Urethane trailing arm bushing experiences?

[Beej '86 325es]

I'm getting ready to completely redo the entire rear underside of the car this spring and have almost all of the parts to do it. Here's a list of what will be done (* indicates what I still need):

Modified subframe with adjustable toe and camber (a nice ebay find)
Refinishing trailing used arms and reinforcing at swaybar mounts
Axles from an M3 in awesome condition
5" length 600 lb. 2.25" springs
Bilstein Sports
ST sways
Macschnell HD shock mounts
RD strut bar
*new wheel bearings
*Powerflex urethane subframe bushings
*Trailing arm bushings (can't decide OEM or urethane) :?
*H&R adjuster sleves (better design than Ground-Control because they don't tear up the trailing arm)
*South Bay Independent sway bar reinforcements

So now you get an idea of how serious the rebuild is, but I can't decide on what whether to go with OEM trailing arm bushings or Powerflex urethane. The cost difference is significant ($60 vs. $160). I know that the OEMs last forever, but I wondered if the urethane ones offered a noticeable difference or if they required frequent greasing.
Thanks.

[nando]

OEM do not last forever!! eventually rubber gets hard and starts to crack.

Anyway, I have urethane in my car, I heartily reccomend them. No difference in noise or ride quality that I noticed, but the rear suspension is totally solid with no play or sloppyness.

But why are you going to pay so much for bushings? there are other places that have them for a hell of a lot less. Try ireland engineering or bmwbushings. I got mine from IE, both the trailing arm and subframe bushings will be less than $160.

[Beej '86 325es]

Well by OEM lasting forever, I was only referring to the trailing arm bushings specifically, because I have 250,000 on my car and they are still in good condition.

I've seen the bushings that you're talking about and do not think they are a quality product. One guy who had those said he had to replace them less than a year later because they cracked up, fell apart, and the sleves rusted really bad.

I like Powerflex's quality a lot. I currently have their control arm bushings and the urethane isn't as quite as hard and plasticy feeling as most, you can tell just by touching it that it's very high quality. Plus Powerflex uses stainless steel for their metal sleves.

Thanks for the input.

[nando]

I dunno, I've had mine for almost a year.. about 10,000 miles on them so far. If you want to overpay, that's your choice.

in any case, I reccomend urethane, especially in the trailing arms. they are a common source of clunking sounds from the rear suspension when they go out.

[Bill 84 318i]

Sounds like a cool project Brandon! I'm torn on OEM and urethane trailing arm bushings myself.

What's better about the H&R adjusters? Do they have a large metal "base"? GC's shouldnt' really tear up the arms that much unless (like you had) there is coil bind.

[Beej '86 325es]

Yeah, the Ground-Control design puts all of the force on a very small area around the little nubby thing on the trailing arm. That nub is something that is just welded on there, the trailing arm is flat underneath it. The main reason I have so much of a problem is like you said, because I had binding very badly. However, since I first noticed the problem, Randy W. from the bmwe30.net board said he was starting to notice some slight denting there as well. I like the H&R design because it covers more area, distributing the force much better. Really, Ground-Control is a very generic setup, they probably use that same sleve on some Honda's strut.

[rscheiring]

BMP Design's urethane trailing arm bushings are only $60. My set is still waiting to go in....

[darien28]

the stock rubber bushings have holes in them right? how about just using urethane window weld and filling it in to make your own semi-solid urethane mounts?

http://importnut.net/motormount.htm

[E30-323ti]

I've just done all my suspension bushes.
I used the POWERFLEX bushes and they are great.
And they are very good quality like you said.

[Digitalwave]

Good luck with Bilstein Sports on 600lb springs.

[Beej '86 325es]

Good luck with Bilstein Sports on 600lb springs.

Actually, I'm already running them. They're a little bouncy, the damping coefficient is too low for the high spring rate. Eventually I'd like to switch to some Konis. I was originally running 450 lb. springs which worked better, and probably would have continued to work better if I lived in California where there are no potholes. The springs eventually binded so much that they damaged my trailing arms.

[Digitalwave]

You can get Bilsteins revalved for around $60-75 per shock.

[E30-323ti]

Are your rear springs 2.25" dia over the full 5" length?? Not bowed out like the stock springs??

Sounds like the straight springs is the reason for the binding, with the stock design the coils can compress within each other giving alot more suspension travel and the stock Bumpstops will still work, thus not damaging your trailing arms when they bottom out.

[Beej '86 325es]

Are your rear springs 2.25" dia over the full 5" length?? Not bowed out like the stock springs??

Sounds like the straight springs is the reason for the binding, with the stock design the coils can compress within each other giving alot more suspension travel and the stock Bumpstops will still work, thus not damaging your trailing arms when they bottom out.

Correct, they are a cylindrical linear spring.

The dealership removed the bumpstops...although I don't even know what they looked like, so I don't even know if they would have worked with these springs. I wonder though, do the barrel shaped springs actually have a consistent spring rate throughout the length? I have heard that they are considered linear springs, but I just don't understand how the same spring rate can be retained with the diameter changing.

[Bryson]

if the spring rate wasn't constant, I don't think they'd advertise it as so.
What do you mean the dealership removed your bumpstops? Did they open up your shocks or something?

edit: I'd also like to add that 600lbs/in is overkill for bilstein sports... 450 is overkill for the stock bil sport valving