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Infiniti fell off the jack stands

I was helping a friend do the rear brakes on his 2003 Infiniti FX35, we had one side jacked up and on a jack stand and doing the other when it rolled forward and came of the jack stand and crashed down. It landed on a piece of the suspension that thankfully saved the rotor, etc.



Two questions, since it landed on this part of the suspension, should we be concerned about any damage? There was no visible, anything we should get checked out.



Secondly, if it is all wheel drive, why would it roll forward if it is in park? The rear wheels also would turn freely when jacked up, normally when a car is in park the drive wheels are locked in place.



Thanks!

“all wheel” is still a fluid coupling, allowing movement. Probably fine since it landed on something meant to take the weight of the car, just like going over a speed bump too fast. Keep an eye on handling and take it easy for the first couple days.

It can roll forward in park even when things are working right. If the parking pawl shears off, it can roll forward even further. It doesn’t take much movement to dislodge a car from a jackstand. That’s why you ALWAYS chock the wheels when you use a jack. You actually learned a very valuable lesson without getting hurt - - you could just as easily been working on the brake with your leg under the wheel well when the car shifted.

This is why you should always chock the wheels before jacking a vehicle. You’re lucky no one was hurt.

If the car has a standard transmission, there is no pawl to prevent the transmission from moving. All wheel drive might add some resistance, but it does not lock the transmission. The car will roll unless it is chocked. I always set the parking brake as well.

I would worry about damage to the point of impact. I would guess the rotor. Otherwise, see how the car feels while driving. Take it in if there seems to be any difference.

If you take one drive wheel off the ground, the car will always try to roll away. The transmission may be locked but the differentials are not. The car may as well be in neutral. Experience is what you end up with if you don’t have the training. Now you have it. Glad nobody was hurt. Your post may help somebody else. Thank you.

Yes, what happens is the the wheel that is off the ground will now turn in the opposite direction that the other wheels roll in.
Next time, the OP needs to put it in park, set the parking brake, and block the wheels remaining on the ground. Also, as level a spot as possible to do this on should be selected.
(Of course, when working on the rear brakes, the parking brake will have to be released after you get the wheels in the air.)

I’ve seen two calls to set the parking brake:

Remember to take the parking brake OFF when you’ve got the car jacked up and you’re about to work on the rear brakes. Especially if it’s an older style that uses the service brakes as the E-brake.