ATF vs. gear oil

[snoboy]

My HHR calls ATF in the manual transmission. Some guys albeit misinformed IMHO are also using ATF in snowmobile chaincases. What are the big differences in lube construction, and function between ATF and regular gear oil. I guess I don't see ATF as gear oil but rather I see it as more like a hydraulic fluid for use in auto trans. I'm looking for some experts here.

snoboy

 

[Whitewolf]

Hi,

Wow, the differences are huge. Let me try to give a simple answer. A true gear oil requires certain EP and Anti-wear agents for good gear protection. An ATF requires a wide number of features, one of the main ones being friction behaviour (that requirement varies dependent on design and material choice).
ATF and gear oils are totally different animals. Having said that, some manufacturers choose to use ATF as an MTF because it is either compatible with their synchro material choice and/or convenient in terms of fluid availability.

 

[Gary Allan]

Easier shifting is what I think they're going for. It's typically fine with chain driven stuff. My t-case is a chain type

 

[mechtech2]

I don't know what an HHR is.

ATF is called for in many modern manual transmisssions and transaxles. Many are retro spec'd, and used to get gear oil.
Dealers have to stock only one fluid for manual trannys, auto trannys, power steering systems, and transfer cases.

ATF is thin, works well at low temps, and is good for a slight decrease in drag [better economy]. A dedicated gear oil is always better for shifting and wear.
It's OK to use ATF, but it is not the best we can do.

 

[aquariuscsm]

My car specs anywhere from a 75W90-75W140 GL4 for it`s manual tranny (according to 1990-1996 Z32 FSM). I went to a thicker 85W90 and shifting improved like day and night. The thinner fluid (Nissan OEM MTF 75W85) made shifting very notchy once the tranny was good and hot. The 85W90 gets only slightly notchy on some shifts but a 100% improvement over the 75W85 and made the shifting action MUCH smoother. I just bought some SAE 140 GL4 and am going to install it here in a couple of days and see how it goes.

 

[JSRT4]

my car specs atf+4 in it's manual transmission, I don't like the way it was shifting, and in my experience it gets worse in very hot temperatures. Being a turbo and with summer approaching in my parts I feel much better with a dedicated MTF fluid in there. So far it is shifting very well.

 

[MolaKule]

Quote:
Some guys albeit misinformed IMHO are also using ATF in snowmobile chaincases. What are the big differences in lube construction, and function between ATF and regular gear oil.


You're discussing three different lubes here:
Chaincase fluid
Differential gear lube
ATF

Differential gear lubes have higher levels of EP additive and higher viscosities than the other two,

ATF's have lower viscosites and lower levels of EP additives.

Chaincase lubes EP additives are about equal that of ATF's but viscosities are about 30 weight.

 

[Tempest]

Does ATF use EP additives or does it just contain AW?

 

[MolaKule]

Quote:
ATF's have lower viscosites and lower levels of EP additives.



Good question and I erred. ATF has AW additives only.

Chaincase lubes have about the same levels of AW additives as do ATF's.

 

[sprintman]

MK I'm seriously interested in importing diff, g'box, and p/s lube from you for my new (used) BMW 2001 325CI. Dave Granquist at Redline say 75W90 diff, D4ATF g'box and p/s but maybe Redline MTL/D4ATF 'blend' for g'box (5-speed Getrag I believe). Please give your opinions and wadvantages over Redline and willingness to ship to Australia? I can afford it trust me

Thanks...s

 

[Tempest]

Thanks Molakule for the clarification. May I ask why ATF's don't use EP additives? There is plenty of metal on metal contact in a trans, I would think EP additives would be very useful.

 

[Gary Allan]

Originally Posted By: Tempest
Thanks Molakule for the clarification. May I ask why ATF's don't use EP additives? There is plenty of metal on metal contact in a trans, I would think EP additives would be very useful.

I would think that it's more along the line of the hypoid gears requiring the EP adds. Helical and (can't pull the term from my fogging memory for gears that push away on one plane) other transmission modalities don't. I would think that this would be exclusive of their corrosive composition. That is, I imagine if EP adds would benefit those applications, that they would be made of resistive metals.

 

[Whitewolf]

The answer is, because you don't really need EP in an ATF. In addition there are so many surface active componants in those formulations already in order to already to balance out all of the other requirements plus the friction that you really don't want to try to make the situation worse if there is no need.

 

[Tempest]

Quote:
In addition there are so many surface active componants in those formulations already in order to already to balance out all of the other requirements plus the friction that you really don't want to try to make the situation worse if there is no need.


The EP chemistry should only be active on ferrous materials (gears, bearings) and not form films on clutch engagment surfaces correct?

 

[MolaKule]

Right, you want extreme pressure films of ferrous phosphates and ferrous sulfates to form on highly loaded gear teeth such as hypoid configurations.

Planetary and sun gears need only AW additives to reduce wear at the lighter loaded tooth interface.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729255#Post729255

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729289#Post729289

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729268#Post729268

 

[MolaKule]

Quote:
There is plenty of metal on metal contact in a trans,


In most AT's, the clutch surfaces are mainly steel/composite interfaces which need special friction modifiers for proper dynamic friction characteristics during engagement or disengagement.

 

[sprintman]

Mola are manufacturing/selling oils yet?

 

[Tempest]

Molakule thanks for the links. I have read those before but it is always good to have a refresher.

I'm just looking at the ATF UOAs that we have here and there is a lot of Fe floating around in them. I would think that EP chemistry would reduce this and help with hard part longevity.

This has been posted on a chlor additive website:
Quote:
* Although MT-10 reduces friction, it has no negative affect on the sprag or clutch friction necessary for the operation of the transmission. As confirmed by Raymark in a letter of October 1986 in testing their SAE clutch pack: "The results of our test indicate no change in the friction levels, thus we do not expect the addition of your additive to have a negative effect on our friction products."


I have used this additive in a trans and there was no obvious change in shifting.

 

[Whitewolf]

An additional consideration is that most EP additives are not good at oxidative stability, which is fairly key in an ATF.

 

[MolaKule]

Quote:
I'm just looking at the ATF UOAs that we have here and there is a lot of Fe floating around in them. I would think that EP chemistry would reduce this and help with hard part longevity.


The sun and plnetary gears in AT's don't have the same loads (forces) on them that hypoid differentials and manual transmissions do. The Fe levels of ATF's from UOA's are comparatively low compared to diffy's and IC engines.