Front differential discussion

[Snacktime]

@Felix808 how many broken tubes have you seen? I am more worried about twisting the splines as that drastically weakends the shaft and not a visible failure. It would be interesting to see if the 29 spline cast Dana housing bolts on.

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[Felix808]

@Felix808 how many broken tubes have you seen? I am more worried about twisting the splines as that drastically weakends the shaft and not a visible failure. It would be interesting to see if the 29 spline cast Dana housing bolts on.

Zero personally, but a handful on the Web that raise some concern. BB just showed his that failed on the road. The ones I have seen the housings were broken at the mount & a few the tube casting failed. As painful as it was to sit though the second video (nearing LB's annoyance level ) , you raise a good point about the spline twist. I'm thinking it's more to due with big throttle & hopping. Again, I'm easy on the throttle and don't get the front bouncing much like some of these Youtube folks.

With all that being said, I just started to run the numbers on the 32 spline UFDU and might consider it, purchasing in stages . I figure I could recoup a few $$$$ selling the RCV's & my axle with original axles. I like to be as bulletproof as I can within reason. I'll be researching for a good bit before jumping in either way.

 

[87-Z28]

He was also thinking the failures of the intermediate shaft were probably due to the flexing of the cast aluminum tube vice the cast iron.

this is a very valid point. Aluminum elastic modulus is likely >2x less than the cast iron. Depending on what grade cast iron. So even without over stressing the tube, bending flex can be significantly greater. Along with some bearing tolerance slop the intermediate axle can get loaded more severely.

 

[Bird Dog Off Road]

My BB tube and RCV axles go on this coming Friday. With the new 38s, I’m hoping it gets me by until the new FDU is within budget.

 

[Snacktime]

Well maybe we should discuss cryo treating the intermediate shaft.

 

[87-Z28]

the intermediate shaft housing is supported by the diff mount about half way along its length. I think this greatly helps elastic deformation or flex.

This can be a a problem for the intermediate shaft. The force from the wheel is not just purely axial. In severe cases the CV angle may reach 30 degrees, so 50% lateral load and 86% axial load. If shaft is not well supported laterally at both ends then bending loads will increase. Add some bending from aluminum housing on top of that. The shaft is also not short so real stresses can develop.

Very interested in the breakdown of this to see the internals. I don’t know if making an indestructible and rigid housing is the answer. It is a good start. However, the shaft and bearings likely need to be addressed. Once again, keeping CV angles and unsprung weight down will help reduce applied loads.

 

[87-Z28]

Also very curious about the detailed differences between the m190 and m210. On the surface, it sure does look like the FAD infrastructure will help provide lateral support.

 

[scotman623]

ANOTHER Great topic from the guys I trust most in this forum… Great info, I will continue to follow and beat my Bronco off-road

 

[Aonarch]

It would be good to know if upgrading from M190 with FAD to the standard M210 is gaining any real advantage, other than possibly changing gears and adding front locker.
Maybe an unlocked M190 can go the distance if you don’t have to have the locker?

What kills IFS is the tire suddenly gaining grip and transferring all of the force or torque through the chain. That is how you break things. Open diff does help, but the M190 still has a lower torque rating than the M210.

 

[Snacktime]

What kills IFS is the tire suddenly gaining grip and transferring all of the force or torque through the chain. That is how you break things. Open diff does help, but the M190 still has a lower torque rating than the M210.

This is assuming the weak point is the actual gears. On a solid axle this is pretty normal as everything is down sized in relation to the ring gear. On our axles it looks like the M190 and M210 share some bearings, seals and hard internals. We already know running the front locker to much will kill the front end.

 

[Felix808]

What kills IFS is the tire suddenly gaining grip and transferring all of the force or torque through the chain. That is how you break things.

This approach will also kill SFA's so not just limited to IFS. Driving habits/ techniques have a lot to do with surviveability

 

[87-Z28]

Shock loads, defined as short duration with steep rise slope, are a challenge to design for. They are essentially unknown and difficult to predict. They are completely related to the driver and terrain. Even the best driver can not eliminate shock loads on some terrain. High factors of safety in the design envelope help to mitigate the unknown loads but at an increasing financial cost.

a rapidly spinning 37” tire that grabs friction instantaneously, qualifies as a shock load. The load, friction multiplied by wheel radius, is transmitted as torque through the system. If the shafts can handle the torque it is transmitted to the gears and they can be challenged. Shaft bearings and housing will be minimally loaded during pure torque.

However there is never just pure torque. The wheel friction occurs due to the normal contact force at the wheel. This provides lateral load to the axle shafts that must be resisted by the housing. The shaft bearings transmit the lateral loads into the housing. This can be extreme when heavy on the gas, spinning wheels, and bouncing hard. The combined torque, lateral loads, and axial loads (depending on force vector of object that wheel strikes) will stress the system.

The shafts must carry much greater loads if they are not well supported by bearings. If they are, then the loads are transmitted to the housing. In the IFS the lateral loads are amplified by the CV angles. Lateral loading is a significant design challenge for the IFS.

 

[87-Z28]

I struggle with technology, but it seems posts are vanishing.

 

[mpeugeot]

I struggle with technology, but it seems posts are vanishing.

When technology becomes too political...

 

[builtMIbronco]

FWIW I grenaded my M190 with a FAD around 4k miles on 37s in a vnotch/washout. I'm not sure the tires ever even broke traction either but I'm assuming I destroyed gears or wiped some teeth off because of all the chunks that drained out. Never tore it down to further inspect just m210 swapped for the locker.

I'm planning on dropping the diff another 3/4" and adding the bb tube when I do gears here soon. I did consider ordering a new shaft and sending it out to get cryod @Snacktime they really don't have a bad price on them from ford. It would save downtime vs sending mine out and I've had good luck with cryo treating in the past.

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