort of an interesting question, but in this case, best leave the the designers.
    The "lighter weight" oil is for better power transfer/mileage. Just leave it as designed.

    Hnstray likes this.
  20. Atwater Mike
    Joined: May 31, 2002
    Posts: 9,104

    Atwater Mike

    My friend Jack bought a new '63 Plymouth Fury, 426 short ram with 3 speed stick gearbox from Eddie Perdue Plymouth in Redwood City, February, 1963.
    I had been reading up on the new "big Valiants" (as I called his Fury, just to razz him) and did some tuning on it...Car was monstrously fast, especially for Jack...who couldn't drive a hog to water!
    Eddie Perdue was an old hot rodder, argued that a 3 speed could beat a 4 speed OR a Torqueflite evenly matched...because of its 'only have to shift twice' resulting in lower E.T.s!
    His 'chief mechanic' convinced him that a lighter bodied model with the 426 and T.F. would be the best bet, so Eddie ordered a new 'race car'...and Jack got a good price on a 426, 3 speed Fury.
    Jack was impressed with the newly found power...but couldn't shift fast...he blamed linkage, clutch, flywheel...
    Tranny had 10 wt. transmission oil in it, so we changed to optional ATF. Still had notable friction coming out of low gear, and the gate had 'blockage' (mechanical, I adjusted linkage more than once)
    There was a new product out then, Justice Bros. marketed it, under the name "SLIP".
    I added a small bottle to the ATF in tranny, Jack drove it one day...Suddenly, the thing shifted like there were no gears or synchros!
    Jack learned to speed shift, (took forever to teach him where the power band was, LOL)
    That was the weirdest stuff I ever saw. After the 1964 drag race season, the product was all gone. J.B. no longer carried it, I didn't really NEED it, my almost new '63 Dodge 330 w/426 was a Torqueflite 727.
    I beat Jack's Fury, but not by much. Mine got into high 11s, respectable then.
    Hnstray likes this.
  21. It is my understanding of the use of ATF now in manual gearboxes is because of the syncros. Modern syncros are carbon based, like a clutch disc, instead of the old brass metal syncros.
    I'm sure the bonus of reduced friction leading to better performance and better fuel economy, especially in modern OEM, is also a factor.

    ATF is now the go to for wet clutches on vintage/classic motorcycles. Pretty much eliminates all the issues of a sticky, dragging clutch that conventional oil would cause.
    Raunchy likes this.
  22. sunbeam
    Joined: Oct 22, 2010
    Posts: 3,819


    All bearing and gears need a film of oil to keep wear down Be it roller ball or sleeve loads tend to squeeze the oil out. So if the roller or ball need to reload when it is not under load to light and it is squeezed out to easy to heavy and it can not run in time. In the 60s Chrysler had a service bulletin to replace 90w with ATF in their manual transmissions. I would error on the lighter side. Some newer trans go with engine oil.
  23. My vintage stock car had a Ford truck 3 speed side shifter converted to a low and high gear w/ reverse . There was no flywheel and clutch used ,direct drive to trans . input shaft . Mainshaft gear was machined in two and a clutch pack from a auto trans. welded in . You pushed a lever with your foot to move in low gear then when you picked up speed you let off lever and shifted into direct drive . This is what I'm getting to , the trans. used half a quart of 50 weight Vavoline racing oil . this was only lube you were to use and trans held up under severe dirt track racing ! IMG_3754.JPG
    Nailhead Jason likes this.
  24. deathrowdave
    Joined: May 27, 2014
    Posts: 1,326

    from NKy

    Giggle Penzoil Syn Torque , this is thin stuff for manual trans . Don’t do the ATF in a red brass containing trans or you will be needing new red brass sooner than you expected . Red Brass = Synchronizers
  25. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,060

    from Quincy, IL

    Ford has a "Manual Transmission Fluid" that is very similar in appearance to ATF....but may not be the same chemically.

  26. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,490


    This is where it gets interesting if you are using a T-5 and maybe other late models depending on year GM used atf, motor oil, and synchromesh lube I don’t think 80-90w but who knows, they might have tried that also!
    chryslerfan55 likes this.
  27. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,009


    Since way back in the early 60s, Mopar suggested ATF in their 4 speeds if the outside temp dropped below a certain temp. The 80/90 got pretty stiff in the winter months. I had one 4 speed I would have to put into 1st gear when I parked it at night during the winter because your couldn't even shift the trans until it ran a few minutes. When I left my house, I had 4 stop signs in a row, then a couple of miles to run. I couldn't ever get it out of 1st until after that last stop sign.
    I remember saying something to my old boss, and he convinced me to change the 80/90 over to ATF. I was pretty concerned, but after the change, I could shift the trans at will regardless of the outside temp. I pounded the living crap out of that 4 speed, the ATF never gave me any problems.

    Power steering? All the old power steering cars used ATF in their power steering originally. Power steering fluid didn't even show up until the 1980s. Gene
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  28. Garpo
    Joined: Jul 16, 2016
    Posts: 128


    There are a truck load of factors here. Early gear boxes relied on thick oil to keep metal away from metal with straight cut or sliding gears. Later boxes used helical gears with synchronizers. Brass or bronze synchros and bushes needed a lubricant the had enough friction for the synchro to work while keeping lubrication in the bushes and bearings.
    Lightweight oil generally shifted better, but could be noisy or shorten 'box life.
    More recent gearboxes are made with better tolerances to take advantage of lighter oil grades. All driven by the C.A.F.E. rules and their cost to the manufactures.
    Bottom line, is to ask the questions and make an educated choice.
    For my money, the GL3/4/5 lube ratings the gearbox manufacturers chose for their products should be looked at. They made their choice from a background of technical knowledge, with reliability and ease of driving in mind. Most lube manufacturers have upgraded their products over the years as technology has improved, but the GL ratings are there on the label and still apply.
    chryslerfan55 likes this.
  29. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,703


    I am not in the business of second-guessing the OEM recommendation for vehicle lubricants.

    From the DSG 6-speed in the wife's VW, to the T56 in my Falcon, to the T5 held aside for another project, to all of the numerous vehicles that I have a hand in designing.

    I know exactly why each lubricant was selected for each, because I am often the guy who selects them.
    chryslerfan55 likes this.
  30. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,703


    That breaks down to:

    Plain gears, directly on the shafts: 50w (Non-World-Class, was Dexron II, but that's long gone).
    Gears with needle roller bearings, riding on the shafts. Dexron III (World-Class).
    Composition of synchronizers/blocker rings. Dexron III+ (World Class).

    80-90w is far too heavy for a T5.
    chryslerfan55 and juan motime like this.

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