scottalexander

There is a bunch of debate on how a hydraulic jack knocks out the rear end alignment when lifting the vehicle using the sub frame.

Is there much merit to that happening? See picture.

audiophool

BMW says you jack using the differential casing, not the subframe, taking care not to jack on protruding aluminium cover parts. I would fear bending the subframe jacking it the way shown in the picture. Jacking by the differential puts the pressure on 4 places on the subframe rather than one.

I like to reverse onto ramps then use the floor jack. Gives you more room to see what you're doing. I have a high lift jack that will lift the wheels 5" clear of the ramps. Same for the front but I use the center subframe jack point. This is the only way to get the car up on jackstands safely.

scottalexander

You mentioned BMW says you jack up the rear using the differential casing.

Take a look at point A, B and C.

Where on the casing is BMW suggesting you lift from?

audiophool

My floor jack has a rubber pad on the saddle, and I place it just forward of the back cover, at point "A" in your picture. The documents I've seen only state to avoid placing the jack on the protruding aluminium cover, which in some cars hangs down and has fins for cooling (V8 and M cars usually). Your (and my) cover doesn't protrude.

scottalexander

I can see how the rubber pad in the saddle of your floor jack would be important.

Maybe this explains one reason why the bottom of my differential is all rusty. That is, who ever had the vehicle before me, jacked it up without a rubber pad and they ripped the black paint off the bottom of the differential?

audiophool

Maybe, but I would never worry about a rust on a cast iron part - there's a lot of metal there. lf it bothers you, paint it with some black Tremclad. The pad is useful to prevent the jack slipping, but a crowned metal lift pad would be fine too.