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FAQ: Kevlar vs. Ceramic Clutches

(Information, and Vendor Comment)

Q.<>: What are the thermal/physical characteristics of KEVLAR vs. CERAMIC clutches? ...technical details; wear, high-temp stability, glazing, holding power that each has over the other...?


A.<>: Kevlar stands up to heat well, supposedly better than standard organic clutch material. I think Kevlar has a lower coefficient of friction than standard organics, so can slip more with same pressure plate loading. I have used Kevlar clutch disc with same pressure plate on my 79 TA (10 second 3500 lb car with slicks) and found the Kevlar version slipped, so had to go back to regular organic disc.

Ceramic puck clutches have very high heat capability, high holding power, but have very harsh engagement characteristics; they usually won't slip on a normal street takeoff, but tend to grab/judder, so hard to take off gracefully. The on-off nature of ceramic type clutch makes it have a high instant shock load which imparts more stress to the driveline (transmission, transfer case etc.) so could break parts more than an organic or Kevlar unit which will smoothly slip while building up torque transfer until lockup.

RPS is hoping to utilize carbon fiber, which has very high heat stability, and "adjustable" friction coefficients, to build a clutch that allows higher holding power while still slipping smoothly like a regular organic--thus their "Carbon Claw" series, still in somewhat experimental phase on learning curve. The first RPS carbon clutches for our cars slipped for some people (not me) due to defect; they replaced disc for free--the replacement I got has carbon on one side, organic with metal weave on the other; I haven't yet had chance to try it.

At least RPS is doing some research into a better solution for us than saying "get the ceramic puck trans/xfer case destroyer, tough luck buddy", but the cost of this is some people having remove/replace costs for RPS...some have even gotten paid for R&R though. I doubt most other companies would do that! When I ran a Centerforce (with only mild mods) and it slipped within 5000 mostly winter miles, Centerforce Co told me to take a hike, no replacement or restitution at all...

I'd prefer an organic, unless a strong enough holding clutch was not available, then puck/ceramic is go-to choice.

There is supposedly an O S Giken clutch out of Japan that uses multiple discs (2 or 3?) with plates, like many circle track designs, to increase torque capacity. I think it may wear more quickly (more surfaces being worn away, a 7.5" triple disc on my TA wore super fast but that is an extreme example) and it costs ?$2000 or more? I have wondered if it were actually manufactured by Tilton or another USA manufacturer, but never searched out the info...
---Jack Tertadian

RPS Comments...<>: As far as we can tell, there are only a very few manufacturing plants in the world that make clutch friction material. There are 2 main manufacturers of Ceramic pucks, and 2 manufacturers of Kevlar pucks and facings. All of the rest of the manufacturers in the world produce organic materials; some with asbestos and most without. RPS is the only clutch company producing a carbon fiber friction material. We do not produce 'carbon carbon' like that used in Formula One. Carbon carbon is very different from carbon fiber, and many times more expensive. Our friction material has 12 different ingredients.

The advantage we have over any other clutch company (i.e. Centerforce, Hays, Ram, ACT, ClutchMasters, etc.), is since we actually manufacture the material ourselves, we can change its characteristics at will. That is a lot easier said than done, I can tell you, but at least we can make changes. We can also mold the material into any shape. A new product line we are looking into is Carbonite (our brand name for the carbon fiber material) pucks. This will allow us the flexibility to manufacture 3,4, and 6 puck discs in any size and with any spline.

Carbonite is very stable at high temperatures and has a very high coefficient of friction. The newest version of carbonite also shows very good wear characteristics. One of the main advantages is its light weight. Carbonite is lighter than factory materials and significantly lighter than both kevlar and ceramics. This is important because the transmission's synchros are designed to slow down and speed up the main input shaft when there is an up-shift and a down-shift. The synchros were designed with the weight of the stock disc in mind. Any heavier material will add undue wear and tear on the synchros. So just imagine how happy the synchros are when the disc is lighter than stock!
---Rob Smith, RPS

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