Why can't you lift by differential?
05-17-2009, 08:48 AM
#1
3rd Gear Member
Thread Starter
Join Date: May 2006
Location: Ofallon, IL
Posts: 502
Why can't you lift by differential?
Reading FAQ page (very informative).
Downloaded manual. What's the problem with lifting by the diff? Is it a saftety issue (slip off). Surely it's not a strength issue on the diff?
This is my primary way of lifting.
Downloaded manual. What's the problem with lifting by the diff? Is it a saftety issue (slip off). Surely it's not a strength issue on the diff?
This is my primary way of lifting.
05-17-2009, 10:49 AM
#7
3rd Gear Member
Join Date: Sep 2008
Location: NY (Capital Region)
Posts: 581
Guys, the axle just wasn't built to hold up the weight of the car from the diff. You don't have to know a lot about cars to see that. It's simple physics.
This is an over-simplification, but I'll try to illustrate it. Take a six foot long piece of rebar. This will stand in as our axle. Now put one end in a vice and try to twist it like a twizzler.
Not going to be very easy, is it? This is the kind of torque exerted on the axle when you're driving. It's got a lot of strength when it comes to that kind of force. That's what it's built for.
Now, as far as it holding up the car, let's get four cinder blocks to stand in for the weight of the car, and the wheels. spread two of the cinder blocks just under six feet apart and bridge the two with the rebar. This is is our wheel/axle set up. Then take the other two cinder blocks and put them on top of the bottom cinder blocks with the rebar between them. This is how the weight of the car is distributed normally.
Not much risk of the rebar bending is there? Now time to lift by the diff. Get rid of one of the bottom/wheel cinder blocks and put the other in the center to stand in for your jack.
How long before that rebar starts to bend?
The diff has a spot for a jack to hold up the weight of the axle while the car is on a lift or jack stands to work on the axle or suspension etc. It's not there to jack up and support the weight of the car. Now, you can tell me how you've been doing that for years now, and how your father did it, and his father before him. I'm just going to say, good luck.
I hope I made some kinda sense. I have my doubts.
This is an over-simplification, but I'll try to illustrate it. Take a six foot long piece of rebar. This will stand in as our axle. Now put one end in a vice and try to twist it like a twizzler.
Not going to be very easy, is it? This is the kind of torque exerted on the axle when you're driving. It's got a lot of strength when it comes to that kind of force. That's what it's built for.
Now, as far as it holding up the car, let's get four cinder blocks to stand in for the weight of the car, and the wheels. spread two of the cinder blocks just under six feet apart and bridge the two with the rebar. This is is our wheel/axle set up. Then take the other two cinder blocks and put them on top of the bottom cinder blocks with the rebar between them. This is how the weight of the car is distributed normally.
Not much risk of the rebar bending is there? Now time to lift by the diff. Get rid of one of the bottom/wheel cinder blocks and put the other in the center to stand in for your jack.
How long before that rebar starts to bend?
The diff has a spot for a jack to hold up the weight of the axle while the car is on a lift or jack stands to work on the axle or suspension etc. It's not there to jack up and support the weight of the car. Now, you can tell me how you've been doing that for years now, and how your father did it, and his father before him. I'm just going to say, good luck.
I hope I made some kinda sense. I have my doubts.
Last edited by digitalcos; 05-17-2009 at 11:09 AM.
05-17-2009, 11:08 AM
#8
6th Gear Member
Join Date: Nov 2007
Location: Montaner
Posts: 6,193
Regardless of whether this is a terrible thing to do or not. Good luck finding a car that hasn't been lifted this way. Mine was before I bought it either by the previous owner or a shop he took it to. I guarantee it isn't the only one either.
05-17-2009, 11:31 AM
#9
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
It pretty much comes down to whether you let your own haste and laziness con you into taking a short cut or if you're committed to doing any job to the highest standards.
There may be enough margin designed in to the axle assembly against things like distortion, fatigue, cracks, and leaks. Or maybe (long term) there isn't. I can't say either way, but since I hate having to fix avoidable screw-ups . . .
I probably have jacked the back end of a car up by the pumpkin. Once, maybe twice in 45 years, and I think the count will stay frozen at whichever it is.
Norm
There may be enough margin designed in to the axle assembly against things like distortion, fatigue, cracks, and leaks. Or maybe (long term) there isn't. I can't say either way, but since I hate having to fix avoidable screw-ups . . .
I probably have jacked the back end of a car up by the pumpkin. Once, maybe twice in 45 years, and I think the count will stay frozen at whichever it is.
Norm
