Spline friction: GL-5 or THF?

[Extreme-Duty]

Hi,

imagine the spline connection between the drive shaft and the diffential in a steerable drive axle. When turning, the shaft has to move back and forth in most axles. The axle in question can either use API GL-5 gear oil or high quality THF.

Which one will provide the lowest possible friction in this regime, a top notch quality S/P-base gear oil, or a top notch quality THF?

MolaKule has been saying there are different friction modifiers for different tasks i.e. increasing efficiency, synchromesh performance, LSDs etc. Does it make a difference if we:

a: use a GL-5 gear oil which is optimized for syncromesh performance?

b: add an LS-additive?

Will an FM even work in highly loaded splines? If not, it may all be a matter of friction of the AW/EP-system.

Any ideas?

 

[FL_Rob]

Whats req'd for the carrier ?Is it a limited slip?

 

[Extreme-Duty]

It is a limited slip diff, but the manufacturer, Carraro, does not require an LS-additive. The look up performance is low, and that is a good thing for our use.

The reason I started this thread, is that the inboard spline friction does affect the load on the outboard shaft bushing in the planetary wheel hub drive. A worn bushing shortens the oil seal's life.

 

[mechtech2]

The splined axles don't move around in their seats.
They are locked with 'C' clips.

I don't know why yo say most axles move around. They don't.

 

[SteveSRT8]

This is not true of all independent rear end designs.

Many times the splines are just like in a driveshaft, they move a bit with suspension travel.

 

[Extreme-Duty]

Originally Posted By: SteveSRT8
This is not true of all independent rear end designs.

Many times the splines are just like in a driveshaft, they move a bit with suspension travel.


Yes, it is similar to the suspension travel of independent wheel hubs. There is an inboard drive shaft, a double U-joint and an outboard drive shaft in the wheel end. When steering, one or both shafts will travel, depending on the axle design. This is very very common in steerable drive axle, at least in off-road equipment.

 

[MolaKule]

I am not aware of any GL-5 differential type lube optimized for synchromesh operation.

If this spline is highly loaded, as most are, you want maximum wear protection which a GL-5 diffy lube would provde. Since most diffy lubes have a certain measure of takifier or high viscosity oils for cling, a GL-5 seems to be btter.

A THF is usually around 10 centistokes in viscosity with a lower AW package and would seem not to cling as as well as a GL-5 gear lube.

I am really suprized that the manf. would spec a choice of a lower viscosity THF or verses a GL-5 in say 16 cSt or higher, unless the manf is concerned about hot weather verses extremly cold weather operation..

 

[FL_Rob]

Man, I'd find a thick 80w140 and never look back.

 

[FusilliJerry82]

Maybe I'm missing something but for a driveshaft spline wouldn't a grease be the proper lube as opposed to gear oil?

I have heard good things about Amsoil 5th Wheel Grease in such an application.

 

[mechtech2]

Originally Posted By: SteveSRT8
This is not true of all independent rear end designs.

Many times the splines are just like in a driveshaft, they move a bit with suspension travel.


Read the original post about steering. I need no correction from you.

 

[Extreme-Duty]

Originally Posted By: MolaKule
I am not aware of any GL-5 differential type lube optimized for synchromesh operation.

If this spline is highly loaded, as most are, you want maximum wear protection which a GL-5 diffy lube would provde. Since most diffy lubes have a certain measure of takifier or high viscosity oils for cling, a GL-5 seems to be btter.

A THF is usually around 10 centistokes in viscosity with a lower AW package and would seem not to cling as as well as a GL-5 gear lube.

I am really suprized that the manf. would spec a choice of a lower viscosity THF or verses a GL-5 in say 16 cSt or higher, unless the manf is concerned about hot weather verses extremly cold weather operation..



OK, GL-5 oil optimized for synchromesh operation is not a perfect description of what is sold as "total driveline lubricants" (TDL) in Europe, but they are GL-5 lubes that do have synchromesh MTs in mind. Look at Mobilube 1 SHC 75w-90.

Carraro seems to prefer THF over GL-5, even for the wheel ends. John Deere wants a THF for all new tractor front axle differentials and for some wheel ends, while other wheel ends have to use GL-5. Cold weather is indeed the reason why JD recommends to switch to a THF in certain units:
Mechanical Front Wheel Drive (MFWD) axle performance in cold weather

Notice they want people to move from a 25-30 cSt to 9-10 cSt lubricant and do not even indicate that there own 75w-90 and 80w-140 synthetic GL-5 oils (launched in 2009, I believe) might be a good choice in between.

Fiat-derived New-Holland front axles use THF as well.

The question is how bad these THFs really are.

 

[Extreme-Duty]

Originally Posted By: FusilliJerry82
Maybe I'm missing something but for a driveshaft spline wouldn't a grease be the proper lube as opposed to gear oil?

I have heard good things about Amsoil 5th Wheel Grease in such an application.


It would be great if any manufacturer build these axles with greasable splines near the U-joint, just like on other automotive drive shafts. Unfortunately, I have never seen it that way.

 

[BBDartCA]

GL-5 is fine. The pressures from the hypoid gear mesh is many times greater than the axle shaft sliding back and forth. By the way, depending on what model Carraro axle it is, the axle shaft may be moving radially, not axially in turns. PM and I will let you know.