urethane rear subframe mounts

[BimmerToad]

Has anyone replaced the rear subframe mounts with harder urethane mounts? I am considering replacing the mounts on my 318ti (E30 rear suspension) with the stiffer powerflex ones. Is the difference in handling and road noise noticable?

[bmwman91]

DEFINITELY DO IT. I did it & I noticed a real difference just pulling out of my driveway on my way out for the first test drive. It is a huge bitch to do because the stock mounts usually get seized in place, but it is worth the work. If you decide to do it, e-mail me & I can give you some real good pointers that will make the job significantly easier. Peace.........

[Ryan Stewart]

just post em BMW man, I am wanting to do these too and any advice would be appreciated.

[Bry]

I agree, post your tips here!

I've heard that with a lot of hard use on them (the poly bushings), they can tear and break down. I'm not really sure what to get...

[BimmerToad]

Did you use the powerflex ones?

Was their anymore road noise as a result?

Is the car that much tighter?

[bmwman91]

I purchased the urethane subframe mounts form BavAuto for $130...on sale now for $120. They have served me well through 3 autocrosses, but I have yet to see how they stand to the test of time. As far as noise...road noise increases, driveline noise is more than road noise. I can even hear the brake pads rubbing the discs in the rear at low speeds. I do have a gutted interior though. Probably wouldn't be as bad if the interior was still there.

Tips:
--> I spent a while figuring out where to jack the car up. You can just rest the rear wheels on ramps...having the subframe disconnected won't really matter since the car sits on the trailing arms/springs/shocks. The subframe will not slide forward or anything since it is bolted to the diff.
--> After unbolting everything, get the "knurled" bolt out of the center of the aluminum shaft...easiest to use a gear puller. Lock the two "claws" onto the little rubber-coated metal side flaps of the mount and center the punch on the bottom of the bolt. That should get ti right out. The rear seat-bottom needs to be removed since the bolts come up in the rear interior (far back corners). The tops of the bolts are covered with ~1.5cm of foam.
--> There are 2 paths removing the mount from the subframe can take (you will know which one once you cut the rubber):
-->The aluminum center shaft will come right out of the body of the car and will make the mount's removal relatively easy.
-->The aluminum center shaft will be totally seized into the body of the car.

--> If the aluminum shaft comes out, you are a very lucky person (I unfortunately was not). First, use a small hand-saw & drill (I ground out a bunch of rubber & started holes for the saw) to completely cut-loose the aluminum center-shaft from the rubber. Using a sledge-hammer and metal rod (~20mm diameter) and pounding from the top/interior, it should pop out. If not, instructions will be provided at the end.

--> Removal of the rest of the mount. Take the small handsaw and cut a vertical slit into the mount, all the way through. BE VERY CAREFUL NOT TO DAMAGE THE SUBFRAME. One complete cut is enough to get it out...lock onto the bottom of it with a large pipe wrench & twist. Or you can make multiple cuts & it will come out really easily.

--> Should the aluminum center-shaft not come right out.....
Get a thread cutting die (to make threads inside the amuluinum shaft). Get a bolt of matching/close diameter & screw it in as far as possible. Next, get a 30cm aluminum rod of about 10mm diameter (must fit in the aluminum shaft so it can rest on the bolt you inserted). Why do all this? Because the rod will just jump out if it is just placed in the 4cm deep, larger diameter hole inside the car, and trust me it can hurt if you have to hold the rod while hitting it with the hammer. The smaller rod will hold itself well inside the aluminum center shaft. Once fully inserted, hammer away until it comes out. Why use aluminum? An iron rod would bounce A LOT. Hitting an iron rod with an iron hammer would be a much more elastic collision than hitting an aluminum rod with an iron hammer (the hammer will bounce off of the iron rod MUCH more voilently than the aluminum rod, reducing the impact time & reducing the force transferred into the aluminum center-shaft, and is just more of a PITA). The rest of the mount can be removed before the aluminum center-shaft if it is stuck.

[bmwman91]

Oh, and yes, there is a GREAT performance difference. As far as I am concerned, the rear subframe & ssupension is independant of the rest of the car with stock rubber bushings. With urethane ones, the car is solid as a rock.

I also did urethane control arm bushings and there was a slight difference there too.

[zeit00]

Good write up. I have been curious about the urethane bushings, I also am kinda concerened about longevity. How long have you had these installed?

Thanks!

[Fraser]

I'm also interested in knowing how well they hold up over time... I've been freaked out by horror stories coming from our local BMW shop (Bimmerhaus) about them completely falling apart when they do fail...

They sure are expensive compared to stock rubber ones...


Fraser

[bmwman91]

I have had them for about 8 months now & I have not had any problems with them.

[jheadley]

You can get them fro $49 from Ireland Engineering.

[bmwman91]

I paid $100 at Turner for mine. They have seen a LOT of hard use and are still good.

[BimmerToad]

Be sure to keep us posted about how the urethane bushings hold up. I'd love to tighten the rear suspension of my car, if it proved to be as reliable . . .