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Fri Nov 29, 2024 9:23 am

Just wanted to check and see if full synthetic 75w-90 gear oil is a good oil to use in my gearbox, it's mild temp here in Georgia so I just wanted to check before I do it because it's all we have at the shop currently

Fri Nov 29, 2024 10:59 am

vw_bud wrote: Just wanted to check and see if full synthetic 75w-90 gear oil is a good oil to use in my gearbox, it's mild temp here in Georgia so I just wanted to check before I do it because it's all we have at the shop currently

Yes.....it's fine as long as its GL-4 type and not GL-5. Ray

Fri Nov 29, 2024 12:27 pm

vw_bud wrote: Just wanted to check and see if full synthetic 75w-90 gear oil is a good oil to use in my gearbox, it's mild temp here in Georgia so I just wanted to check before I do it because it's all we have at the shop currently

The brand is important, some GL-5 are okay and others are not. If it says its okay for use a synchromesh transmission it is likely fine, but if it doesn't specifically say it's okay for use with synchronizers the it's probably best to find another oil.

To the best of my knowledge the only GL-4 oils to avoid are the two thinnest Redline GL-4 oils.

Fri Nov 29, 2024 12:58 pm

Yeah, full synthetic 75w-90 gear oil should work fine for your gearbox, especially with the mild temps in Georgia. It's a good all-around oil and should perform well in most conditions.

Fri Nov 29, 2024 1:49 pm

shaggysboss wrote: Yeah, full synthetic 75w-90 gear oil should work fine for your gearbox, especially with the mild temps in Georgia. It's a good all-around oil and should perform well in most conditions.

Yes...totally agree.....but also heed what Wildthings stated. Not to get deep into it and get this thread locked....but there is years of chatter online about this subject.

There are oils out there where the mfg states "meets both GL-4 and GL-5 standards. Some of them are speaking strictly of performance standards and its not clear whether they care anything about chemical compatibility.

In a nutshell....almost all "full hypoid" final drive gear sets require GL-5 gear oils for the extreme pressure lubrication additives.

The bus does not have a hypoid final drive gear set. It is skew bevel but not hypoid.
But the thing most of these mfg's are not even stating is that most modern hypoid final drive transmissions...also have long since gone to steel on steel synchronizers instead of brass like we have.

This is why it all gets confusing. No one is lying to you...they are just not giving all of the information in one shot.

Whatever 75/90 synthetic you are using....just do a quick google search on it and ask if its "good for yellow metal syncronizers". You will quickly find discussions with answers of yes or no.

But in a pinch it will get you on the road. If you find out its not recommended....just change it out in a few weeks. Ray

Mon Dec 02, 2024 12:28 am

the issue with many late fluids other than GL4 is that they are designed to work with different kinds of synchros. TheMotorOilGeek had a show discussing the importance of getting oils and transmission fluids right. Make sure it is GL4 because if it is too slippery like many GL5, then the transmission may never shift right again based on experiences some transmission builders here have had with clients making that mistake.

In one link below it reads re GL5, "Not for use in systems that contain yellow metal," meaning no brass syncho rings which is what out buses have.

Motor Oil Geek:
Quote: What is the right way to choose an oil? Well, it doesn't start with choosing a brand name. Instead, the application will dictate the chemistry needed. A 750 HP race engine needs a racing oil, not a passenger car oil or diesel oil. A non-synchronized transmission needs a different fluid than a synchronized transmission does, especially if it has brass synchronizers. A hypoid rear gear may or may not have a limited slip differential, which impacts the choice of chemistry needed (limited slip differentials need a limited slip gear oil). As you can see, each of these applications requires a different chemistry, and none of these decisions begin with a brand name.

In this video I'll show you how I choose the engine oil, transmission fluid and gear oil for my Dad's vintage NASCAR race car. He's 76 years old and the engine makes over 750 horsepower, so I have to get these choices right. After making these choices, we will go to the racetrack and see how the car runs. Plus, we will see how much difference a smaller carburetor makes in terms of average lap time!

Here's one of the best FREE resources on lubricants: https://petrocanadalubricants.com/en-ca/lube-source-handbook/automotive/automotive-gear-oils

For help choosing a viscosity grade, check out page 36 of the Driven catalog: https://drivenracingoil.com/rt-5996-c...

To get started with used oil analysis, check out: https://www.speediagnostix.com

Mon Dec 02, 2024 6:39 am

My 65 Bug and my wife's 87 Cabriolet had that typical cold snick when shifting from 1-2. My son recommended that I add some Lucas gear oil to it. I put in about a cup of it when near the end of filling. Drove it and the shift is smooth with no snick. I has stayed that way. It surprised me.

Mon Dec 02, 2024 9:05 am

vwmaniaman wrote: My 65 Bug and my wife's 87 Cabriolet had that typical cold snick when shifting from 1-2. My son recommended that I add some Lucas gear oil to it. I put in about a cup of it when near the end of filling. Drove it and the shift is smooth with no snick. I has stayed that way. It surprised me.

Are you talking about a Lucas additive? or an actual gear oil?

Mon Dec 02, 2024 9:47 am

SGKent wrote: the issue with many late fluids other than GL4 is that they are designed to work with different kinds of synchros. TheMotorOilGeek had a show discussing the importance of getting oils and transmission fluids right. Make sure it is GL4 because if it is too slippery like many GL5, then the transmission may never shift right again based on experiences some transmission builders here have had with clients making that mistake.

In one link below it reads re GL5, "Not for use in systems that contain yellow metal," meaning no brass syncho rings which is what out buses have.

Motor Oil Geek:
Quote: What is the right way to choose an oil? Well, it doesn't start with choosing a brand name. Instead, the application will dictate the chemistry needed. A 750 HP race engine needs a racing oil, not a passenger car oil or diesel oil. A non-synchronized transmission needs a different fluid than a synchronized transmission does, especially if it has brass synchronizers. A hypoid rear gear may or may not have a limited slip differential, which impacts the choice of chemistry needed (limited slip differentials need a limited slip gear oil). As you can see, each of these applications requires a different chemistry, and none of these decisions begin with a brand name.

In this video I'll show you how I choose the engine oil, transmission fluid and gear oil for my Dad's vintage NASCAR race car. He's 76 years old and the engine makes over 750 horsepower, so I have to get these choices right. After making these choices, we will go to the racetrack and see how the car runs. Plus, we will see how much difference a smaller carburetor makes in terms of average lap time!

Here's one of the best FREE resources on lubricants: https://petrocanadalubricants.com/en-ca/lube-source-handbook/automotive/automotive-gear-oils

For help choosing a viscosity grade, check out page 36 of the Driven catalog: https://drivenracingoil.com/rt-5996-c...

To get started with used oil analysis, check out: https://www.speediagnostix.com

Yes! Love that guy!

But just to add a small amount more to what you just stated.

1. Yes, GL-5 is too slippery for our brass synchros
2. Yes, long term, there is too much sulfur for our brass synchros which will break down with age causing corrosion.

I used to believe that the LONG TERM chemical issue with brass synchro was the only problem. And.....I believed that if you just kept the GL-5 in for short intervals it would not damage the synchroa if you did not leave it in long enough to gain moisture and start the breakdown and production of dilute sulfuric acid.

Yes, within that frame of mind....you can get away with SOME GL-5 synchromesh formulations....with some "yellow metal" synchro designs. Not all of them are brass, not all brass or bronze is the same exact alloy and the way they are cut, angled and tooth geometry can allow using SOME Gl-5s with no issues. Been there. The synchros on the type 4....004 transaxle are a little different.

3. BUT.....I used to believe that the ONLY issues with GL-5 were those two....being excessively slick and having a medium to long term chemistry issue.

I do not believe that anymore. Due to well stated information from people I trust....here and in other forums, along with some great threads presenting solid information in other forums.......and......capped off with definitive information from Lake Speed Junior/the oil geek.......the CHEMISTRY issue is not JUST the long term one I already stated.

It is also a very short term issue that can destroy some yellow metal synchros in short order. I would have to dig up the articles and posts....but suffice it to say....do not risk GL-5 or a combined GL-4/GL-5.....unless the mfg SPECIFICALLY states it it is safe for yellow metal synchros and GL-4 applications.

Ray

Mon Dec 02, 2024 12:03 pm

What do you think of Driven STF Synchromesh fluid?

https://drivenracingoil.com/i-30497857-stf-synthetic-synchromesh-transmission-fluid.html

Mon Dec 02, 2024 5:14 pm

Opossum wrote: What do you think of Driven STF Synchromesh fluid?

https://drivenracingoil.com/i-30497857-stf-synthetic-synchromesh-transmission-fluid.html

While Driven probably (from everything I have read) makes a really good synthetic synchromesh oil we could use, I do not think......that particular gear oil is what you want for our types of transmission. Note that it states that it's really for manual transmission that are using ATF, multi-viscosity or straight weight MOTOR OIL as a transmission fluid. That's really common on NASCAR type vehicles with straight cut gears.

It's far too thin for our gears. That being said, a great amount of the modern car syncromeah oils are like REALLY thin.....like 10w oil. The synchromesh oil in my Golf is like 10w oil in consistency......and MUST be changed about every 35k miles.

I have been meaning to look into what Driven does have for us because their stuff is really good and well researched. Ray

Mon Dec 02, 2024 7:30 pm

Opossum wrote: What do you think of Driven STF Synchromesh fluid?

https://drivenracingoil.com/i-30497857-stf-synthetic-synchromesh-transmission-fluid.html

Anything made strictly for racing may not do all that well where it sits in a gear box for years on end slowly collecting water and breaking down/oxidizing.

Tue Dec 03, 2024 9:56 am

When I had my bus trans rebuilt by Transworks, I explained that it was doomed to live its life on the freeway turning 4K. They recommended running full synthetic 75W-140 oil in it, which has so far worked great. FWIW.

Tue Dec 03, 2024 11:15 am

Wildthings wrote: vwmaniaman wrote: My 65 Bug and my wife's 87 Cabriolet had that typical cold snick when shifting from 1-2. My son recommended that I add some Lucas gear oil to it. I put in about a cup of it when near the end of filling. Drove it and the shift is smooth with no snick. I has stayed that way. It surprised me.

Are you talking about a Lucas additive? or an actual gear oil?

I'm curious about this, too.

Tue Dec 03, 2024 12:46 pm

Swepco 201 or 203, depending on how you feel about moly (201 should shift better, 203 box might last longer with big loads)

if you plan to drive when it's quite cold, Swepco + Lubegard gear fluid supplement

Synthetic is not recommended

do not use Redline (in your gear box, their engine oil is very nice)

If you're obsessed with using synthetic, Motul 300V

If you're limping an old crappy gearbox along, GM p/n 88900399

Opinions vary greatly on this topic

Check the Vanagon forums for some very extensive discussion

EDIT: clarified re: moly

Tue Dec 03, 2024 7:45 pm

The Lucas that I used was gear oil and I can't recall if it was the 75-90 or the one to 140, but I imagine it was the 75-90. It listed safe for yellow metals on the jug. Beats me why it works so well but I am sure I only put in like a cup of it.

Tue Dec 03, 2024 7:52 pm

vwmaniaman wrote: The Lucas that I used was gear oil and I can't recall if it was the 75-90 or the one to 140, but I imagine it was the 75-90. It listed safe for yellow metals on the jug. Beats me why it works so well but I am sure I only put in like a cup of it.

Good to know. I was wondering about Lucas gear oil anyway.

Tue Dec 03, 2024 8:19 pm

Swepco 210 is what was recommended from my rebuilder

https://swepcolube.com/wp-content/uploads/2024/07/SWEPCO-210-Multi-Grade-Gear-Lube.pdf

Tue Dec 03, 2024 8:28 pm

Understanding I AM in the bus forum......the Haynes manual always suggested that the gear oil to use in the 411/412with manual transmission was Castrol Hypoy-C.

Now...Hypoy-C is GL-5. The problem is....and you see this in a lot of other forums where the yellow metal issue and GL-4 and GL-5 are being discussed.....you need to remember exactly what kind of car these other people are discussing.

The common comment is that GL-4 is for the "transmission"....meaning the gear sets with synchros....and GL-5 is for the final drive (and most specifically "hypoid" final drive).

Hint....you are dealing with people whose vehicles generally have a separate final drive.

We do not have that luxury. The final drive in a bus is in the same case and oil pool as the transmission section with its yellow metal synchros. It also does not have a "hypoid" final drive. There is nothing in the 002 or 091 that "requires" the slickness of GL-5.

To make matters worse on my 411's and 412's.....our transmissions DO have a hypoid final drive....which is why they suggested that a GL-5 should be used.

The difference in oils that state they "can" work in GL-4 and GL-5...is that yes, they have the friction mofifiers of GL-5 and SOME sulfur....but they also have LESS sulfur....maybe just enough...and they also have one of several buffer agents to prevent damage to the yellow metals by the sulfur.

The problem is how well is this documented?

Some of the better comments in forums actually suggest that if you have this same issue....yellow metal synchros AND a hypoid final drive in the same case....use what is suggested for SOME older Subaru because they have this set up as well. Not sure how true this is yet.

Ray

Wed Dec 04, 2024 10:08 am

Every VW bus manual clearly states hypoid oil is to be used in bus transaxles. The owners manual even puts hypoid in bold.

Robbie