Michaelc said:
Rob,
My apologies if you have been asked this question before (perhaps many times!) but is there no option available for the E39 M5 of a standard sized but uprated clutch i.e. one that does not require a new flywheel?
The fundamental problem with the shortened lifespan of the M5 clutch is specifically tied to the basic clutch characteristics, thes two critical factors being 1) size, and 2) clutch/SAC design.
Size is size. You can't put a bigger clutch disc within the same pressure plate, and you cannot attach a larger pressure plate to the OE flywheel. Even with uprated material, the size is a factor because of too-small maximum clamping force of the pressure plate - the grabbiest material in the world is of little use if the pressure plate cannot adequately hold it between the high-torque motor and the high-mass chassis.
Clutch/SAC design is what I discussed previously. The only "conventional" direct-fit replacement is the Sachs Racing clutch that is designed for use on M3 racecars. It's still not a great solution because you have to modify your original flywheel, machine off an inner lip. With all the labor charges, plus the risk of getting shavings in the dual-mass mechanism, plus the fact that the dual-mass flywheels themselves are only rated for 3 clutch cycles (and usually die during the second or third anyway), that option loses it's attraction. So besides the modification difficulty, short flywheel lifespan, costs of modification labor and the almost $1K racing clutch, you even have one other issue - greatly increased pedal effort.
Failing that, are there flywheels available that do not cause the horrid chatter at idle?
Strictly looking at chatter (gear rattle -
read more by clicking here) as an issue, any solid disk/solid hub clutch will be pretty noisy. Distinctions between brands are insignificant, the condition of the particular car's transmission is more of a factor.
But discarding all of those basic setups, there are only two options that do anything to significantly address the gear rattle.
One is the recent Dinan flywheel that is a modified/lightened BMW dual-mass unit. That retains the mechanism which cushings the power-pulse variations that cause the noise. It works well, but still uses the small OE clutch and retains all of the problems. Additionally, as the dual mass mechanism has a finite life, it is not rated for more than three clutch replacement cycles and will be discarded as part of normal maintenance procedure.
The other option is the sprung-hub clutch disk that UUC uses in the V12 clutch conversion, a design that has the torsional damper built into the clutch instead of the flywheel. This is the basic design of the large V12 clutch has the sprung-hub center as standard... the V12 850 CSi (same weight, power, and same-family gearbox as the M5) used a solid flywheel and this clutch. While there still may be a small amount of residual rattle, it will be dramatically less than a standard lightweight flywheel setup installed in the same car. The upside to this design is that the flywheel itself is a lifetime part, no mechanism to break (surface may need replacing about every 6 clutch replacements, but that's a $100 part). With every clutch replacement, the torsional damper mechanism is refreshed as it is built into the clutch.
- Rob
