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Kirkham Motorsports

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  #1 (permalink)  
Old 01-01-2021, 12:16 PM
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Default twin disk clutch

on my last Cobra (ERA 626) I had a single disk clutch with a hydraulic slave cylinder. It worked great with normal effort to push in the clutch.

just built a new CSX car and I used a twin disk clutch with a hydraulic slave cylinder set up from Kirkham, very nice set up. But I notice that is harder to depress the clutch pedal. I have not driven the car yet and am wondering does the clutch "break in " and get easier to push in? my wife will kill me ... I can deal with it but she wont...
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Old 01-01-2021, 01:08 PM
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The dual disc clutch I have in my Cobra is significantly more difficult to push than the single disc before....course the single disc was not up to the torque of my engine doing autocross starts.
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Old 01-01-2021, 02:14 PM
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That seems odd to me. The guys who have installed McLeod twin disc clutches in ERAs have commented about the light pedal pressure. The twin disc I had in my Shelby GT350 was feather light.
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Old 01-01-2021, 04:00 PM
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Can't say I noticed a differnce.
But when she's all warmed up, she GRABS.
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Old 01-01-2021, 06:13 PM
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Mine is a McCloed.
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Old 01-01-2021, 07:04 PM
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Unless you're going drag racing with really sticky tires, or you're going to repeatedly strap your car down to the chassis dyno so it can't break traction, I don't think it really matters on a mostly street driven car that only has 600 lbs on each rear wheel. My crappy Yokos break loose if I give it any sort of throttle, like maybe 200 ft/lbs or less of throttle. I think a cardboard driven disk and a pressure plate made of bobby pins would hold it all together and the tires just break loose when the torque gets cranking.
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Old 01-02-2021, 01:13 AM
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As Patrickt, said for most street driving, I use my tires as the limiting factory. Easiest & Cheapest to change. Back in the Day, running for a championship, Even Auto-xing in stock class you used a set of tires just for that propose. To tell you how long ago that was the trick tires were (Yoko's 008 RS 2's ). Just wondering Mike, is there a reason you went to a two disc set-up??? Cheers TommyRot.
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Old 01-02-2021, 03:39 AM
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Quote:
Originally Posted by ERA 626 View Post
on my last Cobra (ERA 626) I had a single disk clutch with a hydraulic slave cylinder. It worked great with normal effort to push in the clutch.

just built a new CSX car and I used a twin disk clutch with a hydraulic slave cylinder set up from Kirkham, very nice set up. But I notice that is harder to depress the clutch pedal. I have not driven the car yet and am wondering does the clutch "break in " and get easier to push in? my wife will kill me ... I can deal with it but she wont...
The number of clutch plates does not affect the feel at the pedal.
The pressure plate diaphragm spring, and then the throwout fork/hydraulic cylinder ratio, pedal ratio, determines the pedal effort.

Gary
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Old 01-02-2021, 03:59 AM
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I would check the size of your master cylinder. A twin disc should not be hard to push.
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Old 01-02-2021, 05:12 AM
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Quote:
Originally Posted by Gaz64 View Post
The number of clutch plates does not affect the feel at the pedal.
The pressure plate diaphragm spring, and then the throwout fork/hydraulic cylinder ratio, pedal ratio, determines the pedal effort.

Gary
Yes, but a dual disc design will hold more power than a single disc for a given pedal pressure.
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Old 01-02-2021, 06:10 AM
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I had a Mcleod RXT dual disc in my 640hp C6 Z06 and it was a complete POS. It started slipping with 10K on the clock. It had minimal abuse too. There are much better choices out there.
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Old 01-02-2021, 06:13 AM
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Quote:
Originally Posted by undy View Post
I had a Mcleod RXT dual disc in my 640hp C6 Z06 and it was a complete POS.
You should have gotten my cardboard/bobby-pin clutch from Centerforce. Works like a charm.
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Old 01-02-2021, 06:15 AM
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I have a McLeod RXT in my Cobra and it is probably the nicest clutch I have ever had. The old clutch was a single disk rated for 700 rwhp, and you had to shift into neutral at every stop light just to save your leg from cramping. The pedal feel is awesome and pretty light. It also doesn't chatter like the old clutch had a tendency to do.

My buddy just installed one in his AMX for the same reason I did. He loves it also.
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Old 01-02-2021, 06:18 AM
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I've had even worse luck with Centerfarce. Advance auto remanufactured clutches hold better.
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Old 01-02-2021, 11:55 AM
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Quote:
Originally Posted by Gaz64 View Post
The number of clutch plates does not affect the feel at the pedal.
The pressure plate diaphragm spring, and then the throwout fork/hydraulic cylinder ratio, pedal ratio, determines the pedal effort.

Gary
What Gary said is spot on.

I made my own 10.5" dual disc clutch before McLeod had their RSX/RST versions commercially available. The clutch set up is particularly important if you want the car to drive properly and shift correctly. Here is a picture of my finished, assembled unit;



Here are pictures of the finished components, prior to assembly;



The pressure plate was a 10.5" Ford FRPP component that uses a high leverage diaphragm spring to provide a high clamping force at a low pedal pressure. Like Gary has already pointed out, you have complete control over how this feels by properly selecting the throwout fork/hydraulic cylinder ratio, pedal ratio. My pedal feels very light, very much like an OEM showroom stock vehicle's clutch.

The discs I used are organic McLeod solid hub discs for their older style dual disc clutches. McLeod uses a wavy spring called a Marcel spring between the friction material and the steel disc, friction material, mounting plate. The effect is a gradual compression of the wavy spring as the clutch applies until the friction material, marcel spring and disc substrate stack solid. The driving experience is a silky smooth engagement anyone can easily handle when driving it.

The floater was a Crower floater that I modified to work with the layout on my clutch build. The flywheel was a fabricated unit that I built to use replaceable Crower heat shields from their blown alcohol clutch designs. Here are a few pics of it as I cut the relief for the heat shields;



And then again later as I am drilling the holes around the circumference to remove rotating mass I did not want.



After the perimeter I go in to locate the attaching bolt holes for Crower's heat shields;



This is the finished wheel less the heat shields;



And of course this is what it looks like in final form with the heatshilds attached;



Once I had completed the flywheel, I took it over to the balancer to see how much imbalance I had added to the assembly.



I was surprised to find the wheel was within 1 gram of a perfect balance! Who said blind squirrels can't find acorns?

BTW the cost for the entire shebang was somewhere around $600 or $650 when I did it about 10 years ago.

Driving it, it has a light clutch pedal, smooth engagement and just an all around pleasant driving experience.

If you buy a performance equivalent and you do not pay attention to the clearance stack up in the clutch pack you will not have a happy experience. If you do and you do not screw up your clutch linkage you will be very pleasantly surprised at how light the clutch pedal feel is and how predictable the engagement is.


Ed
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Last edited by eschaider; 01-02-2021 at 12:40 PM.. Reason: Spelling & Grammar
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Old 01-02-2021, 01:13 PM
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Quote:
Originally Posted by undy View Post
I've had even worse luck with Centerfarce. Advance auto remanufactured clutches hold better.

It's because they *are* Advance Auto clutches. The pressure plate is a Luk brand, with counterweights added. The disc is nothing special. Of all the manufacturers, I rarely get a call about an issue with RAM or McLeod. I've had all kinds of emails/calls about Centerforce.

As for the RXT, that's been the only streetable clutch that has held in one of my customer's cars. It's an old Galaxie wagon with a 390. Launches at 6000 on slicks, shifts at 7000. Weighs almost 5000 lbs.

The RST has had issues with higher horsepower applications from what I've seen, but the RXT has been bulletproof on my stuff so far.
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Old 01-02-2021, 02:13 PM
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Quote:
Originally Posted by eschaider View Post
What Gary said is spot on.

I made my own 10.5" dual disc clutch before McLeod had their RSX/RST versions commercially available.
Dang, that's some serious fabrication. Especially when it's spinning at 7000 RPM.
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Old 01-02-2021, 03:00 PM
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Quote:
Originally Posted by blykins View Post
I would check the size of your master cylinder. A twin disc should not be hard to push.
Agreed, a smaller MC may be the fix, though pedal travel will be longer.
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Old 01-02-2021, 06:19 PM
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Dang, that's some serious fabrication. Especially when it's spinning at 7000 RPM.
I know what you mean, Patrick. It is more than a little sobering. That said, the reality of it all did not sink in for me until well after the job was done, in the car and I had spun it up there a couple of times. Even had I bought an aftermarket solution I would have still used the Lakewood can. It can do a great deal to blunt the impact of any clutch / flywheel explosion, home built or otherwise.

I also spent a lot of effort to carefully machine all the pieces and always used high grade / high quality virgin billet steel. As I finished each piece, I worked hard to remove any potential stress risers I could find that were left behind from from the machining process.

Overall I feel as comfortable with it as if I had bought an SFI certified aftermarket piece. At the time there were no aftermarket dual disc setups available for the engine so it was the old hot rodding approach of make it your self if you can't buy one.

What I did with fabricating the clutch is not such a big deal. What Morris did with his car is a BIG deal.


Ed
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Last edited by eschaider; 01-02-2021 at 06:24 PM.. Reason: Spelling & Grammar
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Old 01-02-2021, 06:24 PM
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my master cylinder is .750 with a 7/8" slave. I am considering going with a .625 master, this will improve the clutch effort...
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