Objective bushing comparisons

[Maybe Magpie]

Has anyone done one before? A lot of companies (AKG, Condor, Garagistic, et al.) insist their bushings don't increase NVH but I hear the exact opposite almost universally from other E30 owners. Durometer is durometer but I'm curious if a high durometer rubber and high durometer poly have the same characteristics in terms of NVH, and which bushings to avoid using poly for if I want to keep NVH to a minimum while improving over stock. "Oh they don't squeak and rattle" "Yes they do" he-said-she-said is hard to discern. I would have gotten the Group N bushings but they went out of production sometime after 2019 and are NLA, they're essentially stock but solid rubber.

The thing is one person's "fine" NVH is another's "miserable", so I was hoping to find some sort of meaningful comparison, if not of bushings in-situ, of materials and durometer ratings and the like. I mostly street my car but I don't want to rattle my teeth out on my area's shitty roads. I know the E30 is a 40 year old car, I don't expect it to be silent or perfectly smooth but it's already vibrating enough as it is with an exhaust on it and I don't want to make it miserable to daily.

[digger]

This is a loaded question as the specifics and details matter including the operating environment (type of road surfaces and imperfections encountered) and the application e.g. which bush in particular and intended usage and then there is personal taste/perception and point of reference.

The softer poly might be acceptable to some tastes on certain bush locations depending on usage but will never be as comfortable as the OE rubber period. E.g. Antiroll bar bushes are pretty safe though companies like whiteline and H&R use a better poly than places like IE whos bushes are rubbish (unnecessarily hard)

Which group N bushes are NLA? sub frame were last time i looked

[Maybe Magpie]

This is a loaded question as the specifics and details matter including the operating environment (type of road surfaces and imperfections encountered) and the application e.g. which bush in particular and intended usage and then there is personal taste/perception and point of reference.

The softer poly might be acceptable to some tastes on certain bush locations depending on usage but will never be as comfortable as the OE rubber period. E.g. Antiroll bar bushes are pretty safe though companies like whiteline and H&R use a better poly than places like IE whos bushes are rubbish (unnecessarily hard)

Which group N bushes are NLA? sub frame were last time i looked

Those are the ones I meant, yeah. I haven't ever found Gr.N bushings for the RTABs et. al or anything else, despite some hunting. Wide open to P/Ns if you got 'em. FWIW I'm in the PNW and here we have a ton of elevation and while a decent amount of our roads are okay in smoothness it's really not uncommon to find enormous, shockingly deep potholes or cracked up surface. Some of the more important stretches of interstate are in a not-great way, too.

The thing about it being loaded is that's why I want to figure out some kind of baseline and work from there. For my purposes of street car with occasional autoX and spirited backroad that I daily I want something quite soft but a little stouter than stock, the problem is I don't have access to an E30 with poly to compare NVH against mine, etc. I know durometer is for hardness, is there a good measurement for vibration transmission? Something to do with frequency, maybe?

[digger]

33311417247 group N rear subframe bushes can still be found. they arent cheap and tbh i have a set (not installed) and they are at most a subtle upgrade as the rubber is supposedly slightly stiffer but the geometry looks the same not completely solid. Better to by a stock set and fill the voids with 70 shore A casting rubber. It is possible the legit Group N are superseded and now just the stock version is sold under group N guise (based on what i received it wouldn't surprise me)

https://www.m3-klassik.de/images/TK_E30_N.pdf

[Maybe Magpie]

33311417247 group N rear subframe bushes can still be found. they arent cheap and tbh i have a set (not installed) and they are at most a subtle upgrade as the rubber is supposedly slightly stiffer but the geometry looks the same not completely solid. Better to by a stock set and fill the voids with 70 shore A casting rubber. It is possible the legit Group N are superseded and now just the stock version is sold under group N guise (based on what i received it wouldn't surprise me)

https://www.m3-klassik.de/images/TK_E30_N.pdf

When I looked into it it was NLA on turner and ECS and FCP and all over et. al as well. The stock Febi and Meyle ones are both offshored now, though the genuine 33311130537 (standard type I think vs the Gr. N) appear to still be made in Germany if ECS's CS is to be believed, but $150 for stock-stock rather than N is a hard pill to swallow. If there were ones made in like India or Turkey or Romania or something I'd just fill those and send it but there don't seem to be anymore.

[Panici]

I went from a fresh set of OEM rubber bushings to Revshift 80A Polyurethane Differential, Subframe, Trailing Arm Bushings.
Those were the softest Poly bushings that I could find.

Made the change to control wheel hop while keeping soft spring rates on a 24v swap turbo car.

They definitely met the goal of reducing wheel hop, however I did notice the NVH increase.


If I had left the 24v swap naturally aspirated making less power I would have stuck with the rubber bushings.
But at 300+ WHP I was going to break something with how the tires were shaking in first gear.

[Maybe Magpie]

I went from a fresh set of OEM rubber bushings to Revshift 80A Polyurethane Differential, Subframe, Trailing Arm Bushings.
Those were the softest Poly bushings that I could find.

Made the change to control wheel hop while keeping soft spring rates on a 24v swap turbo car.

They definitely met the goal of reducing wheel hop, however I did notice the NVH increase.


If I had left the 24v swap naturally aspirated making less power I would have stuck with the rubber bushings.
But at 300+ WHP I was going to break something with how the tires were shaking in first gear.

That's good info, thank you. I'm not going to be making that kind of power with an NA M20 bar a five-figure build that isn't on my dance card or in my wallet I think, so I suspect gritting my teeth and shelling out for the Gr. N ones from Schmeidmann might be my best bet even if the cost is ludicrous for what they are. Unfortunately none of the companies that sell poly bushings seem to be willing to sell the metal sleeves the bolts go through by themselves and machine shops want like $800 for all the ones I'd need, otherwise I'd just cast the bastards in 60-70A rubber.

[digger]

That's good info, thank you. I'm not going to be making that kind of power with an NA M20 bar a five-figure build that isn't on my dance card or in my wallet I think, so I suspect gritting my teeth and shelling out for the Gr. N ones from Schmeidmann might be my best bet even if the cost is ludicrous for what they are. Unfortunately none of the companies that sell poly bushings seem to be willing to sell the metal sleeves the bolts go through by themselves and machine shops want like $800 for all the ones I'd need, otherwise I'd just cast the bastards in 60-70A rubber.

you could get a set of the pins/sleeves made for sub $200 with one of the CNC places like Xometry Et al i would think based on what i have gotten made.

[Panici]

You're talking about Group N subframe bushings?

What about just stock rubber bushings and fill the voids up. I seem to recall some threads on here with that discussion.


Regarding front CAB (lollypop) I went with solid rubber E30 M3 offset bushings.

[digger]

You're talking about Group N subframe bushings?

What about just stock rubber bushings and fill the voids up. I seem to recall some threads on here with that discussion.

Ref post 4. i have done this (currently in the car for many years) with some Shore A 70 which is similar hardness to the typically OEM rubber bushes. Hard to say how much difference it makes as wouldnt entertain a A-B test with both parts new its too much of a pita.

At one pint all the rage with the UK guys was to use 2 x curved PVC plastic strips (cut sliced from large tube thick wall tube) the length of the bush and hammer them into the gaps (plastic was the right curvature and thickness to suit the cavity) once the bush was installed into the SF

[Maybe Magpie]

you could get a set of the pins/sleeves made for sub $200 with one of the CNC places like Xometry Et al i would think based on what i have gotten made.

Do tell. I've tried to contact damn near every company that sells the poly kind to get just the metal hardware and they more or less told me to fuck myself in more polite terms, even if I was a repeat customer. I do have some .stl files, but not blueprints, and I know .stls are more for prints than machining work. I talked to a machine shop and they wanted north of $800 (their "get lost" rate, I think).

You're talking about Group N subframe bushings?

What about just stock rubber bushings and fill the voids up. I seem to recall some threads on here with that discussion.


Regarding front CAB (lollypop) I went with solid rubber E30 M3 offset bushings.

I considered that, but I'm picky about parts quality with the decline in QC for everything. If Febi or Meyle or Corteco still made that particular part in the EU (or at least Malaysia, India, Turkey, Taiwan, Mexico, etc) I'd just do that and send it, but it's either cheap crap made in the PRC or the genuine OE ones made in Germany The OE ones are like $130 - and at that point, the Schmeidmann remaining Gr. N ones are only 17 bucks more a pop. If the OE standard ones were like, $70-80 I'd probably get those instead, but $130+ for stock ones is madness.

Up front also went with the offset M3 ones, albeit E36M — I believe those are a slightly stiffer compound but are dimensionally pretty much the same and were significantly cheaper, though still made in Europe. That plus fresh IS front sway bushings, IS shim/spacer doohickies, IS bump stops, fresh tower bushings/shock mounts, adjustable M3 konis from TCK, M3 endlink conversion, E24 motor mounts. An aside but point worth mentioning on the front shock mounts, for now Febi 12431 is still made in Germany and is only 1/4 (approx) the cost of Genuine.

HOWEVER, good news: I've discovered a vendor who does sell unthreaded sleeves in M12x30, M12x70, and M14x100 sizes (Technicalyl I think 120 would be the more correct length but they don't have that and I think either would work). I called and left a message to ask for pricing as they're special-order, I'll report back on what the quote for 4x 12x70 (RTABs), 1x 12x30 (diff), and 2x M14x100 (rear subframe) tallies up to. If it's reasonable I'll probably get them and try my hand at casting, if it's a little steep but a run of them would make it cheaper I might give a run of the things a try if we anyone'd be interested in a group buy, or if anyone'd want me to sell 'em their own set of cast 60 or 70A solid rubber RSBs turnkey. As mentioned Alumilite makes a good castable rubber urethane in those durometers. If I do go down this route I'll use myself and my own car as the guinea pig.

All that said if it's more trouble than it's worth I might just have to go for the damn Gr. Ns.

[digger]

Do tell. I've tried to contact damn near every company that sells the poly kind to get just the metal hardware and they more or less told me to fuck myself in more polite terms, even if I was a repeat customer. I do have some .stl files, but not blueprints, and I know .stls are more for prints than machining work. I talked to a machine shop and they wanted north of $800 (their "get lost" rate, I think).



I considered that, but I'm picky about parts quality with the decline in QC for everything. If Febi or Meyle or Corteco still made that particular part in the EU (or at least Malaysia, India, Turkey, Taiwan, Mexico, etc) I'd just do that and send it, but it's either cheap crap made in the PRC or the genuine OE ones made in Germany The OE ones are like $130 - and at that point, the Schmeidmann remaining Gr. N ones are only 17 bucks more a pop. If the OE standard ones were like, $70-80 I'd probably get those instead, but $130+ for stock ones is madness.

Up front also went with the offset M3 ones, albeit E36M — I believe those are a slightly stiffer compound but are dimensionally pretty much the same and were significantly cheaper, though still made in Europe. That plus fresh IS front sway bushings, IS shim/spacer doohickies, IS bump stops, fresh tower bushings/shock mounts, adjustable M3 konis from TCK, M3 endlink conversion, E24 motor mounts. An aside but point worth mentioning on the front shock mounts, for now Febi 12431 is still made in Germany and is only 1/4 (approx) the cost of Genuine.

HOWEVER, good news: I've discovered a vendor who does sell unthreaded sleeves in M12x30, M12x70, and M14x100 sizes (Technicalyl I think 120 would be the more correct length but they don't have that and I think either would work). I called and left a message to ask for pricing as they're special-order, I'll report back on what the quote for 4x 12x70 (RTABs), 1x 12x30 (diff), and 2x M14x100 (rear subframe) tallies up to. If it's reasonable I'll probably get them and try my hand at casting, if it's a little steep but a run of them would make it cheaper I might give a run of the things a try if we anyone'd be interested in a group buy, or if anyone'd want me to sell 'em their own set of cast 60 or 70A solid rubber RSBs turnkey. As mentioned Alumilite makes a good castable rubber urethane in those durometers. If I do go down this route I'll use myself and my own car as the guinea pig.

All that said if it's more trouble than it's worth I might just have to go for the damn Gr. Ns.

you upload a 3D model of what you want, choose material, tolerances and finish plus if it is complex do a drawing. You usually get a quote straight away for simple things like this just a sleeve that has no special tolerances or requirements and you pay and it arrives a few weeks later.

otherwise buy the cheapest poly bush set and throw away the poly bushes

[Maybe Magpie]

Alright, update. I don't think I'll end up casting my own for reasons I'll explain later in the post, but for anyone who wants to try their hand at it in the future I'll share what I found out to save you some annoying-ass research down the line.

Several suppliers have told me to in effect go fuck myself if I want less than 5000 pieces of the sleeves of the exact sizes so that's something of a bust unless one of you has a lathe and is willing to play ball... sort of. Another thing I've discovered is that while McMaster doesn't have anything of the exact right size, they DO happen to have a few that require minimal modification or some install jank:

For the trailing arms, you'd probably be best served with x4 7811K179 (12x16x75mm), two per arm, one per bushing. They're about 5mm too long if I'm not mistaken. I dunno if they'd still clear the mounting stuff without being trimmed down like that or if you'd be in the clear. If they don't fit as-is and you can grind, saw off, or otherwise turn down the length to 68-70mmish, I think you'd be set? I think that's probably the best option as brass is friendly to rotation like RTAs do, especially if you lubricate the bolt when installing with some silicone grease too or something.

You could also get 92871A376 (12x19x35mm), four per arm, two per bushing. They're stainless instead of brass. This would likely hold up to wear better(?) but also doesn't have brass' lubricating properties and are obviously multi-part instead of one sleeve, and they have a larger OD so adjustment of the bushing ID would be needed as with the 14mm ones below.

For the RSBs, you could go with 4x 7811K26 14x20x22mm from McMaster. These being 4 different ones rather than continuous is non-ideal also but they work out to be the most cost effective option from them. You could also get 2x of the 7811K26s and 2x 7811K198 14x20x75 which gives you about the right length of 90-105mm if I'm not mistaken but the 7811K198s are 16ish bucks a pop as of writing, so you'd be paying about 20 bucks per side for the sleeves. There's also this listing on a powersports shop that might work for a 14x100 spacer sleeve. I dunno if it's quality, but that'd probably do it too? I've also discovered a lot of truck (as in semi tractor-trailer) shops do stock some pretty beefy sleeves in bronze and steel and by my napkin math for the RSBs a bushing that should theoretically work is one with a 9/16ths ID and a 4" OAL (or ~2" OAL and double the number of the suckers). Obviously imperial on a metric car is non-ideal, but... Eh. An option.

Worth noting: the McMaster 14mm ones have an OD of 20mm, and I'd wager the powersports one has an OD of 18 (could be 20 too though) and most of the bushing 3D CAD files I've found for DIY have an OD for the shaft pin thingy/ID for the bushing of 25mmish, so you'd want to modify those accordingly.

For the diff, you'd just need 92871A375 or similar (12x19x30mm). Same proviso applies to sleeve OD/bushing IDs.

In regards to me not casting them from scratch I did manage to get my mitts on a set of EU-mfg'd NOS rear subframe bushings and EU mfg'd RTABs, the former being McQuay-Norris germany-made that was the last set in the US so there's no supplier to share sadly, the latter was from Metzger in Turkey via Autodoc shipped to me from the EU by a friend. Apparently SIDEM makes theirs in Romania still but they didn't get back to me with confirmation before I ordered.The former were cheap enough and in excellent condition for me to not cry over not getting the real Gr. N ones.

So, with that said: Given the voids in the stock subframe and diff bushings, and the fact the Z3M diff bushing is $$$$ these days and additional NVH from poly, what do you all make of the idea of filling the voids in with a similar stiffness rubber to stock to emulate the Group N stuff? A little bit of extra stiffness and VH is tolerable if it's as minimal as just rubber-but-more if I'm imagining it correctly. For products I was considering Smooth-On's stuff, namely PMC-770, PMC-780, or Simpact-80 + anti-UV colorant they offer. I've had a hard time finding solid data on stock bushing durometer rating, and the few numbers I've found tend to contract each other. I've seen stock listed as anything from 55A to 70A and various stiffnesses in between. My gut tells me getting the stiffnesses as close to the rest of the stock part would help avoid separation and premature fatigue, does that track or am I overthinking it? Think I should go 60, 65, 70, or 80 given my prefs?