GL4 or GL5 for brass synchros

[Lawson Cox]

I've researched this on the search engine here on the barn and am as confused as I was when I started. Have a 38 transmission in my 35 pickup and I believe it has brass synchronizer rings, but not positive. Which is best, 4 or 5. OLD inquiring minds want to know.

[JSeery]

It's not a question of better, GL5 will damage your transmission. There are some GL5s on the market which claim to be yellow metal safe, but I wouldn't trust them. Use GL4.

All early synchro transmissions contain yellow metal.

[1937pickup]

I am looking forward to answers to this question. My transmission is a 37 in a pick up. I read on hear someone saying that as long as the gear oil said MT-1 it would be ok. Last fall I put 90-140 gear oil marked MT-1. It really improved my shifting, no more grinding even when double clutching. Since then I read an article about GL-4 and GL-5. The author states that the problem is the phosphorous additive. It is to good in GL-5 and stays on the brass synchros and takes small amounts of metal when shifting. NAPA sell a CRC GL-4 oil that I thinking about putting in the tranny. Only problem is it only comes in 85-90 weight and I really like the heavier oil for shifting.

[rotorwrench]

Originally they used GL-3 but it was superseded by GL-4 a long time back. GL-5 has a lot more EP additive. You can smell the stuff in all the EP lubes. GL-1 has no added Extra Pressure additives and is a basic hydrocarbon lubricant. It is a bit on the weak side for gear face protection and is better suited for worm screw drives. GL-4 is the late type mild EP for straight in axles and transmission with phosphor bronze bushings like the one in the second gear and the one in the reverse idler as well as the thrust washers for the cluster. GL-5 is high EP for gear drives with offset pinion shafts (hypoid drives) like modern vehicles have.

[JSeery]

GL4 and GL5 both contain EP additives, but the amount in GL5 is much higher. The EP additives attach to the metals in the transmission and provide a surface which improves wear. However on yellow metals attach to the EP and then pulls off the base metal. Over time it will destroy the yellow metal.

This shouldn't be confusing, it is fairly stright forward.

[Lawson Cox]

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Thanks for clearing that up in layman's language. Lawson GL4 it is.

[19Fordy]

[B]Lawson, I have spent the last 4 days researching this topic and have concluded that GL4 and GL5 both have additives that attack yellow metals.

However, here's a fellow who says that his research shows that GL4/GL5 gear oil will only begin to attack yellow metals above 300 degrees.
Posted June 16, 2012 - 09:04 PM
"This is one of those areas were you will find the old diehards that will use NOTHING but 90W GL1. These tillers have a bronze gear in the back for the tiller drive, at the time these were built GL1 was very common, but it has since been discontinued, GL1 has very few additives in it. You really need to run an oil with a High Pressure additive to help protect the 2 worm gears in it. They don't recommend GL5 gear oil in these because it can be hard on yellow metals. After a lot of research, I have found that GL5 will only harm yellow metals when the temp gets over 300*. This tiller will never see that high a temp, also this tiller will probably not see more a hours use all year. I was a member of the Troy-Bilt Tiller group, and got in an on-line fight over the use of any other oil other than GL1 oil. I posted all the information on this and was bad mouthed and all the info I posted was ignored. The manual for this was written over 25 years ago, before any of the new oils were created. I run 85W-140 GL4/GL5 in mine. I'm not going to special order GL1 for mine".

I use the Ford 600wt. gear oil in both trans. and diff.

What year did Ford come out with the hypoid gears? I ask because I think these
require different oils.

[JSeery]

That's true 19Fordy, as I already posted, but the EP additive is low enough in GL4 that it does not present a problem (I believe even VanPelt recommends GL4*). If for some reason you believe you need zero EP there are other options, but then you also lose the advantages of the EP. Life is full of compromises!

Personally I think using so-called w600 is a poor choice, and certainly not what Ford recommended.

Note: * This is from memory and I haven't found the reference, so!

[19Fordy]

JSeery: Thanks for your input.
This gear oil question seems to never end.
I wonder what was in the overhead gear oil dispenser hose in the 1960 Esso gas station where I worked on my old car as a kid?
All the cars got the same stuff.

[JSeery]

GL3 or GL4 I would guess, I would have to check the specification dates. None of this was much of an issue until GL5 came along!

OK, GL1, GL2 & GL3 were declared "inactive" in 1995.

[flatheadmurre]

Today some of the manufacturers state their GL-5 to be redmetal safe to.
In the specification it often says API GL-4/5 meaning it has what it takes to fill the specification of GL-5 but should be safe to use in a GL-4 aplication.

[1oldtimer]

I just bought some GL1 (they sell it in the gallon container) from Napa and was going to change the '47 trans fluid. After a few miles since I rebuilt it.

[rotorwrench]

Surphuric and phosphoric EP additives are acidic. They eat into the metal faces to deposit the EP protective materials. It is true that later GL-5 rated lubes have a bit different additive that starts to function at a higher temp but 300 degrees is not very realistic. Most large car and truck hypoid axles don't run over 180 degrees unless there is something wrong with a bearing or the like. They need the EP additive to work at lower temps or it would not work at all. GL-5 is fine for any rear axle that has no phosphor bronze bushings which covers most axles made after 1928 on cars and around 1940 on big trucks (many early Mack Bulldogs still had chain drive rears well up into the 30s). Transmissions are another story. If it is high EP of any type the sulphuric and phosphoric properties of the high EP will have a slow effect on the softer metals.

If you run your stuff lightly and carry light loads, you can get away with SAE 50 motor oil in your transmission and rear axle but if you carry higher loads or work your vehicle on long trips and such, it should have some EP in there. GL-4 will work for all purpose lube but GL-5 can be used in the rear axle. Steering gears and transmissions have bushings that really shouldn't be coated with high EP lube for long periods but for a short period, any lubricant is better than none.

[JSeery]

Originally Posted by flatheadmurre

Today some of the manufacturers state their GL-5 to be redmetal safe to.
In the specification it often says API GL-4/5 meaning it has what it takes to fill the specification of GL-5 but should be safe to use in a GL-4 aplication.

I have read many articles that question this. They find the GL-4/5 rating to be inconsistent and misleading. I would not trust it myself, as long as GL-4 is available why take a chance?

Here are some examples of the confusion.

[RalphG]

I just checked the manuals for my medium duty International trucks and they specify straight mineral oil for the T17 (4 speed) transmissions. #80 or #90 SAE weight. I've been running straight #30 motor oil in my T17 transmission in the IH Loadstar for several years after reading up on some research. So far it has been fine. These transmissions are syncro in the top 3 gears and get a good workout hauling heavy loads. I have some GL1 ready for the next oil change though.

[flatheadmurre]

Originally Posted by JSeery

I have read many articles that question this. They find the GL-4/5 rating to be inconsistent and misleading. I would not trust it myself, as long as GL-4 is available why take a chance?

Here are some examples of the confusion.

Best should be to ask the manufacturers tech department directly if it really is red metal safe.

Over here i can still buy GL-1/GL-3 in 20L from the oil depot but not over the counter.

[JSeery]

LOL, that is where the complaints are coming from, company tech departments claiming compatibility and the products then leading to transmission damage. It doesn't matter to me what anyone uses, just putting out there the claims of problems expressed by others (mainly antique tractors guys). I run a T5 and use ATF!

[Ross F-1]

Originally Posted by flatheadmurre

Best should be to ask the manufacturers tech department directly if it really is red metal safe.

Over here i can still buy GL-1/GL-3 in 20L from the oil depot but not over the counter.

I've posted this before....

[rotorwrench]

If you check out an SAE lubricant compatibility chart, you will see that the viscosity grading is done differently between motor oils and gear lubricants. SAE 40 motor oil is very close to SAE 80 gear lube and SAE 50 motor oil is very close to SAE 90 gear lube. The only problem is that most motor oils are no longer straight grade but are multi viscosity and you can't expect multi vis to hold up well in high load situations. Aircraft motor oil is still relatively easy to get in straight grades so I use the AeroShell SAE 50 grade 100W in my old Borg Warner type overdrive transmissions. However, they make a 100W+ (or plus) type that can not be used due to the addition of a Tricresyl phosphate (TCP) additive put in there for Lycoming engine applications. TCP is just as bad as EP additives used in GL-5. It can make the sprag unit slip on those old OD transmissions so a person has to keep that in mind when shopping aircraft motor oil.

[19Fordy]

Do they make an SAE 140 GL3 gear oil?
That would be "heavier duty" than GL1 but without the EP additives that harm yellow metals.as shown here:
http://www.substech.com/dokuwiki/doku.php?id=gear_oils