• Clutch Masters Twin Disk Series FX850 **FULL REVIEW/DIY**

      Yet another well done review and DIY by Former_Boosted_IS, this time of the Clutch Masters FX850:

      Quote Originally Posted by Former_Boosted_IS View Post
      Many of you know that my clutch began slip badly about a month ago while I was on the dyno putting down about 525 rwhp. At the time, I was not able to finish a clean pull on the dyno to really find the full power that my car can put to the ground. It was a little disappointing, but I knew the stock clutch was not going to handle much over 425 - 450 rwtq. This led me into a search for a number of drive train / shifter upgrades. In this series of reviews, I have reviewed the UUC Short Shift Kit / DSSR, Quaife LSD, and now the clutch kit is the final item reviewed.

      When I began looking for a clutch, just like the rest of you I saw a lot of clutch companies offering a whole lot of products. There are some clutch companies that I was able to eliminate quickly because of their poor reputation over such a wide range of platforms. I began to narrow down the choices and kept coming back to Clutch Masters. Honestly, it is hard to find a single person that has ever had a bad experience with Clutch Masters. Their reputation is beyond stellar whether you ask the clutch users or the companies that install them. I asked a lot of people I trust, and everyone single one said Clutch Masters makes superb clutches. On top of this, their lineup is extensive! They have 8 stages of clutches! Stage 1 through Stage 5 are all single disc clutches and stage 6 through stage 8 are twin disc clutch kits. Any of these clutches can be made with a sprung hub or unsprung hub/rigid disk. Finally, all the Clutch Masters pressure plates have modified fulcrum points allowing stronger pressure plates with less pedal pressure than their competitors. This is an important point to note. Clutch Masters calls this their Hi-Leverage technique. Clutch Masters is the only company I know of to use this process and they describe it best.

      The bottom line is this means Clutch Masters can use high power pressure plates without requiring a power lifter to drive the car. If all else is equal, Clutch Masters should require less pedal pressure than the competition on the same lb. pressure plate.

      1. Stage 1 - FX100 - Full Face Organic Clutch – 450 ft/lbs
      2. Stage 2 - FX200 - Full Face Kevlar Clutch
      3. Stage 3 - FX300 - Full Face Segmented Kevlar Clutch – 510 ft/lbs
      4. Stage 4 - FX400 - 6 Puck Style Ceramic Clutch with Sprung Hub – 575 ft/lbs
      5. Stage 5 - FX500 - 4 or 6 Puck Style Ceramic Clutch with Unsprung Hub
      6. Stage 6 - FX600 - N/A for 135/335
      7. Stage 7 - FX700 - N/A for 1/35335
      8. Stage 8 - FX850 - Full Face 8.5" Twin Disc Clutches w/ Light Weight Flywheel - 675 ft/lbs to 975 ft/lbs

      Depending on your choice of material and pressure plate on the twin discs, you can get holding capacity up to 1200 rwtq.

      I had some decisions to make. How much power would I want it to hold? What increase in pedal pressure could I accept? Do I want to keep the stock flywheel or upgrade to a lightweight billet aluminum flywheel? What level of chatter is acceptable to me? I know I want to make big horsepower, so there would be some compromises I would have to accept, but the question was how much? I quickly realized at bare minimum I need a 6 puck style clutch with ceramic material and on the other end of the spectrum would be a twin disc clutch. What would be the advantage/disadvantage of each?

      Single Disc Clutch Setups

      • Less expensive
      • Can be used with the stock flywheel or light weight flywheel
      • High horsepower applications can result in high pedal pressure
      • High horsepower applications can be very "on/off" like a switch

      Twin Disc Clutch Setups

      • More expensive
      • Comes in a kit with a light weight flywheel
      • High horsepower applications can be easily slipped
      • High horsepower applications are very drivable without the "on/off" feeling
      • Very, very customizable to meet your particular needs
      • Fully rebuildable at a very minimal cost saving tons down the road

      The twin disc offered an incredible mix of high torque/horsepower grip while still maintaining tame drivability. The twin discs can be slipped and traditionally will not lead to a jerky driving experience. The only question I had was how much noise would the single mass billet aluminum light weight flywheel make? The stock flywheel is a dual mass flywheel that is very good at keeping things quiet, but it is also very heavy. Some of the main characteristics of a light weight flywheel are:

      • Less rotational mass allowing your rpms to rise faster equaling a faster car.
      • Requires more rpm to take off smoothly.
      • MUCH easier to rev match.
      • Fully rebuildable for pretty cheap.
      • Susceptible to chatter.

      I felt the upsides were enough and I could accept some chatter, so I decided to get the Clutch Masters Twin Disc FX850. The FX850 comes with the following:

      - Two Clutch Discs (you choose the material)
      - Machined Billet Aluminum Pressure Plate with Pressure Plate Bolts
      - Mid Plate
      - Single Mass Light Weight Billet Aluminum Flywheel machined from 6061-T6 Aluminum
      - Flywheel Bolts
      - Throwout Bearing and Release Lever (normally $75 from dealer!)
      - Splined Clutch Alignment Tool

      I ordered from Luis at Clutch Masters and that launches us into the review.

      Experience With Clutch Masters

      I have to say ordering from Clutch Masters was an absolute pleasure! Luis is tremendously knowledgeable on his products whether it is clutch material, flywheel info, torque capacity, etc. When you order a Clutch Masters Twin Disc FX850, you speak with a tech (Luis is also a tech) so they can make sure the Twin Disk meets you exact needs. The Twin Discs have three styles:

      • 850 – “Full Street”– 675 ft/lbs - 2 fiber tuff discs, one sprung and one rigid disc.
      • 850 – “Street and Race”– 775 ft/lbs - 1 sprung ceramic disc and 1 fiber tuff rigid disc.
      • 850 – “Race” – 925 ft/lbs - 1 ceramic sprung disc and 1 ceramic rigid disc.

      The double fiber discs will be very drivable and tame where the double ceramic are the aggressive big power holding clutches. I told Luis I would like to hold from 800 - 900 rwtq while still maintaining drivability. I didn't mind about 50% increase in pedal pressure. Luis suggested Segmented Kevlar Disc / Ceramic Disc material and that is the route I went. I really wanted to get this installed quickly, so I asked if Clutch Masters could get this to me quickly. Not only did they overnight the clutch to me, but Luis personally called me when the package arrived to make sure I got it and that I was happy with what I saw. Clutch Masters is really a very professional, customer satisfaction oriented organization.

      The package came to me very well prepared and protected assuring the items arrived damage free during the shipping process.

      The Twin Disc Assembly was in one multi-tier box and the hardware/alignment tool in another.

      Here you can see the release lever, throw-out bearing, clutch alignment tool, and flywheel bolts. All are wrapped and well protected.

      This box actually gave me chills. This is the Twin Disc FX850 kit!

      Everything was wrapped and protected well.

      After removing the wrap, you see the Clutch Masters Twin Disc FX850 for the first time. It is so good looking that I almost wanted to put it on my coffee table to show everyone... then decided no.

      The angle shot shows the top pressure plate, ceramic disc, mid plate, segmented kevlar disc, and on the bottom the 6061-T6 billet aluminum flywheel.

      The pressure plate removed from the assembly.

      With the pressure plate removed you get your first look at the full face 8.5" ceramic disc with sprung hub. This also helps you understand how a twin disc assembly works.

      This is the face of the 8.5" ceramic disc with sprung hub.

      Full face segmented kevlar disc with unsprung hub.

      Finally the 6061-T6 billet aluminum flywheel.

      The quality of all of these items is off the charts. Clutch Masters has a reputation of building the best for a reason. Luis even left me his email and told me he would check it Saturday so he could answer any questions I had. I couldn't have had a better ordering and shipping experience period.


      This is just some information about the way I installed this clutch kit and in no way instructions. You choose to do all work on your car at your own risk and accept all responsibility.

      The first question is... "Can I DIY this project?" This is not a job you can do on jack stands or jacks period. This is not a job any novice wants to attempt. This is not a job that should be attempted without TIS info or a Bentley Service Manual. 95% of all people should not even attempt to do this work on their own. If this is your first clutch, then pay someone to do the work!!!

      It is rare that I will suggest a shop doing the work, but in this case it is not for the novice at all. I will give you some ideas on what to suggest your shop look out for and give you an idea of what the installation takes. I will avoid some details because again, I don't want to imply this is for anyone other than a very good wrench turner.

      I decided I was going to do the install myself with a friend. The install requires some special BMW tools and I wanted to cover that a bit. Since you will replace the pressure plate, a lot of the special tools are not needed. Clutch Masters provides a splined centering tool so you don't need the BMW version and to be honest the BMW version is sub par as it is not splined. BMW has a special tool to secure the flywheel in place, but a slip wrench can be used just as easily or you can secure the teeth of the flywheel to prevent it from moving with two people. The only special tool you must have is the 52mm wrench for removing the driveshaft from the rear differential. Fortunately, AR Design makes a spectacular 52 mm thin wrench for removing the driveshaft from the rear differential for about $50 and it is superb quality like everything AR Design makes.

      This install begins like the install for the Quaife Differential. Obviously you are going to need to raise the car up on a lift for this job. The first thing to do is remove underbody panels, exhaust, and heat shields covering the driveshaft.

      This will expose the drive shaft fully. The job really begins when you remove the driveshaft. Make sure you suspend it by wire to protect the universal joint. You can see how I did that in this picture.

      Make sure to mark the driveshaft/flex disk or flex disk/output shaft of tranny with paint to insure correct orientation upon reassembly. Remove the bolts. I chose to remove the flex disk from the output shaft on the transmission.

      Next, brace the rear section of the driveshaft with a wire. Grab your AR Design 52 mm wrench to remove the insert nut by turning the bolt clockwise direction. Do not use the bihexagonal nut for bracing!

      Now the driveshaft should be loose from the differential at the rear and the front. At this point, remove the bolts for the center universal joint while the second person holds it on place. Make sure you are clear on both sides and remove it out of the car taking care not to bend the driveshaft at the universal joint. The universal joint is highlighted below.

      Now you will need to remove the shifter assembly and linkage. For more info on how to remove the shift assembly and linkage, please see my UUC SSK / DSSR review/DIY. Here is the linkage.

      Once it is removed, it will look like this.

      Now you are ready to drop the transmission and I am going to be vague purposely because I don't want to encourage people to do this themselves. First, you will remove all wiring from the transmission like the reverse sensor, remove all brackets, and remove the slave cylinder. At this point you will want to support the transmission with a transmission jack. With the transmission supported, you can unbolt the rear mounting bracket on the transmission. There are numerous torx head bolts around the transmission that must be removed. 5 are large T-12 torx aluminum flex bolts that must be replaced. Most are easy, but two on the top of the bell housing are very difficult to get to. You jack up the front of the engine to access these from under the car. You need two hands, one to guide the wrench onto the bolts and one to remove them. Slide the transmission toward the rear of the car once it is fully unbolted and it should slide right out. That will expose the stock pressure plate, clutch, and dual mass flywheel.

      The pressure plate holds the stock clutch in place, so you will simply unbolt the pressure plate taking care to have your second set of hands hold it in place while you unbolt it. The stock dual mass flywheel is held on by 8 torx bolts and they need to be removed to free the flywheel. Use two sets of hands here again, one to unbolt and one to hold the flywheel in place. The stock flywheel is nothing less than a beast. It weighs nearly 38 lbs!!! For reference, the entire Clutch Masters Twin Disk FX850 weighs under 34 lbs for everything! Once the pressure plate, clutch, and flywheel are removed it will look like this... exposing the crank.

      This is where you will begin bolting up the new single mass Clutch Masters 6061-T6 Light Weight Flywheel. The kit includes bolts or you can purchase new BMW torx bolts. Follow correct procedures in the installation of the flywheel. Here it is bolted up. Note the Clutch Masters splined alignment tool on the flywheel.

      Now you will slide the segmented kevlar disc on making sure the discs are placed on with the correct side facing the flywheel.

      Follow the same procedure to insert the mid plate, then ceramic disc paying close attention to assure the correct orientation for the flywheel side of the clutch. The splined alignment tool is critical for the Twin Disc FX850 so you can assure both clutches are aligned properly or you will never get the input shaft into the disks. At this point leave the alignment tool in place. Finally you will place the pressure plate over the assembly and slowly torque to spec using the correct alternating tightening order. The only sad part of this whole thing is that such a beautiful assembly will be covered up by the transmission.

      Once everything is successfully tightened to spec, you can remove the alignment tool.

      From here you will move over to the transmission itself. The Clutch Masters kit is very much a complete kit so there is no reason to buy a BMW release lever / throw-out bearing because your new kit comes with it. You will note the correct orientation of the stock release lever / TOB, un-latch the spring, and remove it. Install the new Clutch Masters release lever / throw-out bearing in the identical way you removed the stock unit. Note the correct orientation of the nipple so the slave cylinder will line up properly. Below you can see the stock release lever / throw-out bearing versus the Clutch Masters unit correctly installed.

      It is time to get that transmission back up there. You will use your transmission jack to line the transmission up and both guys will get things oriented so you can slide the input shaft on the transmission through the clutch discs into the flywheel. Clutch Masters suggest no oil whatsoever on the input shaft when sliding it back into the clutch and flywheel. I couldn't get it to slide in after working on it for 2 hours, so I applied a very thin coat of oil to the input shaft and it slid in with no effort. Bolt up everything in proper order and according to torque spec. Replace all bolts BMW suggests replacing. Replace all braces, wiring, and bolt up the rear support brace of the transmission. Finally, using caution reinstall the slave cylinder making sure the tip will hit the dimple on the release lever. Now it is onto reassembling the shifter assembly and linkage.

      Reinstall the driveshaft replacing all bolts BMW suggests and correctly support the universal joint at all times. Torque to spec. Install all heat shields and belly plates then the job is done.

      I know this is a bit vague for me, but I just want to insure those that are not qualified will not attempt this. Anyone that wants more info, please PM me and I will be happy to answer questions.

      The installation is about 6 hours of work if you have done this before. The tricks are raising the front of the engine to access top bolts on the transmission bell housing, using the splined alignment tool from Clutch Masters, and care.


      I want to be very detailed here because I know there will be a lot of curiosity about the entire post install experience. I put 8 hours of driving experience in all conditions from stop and go traffic, to highway driving, to full out WOT runs and will try to describe the Clutch Master Twin Disc FX850's performance/noise in each. Specifically I will cover:

      • The break-in process
      • Pedal pressure
      • Gear noise/flywheel chatter
      • The effect on drivability from the light weight flywheel
      • Gripping power under WOT
      • Overall clutch feel

      Break-in Process

      When you install a new clutch, every company suggests a break-in period. Clutch Masters said 200-300 miles should suffice, but if you can get close to 500 miles then that is preferred. The break-in miles should not be getting on the highway and driving away. You need to driving city where there is a lot of shifting involved. I varied RPMS almost the entire process and never exceeded 4000 rpms.

      The first time you start the car, you will notice some flywheel chatter. This is actually pretty common with billet aluminum light weight flywheels and most will tell you it gets better as the clutch breaks in. I can verify this is definitely the case. You will feel considerably more pedal pressure the first time you drive the car and I think most of that is because of the soft, squishy feel of the stock clutch. I would estimate it is about 40-50% more than stock pedal pressure. After 1 day driving it, you will have no problems at all. During the break-in process you will likely have quite a bit of engagement chatter (where the car shakes a little in first when you are releasing the clutch). It gets much better as the break-in process is completed. Finally you will need to learn how to take off from a stop with a 10 lb lighter flywheel. If you rev to 2000 rpms, then the take off is quite easy.

      Once the break-in process is done, you can drive the car as you please and I did. Let's get into what the real day to day experience is like with the Clutch Masters FX850.

      Pedal Pressure

      After the initial realization that the pedal pressure is more than stock, you will get used to this. I drove the car in stop and go traffic for an hour to see if it would be a problem and honestly it wasn't a problem at all. Some clutches are so stiff that you leg hurts, but with the FX850 being so physically large and the Clutch Master Hi-Leverage pressure plates they can minimize the increase pedal pressure and still get grip. It is not as easy as driving stock, but this is by no means a calf buster. I was very pleased here the more I drove the car.

      While driving the car on spirited runs, the increased pressure is fantastic because it helps you engage the clutch nicely through all gears. This in particular is a real benefit during spirited driving. I am tremendously pleased here.

      Gear Noise/Flywheel Chatter

      Flywheel chatter is basically the ticking sound that can be heard when replacing dual mass steel flywheels with billet aluminum single mass flywheels. You have to understand the stock dual mass flywheel was not created for performance reasons, but to dampen sound from the engine pulses. It does a great job at keeping things quiet, but in my opinion hurts the performance of the car a ton. Chatter can be quite loud or very subtle.

      This was the true grey area for me in this entire process. I had no clue what to expect at all and I was actually a bit nervous. Luis at Clutch Masters is very confident in the flywheel building process and their ability to minimize clutch chatter as much as is humanly possible. That helped a little, but I knew the testing process is the only thing that would reveal the true results.

      Let's start with idle and the clutch disengaged or pedal out. Is there flywheel chatter? Yes. Is it noticeable if you are standing next to the car? Yes. Now, how loud is it? This was the important part for me. I don't mind the slight chatter, but I didn't want it to be annoying in the cabin of the car with windows open or closed. The chatter cannot be heard in my car with the windows open or closed unless the car is in the garage. It is simply impossible to hear under those conditions.

      When the clutch is engaged or the pedal is pressed in there is no noise whatsoever.

      When driving the car, you can hear the chatter only from 2000 rpms to 3000 rpms under hard load. It sounds like a hollow sound coming from the transmission. For me is not annoying, but you can hear it lightly with the windows open or closed in those rpms under high load. I suspect the reason has to do with the harmonics of the engine pulses in those rpms, but I cannot say 100%. Above 3000 rpms, the car purrs and sounds just the same as it would stock.

      Effect of Light Weight Flywheel on Drivability

      I was shocked here. I didn't really know how losing about 10 lbs and going from a dual mass flywheel to a single mass flywheel would affect the drivability of the car. To say the single mass lighter flywheel drives better would be an enormous understatement. You can now easily rev match the car without always fighting to find the right RPM. Downshifting is now silky smooth and so much easier to rev match. It seemed I always had a buck shifting on the higher gears no matter how hard I tried to rev match, but with the Clutch Masters Light Weight Flywheel the buck is totally gone. When you are shifting through the gears, it is now very easy to smoothly street drive through the gears without the slight buck I always felt on the stock clutch no matter how hard I tried to make it smooth. So overall the shifting is night and day better.

      The rpms also rev faster now. It is hard to quantify, but I will when I dyno again soon. Losing about 10 lbs of rotational mass from the flywheel makes the car much more nimble and agile. The gas pedal is much more responsive. The car is not as resistant to changes in inertia and what I mean by that is the quick stabs of the throttle. The car really is ready to go on a dime and the response is instaneous. This is a huge improvement! Simply put, the throttle is now connected better to the cars response.

      I am convinced the stock dual mass flywheel is good for only one thing and that is noise suppression. If you ever get a chance to look at the stock flywheel, it is like to flywheels connected. They can float with respect to each other by about 15 - 20 degrees it appears. The means you have a slack that has to be picked up every time you change acceleration. Second, it is like 38 lbs so it is tremendously heavy and resistant to change in acceleration. I personally think the car is much better without it.

      Gripping Power

      What can I say here other than when you drop the clutch the tires turn. It is as simple as that. The version of the Clutch Masters FX850 I have will hold about 900 rwtq. The engagement is just beautiful. I am putting around 525 rwhp through it and it hasn't even flinched. The pull out of each gear shift is now spectacular.

      Overall Experience

      I tested highway driving, soft acceleration, stop and go traffic, WOT straight line acceleration, and twisty road driving. The increase pedal pressure is only a negative in stop and go traffic. That's it and it is not bad. There is engagement chatter when you take off from a stand still and it does take a little more skill here to smoothly take off. Once you get used to the higher rpm take off, then you really minimize the engagement chatter significantly. In soft acceleration, you can now shift the car smoother and with less effort to rev matching each shift. In highway driving, you can shift into 6th easily and without the little buck I always used to feel. In WOT straight line acceleration, the car is an animal now. The pedal pops up fast and you get into gear faster. The pedal grabs in almost the exact same location as stock. There is an engagement area on the pedal too just like stock rather than the "on/off" feel you get with some high horsepower clutc kits. Simply put you can get through your gears more efficiently and faster. Finally, in the twisty roads, you can move up or down through the gears beautifully. With curvy roads, you do a lot of up shifting and down shifting which is one of the real areas the flywheel shines. I absolutely love the windy road experience now banging through the gears.


      I have no illusions that light weight flywheels are for everyone. There are some BMW owners that want a silent car as top priority and for those I will say the chatter is not for you. Those that don't mind a louder exhaust will not mind the chatter of the flywheel either. There is still minor engagement chatter with the Clutch Masters Twin Disc FX850 when taking off from a stand still, but it has gotten better with every mile I put on the car. It is not something that I find embarrassing or bothersome even with a passenger. You may stall the car a few times when learning, but once you understand the launching, then you will minimize any unwanted effects.

      The upsides of the Clutch Masters Twin Disc FX850 are off the chart. The one point to note is the pedal pressure is increased about 50% over stock from what I estimate and something you get used to fast. The lighter flywheel makes the driving experience far superior to the stock dual mass flywheel in my opinion. The gear shifting is now crisp and precise. The up shifting and downshifting has improved enormously. The rev matching has become so much easier as well. The FX850 will hold a boat load of torque and it grabs when you need it to. The Clutch Master Twin Disc FX850 offers a a setup that can handle high horsepower withput the negative "on/off" feel you get with most high horsepower clutches.

      Clutch Masters has a very wide range of products that should be able to meet anyone's needs. Clutch Master's Hi-Leverage pressure plates allow them to have ultimate clamping force without the "calf buster" pedal pressure many other companies suffer from. Their customer service is second to none, even to the point that they called me after the installation to make sure my experience was positive. The packaging was superior, the communication superior, their shipping fast, and their build quality is superb.

      Armed with all the information I have now, I would select the same product if I could do this again. This is such an important part of the car and I am really happy it worked out so well.

      If you want more information on Clutch Masters check out

      This article was originally published in forum thread: Clutch Masters Twin Disk Series FX850 **FULL REVIEW/DIY** started by Sticky View original post