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      07-12-2019, 11:33 AM   #1
VictorH
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Diff bushings replace or not?

I'm going to finally take the plunge and replace my sub-frame bushings with solid Bimmerworld bushings. I'm going to drop the whole sub-frame and take as much stuff apart as I can without messing up the alignment.

My car is daily driver, dual-purpose track car 4-6 events per year, mileage is 143,000.
I have a set of PowerFlex Purple polyurethane diff bushings.

1) Should I replace the diff bushings even if they look good? How much extra noise do I get? Do they wear in and get quieter with time? This is the one I'm most reluctant about as I've heard this is often the biggest noise contributor.

2) The subframe bushings don't come with any directions, is it obvious which way they go in? Same direction as the stock one's were oriented in terms of the flanges? Does freezing the solid mounts make them go in easier, is it worthwhile (I have access to dry ice)?

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      07-12-2019, 12:35 PM   #2
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My understanding is that the sound comes from diff bushings, not the subframe. It also varies between DCT and 6MTs.

At 143K I’d do fresh bushings and mounts all around, but would go with stock diff to keep the sound/whine in check. I think the solid subframe should naturally limit some diff movement as well.

I had 95A subframe and diff mounts in my 46 and there was some mild whine. Didn’t bother me much but I had a higher tolerance for noises in that car.
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      07-12-2019, 01:14 PM   #3
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At that mileage, the old bushings owe you nothing, but I'd replace them with stock diff bushings on a daily driver, based on what I've read. My car has 119,000 on it and had several seasons of relatively heavy autocross on it. I'm anxious to try this solid subframe thing, but with stock diff bushings, inm somebody else's car to see how it feels and if it makes the car any better or worse

So, please do that and then let me drive it
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      07-12-2019, 02:21 PM   #4
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Purple is 80A and should by OK. I have black 95A and there is diff whine noticeable in some speed or rpm ranges.
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      07-12-2019, 06:07 PM   #5
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Getting ready to take the plunge.
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      07-12-2019, 06:18 PM   #6
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Quote:
Originally Posted by Richbot View Post
At that mileage, the old bushings owe you nothing, but I'd replace them with stock diff bushings on a daily driver, based on what I've read. My car has 119,000 on it and had several seasons of relatively heavy autocross on it. I'm anxious to try this solid subframe thing, but with stock diff bushings, inm somebody else's car to see how it feels and if it makes the car any better or worse

So, please do that and then let me drive it
As someone who dailies solid subframe with stock diff bushings, I truly belive that this is how our M3s should have left the factory. Zero downsides, zero NVH, and the solid subframes makes the chassis feel one generation newer and tighter.
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      07-12-2019, 06:24 PM   #7
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^ It’s comments like this that will get me to drop $2K to replace perfectly fine bushings, ugh.

Tbh I didn’t notice much difference when I put 95A subframe bushings in my E46. I’d certainly do solid or nothing here.
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      07-12-2019, 07:13 PM   #8
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Quote:
Originally Posted by Redd View Post
As someone who dailies solid subframe with stock diff bushings, I truly belive that this is how our M3s should have left the factory. Zero downsides, zero NVH, and the solid subframes makes the chassis feel one generation newer and tighter.
100% agreed. Most noticeable mod I've done. Car feels much better applying power now too.
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      07-12-2019, 07:52 PM   #9
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just done purple diff bushing and turner subframe and it whine a lot , i don't hear my exhaust any more (dinan with test pipe)
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      07-12-2019, 08:11 PM   #10
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Quote:
Originally Posted by nickauger View Post
just done purple diff bushing and turner subframe and it whine a lot , i don't hear my exhaust any more (dinan with test pipe)
Now you got to straight pipe it


I have purple diff bushings with stock subframe (bw solid bushings in the mail) and it's noisy but sounds awesome especially on decel.
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      07-12-2019, 08:55 PM   #11
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I have the purple diff bushings in my 6MT. The diff whine was only really annoying at two specific speeds...After I removed the rear seats and the rear trunk floor panel the diff whine became a bit more annoying lol. Even my corsa exhaust has some drone with all of that removed though. It sounds pretty badass in the cabin now, but not very "luxurious".
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      07-12-2019, 09:06 PM   #12
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Quote:
Originally Posted by Bartledoo View Post
I have the purple diff bushings in my 6MT. The diff whine was only really annoying at two specific speeds...After I removed the rear seats and the rear trunk floor panel the diff whine became a bit more annoying lol. Even my corsa exhaust has some drone with all of that removed though. It sounds pretty badass in the cabin now, but not very "luxurious".
Make sense i've remove my seat and trunk trim. Worst is between 60 and 70 but i hope bushing will get softer by the time.
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      07-12-2019, 09:09 PM   #13
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Originally Posted by nickauger View Post
Make sense i've remove my seat and trunk trim. Worst is between 60 and 70 but i hope bushing will get softer by the time.
72 indicated is sooo bad haha.
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      07-12-2019, 11:47 PM   #14
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Poly bushings should not break in or get quieter with time.

I want solid subframe, and stock everything else. But at 50K, it’s so hard to justify the labor when nothing else needs to be refreshed yet.
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      07-13-2019, 09:03 AM   #15
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Moving along slowly. To remove the Y-brace you have to unscrew the front sub-frame bolt. I guess you support that corner with a jack, remove the bolt and then put it back? Seems like maybe it would be better to remove the diff first to get some weight off the sub-frame and then take off the Y-brace. Any opinions?
I don't like to rip up or break any of the plastic retainers. The front end of the fender liner, covering the outer Y-brace bolts (2 of them) has a pin-type retainer. Used a little pin driver to push it back out the way it came, other side didn't want to budge so pushed the little plastic pin further in until it came all the way through.
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      07-13-2019, 12:46 PM   #16
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Almost ready to remove the diff. This job (so far) is much easier than the front sub-frame removal.
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      07-13-2019, 12:51 PM   #17
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Quote:
Originally Posted by jmeek83 View Post
100% agreed. Most noticeable mod I've done. Car feels much better applying power now too.
Curious, how built up is your car?

I am really happy with my ZCP in near-stock guise. Compared to my E46M (TCKs, Dinan monoballs, AKG bushings & mounts) it's a lovely balance for a weekend/canyon car (no track, but also not a daily). What I like is that the suspension "breathes" with real world road imperfections.
I have little desire to tweak the rear suspension in this car, but these aluminum subframe bushings continue to tempt me.
Am I stupid to consider throwing these on an otherwise stock, low mile rear end that doesn't see the track?
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      07-13-2019, 01:19 PM   #18
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Quote:
Originally Posted by wyatth View Post
Curious, how built up is your car?

I am really happy with my ZCP in near-stock guise. Compared to my E46M (TCKs, Dinan monoballs, AKG bushings & mounts) it's a lovely balance for a weekend/canyon car (no track, but also not a daily). What I like is that the suspension "breathes" with real world road imperfections.
I have little desire to tweak the rear suspension in this car, but these aluminum subframe bushings continue to tempt me.
Am I stupid to consider throwing these on an otherwise stock, low mile rear end that doesn't see the track?
I don't think you're stupid. I broke a diff bolt at 32k miles of only street driving, which likely wouldn't have occurred with solid subframe mounting. The connection (driver to rear end) after solid mounting is much better, with no nvh penalty from the subframe bushings alone. I would consider it another preventative maintenance item for an E9x M3 that is driven somewhat hard regularly, with added benefit to the driving experience.
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      07-13-2019, 01:50 PM   #19
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:blushes:

That's true, diff movement/bolts are genuine issue for 6MTs and this would be another way to address that. Though my understanding is that DCTs do not suffer from that issue.
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      07-13-2019, 02:52 PM   #20
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Diff is out. That long third top bolt in a pain in the neck, but other than that not too bad.
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      07-13-2019, 07:50 PM   #21
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Quote:
Originally Posted by Bartledoo View Post
I don't think you're stupid. I broke a diff bolt at 32k miles of only street driving, which likely wouldn't have occurred with solid subframe mounting. The connection (driver to rear end) after solid mounting is much better, with no nvh penalty from the subframe bushings alone. I would consider it another preventative maintenance item for an E9x M3 that is driven somewhat hard regularly, with added benefit to the driving experience.
So I'm going to reply to both of you. This is my fourth MT M3 (2 E36s and 1 E46). I ordered my 2013 new and I am thus the original owner.

Having come from the E36/46 chassis and their subframe woes, I was fully aware the E9X had a totally different suspension design. When I got the car, the rear end would hop like crazy under full throttle. I read some threads from others on the forum and decided to go with turner solid subframe and powerflex purple diff bushings. This was done at the same time as dinan rear toe links.

The car also has a dinan intake and pulley, but still has oem cats and no tune, so power mods are minimal. It's a stripper, and it does have about 90 lbs out of it and most would be out of the rear end. Unfortunately I've been on worn rubber since the rear suspension work was done.

The rear no longer hops, even at next to no fuel and full throttle in first. It will break traction, but there's no more violent wheel hop. The whole rear end loads up power instantly. There's no movement felt at all back there. The car legimately feels more solid. It should have felt this way new.

I do have diff whine (which I actually love the sound of) around 35-45 mph. After that wind noise drowns it out.

I'd do it again. Even without the videos I've seen of E9X diffs shaking like crazy under full load. Now I just can't wait for stock sized rear Pilot Sport 4S to be back in inventory at tire rack!
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      07-13-2019, 08:17 PM   #22
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Quote:
Originally Posted by VictorH View Post
Diff is out. That long third top bolt in a pain in the neck, but other than that not too bad.
you're the first person i've seen with the ac hydraulic long reach jack. how do you like it? will it reach the front center jacking point by chance?
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