Subframe and Diff bushings....

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AndyBeech
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Subframe and Diff bushings....

Post by AndyBeech » Tue Aug 13, 2019 3:34 pm

So next job, replace the worn subframe bushes and I'm thinking at the same time the diff bushings.

Seems pretty clear to use poly bushings for the subframe, anyone have any experience in using Powerflex road (yellow) or black (track) bushings in this area? Seems to be different opinions on the matter but black appears to be a good option....doesn't sound like it increases NVH too much. Any real world opinions?

Also what would people recommended for Diff bushings as thinking may as well do these at the same time?

Cheers!
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bradz
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Subframe and Diff bushings....

Post by bradz » Tue Aug 13, 2019 4:54 pm

I went with Superpro Subframe bushes and Power-flex Front and rear bushes in Black no major difference in NVH to my Z4M

Strangely... I did the same on my e46 m3 and hated them as it increased the NVH massively!

On another note... I have a freshly powder coated sub frame with brand new bushes in if you are interested.
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GuidoK
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Subframe and Diff bushings....

Post by GuidoK » Tue Aug 13, 2019 5:36 pm

Personally I wouldn't use bushings stiffer than shore80A in the subframe (or anywhere else on places that directly touch the chassis, so that are subframebushings, front arb bushings and FCAB's).
To reduce the likelyhood of cracks in the metal of the chassis.
The stiffer the bushing, the higher the peak load/force is transduced to the chassis (and UK roads are full of bumps and potholes etc).
The rest of my suspensionbushings are shore90A. That combination does make the ride a bit more firm, but not by a huge deal (KW coilovers are more of a jump)
Z4 3.0i | ESS TS2+ | Quaife ATB LSD | Brembo/BMW performance BBK front/rear | Schrick FI cams | Schmiedmann headers+cats | fully polybushed | Vibra-technics engine mounts | H&R anti rollbars | KW V3 coilovers | Sachs Race Engineering clutch

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Subframe and Diff bushings....

Post by john-e89 » Tue Aug 13, 2019 5:51 pm

GuidoK wrote:
Tue Aug 13, 2019 5:36 pm
Personally I wouldn't use bushings stiffer than shore80A in the subframe (or anywhere else on places that directly touch the chassis, so that are subframebushings, front arb bushings and FCAB's).
To reduce the likelyhood of cracks in the metal of the chassis.
The stiffer the bushing, the higher the peak load/force is transduced to the chassis (and UK roads are full of bumps and potholes etc).
The rest of my suspensionbushings are shore90A. That combination does make the ride a bit more firm, but not by a huge deal (KW coilovers are more of a jump)
Can I just nip a quick question in...do you know the shore number for the M roady standard bushes please?
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AndyBeech
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Subframe and Diff bushings....

Post by AndyBeech » Tue Aug 13, 2019 8:27 pm

Interesting info, cheers chaps :thumbsup:

Get what you're saying about the subframe bushes Guido, seems like sound logic to me. Obvious varying opinions on this but then there always are! I did read that standard Powerflex bushes on the sub frame might not be much better than OEM and won't last long due to 'mushrooming' but I guess it all depends on the car and there's always going to be different experiences.

I was a bit confused about the Diff bushes and upgrading to Poly means you can't fit this 'magic bolt' that BMW now provide for the diff which is supposed to help / eliminate the M clonk when selecting gears. Might have to read up more on that though.
bradz wrote:
Tue Aug 13, 2019 4:54 pm
I went with Superpro Subframe bushes and Power-flex Front and rear bushes in Black no major difference in NVH to my Z4M

Strangely... I did the same on my e46 m3 and hated them as it increased the NVH massively!

On another note... I have a freshly powder coated sub frame with brand new bushes in if you are interested.
What you've said though Bradz makes sense, seems to be a lot of different experiences using the same parts between cars so what is fine for one person might not work for the next so I guess it's a bit of chance. Thanks for the offer on the subframe....how much are you thinking?
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Subframe and Diff bushings....

Post by GuidoK » Tue Aug 13, 2019 9:59 pm

john-e89 wrote:
Tue Aug 13, 2019 5:51 pm
Can I just nip a quick question in...do you know the shore number for the M roady standard bushes please?
I don't know.
AndyBeech wrote:
Tue Aug 13, 2019 8:27 pm
Interesting info, cheers chaps :thumbsup:

Get what you're saying about the subframe bushes Guido, seems like sound logic to me. Obvious varying opinions on this but then there always are! I did read that standard Powerflex bushes on the sub frame might not be much better than OEM and won't last long due to 'mushrooming' but I guess it all depends on the car and there's always going to be different experiences.
I don't know what you exactly mean by mushrooming, but if you mean what I think you do; thats impossible with polyurethane.
You can't change the shape of polyurethane once its set. (at least not without strong chemicals that dissolve polyurethane).
So it either tears and rips, or it stays in shape.
I have shore80A in there which was quite a bit stiffer than the stock bushings (when you handle them you get a feeling for that). Mind you, mines were normal z4, but I cant imagine that the z4m ones are harder than shore80A as that is already quite stiff, and they would be really quite a bit stiffer than the normal bushings.
Shore95A (so the powerflex black ones) is already that hard that it doesnt feel rubbery anymore and already goes in the direction of a soft plastic.
The yellow powerflex ones are shore70A, which is noticeable softer.
My bushings came from strongflex. I dont know what superflex uses, but they have an interesting 'quick guide' on shore hardnesses and their typical applications:

Guide to Hardness Selection
50, 60, 70 Shore - Typically subframe mountings, replacement of pu foam shock mounts etc. where low NVH is a priority and situations where compliance is desirable.
80, 88 Shore - Typically wishbone, radius rod, non coil over shock eye bushes
90 Shore - Typically leaf spring eyes or more heavily loaded wishbones & radius arms, trunnion bushes where replacing rubber
95 Shore - Typically intensely loaded coil over shock bushes, trunnion bushes where replacing nylon.

So in their eyes, shore80A is in general already above the desired stiffness of subframes.

I was a bit confused about the Diff bushes and upgrading to Poly means you can't fit this 'magic bolt' that BMW now provide for the diff which is supposed to help / eliminate the M clonk when selecting gears. Might have to read up more on that though.
Magic bolt? You have a pic? :? :)
Last edited by GuidoK on Tue Aug 13, 2019 10:20 pm, edited 2 times in total.
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Subframe and Diff bushings....

Post by john-e89 » Tue Aug 13, 2019 10:02 pm

GuidoK wrote:
Tue Aug 13, 2019 9:59 pm
john-e89 wrote:
Tue Aug 13, 2019 5:51 pm
Can I just nip a quick question in...do you know the shore number for the M roady standard bushes please?
I don't know.
No probs, difficult to know which aftermarket bushes to buy without the info but thanks anyway. :thumbsup:
Massey Ferguson 718 GTS....what were they thinking.....and yet I still bought one..... :oops:
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Subframe and Diff bushings....

Post by GuidoK » Tue Aug 13, 2019 10:19 pm

I also threw my old bushings away that came out of the car without measuring their hardness.
i have a shore hardness meter. but with bushings like how they come out of the subframe, measuring their hardness is difficult. Usually you have to cut them in half to try and find an area that is wide and deep enough to do a measurement.
With a polyurethane bushing thats no problem (arb bushings is easy too), and then that meter is pretty accurate (I come within 2 shore with both Powerflex and Strongflex given numbers), but the oem subframe bushings are 2 metal cylinders with not so much rubber in between. I have a spare subframe, maybe that has the oem bushings still in there. I might do that measurement once in the future to quench my curiosity
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Subframe and Diff bushings....

Post by john-e89 » Tue Aug 13, 2019 11:14 pm

Shame no one would agree to a group buy of OEM bushes all round to measure the shore readings, it’s pure guess work which aftermarket to fit without the OEM numbers.
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AndyBeech
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Subframe and Diff bushings....

Post by AndyBeech » Wed Aug 14, 2019 12:56 am

GuidoK wrote:
Tue Aug 13, 2019 9:59 pm
I was a bit confused about the Diff bushes and upgrading to Poly means you can't fit this 'magic bolt' that BMW now provide for the diff which is supposed to help / eliminate the M clonk when selecting gears. Might have to read up more on that though.
Magic bolt? You have a pic? :? :)
Just the kind of advice I was after! I'll have a look into Strongflex as well, hearing good things...

On the magic bolt, yeah not so magic, I think it's just an uprated bolt from BMW for the diff which supposedly helps with the diff clunk. The bolt supplied with the Powerflex diff bushes don't get rave reviews but again not sure on the technical evidence on that. Thread on it here, starts about page 2 / 3 but found the whole thread quite interesting:

https://forums.m3cutters.co.uk/threads/ ... 514/page-3

Can't really decipher the technical stuff but lots of different opinions on bushings for the diff / subframe.

Shore80 sounds like could be a good compromise for the subframe. Maybe powerflex yellows are a bit too soft...
Not sure on the diff though at the moment, 80 as well?
Oh the mushrooming thing was what someone else had mentioned, I guess they meant 'squashed' so one end goes flatter and wider but sounds like that's not technically possible, so yeah not sure on that one.
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Subframe and Diff bushings....

Post by GuidoK » Wed Aug 14, 2019 1:43 am

you mean the bolt in this post?:
https://forums.m3cutters.co.uk/threads/ ... st-2261624
M14 front diff carrier hexbolt edit no, these are also the rear bolts, so M12 but apparantly the hex head fits without problem?

Or these ones?
https://forums.m3cutters.co.uk/threads/ ... st-2261473

M12 rear carrier torx bolts

That first one is an upgrade (or at least a variation) on the stock bolt.
The stock bolt, and for sure the all threaded bolt shown in the 2nd link is a weaker bolt, as the threads run the complete lenght of the shaft.
Threading makes the core thinner. The stock bolt with partly unthreaded shaft is stronger, but the shaft isnt as thick as it could be.
Grade is 10.9
That first bolt (in the pic in the first link) is a DIN931 style bolt. If its the same 10.9 grade its much much stronger (think 30-60% depending on thickness and thread) as a completely threaded bolt. This is because the part of the shaft that isnt threaded is the full thickness of the size of the bolt (so ~12mm with an m12 bolt)

I made a similar upgrade, not because of a clunk but because I broke my rear diffbolt..... (the normal z4 has one long 14cm m14 bolt at the back and 2 smaller ones at the front). So the other way around compared to the z4m
This is a comparison between bolts that I made back then:
Image

All bolts shown are 10.9
My original bolt broke at the point between the central rear bushing and where the diff sits against that bushing. Thats the point where it flexes and shears if force is put on the diff.
The bolt goes all the way through the bushing and through a lug in the diff cover and is held on with a nut on the other side

The lowest one you see in the pic above is the bolt of the stock Z4. It is threaded all the way
The middle bolt is from a 550i. This is basically the same boltstamping but they threaded it only for a part.
This is stronger because wherever you roll threads, you make the core of the bolt thinner by about half the thread depth (~half the thread rolls in and pushes half the thread out, if that makes sense).

The upper one is the din931 style bolt. Its shaft, the unthreaded part, is just as thick as the top of the threads, so about 1,5mm thicker than the 550i bolt and about 3mm thicker than the original bolt (the thread pich is 1,5 and thats roughly the height of the threads.
If you translate that into crosssection of the core, where the oem (full threaded) bolt is 47,5 mm², the DIN931 bolt is 77mm² (the outer mm take up the most area, and thus give the most strenght). If core area equals strenght in a linear way for the shear forces, the din931 bolt would be 62% stronger.
So thats quite an upgrade.

With the stock z4 the Din931 bolt fits fine with the powerflex bushing I use. It fits through the core. The bushing comes with a large ring (that sits between the bushing and diff) and I had to drill that a little bit bigger, just 0,5mm or so not a lot (or file with a round file)

But how things line up with the z4m with z4m powerflex or strongflex bushings, I don't know. But switching to din931 bolts will significantly make for a stronger construction all togheter. IF thats really necessary or not, I dont know. It was on my tuned car.

I've got shore80a also for the diff bushings. I wanted to minimize the risk of whine and still wanted a bushing that has a long lifecycle as on the normal z4 that rear bushging a known failure point as that bushing is a hydrobushing, and my car puts almost 60% more force on that than stock.
I don't really know what the benefit would be for a stiffer bushing; I don't have the feeling that the drivetrain feels sloppy, the jolts through the diff are I think not as strong as jolts coming from the suspension as that puts the car's weight into it. That doesnt happen with the diff.
But I dont think stiffer bushings might damage things or something. Its held in the subframe.
Z4 3.0i | ESS TS2+ | Quaife ATB LSD | Brembo/BMW performance BBK front/rear | Schrick FI cams | Schmiedmann headers+cats | fully polybushed | Vibra-technics engine mounts | H&R anti rollbars | KW V3 coilovers | Sachs Race Engineering clutch

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