Advice On New Clutch - Single vs Twin Disc

[Unique427]

Question for the experts.

In the coming months I plan to replace my clutch and hydraulic throwout
bearing. Current combination has served me pretty well but peak engine power
has been boosted significantly since this clutch was installed some years ago.

Engine dyno now shows 650HP and 640 LB-FT at the flywheel.

The question is should I go twin disc or stay with a stout single disc setup.

Here's the specifics.......

Engine/Drivetrain:
Engine - Ford Racing A460 bored and stroked to 516 Cu. In.
Bellhousing - Lakewood #15220 (requires 184 tooth gear)
Throwout Bearing - McLeod #1305 Bolt On Hydraulic
Transmission - Toploader // Close Ratio // 1-3/8" x 10 Spline Input

Clutch Options:
1) McLeod RST Twin Disc #6911-06 (twin organic 750 LB-FT limit)
Adapts to existing flywheel. Requires assembly to be balanced.

2) RAM FORCE 10.5 Dual Disc #80-2295S Kit. (750 LB-FT limit)
Steel flywheel with 184 tooth gear. Assembly balanced at RAM.

3) Centerforce DYAD 10.4 Dual Disc #413703360 (1000 LB-FT limit)
I've read on Centerforce website this combination can not have
a shim between the hydraulic release bearing and transmission.
Text is confusing as to whether it is not needed or just prohibited.
McLeod bolt-on throwouts use a measured spacer to set gap.
Centerforce appears to not respond to any inquiry regarding this.

4) SPEC Stage II #SF272CJ Single Kevlar Disc (697 LB-FT limit)
Internet review indicate reasonably good street characteristics
up to Stage II+. Kevlar discs require a LONG break-in period.

There's a host of other possibilities for single disc arrangements
handling around 500 LB-FT which I have ruled out for now.

The car is for the most part, street driven.

Any advice based on actual experience is gratefully accepted.

Thank you.

[1795]

I went from a single disc to the McLeod RST twin disc on the race car. It is a nice setup and was not hard to install. The twin disc works great on the race track and feels more connected than the single disc.

However, it is difficult to feather and tends to be either fully engaged or not which can be problematic when you are trying to drive at a slow speed through the paddock on the way to the grid and people are walking all over the place. I have a close ratio top loader, so that means a very tall first gear, if you have a wide ratio it may not be as problematic. The twin disc tends to be more jerky on take off, the single disc allows you to feather the clutch if you are trying to ease into traffic, or a parking spot.

If all depends on what you are planning to do with the car, and your typical driving situation. Good luck with your decision.

Jim

[DanEC]

It’s interesting that you commented on the twin disc being a little difficult to feather. As I recall the discs on the twin disc McLeod clutch lack torsion springs (unsprung) and I wondered how that worked in street driving. I don’t remember anyone commenting on it before.

[DanEC]

It’s interesting that you commented on the twin disc being a little difficult to feather. As I recall the discs on the twin disc McLeod clutch lack torsion springs (unsprung) and I wondered how that worked in street driving. I don’t remember anyone commenting on it before.

[eschaider]

What Jim said about twins is particularly true when you use the more aggressive competition-style friction materials on the discs. A street-driven car's typical organic friction materials will work very nicely for you. The twin will provide a reduced pedal effort. On the 8 or 9-inch versions available from various manufacturers, you will have a very light pedal, even lighter than an OEM daily driver-style unit.

McLeod has two different families of twins. One is the RST/RXT family, and the other is what they call their Original Street Twin. Here are links to each one:

RST/RXT => Click Here
Original Street Twin => Click Here

The RST/RXT versions were developed for the modern-day blown stuff like the Hellcats and supercharged Coyotes and Camaros. The smaller diameter 8 and 9-inch diameter discs make shifting at high engine speeds easier than the larger 10.5" diameter discs used with their Original Street Twins.

In terms of power handling capability, they will all easily exceed 800 hp, which really isn't the issue. Torque capacity is the real issue.

If you use McLeod's HP ratings and assume they are measured at 7000 rpm, then the RST/RXT clutches with their 800 to 2000 HP ratings would be good for engines with 600 to 1500 ft/lbs of torque. McLeod rates those Original Street Twins with their 10.5-inch diameter discs for 1200 ft/lbs of torque.

At first glance, the smaller diameter clutch might seem like the way to go. In fact, it might be, but then again, it might not. The 800 HP version is the organic facing version of the clutch, which is only rated at 600 ft/lbs of TQ! Other than the nice light pedal, this is not significantly better than the clutch you are replacing — and will not likely last any longer.

The McLeod Original Street Twin uses a 10.5-inch diameter disc, and McLeod rates the clutch at a 1200 ft/lbs of TQ transfer capability, this comes with a lighter pedal than you currently have, but not as light as the smaller McLeod RST/RXT clutches. This clutch in one of our cars will substantially outlast your current clutch and McLeod's smaller diameter RST clutch while giving silky smooth engagements in day-to-day operation.

Here is a picture of my own homebrewed 10.5-inch dual disc unit;



This is what the components looked like before assembly;



I used a Ford high ratio, low pedal force 10.5 inch pressure plate with about 2400 lbs of plate load. The discs are McLeod from their Original Street Twin, the floater and heat shields are Crower from their blown alcohol Pedal Glides, and the flywheel is my own, modeled after a combination of aftermarket flywheels, taking the attributes I liked from each and discarding those I didn't like. Predictably, I made a few mistakes in the fab process, but none were show-stoppers.

Two considerations worth mentioning are if you use a drive stand instead of a strap drive for the floater, then when you are stopped, you might hear the ringing of the floater as it bounces back and forth between the drive stands with the clutch disengaged. If you have side pipes, this is virtually impossible to hear! Unlike drive straps, drive stands can not be bent during engine deceleration.

I chose the do-it-yourself path partly because I could and partly because the total cost of the finished clutch and billet steel flywheel was just under $600. If you do not have access to a lathe and a mill, it would be challenging to build the clutch. If you pay someone to do the machine work, buying a ready-made McLeod (or another firm's) twin disc unit would be more cost-effective.

When I was all done, I balanced it, and to no surprise, it was spot on, well within less than a gram.



I have right at 600 ft/lbs of TQ from below 1500 rpm out to almost 7000 rpm; however, that is primarily attributable to the blower and the EFI tune. The dual disc clutch design and velvety smooth engagement is an absolute breath of fresh air compared to the heavy pedal, short life, single disc clutch alternatives.

The McLeod discs I use do not have a sprung hub. McLeod does use what is called a Marcel spring between the friction material and the disc drive plate. A Marcel Spring is a flat wavy plate-style spring that fits between the disc’s friction material and the drive plate. When the pressure plate applies it’s clamping force to the clutch pack, the Marcel Spring slowly flattens out, creating a spring-like tension that provides for that initial controlled slippage necessary for a smooth engagement. The Marcel spring, along with organic facings, provide for a very smooth engagement.

When you pick your discs, you can also use sprung hubs if you have enough stack height available in your clutch can for the throwout bearing to fit and operate. Depending on the depth of your clutch can, you may or may not need to trim the candlestick support for the input shaft to clear the topmost disc. Be sure to check your clearance there.


Postscript

The tougher and more aggressive non-organic disc-facing materials in time will all cause the clutch to chatter on normal acceleration from a dead stop. For a street driven car you want organic facings.

[blykins]

Can't go wrong with the RST. RAM clutch is always a good choice as well.

Definitely no Centerforce or Spec.

As a drivetrain parts dealer, I get to hear from all the guys who have trouble with other brands.

I have RAM and McLeod in stock. Can give a Club Cobra discount.

[Unique427]

Ed, Bill and Jim ... thanks for the input.

[Tommy]

Ditto to the previous comments about clutch material. My Cobra had high friction Kevlar/Ceramic pads and it acted like an on/off switch. It was fine at the track, but less than fun around town.

[eschaider]

Sort of a postscript (larger than I originally thought) to my earlier post #5.

The way I wrote the post, it could be inferred that I might be promoting McLeod. I am not. I am neutral toward the manufacturers, in general. Brent's guidance on his experience retailing the various manufacturer's products and the subsequent customer experience is a good guide/litmus test for who you should be looking at and who you might want to give a pass to. Advertising notwithstanding, real-world customer experiences are typically the best litmus test.

Be circumspect about friction material and your intended use; friction material can profoundly change the character and usefulness of your clutch. The other be sure to check, check point is to make sure you have adequate clearance inside your clutch can for the stack height of your twin disc selection. At the two-disc level, they can virtually always be made to fit; it is just that sometimes the fitment process might take a little more effort.

Another thought that I should have mentioned earlier is for easier shifting at elevated engine speeds, smaller diameter discs have less rotational inertia and are easier on your transmission's synchros. That said, I use a 10.5-inch diameter disc with a TKO that uses Liberty's carbon fiber synchros and shift rails with Liberty's modified interlock timing. This is a big improvement in the TKO shifting experience.

To do a clutch upgrade, you will need to have your transmission out of your car. Once it is out, there will never be a better time to do the Liberty TKO shift improvement kit upgrade with their bronze shift fork pads, billet shift dogs, modified TKO interlock rails, carbon fiber synchros etc. With the advent of the TKX boxes you might want to get to Liberty on the shift improvement stuff sooner rather than later. At some point I would not be surprised to discover that they would stop offering TKO enhancements.



PPS

In order of easiest to most difficult to shift at elevated rpm, your pressure plate choices look like;

1. Diaphragm
2. Borg & Beck
3. Ford Long Style
4. Ford long Style w/counterweights

Anytime a clutch uses counterweights to lock up, it will be more difficult to shift at elevated engine rpms. Counterweights can appear in any of the four choices. Best to stay away from them. Dual disc clutches require less plate load because of increased friction surface area attributable to the second disc.

[Grubby]

I love my Street Twin. It is very drivable, but not cheap.

Good choice for high HP street car.

John

[Grubby]

I love my Street Twin. It is very drivable, but not cheap.

Good choice for high HP street car.

John

[Morris]

Here's a McLoed Flywheel that is 184 Teeth and their 8" competition Clutch.....It's either on or off...no inbetween....

[Morris]

Here's a McLoed Flywheel that is 184 Teeth and their 8" competition Clutch.....It's either on or off...no inbetween....

[eschaider]

Very nice piece there, Morris!

From the visible straps, it appears you are using their dual disc 8-inch unit, which has a very low moment of angular momentum. That must feel like there is no flywheel in the car when you get after it.

[1795]

Originally Posted by Morris

Here's a McLoed Flywheel that is 184 Teeth and their 8" competition Clutch.....It's either on or off...no inbetween....

Morris,

That's the exact same setup that I have, with the exception of it being the 289 version. I try to follow what the smart ones are doing...

Jim

[cobrarkc]

I have the Spec stage2 behind my 402 stroker with 600hp and I love it, it's very streetable and no problem feathering it around town or in traffic.

[undy]

No McLoed clutch for me. My RXT dual disc failed and started slipping on my 640HP Chevy C6 Z06 Vette at a very low mileage. It was setup and installed by a very competent Corvette shop.

I'm running a Ram single disc on my KC 482" Pond side-oiler since day 1, not one single problem or hiccup.

[undy]

Duplicate, another typical forum screwup.

[blykins]

RAM makes a good clutch and so does McLeod. They're the only two that I choose to sell.

I've sold hundreds of clutch kits over the past 18 years and have had to get RAM involved on one kit and McLeod involved on one kit. I feel like I see a much wider sample selection than most guys. Can't go wrong with either one of those companies.