Dual disk clutch does not shift slower than a single.

[MD-LUCKY]

/thread.

Thank you VERY much for the info Peter!! Going to keep a link to this thread as a reference going forward.

 

[MD-LUCKY]

Peter, I do have another question:

What "seperates" the plates? Is it the centrifugal force? Heat? Friction? What causes everything to slide apart when you depress the clutch pedal.. That seems to be about the only question left hanging on how a dual disk could possibly shift slower than a single..

 

[JasonCzerak]

On something like that a 3000 lb diaphragm single disc 6 button ceramic or feramic

I suppose, highrpm low torque. No DD's in road racing?

 

[sb clutch]

Peter, I do have another question:

What "seperates" the plates? Is it the centrifugal force? Heat? Friction? What causes everything to slide apart when you depress the clutch pedal.. That seems to be about the only question left hanging on how a dual disk could possibly shift slower than a single..

The motors have a slight tilt down so centifugal comes into play

 

[sb clutch]

I suppose, highrpm low torque. No DD's in road racing?

Sure, if needed. They would need about 700+ to require one.

 

[BgBlDodge]

I've driven an SBC 3250DD, an SBC 3850DD, and an SBC triple disk and the triple disk was noticeably smoother and quicker and easier shifting than the dual disk. These were all in the same truck.

 

[6006spd]

same here,my 3850sb dd seems close to stock for speed,g56,12cb just hate the rattle in 5th gear low speed,and the noise with the clutch peddle in very loud!but love the fact that it will launch third gear over and over with no complantes also have the hyd upgrade as well great clutches just a little cranky at times,lol.....

 

[outlaw99]

I know a dd or even triple is ten times easier on the motor than a single...lol like wear and tear on the bearings and stuff.

 

[JasonCzerak]

So, the triples are faster to shift. I'm sure they are much loner lasting to.

So, clutch guys;

What about testing triple disks for street/track use? Maybe forgo one of the disks's center section for a hardened hub to keep the space down and have just two sprung hubs. a set of 6 puck disks and 3250# plate. Or maybe change up the number a little. 8 puck disks. 8 pucks = 48 pucks, same a s a dual disk with 12 pucks.

Consider playing with organic material in a triple disk.

I'd have to guess Peter's costs are much lower due to the quantity he sells now for the DD's.

 

[bh10]

I've driven an SBC 3250DD, an SBC 3850DD, and an SBC triple disk and the triple disk was noticeably smoother and quicker and easier shifting than the dual disk. These were all in the same truck.

What plate load was the triple?

So, the triples are faster to shift. I'm sure they are much loner lasting to.

So, clutch guys;

What about testing triple disks for street/track use? Maybe forgo one of the disks's center section for a hardened hub to keep the space down and have just two sprung hubs. a set of 6 puck disks and 3250# plate. Or maybe change up the number a little. 8 puck disks. 8 pucks = 48 pucks, same a s a dual disk with 12 pucks.

Consider playing with organic material in a triple disk.

I'd have to guess Peter's costs are much lower due to the quantity he sells now for the DD's.

x2, and how would lets a a triple disk with your plate load of 3250 handle at the track? And any insight to how much more a triple is to a double?

 

[GOT-Torque]

OK, so this thread started out as the "Dual disk doesn't shift slower than a single" however after some much detailed discussion, it leads to reasons why a dual disk does indeed shift slower than a single.

Now, there is talk that a triple disk clutch was smoother, quicker, and easier than a dual disk?

I know someone that laid down decent numbers rowwing the gears with a dual disk and around 600 hp and now with almost 1000 hp and a triple disk was a atleast a few seconds slower....

 

[MD-LUCKY]

OK, so this thread started out as the "Dual disk doesn't shift slower than a single" however after some much detailed discussion, it leads to reasons why a dual disk does indeed shift slower than a single.

Whoa whoa whoa.. It lead to some THEORIES as to why a dual disk COULD shift slower than a single.. None of which held enough water to stand up to scrutiny. (except MAYBE the diaphragm vs lever pressure plate theory).

A dual disk clutch does NOT shift slower than a single. There is no PHYSICAL explanation why folks think they do. Only psychological.

 

[Valair1]

it's all in your head.LOL

 

[GOT-Torque]

Well, regardless of all the info/theories in this thread, which is very good stuff BTW. My personal experience was that my dual disk shifted slower.

Your statement of "A dual disk clutch does NOT shift slower than a single" is your assumption. Is it based on your experience or is it based on no one providing the direct evidence to prove otherwise?

 

[MD-LUCKY]

Your statement of "A dual disk clutch does NOT shift slower than a single" is your assumption. Is it based on your experience or is it based on no one providing the direct evidence to prove otherwise?

Yes.

It is based on experience (2 different types of dual disk clutches in my truck alone, and several in trucks I'm familiar with) and no one providing direct evidence to prove otherwise. My assumption is that no one can prove otherwise, since there is no direct evidence why a dual disk would shift slower than a single..

If it walks like a duck and talks like a duck..



The entire point of this thread was to squelch a rumor in the DIESEL world that has been driving me bonkers (a dual disk clutch will shift slower than a single disk.) We are the only motorsport I have found ANYWHERE that makes that claim. Has anyone found different? Our RPM levels are nothing compared to any of the hot sports cars that run dual disks, so the increased inertia and centrifugal forces from adding an additional clutch are TINY compared to what their transmissions are going to.. An additional 5 pounds spinning at 3200rpm is VERY different than an additional 5 pounds spinning at 8000rpm.

Are there possible reasons a dual disk clutch COULD shift slower? Yes. But, there is nothing inherent in the design of a dual disk that would cause slower shifting. Possible causes:

1: Warped plates preventing clutches from fully separating. (not an inherent flaw)

2: Damaged/failing pilot and throwout bearings.

3: Damaged input shaft. (If the shaft is warped or twisted, it may not allow the clutches to slide and separate properly, causing slower shifts)

4: Damaged/failing hydraulics (not allowing a full disengagement of pressure plate)

5: Damaged/failing synchros.


Problem is, those will all cause shifting problems with ANY clutch, not just dual disk (although the warped plate is unique to a dual disk). Damaged or failing synchros might be exasperated by the additional weight of a dual disk clutch.. but, that is a transmission flaw that needs to be addressed, not an issue with the clutch itself.

 

[JasonCzerak]

Here's an idea, something that possibly won't work in my area due to the small groups for our dynodays in comparison to some of you folks on the east or west coast.

How about at the next major dyno day with a large group someone does a bind test?

 

[GOT-Torque]

Here's my opinion on the technical reason for a dual disk to shift slower than a single disk:

Roachie already mentioned it...

Im talking about the movement of the floater plate within the grooves in the flywheel. There is nothing to pull the floater back from the 1st disk. There will be some friction between the two. The pressure plate can be a foot away. The floater will still be able to make some limited contact with the disc's.

Not sure what you meant with the following:

You also have spinning force trying to seperate the clutches and floater plate. Stick a paperclip on the end of your pencil and give it a good spin. Does it stay completely stationary?

The spinning force of the clutch does not try to separate the clutches and floater plate. All of the rotational forces are in a direction perpendicular to the axis they are spinning on. Not in the direction of the axis. Peter did mention the fact that the engine/trans is tilted slightly downward so gravity would help to some extent. On the same note though, gravity would continue to pull the front clutch plate into the floater disk as well (while clutch pedal is depressed).

How much weight would actually be against the floater plate with no pressure plate pushing against it? The weight of the clutch? The weight of the floater plate?

Not much weight, but there would be some friction as there is literally nothing trying to push them apart.

More, from centrifugal force pushing them together?

I’m not sure what you mean by this? We are talking with the clutch pedal to the floor right? How would the rotational force of the clutch spinning force them together?

If the pressure plate isn't applying pressure, can the synchros in the transmission even tell that there is additional "friction?"

Definitely yes, isn’t this why it is so hard to get it into reverse with a dual disk? There is enough drag to keep the input shaft spinning fast enough to prevent engagement of the synchro’s for entry into reverse. However, if you bump it into 5th or 6th, then jump up to reverse before the input speeds back up you can get it in fairly easily.

Which begs another question.. If you are at a stop light with the clutch pressed in, are you burning up your clutch since the floater plate hasn't seperated from the clutches?

There is some friction and heat created here, but if my clutch can hold my hp level for sled pulls, 3rd gear launches, etc, with from 0 up to 3800 lbs of plate load (slipping in between) then I wouldn’t worry about it.

 

[GOT-Torque]

Something to consider as well. Transmissions made for cars are much smaller and lighter weight in general compared to our beast. Compare the weight of an input shaft and clutch plate (the mass you are trying slow down) from a dodge truck to any car. Also, the distance this weight is from the axis it is spinning on plays a big role as well, not just the weight comparison.

It all boils down to friction and inertia... You know, the stuff that they tell you to assume is zero in Physics class so that you can prove theories easier...:hehe:

 

[MD-LUCKY]

Here's my opinion on the technical reason for a dual disk to shift slower than a single disk:

Roachie already mentioned it...



Not sure what you meant with the following:

The spinning force of the clutch does not try to separate the clutches and floater plate. All of the rotational forces are in a direction perpendicular to the axis they are spinning on. Not in the direction of the axis. Peter did mention the fact that the engine/trans is tilted slightly downward so gravity would help to some extent. On the same note though, gravity would continue to pull the front clutch plate into the floater disk as well (while clutch pedal is depressed).

The centrifugal angled force is FAR greater than gravity, and would have 0 issue seperating the clutches. Remember, they don't have to be an inch from eachother. Further, the clutches could actually still be in contact with the flywheel and floater plate and be slipping past eachother. With 0 pressure from the pressure plate, the clutch is going to slip.. which will help the synchros do their job and you shift faster. Just as fast as a single disk.

Not much weight, but there would be some friction as there is literally nothing trying to push them apart.

There is "some" friction with a single disk too.. But, is it too much for the synchros to overcome? Nope. Under this logic, a high friction grabby single disk clutch SHOULD shift slower than a low friction orgranic dual disk clutch. Does it?

I’m not sure what you mean by this? We are talking with the clutch pedal to the floor right? How would the rotational force of the clutch spinning force them together?

Just playing devil's advocate for "plausible" explanations...

Definitely yes, isn’t this why it is so hard to get it into reverse with a dual disk? There is enough drag to keep the input shaft spinning fast enough to prevent engagement of the synchro’s for entry into reverse. However, if you bump it into 5th or 6th, then jump up to reverse before the input speeds back up you can get it in fairly easily.

Then, like above, wouldn't a high friction single disc (re: FE) shift harder than a low friction dual disk? Isn't the material of a dual disk less "grabby," which is part of the reason we WANT to go with a dual disk? (By the way, I have no issue with reverse on my pickup. Weird, eh?) If this theory is right, it has FAR more to do with clutch material than the amount of clutches. Plausible? Maybe. But, doesn't explain how a dual disk could shift slower..

There is some friction and heat created here, but if my clutch can hold my hp level for sled pulls, 3rd gear launches, etc, with from 0 up to 3800 lbs of plate load (slipping in between) then I wouldn’t worry about it.

[/quote]

Bingo. But, it's not enough to be of any concern, right? So if they seperate enough at a stop light, why not enough during shifts?

 

[GOT-Torque]

What is providing the centrifugal angled force?

I'm assuming a single disk has alot more room for the clutch to disengage the flywheel than a dual disk... not sure though?

Isn't the material of a dual disk less "grabby," which is part of the reason we WANT to go with a dual disk?

For some people that may be true, for others you simply need a clutch to take more load. I went from a single FE clutch to a dual FB, not for a smoother shifting clutch but to hold more load.

There is "some" friction with a single disk too.. But, is it too much for the synchros to overcome?

Yes there is still some friction, but not as much. I'm sure there are lots of factors that affect how much the input shaft continues to rotate. Clutch material, amount of mass spinning with it, space available to disengage, etc.

So if they seperate enough at a stop light, why not enough during shifts?

I can think of two things that are different between shifting at a stop light or while racing.

The first difference is rpm, while racing the rpms are higher during the shift, therefore there is more inertia to keep the input shaft spinning.

The second difference may be better explained if I use an example:

While driving to work one morning in my 5 spd Fox body mustang, I was making a hard run up to speed and during my quick shift from 3rd to 4th, a coiled up 5' black snake slide out from under my passenger seat.

Why did it slide out? Because when I stabbed the clutch in, the car stopped accelerating, as the car slowed down for this brief 1/3 of a second, the snakes inertia overcame the friction between itself and the floor and it continued forward.

The same thing happens to the clutch plates, as you stab the clutch in, and they start to slip inbetween the pressure plate and floater plate and between the floater plate and flywheel, the inertia of the clutch plates cause them to continue forward and maintain contact with the forward surface.

Maybe this small increase in friction between the plates at precisely when your trying to speed shift your transmission is enough to make it take longer to slow down the input shaft? I don't know?

But I do know that I hate snakes