XP Clutchmasters DSG lightweight flywheel hub failure: did my DL501 xmsn malfunction?

[volvofan]

Cross-posting here as I know lots of folks have added more power to their S6s and S7s than my RS5 will ever make (I'm cool w/ that... can't get enough of that N/A V8 sound at 8,700 RPM), and put GOBS more torque through this same gearbox.

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2013 RS5 with plenty of mods but no forced induction. Bought stock in 2020 with 25k miles, now at almost 60k. In 2022, the flexplate cracked, so we dropped the motor, replaced flexplate AND flywheel with heavy duty Clutchmasters versions, plus did ECS Luft Technik intake, Kline SS catless headers & Inconel exhaust w/ high-flow cats, and JHM lightweight crank pulley. ECM and TCM custom tuned accordingly, she makes 520 HP and ~375 Ft-lbs of torque at the crank on 93 octane.

The car is never tracked and never launched, though she does receive "Italian tune-ups" on a fairly regular basis.

All was running trouble-free since then until a couple months ago. I was cruising on the highway (NOT high-RPM, full-throttle conditions) and lost all gears, with the dash lit up like a Christmas tree. Coasted to side of the road and had the car towed. Engine would not rev past idle and VCDS chucked a bunch of codes, including something about shift forks out of position. I was hoping that maybe it was caused by low fluid level (I suspected a leak in my transmission cooler line as I had been noticing some drips on the driveway a few weeks prior) and that I could simply top things up and she'd be fine, but when I got her up on jackstands and dropped the under trays, I was met with chunks of metal coming out of the inspection hole. No bueno!

Fast forward to this past month as I've been dropping the transmission in a buddy's garage (with a proper lift)... finally got it out today and it's pretty clear why it wouldn't go into gear. The hub of the Clutchmasters flywheel is completely shattered. This was literally the FIRST production one they released, so maybe they hadn't worked all the bugs out of it, but this thing is supposedly pretty well built and should withstand much higher HP/TQ... they're running the same or a similar one in Stage 2 S6s and S7s, after all. So, the question is... is the busted flywheel the disease, or merely a symptom? I don't want to go through all the trouble of replacing it only to have this happen again a few weeks or months down the road. Anyone have any experience with this aftermarket part and/or pushing the DL501 to its limits?

Thanks for any insight you can provide.

-Jon

[Botbasher]

There's a actual mechanical clutch in a DL501 DSG?!?!

Someone 'splain this to me, please!!!

KS

EDIT: I couldn't wait and had to find the answer... so this is a replacement for the standard Dual Mass Flywheel... with a clutch?!? So is it like a mechanical "safety" that slips when you send it a little too hard?

Learn something new everyday!!

Cheers,

KS

[volvofan]

There's a actual mechanical clutch in a DL501 DSG?!?!

Someone 'splain this to me, please!!!

KS

EDIT: I couldn't wait and had to find the answer... so this is a replacement for the standard Dual Mass Flywheel... with a clutch?!? So is it like a mechanical "safety" that slips when you send it a little too hard?

Learn something new everyday!!

Cheers,

KS

KS-

Yes, this unit replaces the OEM dual-mass flywheel. As opposed to ultra-lightweight single-piece versions, this one has a center hub that engages the transmission's input shaft. That hub, in turn, is rotated by the part of the flywheel that bolts to the flexplate on the back of the engine. In between the inner hub and the outer flywheel are the series of springs you see. The radial layout of the springs *LOOKS" very much like a clutch that would be found bolted to a manual transmission. However, there are no friction plates and there is no slippage. The springs only serve to take up a little of the "jolt" from shifts and RPM changes.

It all works together quite well... until it doesn't ;)

-Jon

[Avantly]

Is the manufacturer going to want this back for failure analysis? If not I think you should carefully take it apart and index the location of each piece, and look at the failure surfaces. Of particular interest to me is at about the 5 o'clock position in your second pic, where the upside down U-shaped part of the ring that the springs stop against has cracked on both sides. I wonder if any of the original failure surface is intact or if it has fretted together so much that the original failure is concealed. Find clean (undamaged by sliding/fretting) surfaces and take a very good look at the surfaces of pieces that cracked apart. That U shaped part sure looks like brittle failure and possibly a strong indicator of the origin of the failure. If that ring cracked in those same two spots all the way around I'd suspect you are looking at a brittle-type fatigue failure caused by a material selection issue for that ring.

[dspl1236]

Looks like a spring or the spring hub broke then sheared free in red. Kinda looks like the splined hub that holds the springs failed. Right where the bolts go through to hold it together in yellow. Material fatigue failure. Reminds me of a clutch pressure plate failure.

[volvofan]

Is the manufacturer going to want this back for failure analysis? If not I think you should carefully take it apart and index the location of each piece, and look at the failure surfaces. Of particular interest to me is at about the 5 o'clock position in your second pic, where the upside down U-shaped part of the ring that the springs stop against has cracked on both sides. I wonder if any of the original failure surface is intact or if it has fretted together so much that the original failure is concealed. Find clean (undamaged by sliding/fretting) surfaces and take a very good look at the surfaces of pieces that cracked apart. That U shaped part sure looks like brittle failure and possibly a strong indicator of the origin of the failure. If that ring cracked in those same two spots all the way around I'd suspect you are looking at a brittle-type fatigue failure caused by a material selection issue for that ring.

Thank you, Avantly and dspl1236 for your insight! I'm a mech engineer, too, so am doing post-mortem on the failure as best I can. The engine was idled for some time after the failure, so it's going to be tough to tell what let go originally vs. what was subsequently damaged by shrapnel. Could have been a spring, or the retaining hub. I have not yet had a reply to my inquiry from Clutchmasters.

What I'm more concerned about is figuring out whether this was the disease or just a symptom thereof. Was the rest of the transmission happy as a clam, and this part just decided to let go? Or did the transmission skip a shift or hang up a gear, suddenly putting counter-torque on the input shaft and this was the weakest link? Either presents its own challenges. If it was the flywheel that was the origin of the failure, then what should I replace it with that's even heavier duty than this was supposed to be? If it was something internal to the transmission, then what was it? I believe I may have a pinhole leak in my cooler... could low fluid level have caused something to bind up, and if so, is there internal damage I'll also have to deal with? If that was the root cause (low fluid level) then I suppose I may have gotten off easy, as the internal "guts" may have been spared.

My planned next steps are to drop the mechatronic unit and actuate the shift forks manually, then turn the input shaft and see how the output shafts react. I welcome any other additional insights or proposed troubleshooting steps / failure mode analysis suggestions.

-Jon