Subframe repair or not

[NewB2Beemer]

Hi, I can hear the infamous rear-end clunk occasionally, especially when starting uphill but not always and does not sound that bad. Last weekend I put the rear on stands to check and while the bushings are old I don't see them being in a bad shape.

I did a load test on the rear diff and there is some movement when I put them under load with the parking brake engaged. I just don't know how much movement is too much. I could use some advice if I need to address it in the near future or I can wait a bit before getting to it since the repair is very time consuming. I have never welded in my life but planning to buy a cheap set, practice and tackle this job myself just for the hack of it. Plus it makes no sense to spend that much on a 2000 model as a mechanic would charge.

[harveyottotech]

Ok, I can't tell if your subframe is damaged here or not. It doesn't seem that way. However, the transverse bushing on the rear diff is notorious for clunking, especially on the manual cars, especially on leading or trailing throttle. To really determine if it's the diff bushing, drive about 20 mph leave it in gear and just go between coasting and accelerating with just the throttle, no clutch or brakes. If it clunks each time you apply or release the throttle, it's the diff bushing.
Now you have determined that it needs a diff bushing. The one in question is the bushing mounted into the subframe and bolted to the diff cover. This is not that hard to change, but I recommend using a poly bushing so you won't ever have to do it again.
You get a bushing tool (big threaded rod with nuts and bearings) and use that to take the bushing out and drive the new one in. You probably won't need it going in if you use the poly bushing. To get the bushing out you will need to remove the rear diff. Just bite the bullet and take it out. It's more work, but easier work for when you are trying to replace the bushing.

I hope this helps. If you have any questions please ask.

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[yjsaabman]

Check the engine mounts, as well. I had a clunk in my 2000 that I thought was a diff bushing and it turned out to be a wasted engine mount. It was literally separated and allowing the engine to lift up and thump back down when engaging the clutch or giving it sudden load, especially in lower gears.

There is a fair amount of play in the large diff bushing. I also see a little deflection in the subframe, but it's not much. Neither looks bad enough to be causing a clunking noise.

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[E39 Newbie]

Take a pry bar and pry your diff up and down, while shining a strong light on the bushing. It is torn? Lots of cracks? Does it move pretty easily? If so, perished bushing.

Take a strong light and look up to where the subframe bolts into the chassis. Look around the mount. Do you see cracks, or worse?

[NewB2Beemer]

I replaced the engine mounts a few months ago, the old ones were not cracked and were in a decent shape compared to their age. I will replace the diff bushing in a few weeks and I'll just go from there. Winter is coming and depending on the weather / snowfall the E46 may be out of commission for some time and I may just do the subframe repair while not used.

[harveyottotech]

While I love the idea of doing repairs yourself, welding is more than just an idle curiosity. It's like playing an instrument. Anyone can make noise, but it takes time and practice to get any good at it. Start practicing, watching videos, asking the old guys you know, and start with a MIG welder. Or maybe buy one that can MIG and TIG so you have your options open. Good luck!

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[NewB2Beemer]

I 100% agree on the welding. I always wanted to learn the basics and will find a place take a class before tackling it myself. That's the main reason I was asking how much further I can push out subframe refresh in time. Taking the bimmer to a repair shop for this repair would cost more in our area than the entire car's worth so it makes no sense financially. Fortunately we have spare vehicles so it is absolutely no problem to park it for a few weeks while I do the repair myself at my own pace.

I appreciate all the input!

[vinyldude]

I'm finishing rear subframe mount repair in my 328i. Each mount piece itself is made out of thicker metal and it sits between two layers of sheet metal inside the unibody. Interestingly in my case one of the mount pieces had fallen completely through while the three others were completely fine without even any cracks. The failed mount caused excessive subframe movement and squeaking noises.

Unless the sheet metal has completely failed it is very hard to see whether you have a problem or not without removing the whole subframe.

MIG welding is not very difficult at least for this type of thin sheet metal where you'll only be doing spot and stitch welding anyway. The biggest difficulty is finding good settings on the welder. Well, okay welding upside down under the car is a bit challenging or at least inconvenient. You'll need a real MIG welder with welding gas though.