Why are people running GL5 gear oil in their transmissions?

[rich1]

Maybe I am missing something so help me out.  When HD started approving Syn3 motor oil in the transmission a lot of people thought they had lost their minds. But other manufacturers with integrated engine/transmission have been using engine oil for transmission lube forever. A lot of HD riders like to run hypoid gear oil in their transmissions. Seems to me that hypoid gear oil is no more appropriate for the application than 20W50 motor oil since Harley transmissions don't need the EP additives. So are people running the hypoid gear oil mainly to reduce noise?  I have nothing against using it but it seems the thicker gear oil could rob some power. Just looking for an alternative to Formula + which is nothing but over priced 50W mineral oil according to oil analysis. Thanks.

[chaos901]

I have no opinion on the GL5 Gear Oil in the title but I run Redline Shock-Proof in my bike transmissions. 

It clings very well, transmission shifts great and I never have had a problem.   

[HD95]

I run Amsoil 75-90 synthetic gear oil in mine.Smooth shifts,locates neutral precisely,quiet.I wouldn't run HD syn in anything.

[Slammers]

The way I look at it engines and transmissions have very different lubrication requirements. No one lubricant can do it all. There are trade-offs. If the you have an integrated engine and transmission you have no choice but to compromise. Having a separate transmission allows you to use a lubricant specially designed for that application.
Like Chaos, I use Red-Line Shockproof in the transmission. I feel I'm using the best product that is designed for the application.

[rbabos]

GL5 I believe has EP additives. It should not be used in any trans that has yellow metal bushings. The 6 speed is fine for it's use. Some earlier ones have bronze bushings I believe. In reality, there is no need for GL5 because EP additives only work under, well extreme pressure. The HD gear box won't really generate that kind of heat at any zones for the additive to actually work.
GL4 is plenty. Absolute bare bones of GL1 rated oil for the trans. I have a hard time believing Syn3 has a GL rating. Amsoil 20/50 does and has been used quite often in gear boxes. Me, I prefer a true gear oil for the gearbox.
Ron

[harley_cruiser]

It was explains to me by an oil expert that viscosity rating for gear lube was different than motor oil. That 20w50 was about the same as 75-90.
You do not want to use the 120w in any HD as it starves the inner bushing, as per Danny Peterson.

[WI Bob]

cruiser, you are correct.
I hand these charts out every week. http://www.golftechs.us/Reference/viscross.pdf

[PeteH]

Thanks for that chart!

Gear oil for unsynchronized gnashing gears, same as my lower units.

[mr. pitts]

The way I look at it engines and transmissions have very different lubrication requirements. No one lubricant can do it all. There are trade-offs. If the you have an integrated engine and transmission you have no choice but to compromise. Having a separate transmission allows you to use a lubricant specially designed for that application.
Like Chaos, I use Red-Line Shockproof in the transmission. I feel I'm using the best product that is designed for the application.

+1 on that. I put HD primary/tranny oil in my tranny (96 Electra) kept it in for 50 miles. The tranny was as rough as hell. Changed to Redline shock proof heavy & it's as smooth as butter. Gonna change to Redline primary oil (in the primary) when I've run out of HD oil.

[mp]

I don't know why anyone would want to mix their engine oil with their transmission lube.  It only makes sense to use gear oil to lubricate gears.  And the weight ratings of gear oil are not comparable to the weight ratings of engine oil.  A 75w90 gear oil is about the same viscosity as 10w40 engine oil.

[bigfoot5x]

I did not know that gear lube ratings were different than oil ratings. I wondered how 75w90 gear lube could be replaced by 20w50 Syn3 and have it work. The numbers just never made sense to me.

[Don D]

The viscosity numbers never will make sense because the pour points of a 75W gear oil is about the same as 30W motor oil.
It is a constant mesh gearbox, no syncros, and there are many oils that will work well but not motor oils.
Ron has this nailed

[pumpguy68]

  motor oil is for motors. Gear oil is for gears!


Ray m

[Latrobedyna]

The standard saybolt system either SUS or SSF is the best way to determine viscosity. Sadly most retail marketed oil products lack such information on the containers.

[shovelinabox]

I have no opinion on the GL5 Gear Oil in the title but I run Redline Shock-Proof in my bike transmissions. 

It clings very well, transmission shifts great and I never have had a problem.

[truck]

When you don't use the right gear oil, your bike could catch fire, like these windmills.

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[BUBBIE]

A GL5 rating Gear Oil;  Will Take Heavy Gear Pressure...

extreme-pressure protection of a GL-5.

signed....BUBBIE

[Ultrashovel]

Hmmm, I've used the heavy Redline in my HD transmissions ever since I can remember.....whenever I first heard about it on the market. I've never had a problem with a Harley Transmission. I don't like Syn 3 but it's not something that I would use in a transmission in any case. It's motor oil.

[Big Cahuna]

Oh my God, I've been using GL-5 rated oil for years. When am I gonna start having problems?.,,,

[dr. evil]

Tomorrow.

[Dan89flstc]

Metric bikes have been lubricating transmissions with engine oil since the beginning of time, their gears hold up fine, and transmit a lot of power in many instances.

Theoretically it would seem that gear lube would be the only thing to use. I have never seen a gear that was worn out due to lube failure in a Harley transmission, no matter what the lubricant used, but I have seen many trashed bearings....maybe the gear lube is the wrong lube for the bearings   

I don`t think it is a big deal what you use in these low stressed gearboxes.

[Ultrashovel]

I'm going to add this issue of transmission lubricant to my list of things not to worry about. 

[motorhogman]

 

I'm going to add this issue of transmission lubricant to my list of things not to worry about. 

   

[BUBBIE]

Our Harley Gears are NOT little, light nor Wimpy gears... Gears WILL Chew up motor oil molecules not meant for in between gears... It chews them up and no spitting them out.

I will only use what HAS worked for so many For Years.... Redline ShockProof...I prefer the Heavy...

signed....BUBBIE

[PoorUB]

Better to use a lube that is " over rated" than " under rated"