Not really M5 specific, but I figured I'd share my experience since it seems slightly different than what else I've read/watched.
Approached this with an excessive fear of damaging the arm. I used a torch and aggressive cutting as last resorts, thinking a torch might ruin the paint around the bushing's bore and that cutting into the arm had a risk of ruining it. I reached out to multiple independent Seattle-area shops that either ghosted me or told me they didn't want to work on it.
My revised (half) recommended steps
- Drill the rubber out from around the center through-bolt guide piece.
- Use a torch to burn out all the rubber and the re-enforcement ring. I regret avoiding this step, the paint seemed to be fine, and you're going to have to paint over it anyway if you're using the e34 spherical bushings.
- Thin the ring out with a reamer *
- Make two parallel cuts in the ring that go almost all the way through to the trailing arm, wide enough apart that you can peal back the strip of metal.
- Use a punch (I saw a youtube video with an air hammer that I tried, all I did was mess up the arm and knock pieces of metal off, it seemed way too unwieldy) and hammer to pound the strip into the center of the ring so that it as it curls back, it breaks away at the thin spots you created when making your two cuts. The biggest risk to this step is that the strip of metal you're pealing back breaks off, and you're left with no way to continue the process without damaging the arm bore at least somewhat. I ended up pealing the strip back from both sides with a hammer, punch, and flat head screwdriver when I didn't seem to be making progress and wanted to try to get get the strip to pull away some more. If you do break of the piece you were pealing back, I guess you can try to get it started again by trying to cut the groves in the ring more deeply and then see if a flat head screw driver can get it to start again.
- Use Amazon tool https://www.amazon.com/WINTOOLS-Univers ... B07BH22YCR to push in new bushing.
- Remove the center through-bolt guide piece.
- Grind the walls of the 44mm piece so that it fits into the arm bore without too much effort, otherwise you risk breaking the tool as you try to push the new bushing past the point where the old bushing fit. **
- Use the smallest nuts and rod to push in the bushing. I learned late in the process that the the smaller pieces should only be used with the smaller threaded rod and nuts. The larger nuts don't press on the 44mm sleeve in the correct spot and make it much more difficult to get the new bushing in.
- Be careful with the new bushing's dust boot, I'd avoid twisting the tool and pushing/pulling it on/off the dust boot as much as possible. I tore one side off on my first attempt, and spent a bunch of time getting it on as good as possible and then carefully RTVing it back into place.
- Push the new bushing in from the side that's towards the center of the car and opposite of the wheel, .255" past the flush point that the previous bushing was. **
* I bought an adjustable reamer ($250), thinking I could cut the ring until it was thin enough to come out on it's own. Used an impact gun to help. I think this would have allowed me to get the ring out with a big enough compressor, I ended up not grinding it down all the way because of the time it took for me to wait for my compressor to constantly refill the tank. My battery powered impact gun ran out of juice pretty quickly for something this intensive. On one hand, I recommend it since in theory I think it's harder to damage the arm when using it and since my first attempts to peal back a metal strip like I saw others recommend (and what I ended up doing myself) didn't work because the strip broke off. Potentially a thinner piece of metal can peal back more easily without breaking off. Once the strip breaks off, you're hard pressed to get it started again without damaging the arm. On the other hand, it seems that other people on the forum have been able to get it out without this tool, and reaming causes metal shavings that are a huge mess to clean up.
** I figure there are a few ways to place the bearing. Either, flush with the arm because it doesn't really matter, in a position so that when installed the bushing is centered between the bracket on the subframe, or in a position where it is centered in the arm's bore. I went with centered between the subframe bracket since I thought that was best for the bushing to have the same length of the through-bolt guide sticking out of each side. My math is
trailing arm bore width: 2.044"
old bushing through-bolt guide width: 2.636"
how much the through-bolt guide sticks out from the arm on the inner (opposite of the wheel) side of the arm: .382"
new bushing bore width: 1.362"
new bushing through-bolt guide width: 2.640"
So if I want the new bore to stick out .384" (.382" + (2.640" - 2.636") / 2) (adding half the additional length of the new bushing through-bolt guide, assuming the old bushing was centered in the trailing arm bracket), then I find the length of the through-bolt guide that sticks out past the new bushing's bore (2.640" - 1.362") / 2 = .639 and subtract the amount the old guide sticks out to find how much I want to press the new bushing past the flush point of the trailing arm, .639" - .384" = .255".
Since the tools cost as much as they did, and since I don't see myself ever using them again, feel free to reach out. Part of me wants to recoup the cost of these tools, part of me wants to make it easier/cheaper for anyone else.
Lastly, for both arms, I ended up damaging the bore, the 2nd one a lot less than the first. I used Steelstik to make some attempt to prevent rust, potentially the grinding of that process did more harm than just leaving it.
https://photos.app.goo.gl/BkfydEaRdBEukxkr6