4.10 Gear Failure Info

[GrinderSS]

I had a discussion with a classmate of mine from engineering school who has a friend that's a chassis engineer for Ford. They discussed the gear failure issue and said that without a metallurgy report and the failed gears to examine it would be difficult to determine the exact cause. The critical thing they would need to know is which failed first, the ring or pinion. I told them it seemed to be the pinion, they agreed that it simply may not have enough mass to handle the stress.

They also said it could be the design of the gears; the target gear ratio can be reached through a combination of the pinion/ring size and tooth pitch. Perhaps Richmond went too far with the pinion size reduction when they should have increased the pitch on the gear teeth instead. However, increasing the tooth pitch also increases friction, thus heat. So perhaps Richmond decided to go the smaller pinion route since the rear end lubricant volume is relatively low.

They did offer some suggestions to manage the problem,

1. Assuming it's the pinion teeth failing first. During setup, try to achieve a contact pattern that's as low on the pinion teeth as possible; definitely at or below the tooth centerline. This will move the stress lower on the teeth where they are stronger. They said the installer has to know how to "feel" the correct depth, otherwise the setup will be too tight.

2. For those of us with M6's it will help to use a lighter fly wheel.

3. When launching do not dump the clutch, let it out smoothly.

4. Do not have the RPM's higher than 4K when launching

5. Do not power shift; in other words get out of the accelerator when changing gears.

Nothing earth shattering, but I thought you might want to hear the thoughts from a couple mechanical engineers ;-)

[danhr]

translation: "our gears won't fail as long as you drive like an 80 year old grandma, if you drive like a 75 year old, they will break"

[calbert1999]

Don't understand why everyone is upgrading their gears. I thought the whole purpose of changing stock gears was to be able to drive more aggressively. Am I missing something here?