What kills a final drive/differential?

That's an easy life for that axle. They typically last a long time.

I have seen shafts break and pinions snapped off, but that was extreme off road abuse on large tires. My friend ran a stock unit and competed at the King of The Hammers (KOH) in California for years. I believe the same axle has made it into two cars.

The 14 bolt is probably the most popular rear axle for hardcore wheelers (although I run Dana axles in my trail Jeep and a 35 spline Ford 9" in my tube car). It's super strong, plentiful and cheap. It is heavy though. There are kits to shave the bottom of the housing for added clearance too.
 
I'm sure the material is a combination of bearing and gear material as everything wears in together. Patterns seem "generic" on mass produced axles. That's why they stick a magnet in the bottom.
 
Bearings don't wear in the traditional sense. They won't normally wear and open up tolerances. They only do that if there is horrible damage on the bearing, where they would make noise and need to be changed.

Wear of gear teeth will affect the bearings. Hypoid gears have a significant sliding component to the teeth... more so than any other gear design. Tooth wear is a significant issue.
 
I respectfully disagree, especially in regard to c-clip axles where the carrier bearing supports the weight of the vehicle and also has thrust loads when the vehicle turns (as the bearing at the axle end is typically not tapered). Trailer axles and older non-unit bearing front spindles have tapered roller bearings too. They would wear out all the time, especially trailer axles that are overloaded.
 
My statement is based on 20 years of analyzing post-test bearings and analyzing failed bearings. Your disagreement is based on what? What was this wear?... electrical erosion, abrasive damage, asperity wear, spalling?
 
My statement is based on 20 years of analyzing post-test bearings and analyzing failed bearings. Your disagreement is based on what? What was this wear?... electrical erosion, abrasive damage, asperity wear, spalling?

On an axle bearing?

interesting......
 
I was thinking about this the other day. My Duramax has 3.73 gears and and on stock size tires (235/80/r17), 634 revolutions of the tire represents a mile. That means the ring gear makes 634 revolutions for every mile traveled, and the pinion gear makes 3.73 times that many revolutions, or 2,364.82 revolutions per mile.
In the roughly 24,000 miles my truck has traveled, the ring gear and wheel bearings (full floating rear axle, wheel bearings run in gear oil) have made 15,216,000 revolutions. My pinion and pinion bearings have made 56,755,680 revolutions, with the driveshaft and transfer case output shaft revolutions matching the revolutions of the pinion. The output shaft of the transmission may have accumulated more revolutions than the output of the transfer case, driveshaft and pinion, depending on low range 4x4 usage.
 
If all things correct and equal then you are probably at about 1-2% of the overall L-10 life of the bearings and gears.

But there are a lot of unknown factors in calculating that
 
Is a flying start harder for the diff and even transmission compared to a rolling start? When i got a tuning on my previous car, a Bmw E39 530Dat with a GM 5L40E transmission the torque was higher than the transmission was rated for, i remember the tuner said: "no problem, just avoid flying starts" let the car roll before you floor it. I always did and still do with my current car. I never floor it when standing still, get the 2 tons rolling first :) I know there is alot of electronics today controlling torque in some gears and there is antispin and stuff so is there anything in this theory?
 
Last edited:
Is a flying start harder for the diff and even transmission compared to a rolling start? When i got a tuning on my previous car, a Bmw E39 530Dat with a GM 5L40E transmission the torque was higher than the transmission was rated for, i remember the tuner said: "no problem, just avoid flying starts" let the car roll before you floor it. I always did and still do with my current car. I never floor it when standing still, get the 2 tons rolling first :) I know there is alot of electronics today controlling torque in some gears and there is antispin and stuff so is there anything in this theory?

Just from the gear loading profile alone, any loading that starts easier than a fully dead no movement stop is easier on the gears overall.

Even then, not much difference ( this would exclude applications starting under extreme loading or shock loading conditions)
 
I think the diffs would be the least of my concerns on a BMW.
I changed my daughters fluid at 85k on a 325i it was clear and clean. That being said its at 170k now and Im not touching it again unless its leaking.
 
The mounting flange from the driveshaft to the pinion, in my very limited experience, is the part that goes first in BMW 3-Series I’ve known. Keep good fluid in the diff and enjoy the vehicle. I personally prefer synthetic gear lube unless there is a specific reason to not use it.
 
What kills a differential? Submerging it in water and NEVER changing the fluid.
There are many more, but what I stated, I have seen A LOT of them go to that gear cemetery in the junk yards.
 
Back
Top