RSFB

[WDE82]

Originally Posted by c0bra

Correct me if I'm wrong, but isn't the bushing compliance designed to work with the very non-compliant run flats? With non RFTs, not sure if the flex is necessary. Though you do have me second guessing aluminum now.

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I've got 3 contenders in the fight, all 2 piece for ease of install. Prices are shipped. Decisions decisions!

Whiteline KDT917 "Synthetic Elastomer" - $155

Condor Speed Shop UHMW - $206

Revshift Aluminum - $299

The 4 point rear subframe concept has existed at least since the E36 in BMWs (don't remember what my buddy's E30 had). That had nothing to do with RFTs. Now, the E9X/8X extra soft bushings may be that way to compensate for RFTs, but rubber bushings would be there regardless. So I think some amount of compliance is desired except in a pure track car.

If other people are saying aluminum has been fine for them, then I'm sure it's just fine to install them even on the street. However, they're more expensive and may be a little more difficult to install.

Somehow I got the Whiteline KDT917 for $130 on Walmart.com.

[Suprgnat]

Originally Posted by WDE82

BMW designed the compliance in for a reason

See below.

Originally Posted by c0bra

Correct me if I'm wrong, but isn't the bushing compliance designed to work with the very non-compliant run flats?

Among other compromises including dampers.

Originally Posted by c0bra

Though you do have me second guessing aluminum now.

Don't.

Originally Posted by WDE82

I don't see any reason to go aluminum unless it's basically a track only car. ...compliance...I think there still should be a little on a street/track day car.

Market forces that dictated runcrap tires, soft suspensions, and a general disconnect from the road also dictated that it be done on a budget. The rubber bushings are a compromise meant to address the cheap dampers, immature tire technology, and the desire for people with spendy money to feel as if they're floating down the road while watching DVDs and surfing the internets.

The rear suspension carrier should have always been rigidly attached to the body shell just as the front suspension carrier is.

[WDE82]

Originally Posted by Suprgnat

See below.



Among other compromises including dampers.



Don't.



Market forces that dictated runcrap tires, soft suspensions, and a general disconnect from the road also dictated that it be done on a budget. The rubber bushings are a compromise meant to address the cheap dampers, immature tire technology, and the desire for people with spendy money to feel as if they're floating down the road while watching DVDs and surfing the internets.

The rear suspension carrier should have always been rigidly attached to the body shell just as the front suspension carrier is.

I'm sure the aluminum is fine, but the poly were cheaper and pop right in. Not sure if the aluminums slide with a slip fit or if they're press fit.

[Dekdo]

I think I’m going to play it safe and do M3 RSFBs

[Suprgnat]

Originally Posted by WDE82

I'm sure the aluminum is fine, but the poly were cheaper and pop right in. Not sure if the aluminums slide with a slip fit or if they're press fit.

Any improvement to the rigidity of the RSFBs is welcome.

[dubluv17]

I have a set of AKG 95A bushings on the way. They seem to use the highest quality poly, which is something that hasn't been discussed here yet (quality). I should have them in by the end of next week. I'd say add these to the list, though.

https://www.akgmotorsport.com/produc...yurethane-95a/

[wantmymoneyincash]

I'm looking at getting the condor speed shops RSFB as well. Seems to be a good middle ground thats a bit stiffer than M3 bushings but a bit softer and easier to install than aluminum bushings.

[Abe_73]

Originally Posted by wantmymoneyincash

I'm looking at getting the condor speed shops RSFB as well. Seems to be a good middle ground thats a bit stiffer than M3 bushings but a bit softer and easier to install than aluminum bushings.

Have you installed these yet? How was install? Give a review!!

[wantmymoneyincash]

Originally Posted by Abe_73

Have you installed these yet? How was install? Give a review!!

Not yet, looking to do a full suspension overhaul which will include the RSFB

[weidner]

Originally Posted by wantmymoneyincash

Not yet, looking to do a full suspension overhaul which will include the RSFB

Eager to hear how it went/goes. You get them installed yet?

[dubluv17]

FWIW, the AKG 95A bushings are pretty awesome. I was pretty intimidated to do the install after reading all the horror stories, but it went really well and pretty quickly once I got the hang of it. I just bought a heat gun from harbor freight and heated up around each factory bushing for a few minutes and then used a large socket and the weight of the car to press them out (if you've read any DIYs you'll know what I'm talking about). The car feels a ton more planted vs the OEM bushings (my car had ~115k miles on it) and I really like the results. Look into AKG stuff, it seems like they use really high quality materials. Zero NVH increase that I can notice.

[Petro135]

You just need the tool. Yes it can be done with sockets and stuff. I thought about heating them up too but the one i was looking at was right next to the gas tank. With the tool the rears are super easy the fronts are a little harder to get out. Since i went whiteline 2 piece i only had to loosen the bushing bolts enough to get my fingers in there and put a bolt on top. Maybe an inch. It was the easiest install ive done on this car. Even easier was the trans mounts i did the next day. I spotted the diff bushings and the 2 would be easy with a long bolt, a socket and a couple big washers. The 3rd bushing would have to drop the diff. So i put that job on hold for a little bit.
Since i did rear m3 control arms, rsfb and trans mounts at the same time im not sure what is the best. But my car is much stiffer and handles way better now.
The tool was like $70 on ebay. Whiteline sfb on sale for $95. Trans mounts $45. Rear arms $350. Well worth it. Like a new car in the rear. Made me decide to run my oem struts and springs a while longer

[wantmymoneyincash]

Originally Posted by weidner

Eager to hear how it went/goes. You get them installed yet?

I've got them on order along with f/r m3 bits, coils and dinan plates coming. I built a tool that looks very similar to the post above. Thought $80 was a ripoff. Install will hopefully be in the coming weeks! Tbf, it will be difficult to give a review on the improvement of the RSFB as all this will be going on at once. Can't wait though.

[135ivert]

What is the "hardness" (durometer?) of the Condor Speed Shop? I see the Whiteline and AKG is 95A, but haven't seen a value for the Condor 2-piece.

I need to pull the trigger on one of the two. I've had the solid aluminum ones in my garage for over a year and still haven't had the desire to install them.

[Petro135]

Not sure on the rsfb. Their trans mounts are what i used and they have a poly 70a and a solid race one im sure is like 95a. I used the poly

[wantmymoneyincash]

Originally Posted by 135ivert

What is the "hardness" (durometer?) of the Condor Speed Shop? I see the Whiteline and AKG is 95A, but haven't seen a value for the Condor 2-piece.

I need to pull the trigger on one of the two. I've had the solid aluminum ones in my garage for over a year and still haven't had the desire to install them.

https://www.condorspeedshop.com/pages/faq

[135ivert]

Originally Posted by wantmymoneyincash

https://www.condorspeedshop.com/pages/faq

Thanks!

[135ivert]

I bought the Condor Speed Shop inserts. They should be here Friday, assuming weather doesn't affect delivery. Hopefully I'll get them installed this weekend.

[Biginboca]

After reading about them in this thread I decided to install Condor Speed Shop UHMW subframe inserts this weekend.

This is as low as I could get this drivers front corner of the subframe to drop with 3 bolts still in on my car (328 but I think would be same for 1 series). The trick that worked for me was to support the subframe with a jack and get all 4 subframe bolts all the way out (only remove one at the time so the subframe stays in place!!) and then give them each like 5 turns reinserted. Then you can remove your jack and go back to remove the one bolt from the bushing you want to work on and then tighten the mounting screw diagonal from the screw you removed. The subframe teeter totters and as you tighten the diagonal screw the corner of the subframe with the missing screw will lower more.



This is why I could not lower any more than what I showed. On the drivers side on my car there’s 2 soft brake lines that connect the hard lines on the chassis to the hard lines on the subframe. And they get tight! Watch out for them:



So here’s where I hit a snag. The brake lines are tight and it isn’t looking like there will be enough room to get this top insert installed...



I went ahead anyway and used the eBay tool to remove the bushing. It worked great! This tool is a lifesaver and the bushing removal was super easy with it. No issues at all!

https://www.ebay.com/itm/BMW-E82-E90...-/333158778716





So once that was out back to the problem. There just wasn’t enough room to get the insert installed. And I did not want to mess with disconnecting the brake lines and actually drop the subframe out of the car. So time to improvise...

I decided to cut the top front inserts in half. I still used both the halves i made with my cut in the subframe though, so in essence I made a 3 piece bushing out of the 2 piece bushings . I decided to do this when I checked the stack height of the 2 bushing halves and found they were about 2-3mm shorter than the subframe housing they press into. So that means they actually wouldn’t touch end to end when installed, there would be a 2-3mm gap between them. So I figured I would make a cut and remove another 2mm of material but get the inserts installed easily. There’s a metal sleeve that goes inside the inserts that is what the bolt tightens against. The plastic pieces just float around that metal insert.



This is where I cut. Seems to me like these bushing inserts should be made with the bottom part 2/3 the thickness and the top part 1/3 the thickness. Then they would be an easy install without dropping the subframe too far at all.



After the bushings were cut I drew a line on them with a sharpy so I could keep them oriented the same as they were before the cut. It seemingly wouldn’t matter but if there were any high and low spots where I cut this way they would mate more squarely:



I installed the now 3 piece inserts with the metal sleeve they came with and everything went together nice and snug.



For the rear inserts they went in easily no cutting required. Just installed as they came. After it was done I was so glad to be rid of all this junk! The whiteline inserts were garbage from the start...



I was only able to do a short test drive after install. I just wanted to confirm the alignment didn’t change, which it didn’t. I noticed a little more nvh with these vs stock rubber with whiteline inserts. My diff has some whine it’s on upgraded mounts and the whine went from like a 5 out of 10 to like a 6 out of 10 with these inserts. So even though the word is that they wouldn’t change NVH they will slightly. Very glad I didn’t do aluminum inserts I would not want more NVH than I have and I would not want to have to completely drop the subframe.

Hopefully someone will wise up and start making a 1/3 & 2/3 bushing insert set for the fronts. Can’t see any reason the inserts need to be a 1/2 & 1/2 set.

[asbrr]

Good feedback on the NVH. I think the key point here is your upgraded diff bushings. If you had stock/good condition diff bushings, and you went solid aluminum, you probably wouldn't have too much NVH increase. In fact, I believe it's the rear diff bushing that is the main culprit - if you have a poly/solid bushing there it will introduce significant NVH compared to the subframe bushings.

I have stock Diff bushings, and 2 piece whiteline subframe bushings and there is no NVH in that sense from the back end, just a firm/tight response as you'd want it.

[Biginboca]

Originally Posted by asbrr

Good feedback on the NVH. I think the key point here is your upgraded diff bushings. If you had stock/good condition diff bushings, and you went solid aluminum, you probably wouldn't have too much NVH increase. In fact, I believe it's the rear diff bushing that is the main culprit - if you have a poly/solid bushing there it will introduce significant NVH compared to the subframe bushings.

I have stock Diff bushings, and 2 piece whiteline subframe bushings and there is no NVH in that sense from the back end, just a firm/tight response as you'd want it.

For the record I had the same Diff bushings with zero NVH with a swapped stock 3.73 diff. I’m using the M Factory black higher durometer rubber replacement differential bushings (3). When I installed a 3.91 diff with a LSD later with the same bushings already in place is when I got the whine. I reached out to the diff builder and they wanted me to ship it back and the whine wasn’t super annoying so I just lived with it.

So I don’t know for sure the aftermarket diff bushings are the root cause of diff whine. In my case with a proper oem stock untouched 3.73 diff I had no NVH with the new M Factory diff bushings, so I think the backlash wasn’t set exactly right on my current 3.91 diff and that’s the reason for the whine.

The take away is that the UHMW Bushings did make the whine slightly louder though.

[asbrr]

Ah you know what that makes sense - when you said "NVH" I was only taking the "VH" portion of it lol. The whine is internal to the diff so as you say likely needs looking at - and tightening anything else up related like the RSFB could increase/amplify that.

I should have stated that from a vibrations perspective, people that have gone with a solid diff mounting experienced a hell of a lot more than poly RSFBs or even solid RSFBs.