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I posted some of what I have learned about GL4 - GL5 oils on a VW site that I reference for a beetle that is being restored. What I thought may have been true at one time, but maybe not now. Following is an email (to someone else) from an Amsoil tech regarding 4 vs 5. Or you can check the whole thread here http://www.thesamba.com/vw/forum/viewtopic.php?t=276529


Here's an explanation Bruce sent me almost 2 years ago when I had the same question. Figured I'd help you not to repeat yourself again, great info!

Jeff, All cars made today have brass syncros that look the same as Beetle syncros. To think that the oil companies would make a product that would destroy every gearbox it went into is rediculous. When I first heard this GL-4/GL-5 corrosion thing, I did some research on the oil co web sites. I couldn't find anywhere that said it was harmful, so I sent a tech message to the Amsoil tech guy. His response stated the history of how that myth got started by the ignorant VW people. When GL-5 first came out it was indeed corrosive to brass syncros. But only at temps above 250ºF. Now since it is impossible to get any street driven gear oil to that temp (It is hard to get engine oil that hot!), there will be no problems using regular GL-5. However, just to satisfy the ignorant masses, the API came up with another added rating, called MT-1 which is tacked onto the end of all GL-5 oils you can buy today. With this MT-1, GL-5 oil is not corrosive at any temp.
The difference between GL-4 and GL-5 is the extreme pressure capability. On surfaces that have high pressure where metal to metal contact will happen, the GL-5 is way better at protecting. Spider gear teeth and side gear teeth are one place where GL-5's better EP rating is desperatly needed. I've got 5-6 Bus 091 ZFs in my garage right now that have suffered significant wear on the gear teeth from probably using GL-4.
The nay-sayers like to point out their Bentley recommends GL-4. Of course it does, that's all there was 30 years ago. It also recommends using only mono-grade engine oil, bias ply tires........
The use of synthetic or dino makes no difference. I highly recommend you use syn over dino, you can really feel the difference in the way it shifts. If you buy a fresh gearbox, first put in dino for about 500-1000 miles then dump it and put in syn. It stays there long enough to warrant the extra cost, unlike syn engine oil.
I put my money where my mouth is. My last gearbox was a full out Berg 5 with close 2nd and a near NOS ZF. You couldn't pay me enough to risk damaging it with GL-4's inferior EP performance. Argueably, that gearbox is worth $3500-4k.
I always challenge the guys that say GL-5 is bad by asking them to tell me who do they know that had a failure using GL-5. Still waiting.
Good luck,
Bruce
_________________

So, if this is true, some current GL5 oils are ok for the mog trans. Just thought I would share.
 

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I would contact a tech with another synthetic or otherwise oil company to verify if the above info is correct. MAKE SURE it is a true tech. guy and not a salesman. Asking him where his engineering degree (or chemistry?) is from would be a good way to cover that base.
 

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I would contact a tech with another synthetic or otherwise oil company to verify if the above info is correct. MAKE SURE it is a true tech. guy and not a salesman. Asking him where his engineering degree (or chemistry?) is from would be a good way to cover that base.
Seeing that some of that referenced post came from Amsoil, I would want another reference, too. Amsoil, like any other company, is in business to sell their product and I doubt they have older, GL4 rated, gear oil to sell. As to the "myth got started by the ignorant VW people", I assure you, it's MUCH more widespread then just "ignorant VW people". I have no bias against Amsoil ( never used it or had the opportunity to use it ), but I seem to recall some pretty Evangelical talk coming from so-called factory sources about their products. ;)

Seeing that GL4 rated lube is not all that hard to come by, it seems to boil down to the better high-pressure qualities of GL5. I was under the impression that this feature was only important in hypoid gear-sets, which had a much higher contact pressure then spur or helical gears which ( I think ) inhabit the cases of Mog transmissions. Please educate me if I'm wrong (seriously) !
 

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Discussion Starter #4
Kieth, you're right about the pressure ratings. The beetle trans has the R&P in the trans, that doesn't apply to mogs. I was just throwing it out there for discussion. I agree that contacting a few other techs would be a good idea. In the end, if the MT1 rated GL5 oils are OK for 404 and later transmissions, good news for all. GL4 oil is tough to find here.
 

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I spoke to an "engineer" from Royal Purple that said their "package" of additives made it safe for Unimogs. It is very true that he may have been not accurate or not honest. I'm using it in all my boxes, diffs and hubs. I will let you all know if my stuff takes a dump. My mog is my mostly daily driver. We'l see,
Chas
 

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All cars made today have brass syncros that look the same as Beetle syncros. .
I'm no transmission expert but somewhere recently I read about the "new generation" syncro design that was said to be used in most domestic manual transmissions now. The article was associated with transmission oil and referred to the differing properties required by this design. Sorry, can't lay my hands on it but makes me cautious of the statement above.:confused:
 

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My understanding is that in a syncronized transmission you are trying to find a balance between slipperiness and friction to give long life but also allow the syncronizers to work. There are gear oils out there, most notably to me Schaeffer's and Redline that use large amounts of EP additives such as Moly (MoS2). This is great in a differential, portal box, PTO transmission etc. but not in a syncronized transmission because the moly will not allow them to work.

My Dodge transmission which is a Mercedes G56 calls for ATF +4. Will the gears and bearings last a long time? I doubt it which is why I use a different product. Will it give good cold and warm shifts and last the warranty period? Almost certainly!
 

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I've mentioned this before, but I have found RedLine MTL & MT90 to be superior lubes in both modern and vintage gearboxes. MTL for those boxes spec'd for ATF and MT90 for those running gear oil. Both are GL4 rated and a little pricey - but, if you have no leaks, a fill of synthetic lube could last a lifetime of ownership if you don't put a lot of heavy duty miles on your truck.
 

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My understanding is that in a syncronized transmission you are trying to find a balance between slipperiness and friction to give long life but also allow the syncronizers to work. There are gear oils out there, most notably to me Schaeffer's and Redline that use large amounts of EP additives such as Moly (MoS2). This is great in a differential, portal box, PTO transmission etc. but not in a syncronized transmission because the moly will not allow them to work.
Yes - if your lube is too 'slippery' you can have engagement issues when the syncros fail to do their 'thing' properly. A high percentage of moly probably worsens this effect.
 

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As Black Diesel said it is a balance of friction to spin up the next gear and slick enough to not cause too much drag. The Royal Purple "engineer" said their package addressed these issues. It definitely doesn't shift any worse. When cold 5th gear is always slow and a ham fist I think could cause damage. I'm very delicate when cold...the truck I mean.
Chas
 

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Castrol says

Hi Guys,

I have an Email from castrol dated July 27, 2007 about GL4 vs. GL5.

This is an excerpt:

"API GL-5 gear oil designates service of hypoid and other types of gears
commonly found in rear axles. A GL-4 oil may be employed in certain manual
transmissions.

These differences are mainly distinguished by the level of active additives
employed in the product. Different applications require different additive
levels and different component materials can be affected by the levels of
additives present in the lubricant.

Having said that GL-4 and GL-5 gear oils are not compatible and
manufacturer's recommendations should be adhered to. They cannot meet the
same specifications and the product performance and tests are different.

Typically, a GL-5 gear oil will have about 2 times the active additive level
of a GL-4 product. This additional additive can cause problems with yellow
metals like brass or bronze."

Take it for what it's worth. I put fresh Castrol GL-4 in my tranny and it shifts great now.
Please note too that bronze bearings (bushings) are made from a alloy such as “bronzalloy” or “oilite” that is softer than the alloy used to make syncro rings. Also the bearing would be subject to stress the entire time the transmission is working while the syncro rings see intermittent stresses of short duration. This may be why bearings could be affected but not syncro rings.
I had to get it from Lubrication products specialists and had to buy a 5 gallon bucket.

Regards,

Jeff
 

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Discussion Starter #12

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So, that Swepco document supports what the Amsoil guy said - GL5 MT1 has less detrimental effects on 'yellow metals'.

But, all MT-1 rated lubes may not play nice with syncro's...
 

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You won't care about syncho's if your main shaft is ceased cause the yellow metal in the bushings there got ate up.

In the Mog 404 at least; it is my understanding that the issue has nothing to do with synchros. Its bushings on the main shafts that are yellow metals.

now true..... ifffff you got the reassurance that a GL5 or other oil isssss compatable with yellow metals THENNN you have to consider.... "what about the synchro's"
 

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I talked to a tech at Valvoline about their dual rated GL-4/ GL-5 gear oil. He said there are different additives that can be used to make the oil Extreme Pressure rated ( GL-5) . He said the additives that Valvoline uses in their GL-4/GL-5 will not harm yellow metals .
 

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A lot of this discussion would be easy enough to verify.

From what I have learned about the issue - copper based alloys do not like acid environments. GL-5 gear oils contains EP (extreme pressure) sulfur based additives which may increase the acidity of the oil especially at high temps when the additives tend to break down releasing sulfur and forming sulfuric acid.

Yellow metals = brass & bronze which contain copper.

(By a similar issue exists with jewelry being worn in swimming pools. The chlorine compounds react with the non gold portions of the alloys resulting in embrittlement.)

Here's a simple experiment for anybody who has some extra time.

Compare the effects on a piece of copper placed in different hot gear oils (GL4s and GL5s) after time. Use a microscope for to observe any visual changes and a measuring device to see if there are any dimensional changes. It may be necessary to heat the oils up to higher temps to get a reaction, maybe not. I would think it would be necessary to heat the oil to the operating temp of the gear box to make useful observations. If the GL5 oil was affecting the copper I am pretty sure it would be visible on the metal's surface at about 60X.

The experiment would tell a lot. Any volunteer amateur scientists out there ?
 

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The repair of my 20 speed trans had me looking up replacement oil recomendations here . The GL 4 vs GL 5 API spec controversy looked interesting so i Googled it and found the following on a ford site. A lot of the problem wouod appear to come from someone saying that GL% will `eat up " the brase/ bronze synchronizers. It looks like this was not a chemical attack, but that the additives for extra high pressure (EP) increase the viscosity and cause a lot of wear on these softer parts which need a lot of oil flow to be lubricated correctly. The GL5 is fine for differentials where its additives make it superior for the sliding action of a pinion gear set.
Quote from what reads like the technical watchdog at Ford ( sorry for the bad word , twice), it contains a quote from a lubrication journal.
Dave
`To the best of my knowledge they are not interchangeable. The GL-5 has more Extreme Pressure (EP) additives than the GL-4 and different oxidizers. It is my understanding that GL-5 gear oils are for Highly loaded Hypoid gear differentials only. The Gl-5 can ruin bearings in a GL-4 application.
Here is a quote i lifted: "One must select the proper level of additives to maximize component life. A case in point is a manual transmission with bronze or brass synchronizers. Higher concentration of EP additives in manual transmission oils might cause the softer “yellow” metals (copper, brass and bronze) to wear out more quickly. API GL-4 contains approximately half the additive treat rate of GL-5. API GL-3 contains approximately half the additives of a GL-4. So which is better — GL-1 or GL-5? Again, the answer is neither or both. One must always select the recommended API designation for each specific application." [By Jack Snavely and Vatsal Shah ] National Oil & Lube News.

Here is the link to the entire article www.noln.net/columns/pennzquakerapr04.html
 

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In the WIS (Workshop Information System) Mercedes are very specific about what's to be used in the diffs and gearboxes of UGN/UHNs and SBUs:
In the trans, oils on spec sheet 235.4 or 235.11. These include Castrol Syntrans 75W-85, but nothing available in the US. The U500 owners manual however suggests Delvac Synthetic Transmission Fluid 50 which is about a 90 viscosity trans fluid. It is GL-4 and top-notch for synchro and nonsynchro transmissions, but not for diffs.
In the portals and diffs, 235.8 which include Delvac Synthetic Gear Oil 75W-90.
You don't see any GL-5 diff type oils in the lists of 235.4 and 235.11.
MT-1 is a rating for non-synchronized transmissions and therefore totally irrelevant as far as Unimogs are concerned.

Charlie
 

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Thanks for the redirect esde. You might find it amusing to kow that yours (this) was one of the first threads I happened upon when I began searching all of BenzWorld! During recent discussions, I have quoted parts of your first post here in an effort to explain the need for the spec we are trying to match.
 
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