API GL5 Vs. GL4

[grimreaper]

I just changed the trans fluid to the cheap 80w-90 supertech as a "flush" for the next few hundred miles. RL MT90 up next. I didnt pay attention to the GL specification on it but the tsrm says either is ok for the trans...

What im hearing through the grapevine is GL5 is the devils urine. When it gets hot it eats syncros up. Not to convinced but whats the real deal with the gl5 vs gl4?


what is the ford 75-90 gear oil?

 

[jdub]

Grim - Read this:
http://www.supramania.com/forums/showpost.php?p=614158&postcount=7

(GL-5 is not the devil's urine. Depends on what the gear oil is formulated for...tranny or LSD)

Ford 75W-90 is a GL-4 iirc.

 

[grimreaper]

GL-4 and GL-5 are the API specifications for gear oil:
- API GL-1, GL-2, and GL-6 are inactive.
- API Category GL-4 designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications.
- API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.

GL-4 and GL-5 products typically use the same extreme pressure additive system, with GL-5 having about twice the concentration of a GL-4. Too much of this additive could cause excessive chemical corrosion of the gear surface. If a GL-5 gear oil is used in a application where GL-4 gear oil only is called for, chemical corrosion of "yellow metal" components may occur, such as bronze synchronizers, brass bushings, etc. This may lead to shifting difficulties or shortened tranny life.

In the R154 and W58 transmissions, either GL-4 or GL-5 gear oil is allowed. In gearboxes where a GL-4 *only* is specified, Wingman is correct...using a GL-5 oil can cause damage to the tranny.

Johnathan - What I'm saying here is using RP Synchromax in a tranny with shifting problems *may* help...I'm not recommending it for use in a tranny that is functioning normally. Synchromax has a viscosity of 35.3 cst at 40 deg C and 7.7 cst at 100 deg C...Max-Gear 75W-90 has a viscosity of 144.5 cst at 40 deg C and 21.0 cst at 100 deg C...Max-Gear 80W-90 has a viscosity of 150.3 cst at 40 deg C and 16.8 cst at 100 deg C. Both cold/warm viscosities are much higher than Synchromax and illustrate why a GL-4 or GL-5 gear oil is specified for our manual trannys....per the Red Line tech data sheet:

Quote:
"With most lubricated components, the slipperier the better, but this is not so with manual transmissions. The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear. The time this process takes depends on how easily the synchro ring moves and the rate of frictional energy transfer between the two synchronizer surfaces. Higher viscosity lubricants slow the sliding of the synchro ring on the input shaft and require a longer time for the oil to be squeezed out from between the mating synchronizer surfaces. After the lubricant is squeezed out, the coefficient of friction of the lubricant determines the rate of frictional energy transfer between the two surfaces. Slippery lubricants such as hypoid gear oils (like RP Max-Gear) can take too long to synchronize the gears, which promotes synchronizer wear. Red Line MTL and MT-90 has a coefficient of friction which is greater than conventional oils, allowing a quicker transfer of frictional energy."

The cliff notes version is the R154 and W58 trannys NEED a certain amount of friction to work properly. RP Max-Gear is *too* slippery to provide this friction...RP Synchromax is even more so. It is more an ATF type lubricant and thins out significantly at higher temps. IMO, these 2 gear oils are not well suited for our manual trannys...the success many guys have seen using these oils is due to the slippery characteristics of these gear oils "freeing up" (reducing friction) parts in the R154/W58 that are on the way to failure. This is not fixing the problem...that sound from your tranny is the sound of inevitably.

The reason more modern trannys spec a gear oil like Synchromax (or GM's synchromesh) is to improve cold shifts. The thicker oils in a GL-4/5 category do not shift well at lower temps...they need to warm up. The problem is Synchromax does not have the extreme pressure protection, oil film thickness, and shear stability required...this will increase wear on the gears. Synchromax may help quiet down a worn R154/W58 for a while, but it is not really helping the problem...it's masking it.

Just for comparison, Red Line 75W-90NS is a GL-5 and has a viscosity of 95.0 cst at 40 deg C and 15.6 cst at 100 deg C and Red Line MT-90 is a GL-4 75W-90 and has a viscosity of 90.0 cst at 40 deg C and 15.6 cst at 100 deg C. These two gear oils are almost identical in this respect...the difference is the additives...MT-90 is more suited to the R154/W58. The advantage of these are their low temp viscosities...it will help smooth out shifts until the oil gets warmed up.

BTW - there are quite a few excellent GL-4 gear oils out there, all of with will work fine in a R154/W58...gear oils have a much easier time coping with the enviroment they work in vs motor oil. The biggest reason I like the Red line MT-90 for use in a R154/W58 is it's low temp viscosity characteristics. Especially in the R154...it's not the smoothest shifting tranny and will benefit the most from MT-90.

As usual...the devil is in the details
- JDUB

thought id move it over for future reference. I totally missed that other thread when looking for something GL5/4 specific

 

[jdub]

Speaking of details, note that RL 75W-90NS is a GL-5 gear oil...it is fine to use in a R154 or W58. The difference between it and standard RL 75W-90 is the friction modifier additive for an LSD...the 75W-90NS does not have it. It's not that both oils are a GL-5 that makes it unsuitable for a manual tranny, it's the friction modifier.

What you will see is most GL-5 oils are formulated for an LSD and therefore have the friction modifier additive in the formulation. On the other hand, all GL-4 oils I'm aware of do not have friction modifiers added....if used in an LSD, these oils need the friction modifier added to them.

That's where the "grapevine" might be getting the idea that GL-5 oil is a poor choice. It's not the case...it's the friction modifier that makes an oil a poor choice for a tranny

 

[iwannadie]

Speaking of details, note that RL 75W-90NS is a GL-5 gear oil...it is fine to use in a R154 or W58. The difference between it and standard RL 75W-90 is the friction modifier additive for an LSD...the 75W-90NS does not have it. It's not that both oils are a GL-5 that makes it unsuitable for a manual tranny, it's the friction modifier.

What you will see is most GL-5 oils are formulated for an LSD and therefore have the friction modifier additive in the formulation. On the other hand, all GL-4 oils I'm aware of do not have friction modifiers added....if used in an LSD, these oils need the friction modifier added to them.

That's where the "grapevine" might be getting the idea that GL-5 oil is a poor choice. It's not the case...it's the friction modifier that makes an oil a poor choice for a tranny

Not to go off topic but...

Is it ok to use RL 75w90NS in the supra LSD if you put in the LSD additive? Someone was telling me to go with the NS fluid then slowly add the LSD additive. The idea being its better to be on the low end of LSD additive rather than too much?

 

[jdub]

Of course you can if you want...the 2 versions of RL 75W-90 are the same, except for the friction modifier. You do want to use the RL friction modifier.

 

[iwannadie]

Of course you can if you want...the 2 versions of RL 75W-90 are the same, except for the friction modifier. You do want to use the RL friction modifier.

Thanks, I just wanted a definitive answer from the expert :icon_bigg .

 

[Asterix]

My Secret LSD Sauce is 1 quart of 70W90NS topped off with 75W90. That way I get decent clutch action, but it's still smooth and quiet.

Asterix

 

[jdub]

Adding your own friction modifier to Red Line 75W-90NS or mixing the two types as Asterix suggests sounds reasonable to me. Red Line 75W-90 does have a tendency to chatter in a Supra LSD, especially if it has a lot of miles on it. Cutting down on the friction modifier using either method might just do the trick

 

[Asterix]

When I first got my Supra, I used Mobil 1 gear oil with the slip additive already in it. Since the Supra was my first car with an LSD, it took me a while to discover that the Mobil 1 oil had so much slip additive in it the LSD action was almost nil.

When I started looking into a better option, I discovered Redline offered a choice of with or without slip additive. I called them up and they said the NS is intended for helical-gear LSDs (a-la Torsen), but mixing the two is perfectly fine for adjusting clutch grab in a posi. Adding slip is easy; taking it away requires a drain and refill.

Once I tried MTL or MT90 (I forget which) in my W58, there was no looking back!

Asterix

 

[Doward]

JDub, your thoughts on MTL in the R154?

 

[jdub]

In a stock to moderate HP drive train, MTL will be good to use IMO. It is a significantly thinner gear oil per below:

MT-90 - 15.6 cst @ 100 deg C...90.0 cst @ 40 deg C
MTL - 10.6 cst @ 100 deg C...56.2 cst at 40 deg C

http://www.redlineoil.com/pdf/6.pdf

Both are GL-4 oils which meet the 80W spec for both the W-58 and R-154 trannys. MT-90 will provide additional shear stability under aggressive driving conditions...in short, it will better resist break down. Under normal use, MTL will work quite well and reduce fluid friction to the drive train and help increase gas mileage.

Some additional info on GL-4 vs GL-5:

Most manufacturers of manual transmissions and transaxles recommend an 80W or 90W GL-4 lubricant. GL-5 gears oils which are required in hypoid differentials are not used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half. The extreme pressure requirements of spur gears and helical gears found in transmissions are not nearly
as great as found in rear-wheel drive differentials. A GL-4 lubricant provides adequate protection for most manual transmissions, unless a unique design consideration requires the extra protection of a GL-5.

A GL-5 is allowed per the TSRM in the W-58 and R-154, but IMO it is not necessary and will shorten the live of the tranny. John, you've had the R-154 apart...are there any yellow metals used in it?

 

[Doward]

The case midplate is cast iron, the balls/rods are all steel, the gears are steel, the synchros are brass, the hubs/rings are steel, the shafts are steel, the case is aluminum, and the forks are aluminum (verification pending, Ian believes they may be aluminum coated steel, haven't had a chance to rip it back apart). I believe the speedo drive gear is also aluminum.

Everything aside from the synchros are aluminum, steel, or nylon (spacer and squirter in the rear tail case)

 

[jdub]

The synchros are what I was wondering about...the high pressure additives in a GL-5 gear oil are corrosive (per above) to brass. Based on that, (if it were me) I would avoid GL-5 oils in the R-154. Even though the TSRM allows it.

 

[Doward]

So MT90 and MTL would be good choices?

 

[jdub]

Yes, for the reasons and applications I stated earlier. Both are GL-4 gear oils.

 

[grimreaper]

how quickly then can one expect wear to be detrimental? that supertech im "flushing" with is gl-5 IIRC. We talking months with DD use or years here?

 

[jdub]

Grim - I'm "guessing" it would take a while, especially since the TRSM allows it. I wouldn't leave it in there long though

 

[Doward]

Jdub, let me ask you this - with the TSRM specifying GL4, the MTL vs MT-90 bugs me.

I mean, the MTL only has 66% of the operating temp viscosity of MT-90. Therefore, I'd expect the MTL to be a 'slicker' shifting oil.

I think what I'm asking (lol, always good when I'm not even sure) is this:

Does the MTL provide superior breakdown protection vs what would have normally been available in a GL4 in the early 90s?

 

[jdub]

The GL-4 spec has been around for quite some time...maybe this will help:

http://www.api.org/certifications/engineoil/pubs/upload/1560.pdf

If you are referring to a synthetic GL-4 vs a conventional (dino) GL-4, yes the synthetic is superior in resisting the shear you will find in a tranny. More "slick" is not the issue, either will provide the lubrication necessary. The higher viscosity of the MT-90 will provide a thicker lubrication film and resist shear better as stated earlier....good for heavy duty application. The MTL will do as well lubrication wise, but be more susceptible to shear and not provide the same "impact" protection. Under "normal" driving conditions (i.e. not hard drag launches), the MLT should work well.

Maybe I don't understand what you mean...I hope I'm getting the idea across.