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Discussion Starter · #1 ·
Any good advice on where to place a floor jack onder an E46 to safely jack the car up and get it on jackstands? I've really struggled with this, and have used a point that I am unwilling to use again -- the U-shaped reinforcement rails that run front to back along either side about 12-18" from centerline. I ended up deforming the rails very slightly :eeps: (indented, not bent), and while I don't think If done any serious damage, I don't want to jack from these points again.

BMW will only say that the four factory jack points (two on each side -- where the factory tire jack goes) are the ONLY safe places to lift the car. Problem is, this is where I have to put the jackstands!

So, anyone...help! FYI, I'm doing this work on a 330cic.

Dave
 

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Floor Jack point

In the midline of the car, approximately 30 inches back from the front air dam is a metal bump. The bump is a few inches in diameter and in front of the oil pan. This is a safe jack point to put your floor jack. I use a block of wood on the jack stand.
 

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And what about at the rear of the vehicle? Is there a preferred location to place a floor jack at that end?
 

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Those reinforcement rails are CIC specific and they're not very strong. I bent one and the rear skid plate on road-kill (don't ask). They easily unbolt and I was extremely easy to bend them back into shape.

Not even sure why they're there in the first place.
 

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Canuck BMW said:
Is there a better place to use the floor jack in the rear?
There's a U shaped subframe reinforcement bracket right in front of the differential. This is the STRONGEST and stiffest part of the E46 chasis and it's a good place to jack up the car as well.
 

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dang! i should have checked this forum before i worked on my car last night!! cos i spent like 45 minutes trying to figure out where to jack up my car so that i could put jack stands at the four points, and the stupid bently manual doesn't have that info either.

i guess i never jacked up all four corners at the same time and put my car on jackstands before (although i jack it up every other weekend when mounting/dismounting my race wheels/tires). and it's relieving to know that the places i ended up using as jack points were indeed good jack points: a little bump on a metal plate in the front, in front of the oil pan. and the differential in the back. and wow, the E46 is noticeably heavier than my little MR2. :)

compared to the task of figuring out how to jack up the car, bleeding the brakes last night was nothing! haha.
 

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Discussion Starter · #12 ·
obLu said:
Those reinforcement rails are CIC specific and they're not very strong. I bent one and the rear skid plate on road-kill (don't ask). They easily unbolt and I was extremely easy to bend them back into shape.
I think we're talking about two different things... Are you referring to the V-shaped reinforcing bracket where the apex of the V bolts just under the spare tire well, and the sides of the V run forward and out toward the sides of the car, bolting just about midway under the door near the edge of the underbelly?

That bracket is unique to the convertible. I was referring to the two U-shaped beams (think of a rain gutter) that run parallel to the length of the car, each about 5 feet long or so, about a 12-18" in from the side of the car. The are welded to the frame, and not easily removable (unless I've seriously missed something). The opening of the "U" is the part welded to the body.

Not even sure why they're there in the first place.
The V-bracket provides additional rigidity to counter twisting flex of the body due to the lack of a roof section. If that's what you're referring to, it's not what I was talking about.

Dave
 

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Discussion Starter · #13 ·
Re: Floor Jack point

emiron said:
In the midline of the car, approximately 30 inches back from the front air dam is a metal bump. The bump is a few inches in diameter and in front of the oil pan. This is a safe jack point to put your floor jack. I use a block of wood on the jack stand.
Is this exposed without removing the engine splashguard? You know, that 2x3' plastic cover held on by six screws, and two plastic capture rivets attaching it to the front bumper trim...

Dave
 

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The V-bracket provides additional rigidity to counter twisting flex of the body due to the lack of a roof section. If that's what you're referring to, it's not what I was talking about.
Oh I know that's what they're supposed to be there for. But take them off sometime and see how easy they flex. I was commenting on what a waste of space that bracing is since it's so flimsy.
 

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Discussion Starter · #16 ·
obLu said:


Oh I know that's what they're supposed to be there for. But take them off sometime and see how easy they flex. I was commenting on what a waste of space that bracing is since it's so flimsy.
Unless I'm mistaken, the purpose of the bracket is to stiffen the body through tensioning forces (i.e., stretching forces parallel to the sides of the V), not shear or compression forces on the bracket, which as you poit out, it is not strong enough for -- i.e. it will bend. However, it is plenty strong to resist tension forces -- it's steel, and beefy enough not to stretch easily.

If you consider the geometry of the bracket, the underbody, and the attachment points, you can get an idea of what I'm talking about. It resists twisting of the entire body because the dimension traversed by the sides of the V will lengthen if the body twists along it's long axis in either rotational sense. Seems to me it would help quite a bit in resisting this twisting action, stiffening the frame from that particular sort of deformation.

The bracket would also help stiffen the chassis against "saddle" drooping. Remember that all the upward suppport forces bear on the suspension mounts, while there is an equal and opposite downward force due to gravity that is centered roughly midpoint on the car. In a coupe or sedan, the pillars and roof form a very rigid truss structure that resists any sagging due to metal fatigue over time. The convertible is more susceptible due to the lack of the roof structure. The V bracket will help resist this sagging as well.

As you note, however, it is not a strong construct when it comes to compression or lateral (i.e. normal) forces. As such, any opposing bending action (like scraping the bottom) where the force vectors are reversed from typical will result in easy failure of this component.

Dave
 

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Discussion Starter · #18 ·
obLu said:
Something just blew right over my head, wonder what that was?
No worries ;) Just leave the thing on there and you'll be fine. If it does get bent, it should be straightened, however, and the attachement points on the body should be inspected to make sure they didn't get ripped or deformed.

Dave
 
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