Name that clunk: subframe, differential or other? | Project E46-chassis BMW M3

David S.
Update by David S. Wallens to the BMW M3 project car
Oct 3, 2022 | BMW M3, BimmerWorld, Powerflex

The look on James Clay’s face told us all we needed to know: That clunk from the rear end was serious–and wasn’t going to magically cure itself.

Differential?

Subframe?

Okay, time to dig deeper. We could hear the clunk on acceleration and deceleration. The noise was more of a deeper clunk than a higher-pitched clank. Something heavy had started to move.


The good news: When we replaced our rear subframe bushings, the mounts looked good. The E46-chassis BMW has a reputation for torn subframe mounts, but ours have checked out fine.

To read more about E46-chassis BMW rear subframe mounts, including a full explanation from BimmerWorld’s James Clay on the subject, just head here: E46 Bushings and Subframe Mounts.

To see how James inspects subframe mounts, watch this video.


Soon after purchasing the car, we also replaced the rear differential mounts–a fresh pair, along with a new differential cover, came with our car.

So what was causing the problem now? We put the M3 on the lift for an inspection and found the issue rather quickly: The front differential mount had totally failed. Instead of a mount, we had some dust and air. It was gone.

The E46-chassis BMW’s differential is secured by three mounts: two on the differential cover and then one up front.

We checked out the BimmerWorld catalog for our options:

Stock: about $45.

Powerflex urethane Track Series: about $40.

Solid aluminum and recommended for track only: about $150, a price that includes all three differential bushings.

The Powerflex piece made the most sense. It was stiffer than stock to prevent unwanted movement, came with a lifetime warranty, and was value-priced as well.

Something we've learned from James about Powerflex bushings: Each one is engineered regarding shape and durometer for the specific task at hand. It’s not a one-material-fits-all situation.

So, onto the installation. The Powerflex bushing is a two-piece unit featuring an aluminum center and a urethane outer.

"Unlike the stock E46 M3 part," James explains, "that aluminum piece is slotted for proper differential alignment due to the harder material–a trick borrowed from E36 and Motorsport parts–and must be biased side to side instead of up and down.” The kit also includes all necessary hardware.

We pulled the differential for the installation so we could properly clean out the remains of the old bushing. Always follow the included directions, of course. As Jesse Spiker of Spiker Motorsports demonstrates, properly support that pumpkin, too. 

Did replacing the bushing with the Powerflex piece eliminate our clunk?

Totally. The rear end is now silent, and even though the Powerflex piece is formed of aluminum and urethane, we can’t detect any increase in NVH.

 

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David S. Wallens
David S. Wallens Editorial Director
10/4/22 10:58 a.m.

And, looking back, I should have recorded the clunk.

It was rather clunk-like.

golfduke
golfduke Dork
10/4/22 11:00 a.m.

I have this EXACT issue with my E46 touring... How long was the repair, all-in?  

 

 

David S. Wallens
David S. Wallens Editorial Director
10/4/22 11:05 a.m.
golfduke said:

I have this EXACT issue with my E46 touring... How long was the repair, all-in?  

 

 

Basically pull the diff, clean out the remains of the bushing, fit the new bushing, install the diff. The new bushing just slip in place. 

But it's a major clunk, isn't it? 

glyn ellis
glyn ellis New Reader
10/4/22 11:37 a.m.

In reply to golfduke :

With the correct tools (bushing extractors), it's a 3-4 hour job total. Once you have the diff out, the bushing replacement takes about 10 minutes

golfduke
golfduke Dork
10/4/22 1:28 p.m.
David S. Wallens said:
golfduke said:

I have this EXACT issue with my E46 touring... How long was the repair, all-in?  

 

 

Basically pull the diff, clean out the remains of the bushing, fit the new bushing, install the diff. The new bushing just slip in place. 

But it's a major clunk, isn't it? 

Oh yeah, followed by pretty strong driveline vibration that follows speed and not rpm.  It's... jarring. 

 

Slippery
Slippery GRM+ Memberand PowerDork
10/4/22 2:21 p.m.
glyn ellis said:

In reply to golfduke :

With the correct tools (bushing extractors), it's a 3-4 hour job total. Once you have the diff out, the bushing replacement takes about 10 minutes

The e46 M3 bushings are not sold separately from the factory. You have two options; buy a new cover or buy aftermarket bushings. I chose a new cover on mine and did a differential reseal at the same time.

With that being said, no special tool is needed to remove them as the bushings fall apart and are made of a material that feels like cardboard or dried sealant. Its not like an e30 diff bushing. You do need a tool to remove the front bushing that sits in the subframe, but those do not fail as often as the cover ones.

Cant comment on the non-M e46s.

Slippery
Slippery GRM+ Memberand PowerDork
10/4/22 2:23 p.m.
golfduke said:
David S. Wallens said:
golfduke said:

I have this EXACT issue with my E46 touring... How long was the repair, all-in?  

 

 

Basically pull the diff, clean out the remains of the bushing, fit the new bushing, install the diff. The new bushing just slip in place. 

But it's a major clunk, isn't it? 

Oh yeah, followed by pretty strong driveline vibration that follows speed and not rpm.  It's... jarring. 

 

Mine did not vibrate at all. You could only feel it upon accel/decel. It was a nasty thud and I could minimize it by being nice to the gas pedal.

David S. Wallens
David S. Wallens Editorial Director
10/4/22 3:19 p.m.

I didn't notice the driveline vibration but definitely had the thud on acceleration and deceleration.

We did the two rear diff mounts soon after buying the car. As mentioned above, we replaced the entire rear diff cover: E46 Bushings and Subframe Mounts. (A new diff cover came with the car.)

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
10/4/22 3:56 p.m.
Slippery said:

Mine did not vibrate at all. You could only feel it upon accel/decel. It was a nasty thud and I could minimize it by being nice to the gas pedal.

I will say that with the aluminum bushings that are in mine you hear a LOT of gear whine in the car. :)

David S. Wallens
David S. Wallens Editorial Director
10/4/22 4:24 p.m.

In reply to codrus (Forum Supporter) :

Did you do the fully aluminum replacements like these from BimmerWorld

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
10/4/22 4:48 p.m.
David S. Wallens said:

In reply to codrus (Forum Supporter) :

Did you do the fully aluminum replacements like these from BimmerWorld

I'm not 100% sure (the race shop installed them), but I think they are the BimmerWorld ones, yes.  They are definitely not street-friendly. :)

 

David S. Wallens
David S. Wallens Editorial Director
10/4/22 5:23 p.m.

In reply to codrus (Forum Supporter) :

Ah, just wondering. The Powerflex urethane ones seem quite okay on the street. 

David S. Wallens
David S. Wallens Editorial Director
10/5/22 12:48 p.m.

A benefit of fixing the clunks and assorted issues? Just driving it.

From last night's run to the big box store.

Needed to return some stuff–bought too much for the dryer vent redo. $36 back on the card. 

Caperix
Caperix New Reader
10/5/22 7:20 p.m.
golfduke said:
David S. Wallens said:
golfduke said:

I have this EXACT issue with my E46 touring... How long was the repair, all-in?  

 

 

Basically pull the diff, clean out the remains of the bushing, fit the new bushing, install the diff. The new bushing just slip in place. 

But it's a major clunk, isn't it? 

Oh yeah, followed by pretty strong driveline vibration that follows speed and not rpm.  It's... jarring. 

 

How is your center support bearing?  The non m diffs usually wear the rear mount & it is most noticeable on load changes.  I have never seen one that would move enough to cause a vibration.

David S. Wallens
David S. Wallens Editorial Director
10/6/22 1:29 p.m.

Someone asked about the mileage on our M3: 141k.

David S. Wallens
David S. Wallens Editorial Director
10/11/22 3:03 p.m.

Another evening, another run to a home improvement store. 

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