[Fot] Fwd: Crown and pinion gear break in

Mon Sep 17 09:46:06 MDT 2018

The preload was spot on verified on the bench as 12inlbs of breakover torque. I did not verify after my first session that it was still good, I’ll likely do that going forward. Upon tear down, the breakover torque was thru the roof but that is due to metal paste in the rollers. Also, there was no fore-aft movement in the pinion on tear down. 

I’ll note that after I suspected something was going wrong (second session), I noticed I had lost a little fluid out of the vent. I topped it off and it required less than one stroke on my little hand pump, maybe a few onces of fluid. 

Another note, I was using redline MTL at the time of failure which I always have. After some reading, this is probably not the best for a diff. I  Will be switching to their shock proof oil going forward. 

Sent from my iPhone

> On Sep 17, 2018, at 10:29 AM, Bob Kramer <rkramer56 at gmail.com> wrote:
> 
> I wrote a note to Greg about my thoughts that, looking at the odd pinion wear, I was expecting a tail bearing failure causing the pinion to move in and out on acceleration to be the root cause. In order words, loss of preload!
> 
> Bob Kramer
> 
>> On Mon, Sep 17, 2018 at 8:51 AM, fubog1 via Fot <fot at autox.team.net> wrote:
>> That's definitely not a "normal" failure; the ring gear doesn't look too bad, all considered, compared to the pinion damage.
>> That pattern doesn't look that bad either, with .005 minimum backlash, I don't think it had anything to do with the failure.
>> The only other possible variable would be related to (lack of) pinion preload, but if that was the case I would expect to see more ring damage.
>> I agree with Barry, the teeth do look like they are almost melted, I wonder if it could be a hardness issue?
>> Glen
>> 
>> 
>> -----Original Message-----
>> From: barry rosenberg via Fot <fot at autox.team.net>
>> To: Greg Blake <gblake58tr3 at icloud.com>; Fot <fot at autox.team.net>
>> Sent: Mon, Sep 17, 2018 8:45 am
>> Subject: Re: [Fot] Fwd: Crown and pinion gear break in
>> 
>> From the pictures, I see melted teeth, not broken. It also looks like the front pinion bearing may have spun on the shaft. The ring gear is not nearly as worn as the pinion. I have seen this melting teeth trick and pattern only once before and it was caused by loss of fluid. I used to keep the melted pinion but have lost it over the past two moves.
>> 
>> Barry
>> 
>> 
>> From: Greg Blake via Fot <fot at autox.team.net>
>> To: Fot <fot at autox.team.net> 
>> Sent: Sunday, September 16, 2018 8:53 PM
>> Subject: Re: [Fot] Fwd: Crown and pinion gear break in
>> 
>> I meant to say, looking at the gear mesh, I thought I was close. In fact I started closer to 0.731 pinion depth and reduced it until I got a better mesh pattern. 
>> 
>> Sent from my iPhone
>> 
>> On Sep 16, 2018, at 1:47 PM, Greg Blake via Fot <fot at autox.team.net> wrote:
>> 
>> Here are my setup notes and a few photos from the failed unit. 
>> 
>> Backlash averaged 0.0055” measured at 4 locations 90 degrees apart each. Largest being 0.006 smallest 0.005. 
>> 
>> Depth from bottom of saddle to top of pinion head 0.726”. 
>> 
>> Pictures of gear mesh with this setup. 
>> 
>> 
>> Picture of failed pinion gear. 
>> 
>> 
>> And companion ring gear. 
>> 
>> 
>> I made a hell of a mess.
>> 
>> It looks like I set the pinion too deep into the case by the write ups I’ve reviewed. But looking at the gear mess, it looks like I was pretty close. 
>> 
>> What do y’all think?
>> 
>> Thanks. 
>> 
>> Sent from my iPhone
>> 
>> On Sep 13, 2018, at 3:45 PM, Michael Porter <mdporter at dfn.com> wrote:
>> 
>> On 9/13/2018 4:52 AM, Greg Blake wrote:
>> Speaking of pattern, Chris mentioned that the Bastuck gear sets are Oerlikon as opposed to Gleason gears. Apparently they require a different mesh pattern. Does anyone have a good resource for pictures of the proper mesh pattern for the Oerlikon type gears?  I can not find one. I contacted Bastuck with no luck there. 
>> 
>> This might help:
>> 
>> https://www.cartechbooks.com/techtips/ring-and-pinion-gear-selection-for-optimal-performance/
>> 
>> Note that in the section on hobbed gears (Oerlikon type), I think the first photo has the toe and heel conditions reversed in the description, and it looks to me as if they're using the same set of photos for both types of gear (the hobbed gear has uniform tooth height and the top of the tooth changes thickness from heel to toe, while the milled gear has non-uniform tooth height and uniform tooth thickness at the top, but to me, the dimensions of the teeth look the same in both sets of photos).  There's also general recommendations on break-in.
>> 
>> This is the closest I've come to finding a comparison of the meshing of the two types, even if it has errors, and some shortcuts in the     descriptions.  This, though, is simpler, and might be helpful:
>> 
>> http://canadawideparts.com/downloads/dana_tooth_pattern.pdf
>> 
>> Truthfully, I don't see much difference in the two sets of examples.  With regard to set-up, the crucial difference in the two types is where optimum tooth thickness occurs in relation to optimum backlash.  One thing that these guides don't say is that hypoid gears, whether with standard helical pinions or worm-gear pinions, don't tolerate lack of backlash.  I once worked in the shipping department of Boston Digital in Massachusetts as a lowly temp back in the mid-`80s, and my boss was grumbling about how the company was in trouble and it was going to affect his profit-sharing.  So, what happened?  "Big troubles with the fifth-axis on the 5-axis milling machines."  And?  "They use a hypoid worm and ring gear to operate it and it's failing early."  And?  "The engineers don't understand why."  It turned out that they'd set up the ring gear set to zero backlash to eliminate the slop in the gear set because the encoders they were using couldn't compensate, and, of course, the gears wore out prematurely, and because none of them had an automotive background, they didn't understand that they'd created the failure themselves through bad design.  And, they were Indian, like the rest of management, and the culture in India is that the upper classes are never wrong, so they simply couldn't acknowledge that they'd created the problem.  The answer was to use absolute measurement such as flexible glass rules (which require no correction) and add backlash, but I don't know that they ever did that.
>> 
>> 
>> Cheers.
>> -- 
>> 
>> 
>> Michael Porter
>> Roswell, NM
>> 
>> 
>> Never let anyone drive you crazy when you know it's within walking distance....
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