Track-only car. Differential bushings. Poly/delrin/solid?

[GewoW]

Hey guys

I have solid subframe bushings to be installed shortly. Wondering if there are any strong opinions re: type of bushing for diff.

From my understanding, the main benefit comes from a solid subframe bushing. And you would want to have a somewhat solid diff bushing to prevent the added flex. But would a completely solid bushing offer that much benefit considering a higher risk of damage to diff bearings and half-shaft?

Any opinions appreciated!

[Bartledoo]

As someone who broke a diff bolt with solid subframe mounts and poly diff bushings, I vote solid. User error though. I burn out of the pits to warm my tires up, which involved some wheel hop.

[tlrid3r]

I have solid subframe mount and poly diff power flex street bushing. The subframe was a bigger improvement. Feels solid on acceleration but on track tires I can still get some hop on hard acceleration leaving the pits. I do get a ton off diff whine as well.

For me if I was to do again, because it didn't solve the hop. I would either stay stock or fully solid. I feel the halfway approach on the diff is a waste of time.

[Vybz]

To resolve the wheel hop you need to upgrade the diff bushings, otherwise as Bartledoo you'll still snap diff bolts and you'll still have wheel hop.
Either full solid or a mix of solid and delrin, and you'll never deal with differential headaches again. I have Turner MS solid/delrin bushings and haven't had an issue since installing them.

If it's a dedicated track car, there's no reason to not fully upgrade.

[GewoW]

Yeah I already have solid bushings diff and subframe bushings going in this summer, but some bigtime euro m3 guys are telling me go delrin or poly and not solid! So now I'm on the fence on if I should install them or buy delrin instead! 😭😭

[slowdown_dan]

Originally Posted by GewoW

Yeah I already have solid bushings diff and subframe bushings going in this summer, but some bigtime euro m3 guys are telling me go delrin or poly and not solid! So now I'm on the fence on if I should install them or buy delrin instead! 😭😭

Delrin is solid

[rhyary]

This explains:

https://garagistic.zendesk.com/hc/en...inum-Bushings-

..

This material is excellent for track-oriented or dedicated track vehicles as it does still offer some vibration absorption over solid aluminum while still being extremely rigid. Unlike polyurethane, Delrin does not have the ability to deform slightly and return to its' original shape. If your vehicle is likely to see impacts frequently (drifters) this material may not be the best for you.
..

[//steve\\]

I have the following solid bushings from Alekshop. The rear end just feels so direct and I've never experienced any wheel hop issues. The car either spins the tires a little or it just goes.

http://alekshop.com/products/aleksho...ngs_bmw_e9x_m3
http://alekshop.com/products/aleksho...ngs_bmw_e9x_m3

[tsk94]

Solid aluminum or delrin for a track only car.

[GewoW]

Originally Posted by butte2butte

Delrin is solid

Yes excellent point i mistyped that. I have aluminum. As yes, delrin is solid. Plastic, not metal, but solid.

So i guess my thought process is if i should sell my aluminum and replace with delrin to have a little bit of vibration absorption and hopefully maximize the lifespan of my internal diff components. Or just stick with the aluminum and use the $$ for an extra track day 😂

[Bartledoo]

Originally Posted by GewoW

Yes excellent point i mistyped that. I have aluminum. As yes, delrin is solid. Plastic, not metal, but solid.

So i guess my thought process is if i should sell my aluminum and replace with delrin to have a little bit of vibration absorption and hopefully maximize the lifespan of my internal diff components. Or just stick with the aluminum and use the $$ for an extra track day 😂

I wouldn't worry about the aluminum messing up your diff. You'll want an upgraded diff in the near future anyways haha.

[derbo]

What about a dual-duty car? I have solid BW mounts ready to install, but haven't really decided on Poly (which durometer).

AKG sells a 75D, and 95A



PowerFlex

Stock Replacement - Choose Powerflex Street (Yellow: 70A or Purple: 80A) for stock replacement to maintain ride quality while improving tire life.

Street Performance - Choose Powerflex Street to maintain ride quality or choose Powerflex Race for ultimate performance.

Race (Black: 95A) - Choose Powerflex Race for ultimate performance, autocross, time trials, rally, and road racing.

[Vybz]

Even for a dual duty car, I'd still go with the stiffest material that you can tolerate, just for piece of mind. Wheel hop absolutely sucks, and the only way to be completely rid of it is by going solid. I know that 95a still has the potential to break differential bolts (I've seen it first hand), so if I was doing a dual purpose car, it would be 75d or above, but that's just me.

I don't mind diff whine or howl, and my car is a dedicated track car, BUT just remembering what it was like when I had OEM bushings, I'd never want to deal with that ever again.

GewoW you won't damage your diff internals with solid bushings. Solid bushings completely isolate the movement of the diff. The additional vibration being transferred to the diff will have no effect on your internals, assuming it was assembled & torqued correctly.

[M43S7RO]

Read a comment of Luke Customs on IG where he points out what is mentioned in the OP, does not recommend solid diff bushings because of increased diff bearing wear and additional wear on the half shafts. I have never read of anyone bringing this up when the topic of diff bushings comes up in the past.

Here is the discussion:

[//steve\\]

^ I saw that too and found it quite interesting. The diffs on these cars do seem quite robust though.

I know on the S2000 absolutely no one ever recommended solid even on full track cars due to the extra strain on the diff but that diff was also a pretty puny unit. That also said, I've seen some camera footage specifically showing diff movement with OE like rubber and these things move around/flex a lot more than you'd think.

I think the stress will be a little worse on 6MT cars than DCT but aside from the NVH for any kind of daily/normal driving isn't going to increase wear IMO.

[GewoW]

Originally Posted by M43S7RO

Read a comment of Luke Customs on IG where he points out what is mentioned in the OP, does not recommend solid diff bushings because of increased diff bearing wear and additional wear on the half shafts. I have never read of anyone bringing this up when the topic of diff bushings comes up in the past.

Here is the discussion:

Originally Posted by //steve\\

^ I saw that too and found it quite interesting. The diffs on these cars do seem quite robust though.

I know on the S2000 absolutely no one ever recommended solid even on full track cars due to the extra strain on the diff but that diff was also a pretty puny unit. That also said, I've seen some camera footage specifically showing diff movement with OE like rubber and these things move around/flex a lot more than you'd think.

I think the stress will be a little worse on 6MT cars than DCT but aside from the NVH for any kind of daily/normal driving isn't going to increase wear IMO.

You found it! 😂
Now you see my dilemma.

I think I'm going to install my aluminum ones.
Then when I upgrade the diff, I will get delrin, or stick with aluminum if there's no signs of damage

[roastbeef]

i'd argue the judder from wheel hop is more damaging than a hard load on the driveline.

[tsk94]

Originally Posted by roastbeef

i'd argue the judder from wheel hop is more damaging than a hard load on the driveline.

Agreed.

Until someone provides a proper explanation of why solid diff bushings could cause extra wear to components I'm going to say that comment is 'nonsense'. I've commonly heard the opposite over the years - soft or worn bushings cause wear due to extra twisting and flex under load. Never heard this about solid diff bushing until this thread.

[rhyary]

I am replacing my purple with this.
I already have solid subframe and the purple is 3 years old (90 trackdays)

https://www.turnermotorsport.com/p-1...e82-1m-e9x-m3/

[roastbeef]

Originally Posted by tsk94

Agreed.

Until someone provides a proper explanation of why solid diff bushings could cause extra wear to components I'm going to say that comment is 'nonsense'. I've commonly heard the opposite over the years - soft or worn bushings cause wear due to extra twisting and flex under load. Never heard this about solid diff bushing until this thread.

right. i'm just not buying it. in the offroading world, our axles and cv joints handle extreme torque and load. people mostly break axles and driveline when they are "hopping." in rock crawling, hopping is the same as the judder we experience in these cars with soft or compromised bushings- the sudden grab of grip, and the sudden release of grip in rapid succession. this is usually followed by a loud snap.

on the trail, i always preach to "wheeling with the gears." its ok to use throttle, but once you start hopping, shut it down. its very rare to gain traction from hopping and it is very common to break when hopping. actually having grip and putting the [enormous] torque through the driveline is definitely not as bad as repeated shock weight.

just a weird parallel i thought of when i evaluated this decision for myself.

[derbo]

Food for thought,

AKG mentions this on their page

Remember: The material used for the diff mount bushing location(s) must match the material used for the subframe bushings.

[Vybz]

Originally Posted by roastbeef

i'd argue the judder from wheel hop is more damaging than a hard load on the driveline.

Facts! 100%

Not to mention, the platform has been tracked & raced for almost 13 years now. I haven't heard of a single diff failure due to solid bushings... not even one.