Worn birfs breakage-prone?

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May 26, 2005
If you have broken or seen a broken birf, and inspected the cup, were there typical wear marks in the ball channels? Any other signs of wear? How much mileage on the birf? Tire size? Extreme gearing or power?

I'm investigating a theory that the birfields are more prone to breakage when worn. This was brought up in a recent thread, and after searching I can't find a whole lot of the specific info I crave. The theory is that the balls get stuck in the wear marks when turning under power, and something has to give. The other theory is that the birfield is weak and can explode at any time. For my purposes I will personally discount cases of birfs breaking due to seriously increased stress, i.e; tires over 37", high horsepower powerplants, and/or extremely low gear ratios in t-case or axle, but I'd still like to hear about them.

A new tight birf is stronger than a loose one. The wear happens first in the center of the ball grooves, where the balls ride when the wheels are straight, if you run your finger over the ball grooves on a worn out one you can feel the wear groove or divot. When the steering wheel is turned the balls bind when forced across the divots, then pop out slamming into the cage making the clicking noise. That slamming puts divots in the cage, making it looser, sooner or later something fails.

When we off road raced we dye crack tested, polished then shot peened all the surfaces but the ball grooves on our CV joints to eliminate stress risers. Don't know if it did any good but it made us feel better!
It's only common sense that a worn birfield is going to be weaker than a new birfield. Most of us are driving on birfields with a lot of mileage. The newest US 80s are now pushing 10 years old. All birfs wear in the normal course of use. Just because of this, most broken birfs are going to be worn birfs.

I think a couple of the important concepts to understand is that 1) the birfields can be subjected to maxium stress when the front diff is locked and the steering wheel is turned to the stops and 2) the stock engine and gearing can produce enough torque to break a birfield. So, be careful how much throttle you use when you are in a situation where you have the front locked and are steering at severe angles.

Also try to avoid the situation where you are spinning the front tires with the front diff locked. If and when the front tires hook up and get traction, the sudden torque spike can do the nasty deed. Worst case may be diffs locked up, steering wheel cranked all the way over, front wheels spinning and bouncing, and finally getting a good bite on firm ground.

Another gotcha can occur if a front wheel is wedged, say under an overhanging rock. If you just keeping pressing harder on the gas to try and get going you might again break the birf.

If the thought of a broken birfield is making you concerned, then buy a spare, along with the tools and misc parts necessary to replace, and pack it along with you when you are offroad. If you haven't already done so, best do a repack job at home, so you know what to expect if you have to do same on the trail.
I have several spares, and have done all the maintenance. The birfs on the truck have less than 75,000 miles on them and no visible wear. I'm a curious guy, and also somewhat intimidated by all the talk about how dangerous it is to drive a truck with a birfield. My thought is that because there are thousands of people telling stories here, the actual risk of breaking a birf in good condition is minimal, and the reputation they have might be somewhat unjustified. I wouldn't expect a U-joint in a Dana 60 to last 200,000 miles, and if one did I wouldn't trust it in a locked/turned/wedged situation.
I'm just curious if anyone's broken a birfield that was in good condition.

I think only christo has broken brand new ones from the factory. he was in Hell John in the dakotas a couple of years ago. It was in the short bus, 38.5 tires, bad angles. later robbie
not to hijack this thread, but what about if you can't find or feel wear marks, but have a definite click, I searched quite a while and it seems like there is a dozen theories as to when there is too much wear i.e. you should be changing the birf due to a 1/32 deep groove or 1/16 deep groove...:confused:
In almost all 80 series broken birfield instances the vehicle was in a bad situation and/or had tires much larger than stock and in some cases an engine with significantly more power than stock. That does not mean that it is not possible to break one in a stock truck but you have to try pretty hard to do it.
Worn examples that are making noise are, in my view, a ticking time-bomb regardless of how the vehicle is operated.

Solid OEM birfs in a vehicle with smaller than 35 inch tires would be difficult (but not impossible) to break unless one was deliberately trying to do so.

-Spike- said:
My thought is that because there are thousands of people telling stories here, the actual risk of breaking a birf in good condition is minimal, and the reputation they have might be somewhat unjustified.

Agreed. Some people will rationalize anything. Worn parts of any kind are more prone to failure and as Rich pointed out, there are very few 80's on the road with less than 100k miles. Most 80s are pushing 200k miles and those that had neglected birfields by the PO and are now getting wheeled by us..... well, they are going to break things and the birfield is one of those things that will break.


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