School me for a minute on Gear Oil GL4/GL5

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LoneRanger

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I remember something about GL 5 should not be used in an application that has brass or copper fittings or parts because the higher level of EP additives in GL5 (vs GL4) can cause corrosion to the brass and/or copper parts in the gear box. The brass is most likely to be used for the synchro mesh components? i.e. GL4 is most commonly used in manual transmissions and GL5 in bevel boxes and differentials, especially hypoid gears? I can't remember.
 
Basically, yes. My understanding is that the primary incompatibility is that the higher dose of EP additives in GL5's will, during synchro engagement, take pieces of the surface of the synchro off because the EP deposits on it are harder than the soft metals they're made of.

Although, I'm sure I'm not the only one that has seen transmissions made with yellow metal synchros live quite a while on GL5's.
 
Originally Posted By: LoneRanger
I remember something about GL 5 should not be used in an application that has brass or copper fittings or parts because the higher level of EP additives in GL5 (vs GL4) can cause corrosion to the brass and/or copper parts in the gear box. The brass is most likely to be used for the synchro mesh components? i.e. GL4 is most commonly used in manual transmissions and GL5 in bevel boxes and differentials, especially hypoid gears? I can't remember.



GL-4, 5 are protection ratings.

GL-5 gear lubes contain Extreme Pressure (EP) additives for highly-loaded, hypoid differentials, whereas GL-4 gear lubes for manual transmissions contain Anti-Wear (AW) additives.

Synchro assemblies can be made of brass or of Composite materials.
 
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A GL4 lube is supposedly dedicated to synchronizers in a manual transmission, and no limited-slip clutch assembly is ever found in any manual transmission.
 
Then you have a Subaru with BOTH up front - combo hypoid and MT. I know where the Ranger is at - it guess
smile.gif


Subaru formerly made an excellent MT lube and now Ive read they don't anymore. Don't be fooled by "dual" ratings The MT in some GL5 refers to a non-syncromesh HD truck transmission, not your car trans.

Hope you find something. Both the Sig Other and I are in Autotrans land - for the first time in many decades.
 
My 2014 Focus MT uses a 75W GL-4 MTF that meets a Ford spec. WSS-M2C200-D2.
When I called TORCO they told me that their MTF, which is GL-5, would work fine and have no bad effects on any yellow metal parts. I went with a Volvo MTF which met the Ford spec. but costs less....I'd bet it's identical to
Ford's product since they shared components at one time.
 
Originally Posted By: ARCOgraphite
Then you have a Subaru with BOTH up front - combo hypoid and MT. I know where the Ranger is at - it guess
smile.gif


Subaru formerly made an excellent MT lube and now Ive read they don't anymore. Don't be fooled by "dual" ratings The MT in some GL5 refers to a non-syncromesh HD truck transmission, not your car trans.

Hope you find something. Both the Sig Other and I are in Autotrans land - for the first time in many decades.


Yep. Asking on the Subaru and the Guzzi both. Last time I used a mineral gear oil by ENEOS in the Subaru's manual trans that while rated GL5, was labeled as safe for yellow metals. Subaru is due for manual trans and rear differential oil changes, just need to get around to it. Guzzi is due for its first service which I'm performing myself.

The Guzzi is a head scratcher. In the manual, they have GL4 specified for the final drive bevel box and GL5 for the 6-speed transmission. Seems to me like it should be the other way around.
 
Originally Posted By: ARCOgraphite
Don't be fooled by "dual" ratings The MT in some GL5 refers to a non-syncromesh HD truck transmission, not your car trans.


This is true, but that's not WHY they are relying on it. From what I have understood from looking into this (I am not a lubrication specialist):

The API MT-1 standard includes passing ASTM D-130 copper corrosion test with a IA or IB rating, indicating it's "yellow metal friendly." So if a fluid is BOTH Gl-5 and MT-1 certified, then it's a copper/brass safe GL-5. I have read this is done by substituting boron compounds for the reactive sulphur elements. That doesn't mean everything else in the Gl-5 package is perfect for a synchronized transmission, but it won't harm the brass/copper.

Right now I'm searching for a suitable fluid for a 90s Audi transaxle that has a 5 speed manual and a Torsen Type-1 differential in it (Audi 016). It specs GL-4/75w-90. The factory fluid is a quite good synthetic, but it's $100 to change the transmission fluid. I've been searching for something more reasonably priced, but it's really hard to say what's a good substitute.
 
Most GL-4 and GL-5 gear oils use the exact same additive. The GL-5 just uses twice as much. GL-4 test components are no longer available and have not been for several years. In the past oil companies passed the GL-4 tests with 1/2 the treat rate of the GL-5 with same additive. SO without the ability to test for GL-4 companies use 1/2 the treat rate of their GL-5. Look up the additive PI sheets from the additive companies. To make your own, mix 1/2 GL-5 and 1/2 mineral oil with the same viscosity.
 
Originally Posted By: DWC28
Most GL-4 and GL-5 gear oils use the exact same additive. The GL-5 just uses twice as much. GL-4 test components are no longer available and have not been for several years. In the past oil companies passed the GL-4 tests with 1/2 the treat rate of the GL-5 with same additive. SO without the ability to test for GL-4 companies use 1/2 the treat rate of their GL-5. Look up the additive PI sheets from the additive companies. To make your own, mix 1/2 GL-5 and 1/2 mineral oil with the same viscosity.


Not quite true for modern MT formulations. In the distant past that was the practice but not today.

Today's GL-4 MT specific (dedicated) fluids have an additive package with specialized friction modifiers, AW additives, metal and rust inhibitors, and additional chemistries.
 
Originally Posted By: aquariuscsm
From what I understand,GL4 lubes also never contain limited slip additives,right?


Correct.
 
Originally Posted By: MolaKule
Originally Posted By: aquariuscsm
From what I understand,GL4 lubes also never contain limited slip additives,right?


Correct.


And thus, if you get a Gl-5/Mt-1 fluid that says "Not for limited slip," you then have a fluid that can be used in a Gl-4 spec'd transmission/transaxle. Right?

I think the SuperTech SynBlend 75w-90, which is Gl-5, MT-1, and NOT for limited slip, would thus be a good go-to alternative vs. rare and very pricey factory fluids (presuming 75w-90 is what you need). I think. ??
 
Originally Posted By: Oro_O


And thus, if you get a Gl-5/Mt-1 fluid that says "Not for limited slip," you then have a fluid that can be used in a Gl-4 spec'd transmission/transaxle. Right?


No, because the GL-5/MT1 fluids are rated for HD and over the road transmissions and neither contain the proper additive chemistry, nor have the correct viscosity for car and light truck transmissions.


Originally Posted By: Oro_O
I think the SuperTech SynBlend 75w-90, which is Gl-5, MT-1, and NOT for limited slip, would thus be a good go-to alternative vs. rare and very pricey factory fluids (presuming 75w-90 is what you need). I think. ??



As explained above, this would not be a proper substitute.


https://bobistheoilguy.com/forums/ubbthreads.php/topics/4542195/Re:_Synchromesh_Manual_Transmi#Post4542195
 
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Originally Posted By: MolaKule

No, because the GL-5/MT1 fluids are rated for HD and over the road transmissions and neither contain the proper additive chemistry, nor have the correct viscosity for car and light truck transmissions.


OK, it may not be suitable. I'm trying to understand very precisely why.

The viscosity seems pot on to me (~15cSt @100c), so it must come down to the friction modifiers, correct?

Thus, what is in the basic Gl-5 additive package that prevents proper syncromesh function IF the LSD FM's are not present? E.G., I am trying to reconcile that with your statement (which may not be all there is to say on the subject of course:

Quote:
Note: the specialized FM used in manual transmissions is NOT the same FM used in Limited Slip Differentials, nor is it the same FM used in Automatic Transmissions. It is important to understand that there are different FM chemistries for different automotive applications!


So since this fluid (and others like it) is not for AT or LSD use and is designed w/o the LSD FM's, I am wondering what is otherwise in (or missing from?) Gl-5 that makes it unsuitable in a gearbox. Is there a particular additive for the synchronizers that is present in Gl-4 and absent in Gl-5, perhaps? I can't find out no matter how much I search what the real chemistry difference is between the two.

I know a lot of Subaru owners use this fluid in their problematic gearboxes and are really happy and like it better than the extra-S (I don't own a Subaru). Whether that is actually a good idea or not, I don't know; just trying to understand in detail.
 
It is NOT what is MISSING but rather the DIFFERENCES between gear fluids of different ratings:

Dedicated or Application Specific MTF’s for Manual Transmission or Transaxle use an additive package containing Anti-Wear (AW) additives, rust and corrosion inhibitors, emulsifiers, and specialized Friction Modifiers, and are generally protection rated at the SAE GL-4 level.

Now GL-4 does not necessarily refer to MTF’s, as there are some gear lubes in the
Market place that are GL-4 rated, but are not MTF’s. GL-4 is an SAE wear protection rating.

There are a few MT fluids GL-5 rated for specific vehicles that have common MT and Differential sumps. One such manufacture, Subaru, has transmissions which shares a common sump and require a MTF which is GL-5 rated; but the Subaru-type fluids also contain special friction modification chemistry for the synchro assembly.

Manual Transmission fluids use a different Friction Modifier for synchro engagement,
a modifier that is NOT the same Friction Modifier chemistry as used in differential lubes,
engine oils, or hydraulic fluids.

Here, Friction Modifier or Friction Modification does NOT refer to friction reduction.
Here, Friction Modifier refers to a chemical compound that gives rise to a situation
such that the coefficient of friction (COF) varies Dynamically with respect to the
relative speed of parts that mesh and de-mesh during engagement and disengagement of rotating parts.

In summary:
1. GL-5 and MT1 rated gear lubes have a higher viscosity than MTF's of the same SAE Gear Oil viscosity range,

2. GL-5 and MT1 rated gear lubes have a different additive package than do MTF's; MTF's contain Anti-Wear additives, GL-5 and MT1 rated gear lubes contain Extreme Pressure (EP) chemistry.

3. GL-5 and MT1 rated gear lubes have a different additive package than do MTF's; MTF's contain specialized Friction Modification chemistry; GL-5 and MT1 rated gear lubes containing LS additives have special Friction Modification chemistry that is different than what is found in MTF's.

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4542195/Re:_Synchromesh_Manual_Transmi#Post4542195
 
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