J-Fiber Carbon Fiber driveshaft.

[peter de la mare]

Does anyone run of these on a DCT car with 3.62 final drive?

I’m having a complete nightmare with mine, it vibrates badly over 130mph. I’ve even returned it to Taiwan for them to rebalance it and it’s made zero difference. (This took nearly 4 months)

The problem appears to be that they are only able to spin at 6,400rpm before vibrating, and on a DCT track car with 3.62 final drive, then it’s going to be spinning over 6,400rpm often. The images below are a screenshot showing the 6,400rpm limit, and the spreadsheet is a MPH/rev calculation based on my car’s spec. The DCT 7th gear is 1:1 so the driveshaft will equal the crank speed.

It’s interesting that the car starts shaking itself to bits over 130mph and that correlates pretty much exactly to 6,400rpm.

Swapping back to the OE driveshaft fixes the issue.

[Redd]

Does the driveshaft get rid of the rubber giubo? If it does, it will vibrate. All the one piece shafts that remove the giubo have vibration problems.

YCW/MFactory shafts are balanced to 9k rpms and retain the giubo. Mine has been perfect to redline for many many miles.

[GORDON.M3]

I have mine on a stock final drive, no issues. Solid.

[tdott]

Originally Posted by GORDON.M3

I have mine on a stock final drive, no issues. Solid.

Have you ever taken your car to 130MPH (209kph)?

[wyatth]

^ Wouldn’t redline in a lower gear be a fair test? You can get the same shaft speed at a lower mph in a lower gear. It'd just go by faster, but I think you’d still know if it was prone to vibrating or not.

[e92zero]

Originally Posted by wyatth

^ Wouldn’t redline in a lower gear be a fair test? You can get the same shaft speed at a lower mph in a lower gear. It'd just go by faster, but I think you’d still know if it was prone to vibrating or not.

Not true. Drive shaft is directly locked to the wheel speed by the final drive. Lower mph won't give you the same test. Had my MFactory one and took it to 120, all good here as well.

[Redd]

Correct. Driveshaft rpm is directly proportional to mph, not engine rpm.

[e92zero]

Quite honestly, I think from that advertisement and chart spec from them. They are just overloading you with pointless data. Which leads me to believe they are just junk. You don't need to worry about the final drive to determine the drive shaft speed requirement. DCT gear box has the tallest 7th gear ratio at 1.000. Mate that to our engine 8400 rpm that mean the max rpm the drive shaft will experience is 8400 rpm (or whatever your engine redline is at top speed). If they can only balance their shaft to 6400 rpm, that's not going to play nicely with your car. I believe the MFactory one is balanced to over 10k rpm. Good luck and hope you find a solution.

[roastbeef]

sounds like junk. take it off before it starts wearing on other parts.

[peter de la mare]

Originally Posted by Redd

Does the driveshaft get rid of the rubber giubo? If it does, it will vibrate. All the one piece shafts that remove the giubo have vibration problems.

YCW/MFactory shafts are balanced to 9k rpms and retain the giubo. Mine has been perfect to redline for many many miles.

Standard giubo/flex disc is used.

Maybe it’s the solid diff mounts causing the issue.

[peter de la mare]

I’ve been offered a refund, which I’m going to accept.

This J-Fiber shaft is allegedly the same as the previous MFactory one, as Agemate/J-Fiber supplied the shafts.

[roastbeef]

Originally Posted by peter de la mare

Standard giubo/flex disc is used.

Maybe it’s the solid diff mounts causing the issue.

its not the solid mounts. i have solid sub/diff mounts and the mfactory shaft and i don't have any issues at any rpm and i've probably been up to about 135mph.

Originally Posted by peter de la mare

I’ve been offered a refund, which I’m going to accept.

This J-Fiber shaft is allegedly the same as the previous MFactory one, as Agemate/J-Fiber supplied the shafts.

now that i think about it, it might be the shaft they produced for mfactory and then ripped off the design... i'm not sure if they were that company or not.

[pbonsalb]

I have done 150, 6 speed, but mine is the older jfiber offlabel version of the MFactory (identical). It may be that after their split up, jfiber has different equipment or different staff and that is the problem. MFactory went on the offensive about a year ago and made allegations along those lines but you would have to dig up the threads to find the details.

Sometimes just removing the rear bolts and rotating the shaft 180 and then reinstalling the bolts can make a difference. Driveshaft Shop recommends trying this fir its shafts. And BMW made balance bolts for the diff input that one could experiment with.

[peter de la mare]

Originally Posted by roastbeef

its not the solid mounts. i have solid sub/diff mounts and the mfactory shaft and i don't have any issues at any rpm and i've probably been up to about 135mph

What final drive ratio do you have?

[roastbeef]

Originally Posted by peter de la mare

What final drive ratio do you have?

Oem DCT

[peter de la mare]

Originally Posted by roastbeef

Oem DCT

Your driveshaft wouldn’t have been spinning as high as 6,400 at 135mph with 3.154 final drive.

[roastbeef]

Originally Posted by peter de la mare

Your driveshaft wouldn’t have been spinning as high as 6,400 at 135mph with 3.154 final drive.

I wouldn't be in 7th gear if that makes a difference.

[Redd]

Originally Posted by peter de la mare

I’ve been offered a refund, which I’m going to accept.

This J-Fiber shaft is allegedly the same as the previous MFactory one, as Agemate/J-Fiber supplied the shafts.

Ah that explains it. J-Fiber may have supplied the CF shafts but YCW made the flanges and they claimed that was where the complexity was. If tolerances on the flanges were off, the shaft would vibrate. As part of their business arrangement, J-Fiber would supply CF shafts to YCW, and YCW supplied a batch of flanges to J-Fiber. So the early batch of J-Fiber driveshafts were identical to Gen1 MFactory driveshafts.

After their falling out, your new one probably no longer has the YCW flanges and that's why it vibrates.

[peter de la mare]

Originally Posted by roastbeef

I wouldn't be in 7th gear if that makes a difference.

It doesn’t, 135mph in any gear (only 5th upwards actually as it’s not possible below) your driveshaft will be spinning around 5,750, or thereabouts.

[peter de la mare]

Originally Posted by Redd

Ah that explains it. J-Fiber may have supplied the CF shafts but YCW made the flanges and they claimed that was where the complexity was. If tolerances on the flanges were off, the shaft would vibrate. As part of their business arrangement, J-Fiber would supply CF shafts to YCW, and YCW supplied a batch of flanges to J-Fiber. So the early batch of J-Fiber driveshafts were identical to Gen1 MFactory driveshafts.

After their falling out, your new one probably no longer has the YCW flanges and that's why it vibrates.

Thanks for this.

This driveshaft was part of the group buy held last year on M3Forum. I recall there were roughly 25 in the group, they’ll all have this issue. I suspect that the vast majority will never spin it over 6,400, but I can’t believe I’m the only one who is.

[Lienrocs]

Originally Posted by peter de la mare

It doesn’t, 135mph in any gear your driveshaft will be spinning around 5,750, or thereabouts.

I've taken my Mfactory carbon drive shaft over 130 with zero issues. I haven't found a single downside to that mod. Solid subframe and purple diff bushings as well.

[wyatth]

I stand corrected above! But something isn’t clicking for me conceptually, lol.