This is the 2nd time we run into this problem but finally fix it, QM came up with a heavier flywheel (650usd)for the v drive 7.25 clutch although is not available yet, it supposed to fix the excessive harmonics that the light weight flywheel generated causing to bust 4th gear syncro and in worse scenario broken syncro hubs.

So we decided to do the fix in-house by adding a 3.75kg machined steel ring to the original QM flywheel, the final weigh was 6.89kg ,re-calibrating the clutch assembly and finally balance it.

We have run this for the street for a few weeks now and have gotten not a single issue and the harmonics we could detect at around 2000-3500rpms diminished by good 80%.
Today we took the clutch apart and transmission to check and is just good as new, I know MAP was suffering form this issue with the same clutch on their 2.4L build Evo , Since we are running John stage 2 transmission he recommended to switch to a OS giken clutch but everything looks like it wont be needed.

 

So does every 7.25 qm clutch have this problem? I have one but have yet to install. Good info. Thanks..

 

Curious about the 8 leg clutch now that there is a heavier fly wheel offered for this cluth.

I know I get some decel noise about 3k.

 

hmmm... i run the 8 leg gear drive street... and i had no idea of this issue... anyone heard of it effecting these?

do you guys have barking engagement? mine yelps like a dog getting beaten to death. or at least as terrible as i imagine that sounds...

 

Yes I've had that (noise) with both the old Qm and now the new one.

 

its embarrassing when i go to shows or meets and people look at me like i ran over a puppy as i take off... anyway to make it go away?

when i'm just driving for me i dont mind it cause i know what the clutch is and capable of and i'd rather bark then slip when my turbo kicks in

 

Mine will only bark on 1st gear take off, reversing or if I down shift and dont get the rev match just right.

 

The barking is not a problem , but have any of you experienced a busted syncro yet? or maybe this is an isolated issue with 2.4L engines and quarter masters clucth

 

Are you running a lightweight pulley in place of the crank damper?

 

i get that too. I thought it was my transfer case.

 

No synchro issues yet... But my car might have 1000 miles on the build and i quick shift up and rev match down so that might be help that a bit. I do have an insane amount of chatter on decel which ive attributed to 90durameter bushings and race mustache bar until now. If my walbro 400 hadnt failed on me the other day id post a video for advice on it

 

The 3k rpm resonance is fairly common from what I've read. I'd be interested knowing if the ring will be for sale anytime? I don't mind driving my QM on the weekends but it gets annoying after a bit.

 

gctech, glad to see your post on this. I run carbonetic twin which has bad harmonics passing through. I was planning on adding weight to flywheel next time tranny comes down. I was considered welding a ring to backside but small diameter closer to crank. I dont want to slow the quick rev too much. I bet your clutch is far easier to take off now? how do you quantify 80% harmonics gone? did you get that much reduction of decell noise?

as side note I built my tilton carbon/carbon twin for my dsm with a heavy flywheel. weight of fly was 18.5 pounds (23.5 total weight) if I remember correctly. it has the least harmonics of any solid center clutch I have tried.

dont know why these manufactures are selling these setups with such light flywheels. 90% of them are street driven. heavier fly is a good thing for four cylinder. allows lower rpm launches, better gas mileage, less wear and tear, less harmonics smoother idle, etc etc

 

Seems like several of the twin and triples are still fairly heavy. The exedy is about as heavy as the stock clutch it seems?
The QM is intended specifically to be light and if you're buying it hoping it to be heavy, you bought the wrong clutch.

Still very curious about the crank damper though.

Mitsu doesn't do much to prevent vibrations from progressing from one end of the drivetrain to the other. Dual mass flywheels and driveline isolators seem to be used on lots of other cars. Of course, those parts don't hold up that well to abuse either though.

 

One quick observation...could this lighter clutch cause RPM hang? Since its mass is lower it would tend to kill the engine quicker when you let off the throttle, and the ecu couldnt compensate properly?