Beware of dual disc clutches

[Jac Mac]

[quote=rsimoes]I almost installed a dual disc clutch on my car and changed to single disc last minute due to required modifications I was not comfortable with, like trimming the bearing retainer and shaving part of the bolt heads that hold the bearing retainer on the trans. This sounds more like the normal mods to accomodate a centerline type release brg

What they don't tell you on the phone (tech support) and in the descriptions, is that there are actually many draw backs to this setup. Only the paperwork that comes with it, has all these warnings:

1) It rattles Good on them, because they have a floater plate that has no anti rattle mechanism its going to rattle. At least you then know its 'normal'
2) Should not be used in hot lapping They have told you its not really a race type clutch
3) No engine breaking Oh for a clutch that will stop the engine from 'breaking'- Seriously though, any clutch cover that uses torque/tension straps does not like the huge torque reversals from violent engine braking where you shift down and make no attempt to match the engine rpm that will be required
4) No burning rubber in wet and then hit dry pavement, as it could destroy the clutch Along with a few other things- actually this practice is easier on the driveline etc than a standing start, but the message is dont expect them to warranty any parts that have been mistreated-which if you read the fine print on most of the paperwork for all parts in your car I think you would be scared to start the thing up
5) Should not be used with taller gears than 4.10 (lower numerically) on dyno You got me on this one
6) Miss shifts will ruin the clutch Good chance you will exceed the safe rpm limit of this clutch when you do that
7) Always start in 1st gear Probably sound advice
8) Rev match when downshifting for power, or it could damage the clutch As in 3 above
9) if you really want to race, upgrade to another high performance clutch they make. Thats fairly honest advice

Among other installation modification that may be required depending on application.

Although I don't know if this is an exaggeration so they don't get sued, it makes me uncomfortable putting one in my car. . . as it sounds to defeat the purpose of having a dual disc clutch. . . I would think there were two basic reasons to install a twin plate- one. to obtain more clutch plate surface area without increasing the pedal effort. --two to keep the rotating mass at a smaller dia

Jac Mac

[eschaider]

Here is another good litmus test.

How many single disc failures do you read about on this site. How many single disc street units do you hear the owners complaining about bad manners and driveability issues. Now go out and check the tally for twins.

Again this isn't advanced engineering math. All it takes is simple four function add, subtract, multiply and divide skills. In fact you can be average in three of the four skills as long as you can add.

The guys using the singles who are unhappy far outweigh the guys using the twins who are unhappy. What does that tell you??

Of course if you think you will be different from the majority of single disc users with high power who have experienced single disc problems you should immediately get a new single disc unit in your ride.

Ed

[Excaliber]

It stands to reason the number of owners with single disc AND problems would be far higher than the number of owners with twin discs with problems for one simple reason: Theres considerably more single disc owners!

Another factor more difficult to quantify would be the number of owners who specifically went to dual disc because they ARE driving their car harder than the majority of single disc users. In a case of where you are driving the car at or near it's limits your likely to incur more trouble in general than other cars regardless of the clutch you use.

What clutch release mechanism is commonly used with a dual disc setup?

There are more "internal hydraulic clutch release mechanism" failures than external hydraulic clutch release mechanisms. When you DO have a problem with the internal it's a nightmare repair, especially compared to the external type!

I considered a dual disc after burning up my single plate, but went with a single plate anyway. I burned out my single disc being 'stupid'. The basic problem with EITHER clutch is that you CAN burn it out in a single day if you don't use it correctly! My single plate works fine now because I don't abuse it, but I'm not afraid to use it. The manufacturers 'cover your ass' points made concerning dual disc 'abuse' I believe are valid for both style clutches.

[eschaider]

Ernie,

You're right about the owner's driving style. The best parts can be broken by a determined individual. That's not what we are looking to emulate or evaluate.

The caveats for friction clutches apply equally to both single disc or n-disc clutches. Abuse the unit and you shorten its life. Abuse it a lot and you shorten it a lot.

The clutch manufacturers came out with streetable twins twenty maybe thirty years ago. I believe McLeod was the first but I am not absolutley certain about that. I do know that there are multiple manufacturers that have offered these units for at least ten years, some manufacturers more.

The big benefits are additional friction area, reduced plate loads (softer pedal), silky smooth engagement, and substantial torque capacity reserve. They simply remove the bad manners and reduced service life of the high capacity single disc equivalents.

If you put serious power through the clutch in a drag race environment then you need sintered iron components, floaters that center on clutch stands and are not secured by straps along with a borg & beck or better a long style cover for the more secure locating of the pressure plate. You will benefit from the tunability and adjustability of plate load through in can finger height and adjustable static pressure on these units. These are brutes but they are not street units and should not be compared to them. One is a severe duty race clutch the other a high capacity street clutch.

I think release mechanisms tend to be a preference election of the individual builder and could essentially be anything you choose. Moreover a release mechanism failure is a different animal than a clutch friction component failure. Although a release mechanism failure could induce the other. Release mechanism induced failures tend to fall into the same category as operator misuse induced failures. As you pointed out in your own case the single disc failure was most probably not a shortcoming of the unit but rather an unintentional (I presume) misuse/operation by the driver.

You are absolutely correct about the number of single disc units in service vs the number of twins. I suggested that for evaluation purposes "... All it takes is simple four function add, subtract, multiply and divide skills. In fact you can be average in three of the four skills as long as you can add." However not withstanding the evaluator's ability to be average in three of the four skills, unstated he would still have to be able to divide otherwise you can't determine the failure percentages. Of course a fall back would be a four function calculator and let the machine do the work.

Data collection would probably involve some type of a thread including a poll and suprise suprise we get numbers that not only tell us how many type info but also problem type info. Of course this would only be interesting if the individual wanted to know. If he wanted to complain or perhaps make untoward remarks about products or manufacturers then this approach would yeild less than desireable results.

I think we have enough folks who have replaced one or more clutches and spent good money in the process, that this type of information represents real value to them. It deserves to be made available without potentially misleading remarks that would otherwise obfuscate the real world.

Most people below 550/600 HP don't have the same types of clutch service issues those above 600HP do. When you hit the 600 level a lot of things begin to behave differently especially in terms of wear. The thread's title "Beware of dual disc clutches" along with the poster's admitted non use of the product speaks volumes about the message. Interestingly, although I am sure somebody has, I didn't turn up any posts of dual disc users complaining about those stated "problems".

We should be expolring ways to make things better for each other not clouding up an already demanding variety of choices and decisions to improve our cars and pieces.

Ed

[Ant]

A single disc clutch works okay for street use, but you can get a single plate with puck type linings or a series of what looks like brake pads attached to a disc, these work very well, a lot of rallye and race cars have used this system.
With std and HP normal lined single plate clutches I have had several loose their linings when you race them one of the main problems I had was is if the linings werent bonded and only riveted to the clutch plate, but I think they are better made nowadays!

Their is no comparison if you want to do some racing, any good Tilton AP or other make using ceramic base metallic linings should work okay, the only thing is you may have to replace your clutch discs every 2 - 3 years pending your driving, and using a flexplate or lighter flywheel allows the engine rev nice plus you havent got so much cast iron steel parts flying around that may separate.
I think you will find any good top factory performance cars use multi plate clutches eg. Porsche, Ferrari etc. I used a triple plate sintered bronze AP clutch on the road, I didnt get clutch slip and problems and it lasted surprisingly well providing you positive in your take-offs, but I wanted a compromise between the track and road use!