Insufficient lubrication (gear tooth scoring)

[Kestas]

Our client (a supplier to the NASCAR racing groups) has a problem with their set of third gears. They are scoring on the pressure side of the teeth - not pitting or abrasive wear, but scoring. The pattern of scoring is such that wear is only in the negative sliding region of each tooth (dedendum of the driving teeth & addendum of the driven teeth. The positive sliding regions look okay... there's evidence of meshing and light burnishing on the rest of the tooth. Full engagement of the tooth width is evident, so there is no misalignment in that direction. Lubrication is forced onto the teeth.

We're thinking this is a lubrication issue. The lubricant used in this application is 75W-90, probably Mobil SHC. It seems the oil can't keep up with high rpms of the gear box and we're losing boundary lubrication. There's thought that there may be some misalignment during operation, i.e., deflection in the gear box causing slight separation of the gears, but I'm not convinced this is 100% the answer, or even 10% of the answer.

What can we do to specify a better lube to handle the brutal requirements of speed, load, and temperature?

 

[Steve S]

Try Redline,most people think highly of Redline, put it to the test and let us know?

 

[benjamming]

Neo is used in a lot of racing applications, but I would contact MolaKule with Specialty Formulations.

 

[tdi-rick]

Kestas, it's a 'dog' box, isn't it ?

Off the shelf, I'd be trying Neo 75W-90 RHD. Call them and ask to talk to Paul Baker, who is the boss there.
It solved a lot of transaxle problems in CART, F1, F3000, etc when it first appeared in the late eighties.

Also talk to Molakule and Terry Dyson. (a sample of the used oil would be good

) I believe Terry has a fair bit of racing experience, and between them they would probably be able to brew something extra special up, with a more 'modern' additive package than Neo use.

Let us know how it pans out.

 

[JohnBrowning]

Is the scoreing only from the dry physical contact? I ask becuase you could have heating causeing the gear to soften up as well. Their are several options that can be explored. If it is a heat issue then material change my solve the problem. You can also try solid film coating like ZDDP coating offered by Neo. You can also try upgradeing the lubricant.

I have to ask though why the wear is isolated to the negative sliding region? It seems to me that that area should get just as much lubricant as the positive side? Is their a design issue restricting the lubricant flow to this area?

P.S. Have you checked the hardness of the gear?

 

[ebaker]

If it's a dog box couldn't you run a GL5 lube?

 

[Kestas]

I'm not familiar with the term "dog box". This is a manual transmission application. I apologize for not being clear about that.

We're only in preliminary stages of investigating this problem. We don't yet have full funding to dive into this problem. I hope to eventually analyze the metallurgy of the gear to make sure nothing is substandard, plus I can examine the sliding regions more closely to perhaps get additional info. We have no reason to believe it was run in a dry condition. If the gear overheated, we would've seen heat discoloration, there is no heat color to the part.

The reason wear is limited to the negative sliding region is that these areas are the first to suffer from substandard lubrication. It also struck me as odd at first, but after reading some books I find this pattern isn't that odd. (My dad worked 33 years as a transmission designer at Ford - I wish he was still around - but at least I have his books!)

Some additional info... the finish on the gear teeth is rather rough. It was run on the as-shot-peened surface, which is a little rougher than we'd like to see. Plus, I don't believe these gears were run-in ("seasoned" or burnished), which can have a significant effect on preventing scoring. So we're ready to attack this problem from many angles in addition to looking at the lubricant. My part is mainly metallurgy. My partner is the lubrication expert, though I've learned a lot from himself and this web site. I'll pass on to him any references on lubrication.

 

[tdi-rick]

dog box means a non-synchronised face dog engagement gear box.

It is a much faster, stronger gear selection.
It also means you don't need to worry about using a gear oil with the 'right' co-efficient of friction for the synchro cones, so a really good slippery GL5 type lube can be used.

 

[Kestas]

Yes, this is a dog box. Now that I think about it, my client kept using the term "dogs", while I kept saying "dovetails".

 

[MolaKule]

It sounds as you may have two or three problems:

1. The finish is substandard,

2. The case hardening of the teeth is below par,

3. The EP additive package isn't doing it's job.


Fluid AND metallurgical analysis seems to be in order.

You could still have enough fluid to cool the teeth, but the contact stresses may be too high for the weak additive package.

 

[Terry]

Kestas, another consideration is what the trans is used for in NASCAR and what level.

Ovals or Road Courses. We have found that the trans will be affected significantly by the bias of left turns all day vs the up and down and left and right of the road course.

The slush box is not the only driveline or powerplant item affected either. Give us a jingle we would love to help.

 

[JohnBrowning]

Gears always need to be laped to the desired final finish! In an OEM setting they can use lesser level of lapping and just demand a slow easy 500 mile break in period! In a performance setting they must be ready to run right out of the box! You definatly need to improve surface finish!!! In OEM manual transmission it often takes up to 10,000 miles of normal usuage to wear the gears to the desired final finish. Ring and pionons usualy need 500 miles. In a race setting the surface finish must be as close to the idle as you can get it!

 

[tdi-rick]

adding to Johns comment's, all the Hewland and Staffs gears I've seen/used all had very good surface finishes without any obvious signs of the shot peening process, (without using a microscope

)and I believe their stuff for the higher echelons of motorsport made the stuff we used look ordinary.

Any team I've known always runs in the crown wheel and pinion (R&P), regardless of who makes it, just to be sure.

BTW, there's been some excellent articles over the years in both Racetech and Racecar Engineering (both English mags aimed at the professional engineer) on Emco, Hewland, Xtrac, et al, and how they have done things, processes used, etc. Obviously nothing proprietory, but illuminating nonetheless.

They are considered essential reading by most motorsport teams/mechanics/engineers I've known.

 

[Elroy the Unique]

http://www.lubegard.com/automotive/gear_fluid_supp.html

You need Lubegard Gear Fluid Supplement. Lubegard and AutoRX are the two best additives recommended on this board.

 

[1sttruck]

The Dodge recommendations for towing state something like holding speeds at 50 mph or below for the first 500 miles, I guess to wear/lap in the gears in the axle properly. Need a towhitch on those race cars :^)

 

[Leo]

If you dont want to use Redline, I would highly suggest you consider using Motul Gear 300!!