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Discussion Starter · #1 ·
I replaced the trailing arm bushings on my 2002 330i today and I'm finished except for one bolt that I suspect that I've cross threaded. It's one of the three bolts on one side that hold the bracket to the body. The bolt turns easily and then binds completely with at least a 1/2-inch to go.

I'm an amateur machinist so I have some skills, but I haven't done this this type of repair and I'm worried that I only have one shot to fix this correctly without creating an even bigger headache for myself.

So I'd really appreciate some advice.

The bolt appears to be a M12x1.5
 

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Discussion Starter · #3 ·
I retapped the hole. The bolt went in easily but I'm a little nervous because the threads won't be as strong. The car is going to get an alignment this week and I'm hoping they won't have a problem with that bolt.

If they do, then I assume the next step would be to install a helicoil.
 

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Generally when you cross-thread a bolt it will start binding within the first few threads, which you should be able to feel at the beginning. When it goes in easily and binds near the end its usually because their is dirt or rust in the bottom stopping the bolt from going further inside, or the bolts threads/hole threads are damaged. If you continue trying to tighten it, you will strip the threads. Re-tapping the hole won't make the threads any larger, if its the correct tap and size it will simply clean the threads. But, the buildup that the tap cleaned off has to go somewhere, perhaps that's whats blocking the bottom of the hole? Make sure the hole is totally clean of debris, lube the threads a bit and slowly tighten it in. Before doing that, check the depth of the hole with a drill bit or nail and compare the length to the bolt if the hole is clear and the depth is as it should be, you should be able to get it in without any issues.
 

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Discussion Starter · #5 · (Edited)
I started the bolt with my fingers and it seemed to turn easily, but then I switched to a power ratchet. I now think it went in crooked because the bracket wasn't seated completely.

But the real reason is that I was tired, careless and in a hurry to finish up a troublesome repair that had taken all day in extreme heat and humidity. The videos I'd watched and the forum posts I'd read indicated this was going to be an fairly easy job but it wasn't. The arms didn't drop down far enough to be in a convenient position, the nuts and bolts that attached the bushings to the brackets were frozen and it was extremely difficult to get the bushings out of the arms even with the proper tool. And on the first side I had a lot of trouble getting the bracket back into place.

That first side took at least 4 hours, not including two trips to the store, delays caused by passing thunderstorms, a break to avoid imminent heat exhaustion, adjusting the emergency brakes and cleaning the inside of my wheels. Because I'd learned to use lots of heat and penetrating oil the second side was on track to take only about an hour until I cross threaded that bolt when it was nearly dark at 9 PM.

The car's back together and the new bushings have made a big difference, even though the old ones still looked good at 120k miles.
 

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Sounds like things went about as usual, when working under the car; everything takes longer, especially if you are working on jack stands instead of a lift. I've also cross-threaded using a power ratchet, so now I save the power for removal and gentle tightening after I've started the bolt with a hand ratchet.
 

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It's been a while since I've done these (i've done about 20 or more of these jobs) but from what I remember you undo the shock bolts and you'll have like tons of room to drop it. maybe undo something else i forget. did you JUST undo the 3 bolts and that was it?

That's a 30 min job at most per side if you undo all the right things (that includes undoing said things)

As far as the bolt, when the guy does the alignment, he shouldn't have to undo them all the way. but just tell him to do it by hand. no machines should be used on parts like that. not worth it.
 

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Discussion Starter · #8 · (Edited)
I did remove the bottom shock bolts which got me an extra 2 or 3 inches, but the arm/bushing never dropped completely clear of the body like it was on the Bimmerworld video I watched that made it look very easy. I even jammed a piece of wood between the arm and body.

I quickly broke the bushing tool's threaded rod when I tried to remove the first bushing, which meant a trip to Home Depot. I eventually found out that the bushings come out easier if you tighten the nut on the tool until you think the rod is close to breaking and then heat the arm around the bushing with a propane torch before turning the nut some more. I think it also helps to tap on the end of the threaded rod with a hammer in the direction that the bushing needs to go.

I have an electric impact wrench but I was afraid to use it. Maybe I should have.

I still have to change the same bushings on a Z4 but I'm going to wait for a nice cool fall day.
 
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