Originally Posted by BigJ
Apparently, Ford is seeing a disproportionate number of warranty claims on 2012+ Raptors with the Torsen diff; the CV axles are failing.
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Do you know of any specifics as to which part of the CV shafts are failing?
I know there are a couple of companies that make upgraded CVs using upgraded materials (usually 300M or similar). I am not aware of anything like that out there for our application.
Here is an example for the G8:
300m Axles for the G8
Here is the company (they specialize in GM):
GFORCE ENGINEERING, LLC
As a note, these axle upgrades run about $1500 and up (relatively custom and low volume). Find another, stronger application to adapt, the cost comes down.
Originally Posted by BigJ
There's something called a "safety factor" when it comes to parts like these. A safety factor of 1, for example, means that the part is exactly as strong as it needs to be, to handle a load exactly equal to the max its ever expected to handle. So if PartA is designed to handle 100lbs of weight with a safety factor of 1, that part will (in theory) fail when 101lbs is applied. If it had a safety factor of 1.5, that means it will not fail until 151lbs is applied and so forth.
I've learned that a "good rule of thumb" when it comes to axle strength and safety factors is this:
-for an open diff, the part should have a safety factor of 2.
-for a limited slip diff (like the Torsen), the safety factor should be 5.
-for a fully locking diff, the safety factor should be 10.
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I wouldn't look at it as a different safety factor. The difference is that the limit load increases as you become "more locked". The safety factor would very likely be the same for all three cases.
Following J's thinking using example numbers:
Open limit load = 1000 ft-lbs; with safety factor (2) = 2000 ft-lbs design limit / component capability
Torsen limit load = 2500 ft-lbs; with safety factor (2) = 5000 ft-lbs design limit / component capability
Locked limit load = 5000 ft-lbs; with safety factor (2) = 10000 ft-lbs design limit / component capability
Using this example, the limit load for the Torsen is already 500 ft-lbs over the design limit (limit load + safety factor) for the stock shafts.
NOTE: These are made up numbers, DO NOT take them to the bank.
For further discussion, safety factors for aerospace are 1.0 for yielding (metal twists, stretches, bends - what we would consider broken) and 1.4 ultimate (metal has ruptured, broken into multiple pieces). For construction equipment (backhoes, dozers, etc.), they use 1.15 FSy and 1.5 FSu (for one manufacturer that I am aware of). I would suspect that automotive would be similar to that. As the factor of safety goes up, so does weight, size and cost.
Keep in mind that in first gear, low range you are looking at a 45:1 torque multiplication of a 430 ish ft-lb engine.
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