On anything, if you put incorrect force against the design, it can fail.
It’s like a hen’s egg which you can't crush one way, and has almost no resistance the other way.

I have watched guys in shops ruin cars by grabbing the wrong place with the lift.
Unibody cars that will drive hundreds of thousands of miles can be totaled with one misaligned lift.
It's not about strength; it's about where you apply the force.
Chris

 

Yes, but where is that torque going to. It is going to the ends of the axles where your wheels are. Hopefully the pass thru of the diff is free spinning.
I myself am more concerned about the seals and attachment points of the axle housing to the pumpkin, than the strength of the pumpkin itself. Back in the days of the old 9" Ford rears, where everything was welded together, I would not have had that concern. Now they are pressed in and riveted, with some kind of seal to keep it from leaking.

 

The torque is applied to the entire axle tube - even the pressed in portion where it sits in the pumpkin. On hard accleration, the pumpkin wants to rotate around the axle tubes. If it can take that much torque, I don't see how the floor of the pumpkin can be so thin that a jack will damage the unit.

And even further, I don't see how that much torque can be handled and they start to LEAK where the tubes are pressed in because you jacked up the 2500lbs from that point? Again, thousands of pounds of torque can't spin the tube in the pumpkin (or more like the pumpkin around the tube), how can jacking it up in the middle make the tubes leak

I do understand the egg analogy, and we may be coming up against something like that, but again, I think it's really the rear cover seal they are worried about.

My old Dana 60 in my '74 highboy was pressed and riveted not welded together ... I never once thought twice about jacking it up from the pumpkin. It had 300K+ miles on it...

My '96 t-bird owner's manual mentioned not to jack it up using the differential housing (pumpkin), but that's an IRS car. And...

One other thing, Ford is going to tell you not to jack from the pumpkin because the darn thing can fall over real easy. They are going to tell you to take only one wheel off the ground at a time. Because it's the safest way to change a tire. Also, the only way, unless you have a heck of a locker in it or very good parking brakes neither of which are assumed from the factory

What's the actual wording in the owner's manual for the truck we're discussing?

 

Here is the actual words.

Never use the front or rear
differential as a jacking point.

Edit - I agree that that much force is going thru the diff/housing. However, with the bearings and gears, that much force is not working on twisting or bending it at the joints. It is just passing thru without putting near that much force on the housing.

 

Any more context than that? What's the previous few sentences, what section is this in, etc? Changing a tire?

That sounds like you shouldn't use the pumpkins because of safety.

Again, with all the torsional forces working on both the pumpkin and the pumpkin/axle-tube interface, jacking from the pumpkin isn't going to hurt anything.

Whether or not it's safe to do so, until you get jackstands under it, that's another matter entirely.

 

Sorry, that is all the warning. Yes it is in the roadside emergencies section.
As far as tortional force, think about something like a drill. Can you physically stop the drill from turning by holding onto the chuck? No. Yet you can hold onto the drill itself without much effort, and without your arm twisting when you turn it on. That's because all that torque is passing thru and not putting a fraction of the force that is passing thru.

Edit - An even better example would be a flexible driveline that would attach to the drill. The chuck is moving, the end of the flexible driveline is moving, but the flexible line is not.

Also if that much force was working directly on the diff/axle housing, one side would go way up and the other way down when you applied the gas. The suspension could not handle it.

 

Then it's probably safety related and not about damaging anything.

Regardless of the drill analogy, where the axle tubes go into the pumpkin is still subjected to a lot of torque, it does not "pass through".

The axles torque one way, the axle housing torques in the opposite direction. The axle-tube/pumpkin interface still has to withstand all that torque.

I do understand that jacking from the pumpkin puts a lot more force on the axle-tube/pumpkin interface than it would endure under normal jacking from the outside, but still, to take all that torque at that point, that interface is probably the strongest part in the housing.

Anyway...

 

Theres a big difference between torsional force and the concentrated weight in a small area!

 

I recall having that same warning back on my '88 F150.

 

think of a 2x4 sitting on two rails 45 inches apart. jacking up on the pumpkin is the same as standing on the middle of that 2x4, jacking under the leaf spring is the same as standing on that 2x4 right over the rail.

persoanlly i think its ford just co vering their butt, so they dont have to deal with idiots peeling their diff cover and all the oil leaking out, or someone trying to jack up their truck with 2 tons in the bed of something.

i would be worried about an 8.8(the pumpkins are easy to crack around the tubes)

but the 9.75 housing is stout

look at all the trussing across the bottom and top from the front of the axle.

the tubes ar epressed in and plus welded. ive seen them spun on a 10.5 sterling before, but its not easy

hell if your worried abotu it, but you still want to jack it up by the pumpkin, just build a simple truss to go over the top of the pumpkin, from tube to tube.

 

Technically isn't the "differential" the entire axle assembly? If so the manual is telling you not to lift by any point on the housing. Which means not even directly under the spring mounts!!
This must be a "cover your rear" issue for the manufacturer because where the springs mount is on a smooth tube(less the bracket to center the leafs) so why would it matter at what point you apply pressure. A tube is a tube, if you apply equal forces to opposite sides it will not flex unless you apply enough force to crush the tube. If you were to lift directly under the spring mounting points,which is where the truck weight is applied, you would be lifting with the same force as the truck is pushing down with. Regardless of how much the vehicle weighs.
Until my rear end falls out I'm gonna do as I have done for years!!! when & if it fails I'll start a crow eating thread

 

And that was probably by someone running in 4x4 low, which I can see putting over 12000ft/lbs of torque to those tubes, using 350ft/lbs from the engine as a variable in the equation. It's easy to put out much more than that, beit diesel or V10, that can be as high as 15-20000ft/lbs.

Let's use 12K ft/lbs as a reference. That's 12000 lbs (and more) trying to turn that pumpkin around the tubes. The pinion is seeing that much load too, trying to push it upwards - the entire pumpkin case has to take that loading, including the BOTTOM. As the torque increases, the case wants to split asunder because the diff carrier bearings are pushing away from each other, and the ring gear wants to seperate from the pinion. All that torsional force is there in that pumpkin.

Given all that force, I do not think jacking up, maybe, 2000-2500lbs (F150 rear end weight) from the bottom of the pumpkin is really a concern.

I do understand the 2x4 analogy - do you understand how much TORQUE is applied to the ground and what the entire diff assembly has to take?

You do have 4LOW in these 1/2tons, right?

The IFS front-diff, I wouldn't jack on, just because it might rip it's mounts (if there are any, I'm sure there is).

 

Um, no the differential is the center piece only. The rear axle housing, or sometimes just the 'rear end' may refer to the whole assembly.

They are quite specific about where to jack it, and that does include under the spring mounts.
Remember, lifting one from a corner is less than half of lifting the whole rear.
Leverage is on your side when you just lift a corner.



The following is in no way personal, gpeade, just a set of observations;


On these forums I have seen people suggest that you don't need to pay attention to;

Oil change interval. Some suggestions range from 7000 miles to never change the oil.

Break in periods, ranging from half the suggested miles to 'hot rod it from the sales floor'.

Oil weight and brand, from exceeding the requirements (rare) to 40 weight conventional oil.

Oil filters that plainly do not meet the requirements on this motor.

Tire pressure, up to double recommended.

Torque on wheel lugs, all over the place, sometimes 'whatever you feel like'.

Speeds in gears, up to 1.5 times the red line.

Towing, suggestions ranging to more than twice legal maximum.

Tire sizes that would be the equivalent of re-gearing the truck to 3.00 or even higher.

Load carrying to three or more times the legal amount.

Removing speed limiters so the truck can be run at a steady 110.

I will stop now, but there are hundreds of other interesting ones...

I think I may stop recommending people buy used...

Chris

 

They are quite specific about where to jack it because the owner's manual assumes you are using the stock jack. In my Superduty, I wouldn't ever ask the stock bottle jack to lift the entire rear-end off the ground, nor would it be SAFE because the jack isn't made to deal with it. Nor would I ask that of any stock jack ...

If a solid axle can't be jacked up under the pumpkin, that unit won't last past the first pothole/burnout/launch. They aren't that weak

Just make sure you stay away from the rear cover...

As a side note: This is not one of those "ignore a good thing" ... It's a "read the manual, and in the context it's written, they are talking about road-side tire changes". Lifting it from the center with the stock jack is unsafe, unwise, and plain stupid. That's what Ford is trying to avoid. You killing yourself.

With a good floor jack, that pumpkin better handle it, or else it won't get 2 miles down the road if you like to drive with a heavy foot - or tow - or 4x4 in deep stuff - or anything else that truck can do ...

This isn't like the front-end of a Taurus or T-bird where the strut-rod (or whatever it's called) that goes from the lower control arm up into the frame. Do not jack there, it'll bend right up.

Come on, you're talking 8.8", 9.75" or 10.25" housings - all of them can stand anything you can throw at them with a floor jack.

 

It is obvious you haven't looked at the owners manual. The picture they show is a floor jack. With a slash through it. Not a bottle jack.