Gary Z

Why do brakes survive extreme slipping and heating, but clutches do not? Obviously, material selection is driven by the facts that normal clutch operation requires lockup while normal brake operation requires slipping. But drag racing a manual transmission car, particularly during launch, requires some clutch slippage for best acceleration. Yet drag racing destroys clutch materials with symptoms not usually seen in brake materials. Despite extreme heating, brakes just wear; clutches burn. Flywheels and pressure-plates become glazed and blued. Clutch discs disintegrate; brake pads don’t. Brakes prove that friction materials are able to survive extreme slipping and heating. Why aren’t drag racing clutches made with brake-like materials?

onecamaro1

Here is my part at an attempt............I know brakes share the load and they start from high rpm to low. Clutch material is thinner, covering a larger radius, therefore creating much more speed across the surface and going from roughly 3k (at the line)and increasing in rpm till maxed out. Brake pads only cover a portion of the disc, so i'm sure they get some kind of cooling from the air rushing past them, clutches do not. I see the flywheel as never getting a brak from heat stress, both from the motor heat and the disc friction. You apply the brakes to stop, but if you drive with the emergency brake on, i bet they turn blue then. just my 2c

Old SStroker

Brakes are disigned to generate heat and then dissipate the heat created by exposing the rotors to airflow. They turn the kenitic energy of the vehicle into heat energy. They also have lots of surface area for the mass involved which helps get rid of the heat. There are usually 4 brakes vs one clutch.

Conventional clutches as used on OEM and most street driven vehicles are not meant to do a lot of high hp slipping. Those that are do use multiple discs and friction material not unlike brake pad material.

For the street driven/drag race vehicle you can purchase a clutch that will take everything your engine/chassis can give it. If you are toasting your flywheel, disintegrating clutch discs, etc. perhaps you need to upgrade the clutch as much as you have upgraded the engine and bite.

Gary Z

Few expect a stock clutch to survive drag racing. The majority of the countless clutch woe threads concern expensive street/strip clutches.

rss0694

iTrader: (2)

Good answer...I totaly agree.

gametech

iTrader: (1)

The better question is how clutches survive with no reasonable means of cooling available to them. By comparison brakes get exponentially more airflow. BTW, am I the only one who wishes Old SStroker would say something completely assinine so we wouldn't have to always agree with him? I really like to argue with people, and I can't do it when they are right.

RoDan

exactly, clutches get no air stuck in that bell housing... Brakes absorb the kenetic energy of the car and turn it into heat. Clutches overcome the inertia of the car by creating heat and then eventually motion. Never thought about that before.

Jakes Dad

Well, you've got one clutch and four brakes, right? But I really question your question. I've seen BRAKES that needed replaced at 30K, A Clutch normally last longer.

If you changed your clutch, even went bigger, then went race you more than likely glazed your new clutch. The whole reason why normal driving is needed before you went racing to see how your clutch worked

dan@masportspeedshop

iTrader: (6)

I'm reminded of my high school physics teacher, Mr. Beauman, telling us all...
"Remember one thing kids! Heat is ALWAYS the final form of energy"
At the time I believe I made a joke about cremation, nonetheless I'm glad I somewhat paid attention that day.

Gary Z

Much less energy goes into the clutch than brakes. Remember, unless it is failing (slipping continuously), the clutch only generates heat for a short time at the end of each shift while it engages. While engaged, the disc is cooled by contact with the flywheel and pressure plate, two large masses that can absorb considerable heat. Destroyed flywheels and PPs show clear signs of high surface temperatures but the average temperature of these large masses is never anywhere near as high as brake discs which can become red hot.

CamaroZstyle28

iTrader: (1)

Hey, not disagreeing with what your are saying .. that brakes outlive clutches -- but I've replaced my brakes quite a few times and am still using my orginal clutch at 110,000. I'm changing it this summer, but it still has some life in it !!

Reznor

iTrader: (4)

4 rotors + 8 pads vs. 1 "rotor" and pad

Asmodeus

So.. what if a clutch assembly was redesigned.. from the flywheel back to the trans input shaft.. in an effort to imitate a brake/rotor setup.. and eliminate the clutch disc in favor of a dual sided "brake" for the flywheel.

Let's extend the flywheel off the back of the crank a couple inches, then place a lightweight "caliper" at the top, bottom, and both sides of the flywheel.. each holding a clutch puck on the inner (reason for extending the flywheel out) and outer sides.. but instead of acting as a direct brake and being held by brackets, they could be free floating and connected to a common tube to slip over the trans input shaft, or a disc connected to the trans input shaft.. maybe via something like a u-joint.. removing the "side" calipers for descriptive purposes.. the top || and bottom || representing the top and bottom "calipers", the \\ and // representing the shaft from the "rotating" "caliper" tied together into a tube slipping over the trans nput shaft ala a pressure plate..

||. . . . ______
F-\\ __| ------\____________________
L--\\__|TRANS-|___________________
Y-//. . |______/
W//
||
Maybe it would rob too much power, maybe it would have too much reciprocating weight.. maybe I can't explain how I see it in my mind.. but to me, it would be like a 4 puck clutch, but with grab on both sides of the flywheel.. and it would have to be balanced since once pressure is applied and the pucks/pads grab the flywheel, the "calipers" now also become a rotating mass.. yeah the more I think about it, the less I see it being viable for a daily driver..

just throwing a thought out there..

GIVE EM' THE BIRD

iTrader: (1)

im on the factory clutch at 120,000 with no signs of slippage and i raced a week ago

slick1851

This is going to sound dumb but what if somthing kept the clutch cool?

GIVE EM' THE BIRD

iTrader: (1)

there should be something to cool it, but it relies on heat disapation through the pp's and flywheel.

gametech

iTrader: (1)

Asmodeus gets the "WTF?" of the year award. Rube Goldberg, anyone?

edcmat-l1

iTrader: (10)

^^
I think the idea of more surface area for gription (my word hehe) has already been answered with dual discs. And mutiple discs for racing apps.
And dont ya'll go stealin my word!!

Asmodeus

lol I'm a winner!! yay!! I've got mail, I've got mail!! YAY!!!

haha seriously.. the Rube Goldberg comment cracked me up, and definately applies!

Sparetire

I am no engineer. I know. I tried mech engineering school and concluded that I would go insane looking at that many excel sread sheets.

But one thing stuck with me more than any other. Find a simple solution.

Why cant we just vent the bell housing better? All the ones I have seen have pathetic little plastic rigs that have an opening about 3/4 inch area tops. The clutch disk in a normal type clutch does see air on the PP side. Puck types probably get airflow between the pucks. I'll bet some airflow is happening in a multi disk too. It would not be hard to beef up ribs on the bell housing to maintain or even improve strength.

More complex but using well developed tech: Use a clutch system similar to what some LSDs use. The clutch is surrounded by heat sensitive fluid. Fluid gets hot, clutch enages, as when slippage happens. This fluid could be used a cooling system, much as some hi-po LSDs on hard core road race apps use diff coolers. It might be perfect for slipper application on the drag strip. Might be hard to do on a street car at cruise though. Some sort of lock-up system at speed might be needed so that it acts normal after you initialy start out.

Meh, I like #1. Complexity is the enemy. A nesesary evil.