JROW

Replacing the diff cover seal on my buddys 03 cobra today and found this...





...metal shavings/pieces and a broken tooth on one of the gears. Didn't hear any noise while driving and havn't had any driving issues. Should my buddy be worried? If he needs to go ahead and replace, what do you guys recommend?

Thanks guys.



Oh, sorry for saying musturds, this cobra would totally smoke my vette

Fabrik8

I love mustard! Hey wait..


Those gears definitely need replacement. That's a failure waiting to happen, and if he's lucky it won't strand him out in the middle of nowhere when it does. You don't want to see what happens when one of those teeth shears and gets caught between the ring and pinion.

My question is, what caused that? Has he been doing a lot of launching? I'm assuming that he's got the stock Cobra IRS setup with the rubber bushings, and the shock loading with wheelhop is probably killing that diff.

JROW

He hasn't launched or tracked it at all. Just bought it a month or so ago. It is pullied, tuned, exhaust, maf, making 421whp 456 wtq and as far as we can tell everything in the rear is stock. My parts manager said it may not cause any issues for a long time since we got all the metal out, any truth to this, or is it foolish to not replace the gears now?

vmspionage

I would tend to agree with this. If it's just a slight chip and not driven hard then no biggie, but I wouldn't be surprised if it grenades after abuse.

JROW

Kind of what I was thinking. He really only drives it on the weekends and babys it for the most part.

Any other opinions? Where is flimflam, I'm pretty sure the mods were done at your shop actually, not to say that has anything at all to do with it, but I know you know these cars pretty well.

91 Hatch

It that's the power its making, your vette should put up a good fight lol. If the car doesn't get that much abuse it will be fine. I've seen a lot worse in some f150's that last a long time with no problems. If he wants to beat on it hard I would change it out, I would suggest a true track

Fabrik8

Getting the metal out will only solve one problem, which is the random metal bits getting lodged between stuff and doing damage. The real problem here is that you have damaged gear teeth, and damaged gear teeth aren't very good at transmitting power to another gear. So if you have a helical or helical hypoid ring and pinion set, power is transmitted by more than one tooth at a time as the pinion rotates, which is why you can't feel the damage. BUT if you're missing pieces of some gear teeth, the other teeth have to handle more power to make up for it and are now have higher stress.
The gears in the picture are straight cut, which means that all the power is transmitted by a single tooth at a time. So if those are damaged, then you not only lose the ability to transmit power, but the chipped/broken teeth also become a great stress concentrator that weakens the rest of the tooth a lot.

It's like breaking off a lug stud (or two) on one of your wheels. It may do OK for a while, but now the remaining studs have a higher load and the load isn't spread uniformly any more.

I'm just not sure why "I broke a diff gear tooth, do I need to replace it" is something that can actually be debated.

Lord Humongous

It's been launched hard. The case twists without a brace and causes that type of damage.
Get a BF diff brace and replace those gears

slo-180sx

Or tell him to buy a solid axle.

DRAY

go ahead and replace. a lil damage will turn into major damage.