[TurboBimmer]

As you probably know the non-M3 E9x come with rather soft suspension bushings from the factory. This is mainly due to make the ride compliant with RFT-tires. Once you switch to non-RFTs you'll actually notice how wobbly the suspension is when the car is pushed hard.

First step to get rid of this is to install suspension arms from the M3 which come with notably stiffer bushings. However in the rear we can only swap the subframe bushings, sway bar, the upper links and the guide rods. The lower camber links, the toe arms and the trail arms (the ones with alot of holes in it) from the M3 are not a direct swap.

So with the M3 suspension bits installed many still feel some looseness in the rear end, like it's moving from side to side a bit under WOT. The rear just doesn't feel planted as it should and this behaviour is certainly not reassuring the driver.

I looked at how this could be improved. First, it's obvious the toe links are a weak link Under load, they flex and the toe in alignment (1° on my car) may actually become a toe out which is NOT something you want in the rear! Preventing this from happening will improve stability ALOT. I decided to get the Rogue Engineering toe links from HP Autowerks, as they could be anodized in black (stealth look is a must for me, due to technical inspection) and come with dust caps. Installation was more or less straightforward. The adjustability of the new links is a big plus when it comes to aligning the car.

I'll get more into the driving experience later.

Next, I decided to replace the main differential bearing (the rear one out of the three) with a Powerflex polyurethane bushing which is WAY stiffer then stock. Installation proved to be quite a PIA as the the stock bushing needs to be pushed out with a special tool and space is limited. My shop had to lower the diff and the subframe a bit to get things done.

Finally, I replaced the inner bushing which connects the lower camber link to the chassis.

So, now to the proper driving impressions: rear end trailing is finally GONE

I step on it, and the car just pulls, precisely, as on rails. The car never felt this good. Seriously! No more wobbling (unless tires break traction of course), just a tight and precise rear end The difference is amazing!

NVH:

Yes, there is a bit more noise. The diff bushing induced some humming in the 3k rpm area. But nowhere as bad as exhaust drone. I still thought I'd mention it as some are sensitive to this.

Vibrations: nope.

Harshness: Holy crap, replacing just this few parts has stiffend up the rear quite alot! I used to dial the Bilstein dampers on a 8 out of 10 stiffness setting. Which was ok for daily driving and good for tracking. Now not so much. Was a bit too harsh and at highway speeds on the german autobahn (up to 150mph) the rear got quite a bit unsettled on road imperfections/bumps. I now set the dampers to 6 which feels better for daily driving.

Overall verdict: highly recommended!

For street use, I would only replace the toe links, but if you're a track junkie like me you may want to consider the powerflex bushings too.

PS: Sorry if this got a bit long

[turugara]

Great review.

[tofu-]

I just ordered the poweflex full replacement rear subframe bushes. I see not too many people on the forum choose these over the oem m3.

I am a bit disappointed to hear that the rear end will still be squirmy with them.

[TurboBimmer]

Originally Posted by tofu-

I just ordered the poweflex full replacement rear subframe bushes. I see not too many people on the forum choose these over the oem m3.

I am a bit disappointed to hear that the rear end will still be squirmy with them.

Not sure if the Powerflex subframe bushings will make the ride overly harsh. They are most probably stiffer than the M3 ones, but not all bushings affect the ride to the same extent. Some even put solid subframe bushings in and the ride still seems to be ok even for daily driving.

Looking forward to your impressions!

[tofu-]

Ah, you did not opt for them? are you still on the stock ones? Or you went oem m3 for the subframe?

i read the same about the solid bushings not having much effect on NVH. I personally was looking for a balance between oem m3 and solid, and powerflex fits the bill. Well, so do those other $800 rear subframe bushings offered by BMW for some performance line lol. We'll see what happens. The e46 guys hate them (powerflex)

[TurboBimmer]

Originally Posted by tofu-

Ah, you did not opt for them? are you still on the stock ones? Or you went oem m3 for the subframe?

i read the same about the solid bushings not having much effect on NVH. I personally was looking for a balance between oem m3 and solid, and powerflex fits the bill. Well, so do those other $800 rear subframe bushings offered by BMW for some performance line lol. We'll see what happens. The e46 guys hate them (powerflex)

I have the M3 subframe bushings. I guess they are ok but I would love to compare them to solid ones. Unfortunately the install is quite expensive.

Next I'm considering getting group N motorsport bushings for the trail arm. Those aren't overly expensive (compared to the subframe bushings at least ).

[cvc 22349a]

Originally Posted by Autobahn335i

I have the M3 subframe bushings. I guess they are ok but I would love to compare them to solid ones. Unfortunately the install is quite expensive.

Next I'm considering getting group N motorsport bushings for the trail arm. Those aren't overly expensive (compared to the subframe bushings at least ).

Which is the trail arm? The one's with the holes?
Why did you only install the rear diff bushing instead of all 3?

[tofu-]

Originally Posted by cvc 22349a

Which is the trail arm? The one's with the holes?
Why did you only install the rear diff bushing instead of all 3?

not sure about OP's reasoning, but from what i read, poly bushes for the diff add a ton of NVH

[TurboBimmer]

Originally Posted by cvc 22349a

Which is the trail arm? The one's with the holes?
Why did you only install the rear diff bushing instead of all 3?

Yes the trail arm is the one located towards the front of the rear suspension, with the holes in it.

As I wasn't sure how the diff bushings would affect NVH, I decided to replace only the rear, bigger one and see how things go.

[nitehawk]

Thanks for the review. How difficult was it to replace the camber link bushing? Whats involved exactly?

[TurboBimmer]

Originally Posted by nitehawk

Thanks for the review. How difficult was it to replace the camber link bushing? Whats involved exactly?

You just need a tool to push out the old bushing. And an alignment is needed after the install.

[cvc 22349a]

Originally Posted by Autobahn335i

You just need a tool to push out the old bushing. And an alignment is needed after the install.

Did you use powerflex or group n for the camber links?
Thanks for the review. I'm reconsidering using powerflex for the diff bushings as I don't want the added NVH for my street driven car and have resigned myself to living with the rear tracking problem under wot.

[TurboBimmer]

Originally Posted by cvc 22349a

Did you use powerflex or group n for the camber links?
Thanks for the review. I'm reconsidering using powerflex for the diff bushings as I don't want the added NVH for my street driven car and have resigned myself to living with the rear tracking problem under wot.

I used Powerflex for the camberlink-to-chassis bushing.

The Group N should be even stiffer. I'm considering to get those for the trailing arm as a next step. You can flex the stock bushings in the trailing arm easily by hand, by twisting the trailing arm. That can't be good for the car's handling...

[E90335iflyer]

Great review!

Looks like I will pick up a set of the toe arms from HP first. I think M3 arms and bushings will be the extend for me, urethane might be a bit much for my DD.

[madmanhiker]

These are the rear toe control arms being referenced, correct?

http://hpashop.com/HP-Autowerks-E8x-...2-e9x-nonM.htm

[BMW///Motorsport]

I want to do this now

[neilvosko]

a lot of track cars on the street with the solid bushings