F8X M3/M4 CF Drive shaft mod

[Epsilon]

Also have the YFCM DS and had to remove the front diff bolt and loosen the rears. I didn't have to lower the subframe though. I really wanted to avoid loosening the diff, but I just couldn't get that extra 2 to 3 mm to slip into the front diff flange.

On a side note, the weight savings of the YFCM DS is where it shines, IMO. As Slavic mentioned above, shifts are "more direct and the clunk is a lot less noticeable". There is also faint whirl sound at high speeds over 100+ mph like an electric motor. lol

[slavik1988]

Drop the diff entirely? Or just remove the front bolt to allow movement of the front of the diff?

I had to remove the front bolt and loosen the rears as well as lower the whole rear subframe.

[bimmerfan08]

I run a YFCM carbon driveshaft. I did a before drive in the mountains and then directly after the install. The shifts definitely feel more direct and the clunk is a lot less noticeable. No increase in NVH whatsoever. Installing a 1-piece driveshaft is a PITA. Had to drop the rear differential to get it in.

Drop the diff entirely? Or just remove the front bolt to allow movement of the front of the diff?

[heinzboehmer]

If you have a driveshaft out I can ultrasonically measure thickness without cutting anything

Hmm, doesn't tlow98 have an extra one?

[slavik1988]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

I run a YFCM carbon driveshaft. I did a before drive in the mountains and then directly after the install. The shifts definitely feel more direct and the clunk is a lot less noticeable. No increase in NVH whatsoever. Installing a 1-piece driveshaft is a PITA. Had to drop the rear differential to get it in.

[Bry5on]

Ooh that cutaway picture is great. Can estimate wall thickness pretty well with that. Now we just need someone to cut open a stock driveshaft and measure the wall thickness at all its different diameters

If you have a driveshaft out I can ultrasonically measure thickness without cutting anything

[heinzboehmer]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

Ooh that cutaway picture is great. Can estimate wall thickness pretty well with that. Now we just need someone to cut open a stock driveshaft and measure the wall thickness at all its different diameters

[Bry5on]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

Clever, I wonder what adhesive is used that’s able to be removed. That might also be useful on our driveshaft and half shaft CV splines..

[meowth]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

[heinzboehmer]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

Yeah those things definitely make this mod appealing. But still waiting on radii measurements to see if there will be any actual inertial reduction

[Bry5on]

I'll add to.

Just thinking out loud here, but any adverse side effects to the rest of the drivetrain? I.e., increasing the stiffness of the driveshaft potentially impacts XYZ because...

What about NVH? Increase, decrease, or no change?

*Should* be a reduction in harshness on abrupt throttle changes and shifting. Vibration will increase if the balance wasn’t good, and it is a bit harder to balance the longer shaft, although the stiffer/lighter carbon helps mitigate this. Otherwise, I’d estimate no noticeable impact to NVH.

[bimmerfan08]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

I'll add to.

Just thinking out loud here, but any adverse side effects to the rest of the drivetrain? I.e., increasing the stiffness of the driveshaft potentially impacts XYZ because...

What about NVH? Increase, decrease, or no change?

[Bry5on]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

[Obioban]

its a nice advantage (and it is true for this piece).

i only wanted to draw attention to the weight figures and warn people not getting overexpectations with this piece, cause i'm sure most people expect weight reduction due to the "aerospace material" usage .

my own opinion, that for looking as an upgrade for this piece, i'd prefer to get 6-6.5 kg weight over 8.5kg standard. in this case, it could named as an upgrade (i would be happy with less than 6kg weight, but okay, i'm realistic ). and i'd think twice to do this mod, if weight loss will be up to 1kg.

My recollection from Altaran‘a post was that the e46m and f8x shafts where pretty similar weights stock, but, once you put the lighter e46 flanges on the cf shaft, the weight difference was a couple lbs. Not the case?

[0-60motorsports]

its a nice advantage (and it is true for this piece).

i only wanted to draw attention to the weight figures and warn people not getting overexpectations with this piece, cause i'm sure most people expect weight reduction due to the "aerospace material" usage .

my own opinion, that for looking as an upgrade for this piece, i'd prefer to get 6-6.5 kg weight over 8.5kg standard. in this case, it could named as an upgrade (i would be happy with less than 6kg weight, but okay, i'm realistic ). and i'd think twice to do this mod, if weight loss will be up to 1kg.

Yes, Agreed. Thanks for posting what you already did a year back. Shame the RX8 CF DS did not work out.