# Gear Oil: GL-4 vs GL-5?



## KT54g60 (Aug 1, 2003)

From what I've gathered via reading/ searching, GL-5 is more "advanced" than GL-4, but may contain corrosive materials that can harm the synchros. Can anyone shed some light on this issue? My specific application is an 02A w/ Peloquin LSD. I will be using 75W90 redline, but there are still 3 options there... 

So is there a difference/ which one is appropriate for certain applications and which should be avoided?


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## Super Hans (May 27, 2011)

That's pretty much all wrong. GL-4 is for manual trans GL-5 is for diffs, "gear oil". Mobil 1 makes a fine GL-5.

GL-4 MTF leaves a lot of room for "customizing". New VW MTs come with a very thin fluid, as thin as ATF. Old school MTF is as thick as 75w-90 gear oil, so somewhere inbetween is a good place to be.


For your diff, just use what the mfg calls for, GL-5, maybe with a LSD additive.


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## KT54g60 (Aug 1, 2003)

Super Hans said:


> GL-4 is for manual trans GL-5 is for diffs, "gear oil".
> GL-4 MTF leaves a lot of room for "customizing". New VW MTs come with a very thin fluid, as thin as ATF. Old school MTF is as thick as 75w-90 gear oil, so somewhere inbetween is a good place to be.
> 
> 
> For your diff, just use what the mfg calls for, GL-5, maybe with a LSD additive.


This was not helpful as the link below is specified for a manual trans and it's a GL-5

http://www.redlineoil.com/product.aspx?pid=47&pcid=7

Even says it right on the bottle (see pic below)










I am still confused.


edit:
i did get an answer from Gary Peloquin basically saying to use whatever VW specifies, so I'm just going to run with that I suppose.

and VW specifies part# G060726A2 for an 02A, which is a GL-4, if anyone cares.






also... i dislike you. you did not effectively answer any of my questions and you don't put your sentences together very well. Why would I care what comes in a new VW MT and WTF is "inbetween"?


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## Super Hans (May 27, 2011)

Guess what, you're not the only person reading the replies. Considering the amount of confusion surrounding GL-4 vs GL-5, it seemed like a complete answer was appropriate. 

You might try reading the entirety of the link, as that Redline product is not a typical GL-5...

"Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness"

Sorry that you found either too much or too little information in my post. It wasn't intended to confuse you to such a tragic degree. Apparently, my reply did contain the correct info- to follow the mfg guideline. 

Considering the diff and gearbox syncros share the same fluid, a GL-5 is unacceptable, although it's optimal for stand-alone diffs. That Redline product is ideal, as it won't bork the syncros, but has maximum protection for the diff. 

Try a little patience next time. Really.


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## KT54g60 (Aug 1, 2003)

Super Hans said:


> Guess what, you're not the only person reading the replies. Considering the amount of confusion surrounding GL-4 vs GL-5, it seemed like a complete answer was appropriate.


I did not find your answer complete





Super Hans said:


> You might try reading the entirety of the link, as that Redline product is not a typical GL-5...
> 
> "Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness"


I did read it and even researched to find out what the NS stands for (No slippery additives), but that doesn't mean anything to me. I'm not here asking questions because I already know everything, I'm asking because I DON'T and I am trying to understand. Telling me something is thicker or thinner doesn't explain anything.



Super Hans said:


> Considering the diff and gearbox syncros share the same fluid, a GL-5 is unacceptable, although it's optimal for stand-alone diffs. That Redline product is ideal, as it won't bork the syncros, but has maximum protection for the diff.
> 
> Try a little patience next time. Really.


I almost want to buy and use a GL-5 just to prove to you that it is perfectly acceptable, but I'm looking for what is the best fluid in regards to performance and longevity.

Did I seem like I was in a hurry? Or do I need to have patience when having a conversation with you? Not following what you are trying to say...

Anyway, I was trying to get an understanding of how one oil would be classified as a GL-4 and another as a GL-5. There must be a difference besides "thickness". 

Stuper Hans, feel free to resist a reply unless you have useful information. I'm not interested in having an internet piss fight with you.


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## Super Hans (May 27, 2011)

KT54g60 said:


> From what I've gathered via reading/ searching, GL-5 is more "advanced" than GL-4, but may contain corrosive materials that can harm the synchros. Can anyone shed some light on this issue? My specific application is an 02A w/ Peloquin LSD. I will be using 75W90 redline, but there are still 3 options there...
> 
> So is there a difference/ which one is appropriate for certain applications and which should be avoided?



When you lead off with nothing but incorrect conclusions, shall I conclude that you did your research?

GL-5 is not "more advanced"

You jumbled so many other "facts", it is indeed apparent (to me) that you rushed through the material without reading for comprehension. It's not "corrosive material" that will harm the syncros, it's the fact that GL-5 has higher levels of friction modifiers, and is too slick to allow proper syncro ENGAGEMENT. The "corrosive material" myth is in reference to the yellow metals, brass and bronze, and is indeed incorrect as well.

My answer about "inbetween" viscs is entirely correct and goes to your declaration that 75w-90 is for some reason the only visc to consider, when in fact OE fluids are now 1/2 as thick.

Speaking of thick, I'll let you know when you get something right.

Also, I don't care if you "like" me, this is a technical forum, not a dating site. 

Work on your people skills and your technical skills, all the info I posted can be inferred from the material you supposedly read. "GL-5 NS"....pretty obvious.

Why don't you read up (again) and tell us what you think the difference between GL-4 & 5 actually is, and we'll go from there.


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## Tofie (Feb 27, 2011)

thickness is actually part of everything geared towards oil and gear oil.

if you put some more research than just typing a question in google,
you would find the API test their oil on how long it takes it to drip through a plastic
tube and the oil(s) being "thick" has everything to do with the amount of seconds 
and grade that oil is rated out to be .

so thick and thin is everything in oil.


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## KT54g60 (Aug 1, 2003)

KT54g60 said:


> From what I've gathered via reading/ searching, GL-5 is more "advanced" than GL-4, but may contain corrosive materials that can harm the synchros. Can anyone shed some light on this issue? My specific application is an 02A w/ Peloquin LSD. I will be using 75W90 redline, but there are still 3 options there...
> 
> So is there a difference/ which one is appropriate for certain applications and which should be avoided?


I know i jumbled a **** ton of facts in the above statement so I will restate my original post for clarification...

I tried researching the internet to get a better understanding of the difference between GL-4 and GL-5 oil for my transmission. My search has left me with information that I'm unsure about in that I don't know if it is correct and/ or don't quite understand the technical jargon I am reading. Can anyone be helpful and explain to me the difference between the 2 classifications/ ratings (GL-4 and GL-5)?

I am asking because I want to make sure I use the best suited oil for my application, which is a corrado 02A transmission with a Peloquin Limited slip differential. I was hoping to use 75W90 redline gear oil, but there seems to be 3 of them available and I do not want to use the wrong one and damage my car parts.

I do understand the concept of viscosity, but not well enough to understand technical info pages regarding gear oil or transmission fluids.

I am hoping to find the vortex useful for once, but won't be shocked if it's a massive failure. I know that I am at least trying to understand and learn something instead of just using what everyone says works well.


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## 90crvtec (Nov 17, 2010)

KT54g60 said:


> I know i jumbled a **** ton of facts in the above statement so I will restate my original post for clarification...
> 
> I tried researching the internet to get a better understanding of the difference between GL-4 and GL-5 oil for my transmission. My search has left me with information that I'm unsure about in that I don't know if it is correct and/ or don't quite understand the technical jargon I am reading. Can anyone be helpful and explain to me the difference between the 2 classifications/ ratings (GL-4 and GL-5)?
> 
> ...


 Rather than bash you for making some assumptions, I'll try to add what I know about these two specifications.

GL4 and GL5 are used interchangeably on most gear oils, the majority of 75w90 gear oils will claim to be GL4/5 compliant.

The main difference between GL4 and GL5 is that a GL4 spec oil has about half of the extreme pressure (EP) additives when compared to a GL5 oil of the same weight. Way back when GL5 first came out, the high concentration of EP additives in GL5 would sometimes cause metal corrosion issues with yellow metals (brass, copper, etc. etc.). This primarily effected synchronizers on manual transmissions.

GL4 oils are making a comeback at boutique companies like Redline and Amsoil because they saw a market need to formulate a GL4 based gear oil that was designed to be extra safe to use with yellow metals in manual transmissions. Also, most of the MTF formulated GL4 oils are blended with an additive base that is designed to help your synchronizers function more efficiently while still protecting the gearset in the transmission. Read "better shift quality."

Amsoil MTF, Redline MTL, and even Pennzoil Synchromesh are all excellent choices for a GL4 gear oil for a manual transmission. There are still plenty of people that use GL5 oil in their manual transmissions and most don't seem to report any problems with it. Also, with current oil and additive formulations, GL5 doesn't seem to be a problem even when used with yellow metals. This is why you will see a lot of GL5 spec oils also being listed as compatible with a manual transmission.

Me personally, I always ran a GL4 oil that was designed to be an MTF in my manual transmissions. My favorite was always Amsoil MTF, but Pennzoil Synchromesh is a close second and is available over the counter at most auto parts stores. I didn't run it for the GL4 so much as I ran it because it was designed to be a dedicated MTF and was formulated with better synchronizer function in mind. A GL5 gear oil designed for hypoid gearsets in a differential will work for an MTF but, I'd rather use a fluid designed to be an MTF in the first place.

Hopefully this helps you make a decision. The good news here is that either one will probably work for you, it's up to you which one you'd be more comfortable using.


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## KT54g60 (Aug 1, 2003)

90crvtec, thank you!
tofie, just by typing "API" you helped me as well

i found this link (which i found helpful):

http://www.unitedoil.com.au/products/gear.htm


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## gmikel (Nov 10, 2010)

*very good*



90crvtec said:


> Rather than bash you for making some assumptions, I'll try to add what I know about these two specifications.
> 
> GL4 and GL5 are used interchangeably on most gear oils, the majority of 75w90 gear oils will claim to be GL4/5 compliant.
> 
> ...


:thumbup:


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## Capt.Dreadz (Jun 4, 2003)

I'm using RL Heavy/Light Shock Proof mix in my 02a.









Syncro friendly & great for those boost tranny's.


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## Super Hans (May 27, 2011)

Now I want a LSD.


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## gmikel (Nov 10, 2010)

*you don't need it*



Super Hans said:


> Now I want a LSD.


you're far enough out now


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## a2gtinut (Dec 2, 1999)

020 - Redline MTL
02A - Redline MT-90


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