Kevlar Friction material - An Update

[Glacier991]

Some of you may recall my angst as i debated using kevlar bands in my rebuilds in the diaries. For a number of reasons I was a skeptic.... and my legitimate questions never got answered. Well now the word on the street is that Kevlar was NOT all that good.. and the new "high performance" material is carbon fiber.

Call me a hard core skeptic.....What most bands turn into during use, is a cabon based material.... ok it is not a fiber, but carbonized material never the less.

I'll watch carbon fiber and investigate, but I think we are seeing Madison Avenue enter into trans rebuilding materials. Ads pump it up, but it is all fluff. The old time proven materials still rank high in my mind.... frictions and bands in a healthy tranny rarely wear out.


ps. I never believed in Kevlar anyway.

pps. I believe in Santa Claus though.

 

[gijoecam]

Agreed... From a sales standpoint, CF is probably just a gimmick. Kevlar and CF are, at their core, just another woven fibrous material that can be adhered to a backing material (in this case, a clutch band). Any friction material is going to wear as it's used, but the goal in changing friction materials is generally to use something with a higher coefficient of friction that wears as little as possible. (Like the utopic brake pad that stops faster than anything else and never wears out)

Yes, all friction materials get reduced to a slushy goo when mixed with trans fluid, hence the reason transmissions aren't 'lubed for life' like the t-case or axles where you have strictly metal-on-metal contact. Whether that slushy goo os made of trans fluid plus asbestos or trans fluid pluc carbon fiber is irrelevant IMHO. The bigger concern is how does it wear against the metal parts of the transmission when bathed in trans fluid.

Now, the theory behind both of them is sound... Both CF and Kevlar *should*, under normal conditions, last longer and exhibit a higher coefficient of friction than standard friction materials. I know that, in braking systems at least, the drawback is that those performance gains don't become apparent until the friction materials get VERY hot (like cherry-red). If you've ever seen race cars with cherry red brakes diving into turns, that's not als=ways a bad thing.... I've heard of a few race vehicles that will use a brake system that keeps pressure on the pads with your foot off the brakes just to maintain contact (and therefore heat) between the pads and rotors.

Like I said, the theory is sound. Is it absolutely necessary? Probably not... like you said, a well-used but not abused trans should out-last the vehicle. Think about how many time police cars or taxis get new transmissions? Maybe once in their life?

-Joe

 

[CDW6212R]

I agree with the theory stuff also, but back up on that thought about police cars and taxis. I have owned four ex-police cars, and spoken with lots of people who worked on them. They do not last longer, they are taken care of better though, that's the magic. Most taxis are old police cars, because of the heavy duty parts in them.

My first was an 86 Crown Vic, and it went 212,000 miles until an OD servo piston broke(separate)(lost pressure). I rebuilt it and it went to 335,000 when a friend died in a wreck with it.

The Kevlar does sound good, but there are countless examples of high performance vehicles using regular frictions, successfully. Regards,

 

[Glacier991]

I was never able to get an absolute number for the wet coefficient of friction of Kevlar... but knew it's thermal conductvity was low... a drawback in my mind. I was never able to confirm any difference in the c/f between a regular band and kevlar. Like you I figured the biggest benefit was that Kevlar was more indestructable.