Spline failures and its cause(s)

[BonS]

I've examined four Valkyrie rear ends in the past two weeks or so and all looked good but I find myself worrying about the day when I open one up and see what many here have as I'll carry the burden of responsibility if I did something to cause this. I've also been researching a bit to get a better understanding why our drive splines fail and found a few things that help shed some light on this phenomena. I may be preaching to the choir by telling some what they already know but I found the following information useful:

First, it is common to case-harden splines. This means that the bulk of the steel used in our splines is relatively soft. Case hardening is the process of heating and quenching a steel alloy that leaves the interior relatively soft but hardens the outer surface against wear. The outer case-hardened surface is typically only 0.010" deep.

Second, in one case study they analyzed the red oxide powder that is found in such a failure. The oxide powder contained the same material found in the splines themselves. So the red powder is not the failed lubrication material but it is the spline material being worn away.

Third, the conclusion in the case study as to the cause of the rapid wear of the case-hardened layer was inadequate lubrication to the splines.

So, the take-away for me is that when we have inadequate lubrication in our drive splines and the wear erodes through the case-hardened layer then the underbelly of soft steel will wear away quickly and fail.

In the some discussions about spline failure on this Board some have speculated that the splines may fail first and result in the heating and  breakdown of the lubrication. The opposite appears to be the more likely cause, however, that there is inadequate lubrication first and then the rapid wear follows.

I'll be using moly grease and paste in recommended amounts and always blowing out the two oil transfer holes at the base of the pinion cup along with making sure that I have the recommended fill level in the final drive. The four bikes that I serviced recently were wet and all had signs of oil exchange in the pinion cup, still had a grease coating, and the drive shaft splines and pinion cup and all were in good health. Thank goodness.

[Grandpot]

Very interesting.  Sounds like good research, rather than just an opinion.

[Daniel Meyer]

Alignment is the key if we are talking wheel hub (star) splines.

Come to Inzane. I'll show you.

[BonS]

Alignment is the key if we are talking wheel hub (star) splines.

Come to Inzane. I'll show you.

No doubt you're correct Daniel. There are quite a few other "initial failure" modes and one is extreme pressure. If the rear wheel star splines and final drive are out of alignment then higher gear tooth face pressure will result. The stress from the misalignment may cause the lubrication to overheat and fail from thinning. The thinning of the lubrication film further contributes to leaving the splines surface unprotected from the extreme pressure, producing more friction, more heat, more wear. This leads to more frequent servicing, repair and towing bills.

[Blues]

I watched Daniel's demo last year and it was very helpful. He sure made it look easy. Unfortunately, my memory is so bad that I really need him right beside me while I'm doing the work.  I've been worried about my drive connections... particularly since I had my local dealership install a new back tire a couple thousand miles ago.  Since that time, I've been dying to tear into it myself just to check the condition.

That leads to a question... If I find damage, I'll have to evaluate what I will need for repair; however, assuming that I do not find any trouble, what do I need to have on hand for the inspection?... grease, other lubricant, washers, etc.  I know when Daniel did it last year, he just took it off and put it back on.  I'm worried that I may need to replace lubes or parts due to the inspection itself.  Also, should I worry about my u-joint as well?  From the sound of comments, I don't want to get into that mess.  On the other hand, for peace of mind, I probably should inspect the u-joint... Thanks in advance for any recommendations or opinions!

OBTW, I have an '03 standard with about 20,000 miles...

[Daniel Meyer]

There's 3 o-rings and a thrust washer that possibly may need to be replaced. I always have them on hand on a rear wheel removal.

I don't change the rings unless they are flat or torn...the thrust washer ONLY needs changed if it's cracked or missing. It is critical though...do NOT run without it...it will cost you a wheel.

I just use hi-temp wheel-bearing grease.

I wouldn't sweat the ujoint at such low mileage, but it's really not that much trouble to check.

I WOULD check/clean the pinion joint every 20k miles or so...

Coming to Inzane this year? We'll be doing that same demo again.

[salty1]

BonS and Daniel I always enjoy reading your posts, you guys know what your talking about! BonS the synthesis on final drive failures was very informative. Thank you! 

[RP#62]

Not that it matters much in this discussion, but, case hardening is the process of taking a low carbon steel i.e. one that has insufficient carbon content to allow hardening by heat treating and packing it in a high carbon material like bone meal (and sealing out all the oxygen) and bringing it up to a red heat for several hours.  Over time, the carbon will be absorbed into the surface of the steel  - at a depth of so many thousandths per hour, I forget the rate.  It results in a high-carbon, i.e. heat-treatable "case" around the low carbon core.  There are some commercial hardening compounds that will impart different colors in the metal's surface hence "color case-hardened".

A friend of mine used to make shaping tools for woodworking out of common bolts by this method.  Once you have a high carbon surface on the metal, then you can heat treat it to get the hardness that you want.

-RP

[Mildew]

So there's more to lining it up right than saving the last 4 fourteen mill nuts to tighten on the shaft. I never done that when I first owned it and I was showing some wear. After that I learned to tighten  last and it looks no different now than it did many years ago. Maybe I'm just getting lucky.

[F6Dave]

As far as I know, the only way to cause any significant wear of the drive splines is to misalign the rear wheel and final drive.  This can happen because the four holes at the rear of the driveshaft tube are larger than the studs in the final drive.  This loose fit allows the final drive to be tilted slightly (and therefore misaligned) during installation.

If the axle nut is tightened while the four final drive nuts are still loose, the final drive is allowed to tilt so that it aligns itself with the right side of the wheel and the two faces are parallel.  This assures that the splines are mated squarely.  In this case there is virtually no movement of these parts during operation and they should last almost forever.  Their function is similar to that of the studs and lug nuts on a car's wheel and there's no reason they can't last as long.

However, if the final drive nuts are tightened before installing the wheel, there's a good chance the wheel and final drive faces will not be parallel, and the splines will mate at a slight angle.  Now, the splines are forced to act as a u-joint, and rather than simply transmitting power with no movement, they will grind against each other with every revolution of the wheel.  Even a slight misalignment will cause a lot of wear, and severe misalignment can destroy them in a few thousand miles.

Now here's some heresy:  it makes little difference how you lube them.  Properly aligned dry splines may get rusty but will still last a very long time.  And misaligned splines will wear very quickly regardless of how well they are lubed.  For nearly 100K miles I lubed the splines on my Tourer with some Valvoline multi purpose grease from a can I bought in the '70s.  That ran out and I now use wheel bearing grease because the sticky quality keeps it put.  I just changed the tire and at 165K everything still looks new.  I could probably lube them with K-Y Jelly or WD-40!

Here's some more heresy.  If the splines are properly aligned, and you don't pull the final drive during a tire change, they will still be aligned when you reinstall the tire.  The alignment can't change if you don't loosen those four nuts.  I never pulled my final drive until the bike had 38K miles, and when I did everything was fine.  These days I pull it at every tire change just to have a look, but I could probably do that every other, or even every third, tire change.

[Misfit]

As far as I know, the only way to cause any significant wear of the drive splines is to misalign the rear wheel and final drive.  This can happen because the four holes at the rear of the driveshaft tube are larger than the studs in the final drive.  This loose fit allows the final drive to be tilted slightly (and therefore misaligned) during installation.

If the axle nut is tightened while the four final drive nuts are still loose, the final drive is allowed to tilt so that it aligns itself with the right side of the wheel and the two faces are parallel.  This assures that the splines are mated squarely.  In this case there is virtually no movement of these parts during operation and they should last almost forever.  Their function is similar to that of the studs and lug nuts on a car's wheel and there's no reason they can't last as long.

However, if the final drive nuts are tightened before installing the wheel, there's a good chance the wheel and final drive faces will not be parallel, and the splines will mate at a slight angle.  Now, the splines are forced to act as a u-joint, and rather than simply transmitting power with no movement, they will grind against each other with every revolution of the wheel.  Even a slight misalignment will cause a lot of wear, and severe misalignment can destroy them in a few thousand miles.

Now here's some heresy:  it makes little difference how you lube them.  Properly aligned dry splines may get rusty but will still last a very long time.  And misaligned splines will wear very quickly regardless of how well they are lubed.  For nearly 100K miles I lubed the splines on my Tourer with some Valvoline multi purpose grease from a can I bought in the '70s.  That ran out and I now use wheel bearing grease because the sticky quality keeps it put.  I just changed the tire and at 165K everything still looks new.  I could probably lube them with K-Y Jelly or WD-40!

Here's some more heresy.  If the splines are properly aligned, and you don't pull the final drive during a tire change, they will still be aligned when you reinstall the tire.  The alignment can't change if you don't loosen those four nuts.  I never pulled my final drive until the bike had 38K miles, and when I did everything was fine.  These days I pull it at every tire change just to have a look, but I could probably do that every other, or even every third, tire change.

. Dave is right. It is very simple to maintain these splines. The drive splines are not a weak link on the Valkyrie. Improper alignment is the weak link to these splines.

[Ricky-D]

It is certainly not correct to say that no lubrication on the splines is needed.

I doubt that there is any engineering/automotive/motorcycle authority that would agree that no lubricant is necessary between moving parts such as the splines.

***

[Blues]

Thanks for the information... felt bad that I might have hijacked the thread.  It doesn't look like I can make Inzane this year.  Too bad!  Lots of good information to be had... and some beautiful bikes to look at!  I do need to get the o-rings and thrust washer, plus the lube.  Wouldn't want to need them and not have them with it torn down.  As far as I know, my local dealer doesn't know anything about alignment on these older bikes...

[BobB]

On June 28th I went in to my independent bike shop to order a new rear tire and drop off the wheel.  There was a black IS up on a lift and the guys there indicated that the rear wheel drive flange spline had failed.  Went back on July 2nd and watched as my tire was being mounted and balanced.  In talking to the mechanic the subject of the failed flange spline came up.  I passed along the procedure of loosing the four pumpkin flange nuts before re-installing the rear wheel, which it seemed was news to them.  He showed me the flange off the IS, and informed me that the bearing within the pumpkin had also failed.  There was sighs of wear on the spline with much more acute angles than would be possible without a bearing failure.  But who knows if any miss-alignment could also be the cause of the bearing failure. 

Case harding is typically used to prevent wear or to maintain a cutting edge on steal.  The process has been around for almost 2000 years.  However in a correctly assembled spline, there should be no surface on surface movement and therefore no possibility of wear.  So the answer is to inspect your bearings, o-rings, etc. and insure alignment of this assembly as Daniel Meyer has always recommended.   

[Ricky-D]

Well, I guess that would be correct in normal spline assemblies but, that is not the condition of the assembly of the rear wheel spline.

There is only minimally controlled alignment of the splines on the drive flange.

On the one end it is the spline connection itself that hold the alignment steady and there is engineered play in that connection.

On the other end is the rubber shock bushings that control movement.

Every time you accelerate and/or decelerate there is an attempted twisting motion imparted to the flange, splines and bushings.  The more play in the bushing assemblies and the more twisting the flange assembly is exposed to.

It's more easily to compare the flange splines and the motion thereof to the drive shaft splines and the pinion cup.

They are made to allow movement and be able to absorb a slight degree of misalignment while operating.  Easier to compare them to a constant velocity joint.

Movement in the spline connection. You bet, and lots of it.

Grease is your friend.

[Valkpilot]

There is only minimally controlled alignment of the splines on the drive flange.

On the one end it is the spline connection itself that hold the alignment steady and there is engineered play in that connection.

On the other end is the rubber shock bushings that control movement.

I think you've overstated the amount of flex that goes on in a properly aligned and torqued rear drive and wheel assembly.

There is a concatenation of components from the drive housing through to the left side swing arm that forms a rigid transverse column when the axle is torqued in place. 

It is the proper mating of the faces of the components such as spacers and bearing races that requires that the four pumpkin nuts be left loose when tightening the axle nut. 

Once properly aligned and torqued, that column cannot flex as much as you imply unless the axle is flexing as well.

[Ricky-D]

A closer examination would reveal that the drive flange/spline assembly is simply captured by the "column" of components that are compressed when the axle is tightened, and not involved in the stack-up of compression.

The ability of the flange to "move" is the main reason for incorporating the thrust washer. To prevent wear of the bearing boss on that side of the rear wheel.  The spline assembly absorbs wear on the other end of the flange.

This discussion is merely a reaction to a statement about splines not needing lubricant.

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