Monday, August 29, 2011

BMW e46 sub frame bushings

Older e46's have an infamous thump noise coming from the rear when you hit or let off the gas suddenly. The bushings for the differential and sub frame get old and don't dampen torsion movement as well as they used to. Sometimes the extra movement is enough to crack the sheet metal body if you drive the car hard enough. (There was a class action lawsuit about this defect in e46's.)

To get rid of the noise and prevent future damage, I did a sub frame drop and replaced all the bushings. It took me two days just to get to the point in photo #1 and a few more to figure out how to remove the old bushings. I first started to with a barbaric drill/jigsaw/hammer/chisel method, which was fun at first, but was too much work. I got my dad to help me fabricate some custom tools to pull the rest of the bushings out and push the new ones in.

Total cost was $150 in parts (6 new bushings) and about 4 days of work. I'm sure an independent shop would charge around a grand for this job. Definitely not an easy DIY. I wouldn't want to do this one again :P

I used this DIY from E46Fanatics as a guide. Check it out if you want to see the complete step-by-step.


Alex said...

Thanks for the write up! I think I have the same issue with my 04 325i. Milleage is 112K and I have a thump noise coming from the rear. I changed out almost everything: front struts/mounts, control arms, engine/tranny mounts, rear shocks/mounts, front/rear sway bar links/mounts, differential mounts, flex disc and center drive shaft bearing mount. Is there another way to diagnose that this is the issue other than removing the rear subframe? Thanks again!

Khang said...

Hi Alex,

I don't think there's one sure way to determine the cause of the thump. I've been following some forum threads where people have solved the noise by replacing something entirely different than another person.

However, it seems like most people have found to cause to be one or a combination of three things: center support bushing, differential bushings, or subframe bushings.

You said you already did the csb, and diff bushings, so my guess is that it's still the subframe bushings are bad. I did the differential bushing first on my car, but the noise came back, so that's what led me to believe the subframe bushings were the weak link.

There were no cracks or signs of wear on my old bushings even though they were weak. So I don't think there's a way to visually diagnose the problem unfortunately.

Anonymous said...

Looks like I'm going to have my indy mechanic do this since this is to much of a dyi for me and I want to get this done in order to avoid any sheet metal tear. Questions:
1) Did you use BMW OE parts? Lately I've been using Lemforder german parts since the price different is pretty significant sometimes.

2) Did you think about changing the other 2 trailing arm bushings and wishbone bushing? Don't know if these parts get much wear as the other bushings but seems a like a good idea since everything is out.

Thanks again!!

Alex said...

Previosu comment was from me. Forgot to add my name.

Khang said...

I also used Lemforder and it's been good so far.

I didn't change any arm bushings because they seemed to be fine. Another option is to upgrade to adjustable control arms if you want to get into tweaking your rear camber.

If you decide not to do any of the arms until later, at least it won't require a subframe drop.

Alex said...

Lemforder it is then! I think I'm going to try and change the trailer arm bushings first before I decide to have the subframe dropped.

On last thing I would appreciate if you could help me with; can you give me the measurements/part names for the tool you created and if this something I can find in my local hardware? I see there's a site that rent this tool for $100 but it seems pretty cheap to put together.

Thanks a million! I've been trying to get rid of this noise for months and I think I'm finally getting there.

Khang said...

The parts were made from scraps from my dad's machine shop. It's basically two aluminum L's and one slab with a slot cut in it. Measurements don't matter since you can slide the L's out to the appropriate width. Just make sure it's deep enough to pull the entire bushing out.

Then you just need a washer at the bottom that's the same width as the bushing. The rest of the nuts and bolts can be found at a hardware store.

I can even lend you the tool for free if you want. Just pay for shipping. I'll have to check if I still have all the pieces though.

Alex said...

Awesome! Let me know if you still have it and I'll paypal you the shipping costs. Glad to hear it's ajustable since I'll be working on the trailer arms first just for now. I plan on tackling this project the weekend of Sat FEB10.

Peter Slater said...

great write-up. i'd love to rent that tool from you - do you still have it?

Khang said...

Sorry, I don't have it anymore. I sent it out and never got it back.

Peter Slater said...

ahhh, that sucks!

thanks for the quick reply.