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      03-01-2020, 09:33 AM   #146
chalbe
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Drives: e92 m3, jeeps
Join Date: Aug 2017
Location: Columbus, Ohio

iTrader: (1)

I just replaced the rear subframe and diff bushings and thought it might be worth sharing my experience. This thread seemed like a good place to make a post. I installed AKG 75D subframe bushings and PowerFlex purple diff bushings. I read this work (with split poly bushings) could be done without complete removal from the car. I gave it a try and it worked out. Replacing the engine mounts has a sort of similar process for lowering the front subframe. Photos added at the end of the post.

Getting the diff out was easy, and to that point my work was basically a duplicate of Victors. I was able to replace the diff bushings with the subframe in the car.

I bought the eBay subframe bushing tool that Victor used for removal and ended up stripping the threads of both shouldered nuts and the threaded rod while working on the front bushings. Either my electric impact broke the tool, or I did something to break it. I have other press tools that I could scavenge from and made something work but could only use hand tools. The rear bushings could be removed from the bottom, but not the fronts. For the fronts, I needed enough room between the body and subframe to pull from the top. The bushings have a rubber coated metal shoulder that wouldn’t come out the bottom with the tools I have. Like Victor said the shoulder seems to break on purpose and that’s a good thing. Disconnecting the hydraulic brake lines is still mandatory.

As far as subframe alignment, I marked points on the subframe and body. The AKG bushings have a very tight fit on the front alignment dowel. I could not move the subframe around once the dowels were in the bushings. Fortunately, all my marks were aligned, and no further adjustment appeared needed.

Torque specs from TIS that matter:
Front and Rear Diff Bolts – 100 Nm
Lower shock bolt – 100 Nm
Axel Bolts – 120 Nm
Driveshaft – 20 Nm + 90 degrees
Subframe Bolts – 108 Nm
X-pipe Bracket – 24 Nm
Tension Strut Rear Bolts - 47 Nm + 90 degrees

Here is what seemed notable to me:
1. Hydraulic brake lines: In addition to the brake/clutch pedal hold tool I used these line plugs: https://www.belmetric.com/advanced_s...rake+line+plug
2. Lowering the subframe: I used a floor jack at the rear of the subframe and a harbor freight transmission jack at the front, with rubber jack blocks between each jack and the subframe. To be honest, it was a little wobbly when I was doing the work, but I did not feel unsafe since I was not under the car and it never felt like it was going to tip over. If I were going to use a different lifting tool I would use a motorcycle jack and build a wood platform (similar to what Victor used), which I will likely buy anyway since it looks like it will work well for other things. The process is to lower it a little at each end until there is enough room to pull the bushings.
2. There are two bolts holding the parking brake cables to the body in the drivetrain tunnel above the driveshaft. I removed those to permit some additional clearance and flexibility. The parking brake cables can flex a good amount. This may not be necessary, but I did it while I was trouble shooting early in the process and it looked like an issue then. If someone does this, then do it before you remove the diff, and reinstall after the diff is in place and bolts are torqued to spec. There is more room to R/R the front diff bolts this way.
3. The electric wires in the back of the rear wheel wells need released from their plastic clips on the subframe, same as Victor did. I did not remove the wheel well liners, nor did I undo the electric connectors.
4. Removing the rear tension strut bracing was mostly similar, but not different enough to really need a description; it depends on how someone would support the driveshaft and x-pipe. Two of these bolts are the front subframe bolts. I did one side at a time and threaded the bolts back in when one tension strut was removed.
5. Driveshaft: TIS says the driveshaft is balanced, that there are marks on diff input flange and there is a corresponding bolt with a washer. I had the marks on the diff flange and a bolt had a washer, but they were not aligned like TIS says…..I am guessing a previous owner had work done in the area. In any case, I marked things before disassembly and just put things back together in the same spots since I did not have any vibrations previously.
6. Axel bolts: Releasing the parking brake cable from the hooks on the subframe can provide a little more access to axel bolts, but you will still have to put your car in neutral and rotate the axels to get the specified torque on each of the bolts. For manuals this means parking brake off and out of gear. I have a DCT and it was easiest for me to turn the car on for a few seconds, put it neutral with parking brake off and rotate an axel by hand. I figured people here know that but reading some threads on this website it’s clearly not common knowledge. “Good and tight” and “TAF torque spec” doesn't work for me. Same deal with the driveshaft.

The difficulty of this project does not match its reputation. It’s big and heavy parts, but it’s not complicated. If someone has a way to lift and hold with multiple tools that is half of what there is to figure out. The other half is having a way to R/R the bushings. This ended up being a much longer post than I wanted to write, and I did not write everything out. Most of what Victor posted applies to just lowering the subframe, so, there was no need to rewrite everything. The online version of TIS has all the information and there is no need to duplicate that either.

Rear Diff bushing


Front Diff Bushing


Rear Subframe


Front Subframe


Subframe gap

Last edited by chalbe; 03-08-2020 at 03:45 PM.. Reason: added torque spec for tension strut bolts
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