CM725 Twin Disk Issues

[Dahgz]

A couple months ago my 2012 135i (typical bolt on, mhd 2+) suddenly started making gearbox chatter and began having issues shifting.

In gear while driving the noises weren't really present, but when trying to shift it was as if you weren't pressing the clutch, just kinda not going into gear unless I revved it a bit. This happened very suddenly while hopping on the freeway from getting lunch 15 mins from work, and by the time I got back to the shop it practically wouldn't go into gear at all. Combined with noises at idle with the clutch in or out, I parked the car figuring it was time for a clutch and expecting dual mass flywheel failure. This later turned out to be the case it would seem, as the flywheel was welded stuck.

Unfortunately I was/am in a bit of a pickle financially after some unexpected bills and follies. Purchasing a new dmf or smf and clutch kit was/is just not feasible for the time being.

I checked Facebook marketplace every few days keeping my eye out for something new or somehow lightly used. Ended up finding a Clutch Masters 725 in seemingly great shape that was removed shortly after installation because the owner didn't like the feel of the clutch.

03075-TD7S-A appears to be the CM part number.

At a crazy low price considering their 1800 dollar price tag new, I figured f it, I'll run it for a few months knowing I don't need it and won't like it, then replace it with a smf setup.

I used a new fork and throw out bearing installed on the low setting. Threw in a brass pin, some new 80a poly trans mounts, poly rear Shifter mount, dssr and Teflon shift pin bushings that I had laying around waiting for the car to be in the air. I have 80a poly engine mounts waiting to go in too but did not install them during this process bc tired lol.

The clutch works. But holy hell, is it worse than I thought. I've driven twin disk setups before, I knew they kinda suck and to expect noise and vibration, but it feels like something is wrong.

No noise at idle with the clutch pushed in at all. Expected chatter with clutch out at idle and it's pretty loud. Engagement is as I would expect a small twin disk feels, sudden and towards the top of the pedal. Chatter doesn't really change if I raise idle rpm to like 1k, changes a bit at like 1150 but by 1250 comes back. It also sounds like something is grinding while accelerating, unless doing so very lightly.

The chatter basically doesn't go away either while in gear and accelerating. 2nd gear accel vibrations are pretty bad, a rotational bump almost. Csb was in good shape but the heat shield might be against it or something. While cruising in 4th, 5th, or 6th, anything other than very light throttle produces the grinding sound. It...goes though.

I also rode in a buddies n54 e90 last night that has a cm850 and none of this seemed to be a thing except the normal idle chatter, harsh engagement etc.

Should I have put the throwout on the high setting? Is something wrong with the twin disk? Is this partly because I didn't do the poly engine mounts at the same time as the poly trans mounts? Is my gearbox dying? Am I crazy and all of this is normal? Lmao.

Either way, I'm definitely going back to a single disk smf setup, but I need to make it another month or two if I can.

Any input here would be great. Going to get some videos in the morning showing the sounds its making.

[PRTSB1M]

Originally Posted by Dahgz

I used a new fork and throw out bearing installed on the low setting. Threw in a brass pin, some new 80a poly trans mounts, poly rear Shifter mount, dssr and Teflon shift pin bushings that I had laying around waiting for the car to be in the air. I have 80a poly engine mounts waiting to go in too but did not install them during this process bc tired lol.

Should I have put the throwout on the high setting? Is something wrong with the twin disk? Is this partly because I didn't do the poly engine mounts at the same time as the poly trans mounts? Is my gearbox dying? Am I crazy and all of this is normal? Lmao.

I haven't experienced this personally, but read posts on here stating that adding stiffer trans mounts with stock engine mounts can cause issues. It sounds like you took every bit of NVH dampening out of the drivetrain at the transmission. Video with sound might help; if it isn't spitting out metal or smoke there's a chance it's fine. Can you be more elaborate about what "feels wrong?"

I can personally attest that adding the poly rear shifter bushing with stiffer front shifter bushings results in what sounds like a shaft constantly rubbing against a heat-shield while in gear and moving (although this is very faint w/stock clutch and selector rod). Adjusting idle is typically only for NVH from stiffer engine mounts, so raising the idle likely wouldn't reduce your issue.

[xrockoutx]

Originally Posted by PRTSB1M

I haven't experienced this personally, but read posts on here stating that adding stiffer trans mounts with stock engine mounts can cause issues.

I had Condor trans mounts on 2 different cars (both stock motor mounts)...and they only lasted a week. The vibrations were way too intense and annoying...never could get used to it. Not saying that's the issue here.

[ErvGotti]

It's the poly trans mounts, I had polys on mine when I upgraded to SMFW and 550i clutch, and it was exactly how you described with the noise, People thought my car was broken. I have switched to solid rubber instead and it's once again a daily drivable.

[AshwinLB]

I say trans mounts too. Get Rogue Engineering solid rubber bushings