M3 Rear Subframe Bushings Rubber vs. Aluminum

[ShocknAwe]

Originally Posted by duder13

Unless you're doing the job yourself, because the 2-piece poly install is easier.

You're not wrong. The 2pc aren't bad, but I'm not convinced they are value for money. I genuinely think this is one of those items best done by a shop if that's the case though. This chassis is so finicky.

[duder13]

Originally Posted by ShocknAwe

You're not wrong. The 2pc aren't bad, but I'm not convinced they are value for money. I genuinely think this is one of those items best done by a shop if that's the case though. This chassis is so finicky.

I don't know. They are cheaper than both the M3 and aluminum bushings, and they're stiffer than the M3, but, yeah, unless you're doing the install, I say may as well go aluminum.

[MN.BIMMER]

I personally will be going with the AKG 75D poly inserts for differential and subframe. Per this chart, it looks like these poly ones will be the hardest available, outside of aluminum. I'll be doing it with jackstands and hand tools, so the 2 piece bushings really seem like the best way for me at least. If my 1er wasn't on daily duty, I'd think more towards full solid bushings everythwere vs full poly.

[Tallicia]

Originally Posted by ShocknAwe

Seriously, go aluminum or just do inserts.

Key thing in all this though is to keep the diff mounts STOCK.

The M3 or whiteline diff bushings are not beneficial or an upgrade? Please, elucidate!

[ShocknAwe]

Originally Posted by Tallicia

The M3 or whiteline diff bushings are not beneficial or an upgrade? Please, elucidate!

They are. But aluminum is substantially better without much in the way of extra work over the M3 rubbers. So just do that instead. It's not really a secret or groundbreaking.

[duder13]

Originally Posted by ShocknAwe

They are. But aluminum is substantially better without much in the way of extra work over the M3 rubbers. So just do that instead. It's not really a secret or groundbreaking.

I'd also go aluminum, because why not? But, how are we quantifying substantial? I'd imagine that move from standard to poly is more than the move from poly to aluminum. With the standard bushings, you can move the subframe with a screwdriver!

[10"]

Originally Posted by zx10guy

Unless you have smooth as glass roads or this is a track only car, I cringe at how harsh the ride would be with solid bushings.

This. Putting in solid bushings sounds like a terrible idea LOL

[duder13]

Originally Posted by 10"

This. Putting in solid bushings sounds like a terrible idea LOL

From all that I’ve read, it apparently isn’t an issue (newer M cars even have a bolted down subframe.) My poly bushings, which are stiffer than the M bushings (and probably the BMW motorsports bushings,) don’t have NVH issues at all.

[10"]

Originally Posted by duder13

From all that I’ve read, it apparently isn’t an issue (newer M cars even have a bolted down subframe.) My poly bushings, which are stiffer than the M bushings (and probably the BMW motorsports bushings,) don’t have NVH issues at all.

Don't think I'd put these on. See what AKG say about the aluminum bushings they sell:

"Although solid aluminum bushings are the hardest available and have a longer life span than other bushings, they are also extremely harsh and unforgiving on the chassis. Cracks may occur around the mount. Any area using aluminum bushings should be reinforced and consistently checked before/after each race."

https://www.akgmotorsport.com/produc...90-e92-e93-m3/

[duder13]

Originally Posted by 10"

Don't think I'd put these on. See what AKG say about the aluminum bushings they sell:

"Although solid aluminum bushings are the hardest available and have a longer life span than other bushings, they are also extremely harsh and unforgiving on the chassis. Cracks may occur around the mount. Any area using aluminum bushings should be reinforced and consistently checked before/after each race."

https://www.akgmotorsport.com/produc...90-e92-e93-m3/

Interesting. That certainly makes me reconsider my opinion on them, and I may be glad I ended doing poly after all.

[Suprgnat]

Originally Posted by duder13

Interesting. That certainly makes me reconsider my opinion on them, and I may be glad I ended doing poly after all.

Or just get the Bimmerworld or Turner solid aluminum bushings who don't feel the need to have that caveat and specifically state they are also suitable for the street.

But what would Bimmerworld or Turner know about BMWs?

[duder13]

Originally Posted by Suprgnat

Or just get the Bimmerworld or Turner solid aluminum bushings who don't feel the need to have that caveat and specifically state they are also suitable for the street.

But what would Bimmerworld or Turner know about BMWs?

I don't know, I've seen mention of potential subframe issues with stiffer bushings before, but I hadn't seen a bushing manufacturer actually mention it.

I'd imagine that BMW knows better than all three, yet they decided on rubber for the M3, and even their Motorsport bushing upgrade from that is still just a harder rubber bushing.

Considering BMW's history with subframe and strut tower cracking, AKG's warning doesn't exactly shock me, no pun intended.

[Suprgnat]

Originally Posted by duder13

I'd imagine that BMW knows better than all three, yet they decided on rubber for the M3...

Considering BMW's history with subframe and strut tower cracking, AKG's warning doesn't exactly shock me, no pun intended.

Agreed but , they offer the very stiff Group N rubber for racing classes that require that cars stick with the original bushing material and then switched to solid aluminum in the next generation road cars. My bet is that they use solid when they can when racing, but I could be wrong.

I get that, too, but anecdotally I've not read a single account of the subframe mounting points failing in any way on the E8x/E9x platform due to the use of aluminum subframe bushings, or any other reason. There's 15 years of history there, so if it does happen it's extremely rare.

[duder13]

Originally Posted by Suprgnat

Agreed but , they offer the very stiff Group N rubber for racing classes that require that cars stick with the original bushing material and then switched to solid aluminum in the next generation road cars. My bet is that they use solid when they can when racing, but I could be wrong.

I get that, too, but anecdotally I've not read a single account of the subframe mounting points failing in any way on the E8x/E9x platform due to the use of aluminum subframe bushings, or any other reason. There's 15 years of history there, so if it does happen it's extremely rare.

Yeah, I’m not sure of the subframe differences with the newer road cars. Surely their subframes were designed with solid mounts in mind.

The bushings for the racing class cars probably aren’t applicable, since they’re not worried about a rough street.

I agree about the history around here, but I don’t see a TON of users with aluminum, and most of them seem to have done it more recently (like last 6-7 years?) so the sample size isn’t exactly huge.

[Suprgnat]

Originally Posted by duder13

Yeah, I’m not sure of the subframe differences with the newer road cars. Surely their subframes were designed with solid mounts in mind.

The bushings for the racing class cars probably aren’t applicable, since they’re not worried about a rough street.

I agree about the history around here, but I don’t see a TON of users with aluminum, and most of them seem to have done it more recently (like last 6-7 years?) so the sample size isn’t exactly huge.

When I get around to replacing my M3 bushings with solid I'll let you know how it goes. probably won't happen until mid-2020 though.

[ShocknAwe]

Skeptical of warning from AKG on a product that to my knowledge they dont offer.

[duder13]

Originally Posted by ShocknAwe

Skeptical of warning from AKG on a product that to my knowledge they dont offer.

https://www.akgmotorsport.com/produc...m-e90-e92-e82/

[chris_flies]

I went with Condor Speed Shop UHMW subframe bushings. I love them. I think they actually improved the ride quality (much more taught and controlled), but I have different tastes for NVH than most (still rockin' solid motor mounts). Don't do the diff bushings! Event the M3 ones made too much noise, it didn't help that that particular diff's bearings were shot...

The big thing with solid aluminum is that there is ZERO damping in the bushing. Even delrin or polyurethane damp the vibrations in the subframe before they get to the chassis. The vibrations contribute to NVH the most, and are what can cause structural issues (why airplanes are flutter tested) down the road. E36's apparently needed serious reinforcement of the engine mount arms in order to safely run solid motor mounts because the vibrations would cause them to disintegrate.

[10"]

Originally Posted by duder13

https://www.akgmotorsport.com/produc...m-e90-e92-e82/

actually makes me trust AKG *a lot* to see them giving a warning on their OWN product like that which will lead to less sales. A really good company...i'd be really careful with aluminum bushings on a car that was not intended to use them. Sure they might feel good for 1-2 years but long term useability will definitely be questionable...

[Tallicia]

Thanks all for inputs here. solid mounts for daily hard driving worry me. track use, they're great.

Putting 20k+ very hard ( think occasionally/maybe often airborne fun ) miles on my car a year, I think a little give from poly would be less likely to split the frame and hopefully just the sub frame when the usual forces of nature do what they do best.

[Mr Gasser]

I had solid bushings on the front motor mounts of a different car and the whole car vibrated like crazy and sounded like a crate...road racer...dodon't know if that's what you want...

on the other hand, the rear subframe may not vibrate and if fact becomes extremely solid as in one piece...not sure if the engineers wanted it to behave that way. The M3 bushing delivers the best of both worlds and are standard on all high-end performance bimmers.

That being said I do have a set of Whitelines and they work great, with the right amount of flex, just be sure to grease them up before putting them in place.

With the M3s, they just press in and go.