Bad contact pattern gearset 1

[Strinski]

I am having a problem with a "double spot" on the crown wheel drive side of the crown wheel/pinion gearset, see attachment.
Does anyone have experience with such a contact pattern?

 

[gruntguru]

Is that a new crown wheel?
Is the pinion new?
Have they been running together long enough to bed-in?
Were they bedded-in in the same setup used to produce the marks in the photo?

je suis charlie

 

[Strinski]

Thanks for the reply,

Yes, all parts are new. It is a problem we have in the production of the gear set.
The gearset has been bedded-in according to standard procedure in a bedding in equipment.
The gearset is not assembled in a vehicle.

 

[tbuelna]

I'm not an expert at interpreting contact patterns on (hypoid?) gear teeth. But one suggestion I have is that if you have a profile inspection chart for this particular gear, check it for a hollow condition at this location.

 

[gruntguru]

Yeah, it almost has to be a hollow on either crown wheel or pinion doesn't it.

je suis charlie

 

[pontiacjack]

Maybe I'm seeing it wrong, but it appears to me that the picture is of the so-called "coast" side of the teeth, not the "drive" side?

 

[tbuelna]

No, the convex flank of the ring gear teeth is normally the drive side.

You can see the coast side contact pattern on the tooth flank at the bottom of the photo. It looks biased towards the toe and way above the pitch line. I believe both drive and coast side contact patterns of a new hypoid gear set run with minimal load should be fairly similar with a slight toe bias. As load is increased during service and the gears bed in, the contact pattern should spread out and move towards the heel.

One issue that this gear seems to have is that is was manufactured with a lower level of precision. Obviously it was not finish ground, since there are machining marks present on all surfaces, including flanks, roots and tips. I assume this gear was case hardened, and if the gear is not going to be finish ground after hardening, you might consider adding some correction to the machined tooth profile to compensate for heat treat distortions.