Cracked Front Diff Housing

[amschind]

The one issue with the VAS support is that it is COMPLETEY INCOMPATIBLE with skid plates. Not "a little fudging makes it work", but "100% never gonna happen". I talked to the guys at VAS and at Talons Garage, and both directly confirmed it. They are both in Houston, and I encouraged them to chat and figure out a combination solution.....no idea if that would ever happen.

On the flip side, I strongly support the "poor QC" theory. I'm not sure that an external support is going to fix a casting with a bunch of voids in it.

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[Gros Ventre]

The one issue with the VAS support is that it is COMPLETEY INCOMPATIBLE with skid plates. Not "a little fudging makes it work", but "100% never gonna happen". I talked to the guys at VAS and at Talons Garage, and both directly confirmed it. They are both in Houston, and I encouraged them to chat and figure out a combination solution.....no idea if that would ever happen.

On the flip side, I strongly support the "poor QC" theory. I'm not sure that an external support is going to fix a casting with a bunch of voids in it.

Oh, it won't fix a poor casting... and I like that theory best... But the method of suspending the differential casing seems less than needed for rough service.

 

[Snakebitten]

While neither VAS or Talons might agree to altering their product for compatability, there is nothing to stop someone from cutting into their Talons (or others) to accommodate the interference.

Not everyone would take on the challenge, but there's plenty that would.

 

[powerboatr]

If the picture above of the mounting resilient mounts is accurate in that those two are the only mounts or suspension points, then a real whopper of a load imposed suddenly, would wrap the casing along the axis of the two wheel shafts. Not good. In turn this could crack the casing. Go look at the cracks and see if they could be imposed by such a wrapping motion along the axis of the wheel shafts. If a crack starts, it then propagates (and is very difficult to stop) because the stresses are concentrated at the head of the crack which is a point loading.

no doubt a torque load applied back through the wheel end to the half shafts up to the differential case could cause damage or failures. absolutely without question, i was lack in my thoughts. see below
sudden stoppage of a rotating assembly creates very high back feed torque loads to bearings, supports, shafts and mounts. yes

my question is the based on the fact the diff is held semi rigid within the frame and does not move based on wheel movement up and down . the LCA and UCA and struts take the role or keeping tire in contact with road. not the differential case or its supports.

i just don't understand, and it might very well stop wheel hop, but from a mechanical view or opinion
the additional brace does not, by what i can see, would stop wheel hop. it has nothing to do with controlling tire contact, but it does add support to the diff case and the case extension. which in turn does provide more support, just not support to the tires or wheels
thats all i was trying to get across, but my old hands failed to type the thoughts in the brain

one does have to wonder why ford has an extra mount boss on the case??\

clear as mud correct?

 

[Gros Ventre]

no doubt a torque load applied back through the wheel end to the half shafts up to the differential case could cause damage or failures. absolutely without question, i was lack in my thoughts. see below
sudden stoppage of a rotating assembly creates very high back feed torque loads to bearings, supports, shafts and mounts. yes

my question is the based on the fact the diff is held semi rigid within the frame and does not move based on wheel movement up and down . the LCA and UCA and struts take the role or keeping tire in contact with road. not the differential case or its supports.

i just don't understand, and it might very well stop wheel hop, but from a mechanical view or opinion
the additional brace does not, by what i can see, would stop wheel hop. it has nothing to do with controlling tire contact, but it does add support to the diff case and the case extension. which in turn does provide more support, just not support to the tires or wheels
thats all i was trying to get across, but my old hands failed to type the thoughts in the brain

one does have to wonder why ford has an extra mount boss on the case??\

clear as mud correct?

Yep, clear as mud... Ya know, I'm just wondering if the chasing of weight reduction has something to do with not using that differential ear. It just looks like it's set up for the third axis restraint... Will have to think about your above info.

 

[Snakebitten]

Think oscillation?
Since that unused mount is the axis that would inhibit twist, then it's possible for twist/untwist to take place if forces were applied on that plane.

Imagine torque being quickly applied (boost launch) in quantity that is taxing/exceeding contact patch traction. Some of that torque will be absorbed by the twist-rotating of the differential. (similar to axle wrap)
At the moment traction is exceeded, the differential could/would become unloaded and untwist in the other direction. This back and forth oscillation can exacerbate the already existing tension of the tires going back and forth between traction and loss of traction. A chatter, if you will?
Have you never experienced rear wheel hop in an unloaded truck? (modern traction control makes it far less likely, of course)

If you were on ice, the transition back and forth would be smooth. The difference in force between having bite and no bite would be very similar.
But on a really good traction surface where a ton of torque can be transfered to forward motion and then the sudden loss of that traction.... A big disparity in torque between the two minute fractions of time.

Wheel hop is wheel hop. Front suspension or rear. Keeping either differential from twisting back and forth reduces the severity of wheel hop. (there are others of course. I'm sure I am oversimplifying)

 

[Snakebitten]

A video that addresses wheel hop and uses both front and rear differential braces.
(looks like a front brace that might be compatible with skid plates?)

 

[powerboatr]

welllll
dammmm
yes i can see chatter of load and unload of torque based on loss of traction or high traction
live axle with leaves it easy to see that moment in action or feel it and break stuff real quick

but with front diff basically caged by the frame and is not moving .. the torque feed back could be extreme right into the bearings or other parts.
for me HOP is hop not slip and then grip
we need a better dictionary ?
hop wheel goes up and down, while still spinning

chatter; it slips then grips which is horrible on a driveline or transmission of power to any device,
the extra mount, might help absorb that torque , and redistribute it over a wider area of sorts.
hence the vas system
ford had a reason to leave it un-attached.. why? who knows weight or did they feel the diff had enough support?
at least we are having a discussion, we only learn that way
bottom line LOAD then UNLOAD in rapid pace is not good under heavy power application

the video is no bueno to load


what i am saying is the VAS does not control wheel hop or chatter in a sense
but it may help minimize torque reactions applied to housing when wheel hop or chatter happens as in torque being applied and released under high torque applications being applied to front tires
if the torque is better applied, it could also help to limit the oscillations of the case and twisting moment which would then be applied to help prevent damage of case. wheeeew

 

[Snakebitten]

The front differential is not "caged" by the frame. Quite the opposite if you envision the way it is mounted without that cast-in mounting point.

That 3rd mounting point begs to be attached in order to "cage" it. (Albeit with an additional flexible bushing, like the two hanger mounts)

The youtube video has a link in the post?

 

[Gros Ventre]

Oscillation of the differential case would certainly lead to cracking. That repeated loading/unloading is precisely the mechanism that could lead to crack initiation.

 

[powerboatr]

got it

 

[amschind]

While neither VAS or Talons might agree to altering their product for compatability, there is nothing to stop someone from cutting into their Talons (or others) to accommodate the interference.

Not everyone would take on the challenge, but there's plenty that would.

I looked at it for a while, but I don't think so on this one. The Talons and indeed most skid plates bolt flush to the frame crossmember where the VAS brace bolts on.....they both require the same real estate. The VAS brace extends vertically down slightly beneath and around the flat plate that bolts to the crossmember to provide a place for the vertical member to be welded to the horizontal member. To make it work, you'd have to use spacers between the skid plate and the crossmember, which would screw up the transmission and transfer case skid plates because they both interface with the front engine skid plate.

All that said, you could weld a brace to the top of the skid plate, but that raises two big issues:
1) how are you gonna get around the skid plate to bolt it to the diff housing, because that has to be done after the skid plate is installed and
2) if the skid plate does its job, some of that force is going to be pushed directly into the diff housing.

I really think that a compatible brace would require a different frame mounting point, but I'm not sure where that would be.

 

[amschind]

Oh, it won't fix a poor casting... and I like that theory best... But the method of suspending the differential casing seems less than needed for rough service.

I have zero idea why they cast a mounting point into the housing and then refused to utilize it. I have added this to the list of head-scratchers.

 

[Snakebitten]

I have zero idea why they cast a mounting point into the housing and then refused to utilize it. I have added this to the list of head-scratchers.

It's been unused for years. Previous generation F150's.
Which still points to the current fragile front differential as being inferior in some way.

 

[Snakebitten]

I looked at it for a while, but I don't think so on this one. The Talons and indeed most skid plates bolt flush to the frame crossmember where the VAS brace bolts on.....they both require the same real estate. The VAS brace extends vertically down slightly beneath and around the flat plate that bolts to the crossmember to provide a place for the vertical member to be welded to the horizontal member. To make it work, you'd have to use spacers between the skid plate and the crossmember, which would screw up the transmission and transfer case skid plates because they both interface with the front engine skid plate.

All that said, you could weld a brace to the top of the skid plate, but that raises two big issues:
1) how are you gonna get around the skid plate to bolt it to the diff housing, because that has to be done after the skid plate is installed and
2) if the skid plate does its job, some of that force is going to be pushed directly into the diff housing.

I really think that a compatible brace would require a different frame mounting point, but I'm not sure where that would be.

Why couldn't they skid plate just mounted to the surface of the differential braces?
Effectively hanging lower by the thickness of the braces mounting plate?

If they both/all use the same mounting bolts, no big deal?

It would require the same slit cut into the skid plate as I had to cut in the oem plate on my 2018 FX4. Admittedly not near as robust as the Talons.

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