Looking at my manual, it states not to jack up the truck from under the rear diff. Well, just a couple weeks ago mine was jacked up at a LesSchwab from just under the rear diff.
So are you doing it? What is the reason the manual says not to use the diff? Is it safety concerns, or the possibility of damage?

 

I use the diff but just long enough to get jack stands under the axle tubes. If your not careful you can mess up the diff cover by jacking it up that way.

 

First, I would never use that Les Schwab again! Companies aren't making rear axles as sturdy as they used to be to save weight. Jacking up a vehicle on the differential case is putting stress on the axle that the axle is not designed to take.

Second, I would check (or have a shop check) the rear axle to make sure it isn't bent. You can do a rough check by jacking up the back of the truck, either on a garage lift or by putting it on jack stands, so the axle hangs and the wheels are free to rotate (you need to be able to easily see the bottoms of the tires).

Place a large piece of duct tape in the center of each tire tread and make a mark on the duct tape. Rotate the tires so the marks are on the top of the tires and measure the distance between the marks. If the frame gets in the way, just rotate as much as you can without the frame being in the way. It might be necessary to remove the rims and use the outside edge of the brake drums or rotors for your measurements (harder to do since misalingment won't be as easily measured.

Then rotate the tires so the marks are on the bottom. Again measure the distance between the marks. It should be the same as the first measurement. If not, your axle is probably bent, especially if the top distance between the marks is greater than the bottom. If it appears to be bent, I would take it to an alignment shop to have the measurements verified and to see if any misalignment can be corrected. Based on what the shop says, you might need to have a "friendly" discussion with Les Swabb about picking up the tab.

 

You are saying that lifting the truck by the diff has bent the axle? That seems a bit extreme, especially if one could measure this with your method. In that case, using a level on both rear wheels should show it as well, when parked on a flat surface.
I have seen many shops jack trucks from the rear axle.

 

I've jacked all my trucks up by the diff for years....I still do with my 12'.....I'm assuming they are worried about the diff slipping on the jack and causing injury or damage. They also expect it's when you're using the factory jack which I'm not sure is designed to pick up the weight of the entire truck.


If you're axle bends that easy I wouldn't find a new mechanic....I'd trade it in on a Chevy or Dodge.

 

The 9.75" gear housing isn't as well designed for balance as the Ford 8.8. I'd be real concerned about one side of the truck leaning hard while jacking from the diff cover. I would commonly lift my old '88 from the diff housing and had no issues but it was unstable.

I lift my Expy from the frame as it has the IRS. I'll have to consult the owners guide to see what it says about these trucks.

 

Are you sure the axle tubes are supposed to be parallel? Sometimes there is an intentional slope from end to end.
Are you sure the wheels are perfectly vertical or do they have camber?

I don't know what is supposed to be the case on his truck, but I'm wondering if you know either.

 

I checked mine with a level - they are either straight or slightly inwards at the top, kind of hard to tell since the tire bulges a little at the bottom. They definitely are not out at the top. To do it right with a level, I'd need a narrow piece of wood that's 17" long (equal to the wheel diameter), but it's close enough without it, I think.
I don't think you can bend the axle by lifting it from under the diff - that would not be a good thing. I am sure the comment is in the manual for safety reasons.
Thanks for all the replies!

 

Cool.

I'm going to guess the people that know you won't even blink an eye after they ask what you did last night and you say, "I was under the truck with a level bar checking axle tubes and tires."

 

LOL, you are probably right.
I never really was under the truck though, just slightly to the left and right of the bed while using the level on the wheels in my driveway. Took like a minute, I was kind of curious about the result. You know, the engineer in me ....

 

in the good Lady's defense, she is correct in saying that it could cause a problem

by jacking in the center, you are trying to bend the axle in the exact oposite way it is designed to bend. with a normal load, the weight on the springs will try to bend the center of the diff toward the ground. the diff is designed to resist this bending force, and part of that design *could* include some camber in the axle.

my best guess is that the axle is straight, but it could be cambered such that the tops of the wheels point out under zero load. this would allow them to tip in a little less at the top under max load (which is what they will do natrually)

all of that being said .... i doubt the dead weight of the truck alone would be enough to do any harm. but if you were to do it with the max payload in the bed, then i'd say take a look at it.

 

Given the theory that jacking by the diff will ruin your rear axle...what do you guys do when you go offroad? If you hit a rock and hang your truck up do you replace the complete rear axle each time?


Jacking the rear of the truck puts what maybe 2000lbs on the differential? It's not like you're jacking up an individual tube with a .100 wall here....the differential is fairly robust and designed to take a lot of beating...compared to the torque loads put on the powertrain I'd think jacking up is nothing.

 

A local tire shop jacked up the Crown Vic at work & damaged the cover. I was on my way out of town & noticed a leak. $160 later at the local lube shop & I was on my way (synthetic fluid). The engineers know what they are talking about & they wouldn't have rules like that for no reason. And it is true that the housings aren't built like they used to be.

 

Sounds like there are some lazy workers at Les Schwab.
Never jack up a vehicle by any point other than the frame points.
Things will get bent.
The shaving of weight, in order to improve MPG, has resulted in reduced structural integrity.

Remember bumper jacks?

You will fold the end points of a newer vehicle if you tried such a lift.

 

Yeah, good point. And in that case, it could also actually get a hit in addition.
Has anybody ever heard of a (confirmed) case where jacking from under the diff bent the axle?