Learning about clutch set-ups. Need a little help

[Tallguy]

I spent the last couple hours learning about the different ways to set up the clutch to clutch pedal linkage. It seems like most use a hydraulic set-up with a master and external slave cylinder.

I am trying to figure out what options I have to get the shortest pedal stroke and still have a clutch that is not too stiff. I am too tall for a Cobra, but I'll fit somehow. Thinking that if I use a bigger master than slave, I can mount the pedals more forward and still not hit the firewall. I can see how this might work on a bottom mount pedal like ERA, but what about top mounted pedals where the master sits on outside the firewall. Aren't these already mounted at the firewall?? Maybe I could fab an offset pedal along with the larger master to gain some leg room.

I guess the question is what are the best options to get the pedals closer to the firewall for more legroom?? What are the limitations

Thanks,
Mark

[Blittleton]

Tallguy,

The shortest throw that I have found is with a hydraulic throwout bearing. They work really well. I like them but they are more expensive. $450 with fittings and TKO adapter with a tilton throw out bearing.

Just my .02 worth.

Bill

[strictlypersonl]

There are pedal assemblies with cylinders on the same side as the pedal faces, like this Tilton.

[Michael C Henry]

My car has three Tilton master cylinder under the floor board , one for the clutch and two for the brakes. Two pedal arms come up from there and have AC on the pedals. The two brake master cylinders have one arm and pedal with an adjustable balance bar between them to get the correct brake bias front to rear. The two cylinder resivoirs are mounted above on the fire wall in plan sight and are connected by hoses to the master cylinders. Bleeding has never been problem. The only problem I ever had was the Clutch 7/8"ID master cylinder that came with the car originally, wasn't large enough to move the volume to get free travel and full clutch release. I gave up leverage for volume moved up to a 15/16"ID master cylinder . The Tilton master cylinder came as a kit in a box with multible resivoir options. The increase in foot presure needed to operate the larger master cylinder wasn't appreaciable to me.

I'm using the original style throw out bearing and arm with a hydraulic slave cylinder mounted to the frame in front of the arm. I have a Ford toploader 4spd transmission with the 1 3/8" input shaft. McLeod alluminum flywheel ,11 1/2" clutch and pressure plate. the McLeod alluminum flywheel has a a steel heat sheald and multible pressure plate holes to accept any size clutch up to 12". The bottom of the Cobra cast alluminum oilpan is right at 3" off the ground. The 11 1/2" clutch was Fords answer in the day to the power and loads generated by the engines mid sixties. Which ever way you chose it will have trade offs.

[Tommy]

Mark -
Perhaps this will keep you from hunting too many wild geese in your search for the ideal clutch assembly. A typical clutch assembly uses a combination of lever arms and hydraulic pistons to cause the throw out bearing (TOB) to move the spring loaded fingers on the clutch. A working system must be capable of exerting enough force to move the TOB and have enough travel to allow the TOB to disengage the clutch. Regardless of its components, there is a consistent relationship between the force and travel of the TOB and the force and travel of the clutch pedal. If, for example, your TOB must exert 100 pounds of force and travel one inch, you can select your components to give you a relatively light 20 pounds of force at the pedal, and it will have to travel 5 inches. If, on the other hand, you have room for only two inches of pedal travel, you'll have to select components that will require 50 pounds of force. The bottom line is this - regardless of how you mount your clutch pedal, you'll have to choose between lighter pedal force and shorter pedal travel. You can't have both without some sort of power assist.

[Tallguy]

Thanks for the replies.

Blittleton - I have heard good and bad about HTOB, but it seems this is due a lot to improper set-up.

Bob - Thanks for the link. It makes sense.

M. Henry - Thanks for sharinng your set-up. Helps me to understand better.

Tommy - Good stuff. I understand the mechanics of how the hydraulics work, but I am unclear as to the limitations on what is available and/or "standard". For example, can you get a pedal with 2" of travel, and is it usable to the average driver. How much force can the leg reasonably exert.

Thanks,
Mark

[Tommy]

Originally Posted by Tallguy

For example, can you get a pedal with 2" of travel, and is it usable to the average driver. How much force can the leg reasonably exert.

Thanks,
Mark

On the hydraulic master/slave systems I know, the clutch pedal is at the end of an arm that swings from a pivot point. Somewhere along the arm is a point where the arm pushes a rod that goes into the clutch master cylinder. That point is typically located so that full travel of the clutch pedal will fully insert the rod into the master cylinder. If the pivot point, the point where the rod meets the arm or the location of the pedal along the arm is moved, the geometry of the system will change. Here's an example.

Suppose the pivot point is at one end of an 8" long arm and the pedal is at the opposite end. If the rod meets the arm 2" from the pivot point, it will move about one inch when the pedal moves four inches. If the master cylinder has the same bore as the slave cylinder, the rod from the slave will protrude the same one inch out as the rod into the master cylinder goes in. ... Now suppose you want to modify this system to allow the same movement of the slave rod with less pedal travel. One way would be to cut off half of the clutch arm and weld a pedal on the end of the shortened (4") arm. With this configuration, the pedal would only need to travel two inches to move the master cylinder rod (and the slave rod) one inch. Of course, the operator would have to push on the clutch pedal twice as hard as before to get it to move.

The level of clutch force a driver can tolerate is an individual thing. Maybe a trip to the local gym would give you an answer.

[Tallguy]

Thanks Tommy,

I guess the bottom line is that a guy could custom fab anything, as long as it is able to be operated, and you get the proper strokes to disengage the clutch.

I am going to do more research to find out what is available that is stock, and then figure out what can be modified if needed.

As for the leg test in the gym, I like that idea. I guess that will give me a measure of "foot pounds"

Mark

[Michael C Henry]

Tilton and Willwood cylinders look as if they came from the same factory. They can come as kit or bought as individual componets. I beleive the master cylinders come in varyng 1/16" IDs . I'm unsure how smal or how large tey go. I have 3/4"ID brake master cylinders. I went from 7/8"ID to 15/16"ID for the clutch master cylinder, all the same design. I made the change of the clutch master cylinder after encountering a problem. I went and bought a Tilton 1" ID cylinder kit but after concidering all the warnings of over traveling went and bought another Tilton master cylinder kit in 15/16" ID. which I actually usde. A very simple solution for my situation. remember area x travel = volume potential. If you can't increase the travel ,increasing the area increases the effort needed to move the same resistance load. Im sure if you contact the sales departments at these manufactures they wiil connect you with Tech which has allready organized a complete system for your situation.

[uncltodd]

Check the horizontal spacing on your pedals.

Until an old hot rod/machinist friend of mine made some mods, I had to take both of my 11-1/2 EEE's off and drive with stocking feet!!!

I know it sounds kinda stupid, but it's nice being able to drive my dream car with my shoes on.

[Tallguy]

Thanks MCH and uncltodd. Peddle spacing is a concern, and shoeless is an option.


I do have one last question. I have modeled the clutch leverage system in a spreadsheet to figure out where I can trade off for less pedal travel. I have specs for pedal leverage and understand the master/slave cyl relationship. What I can not find are the dimensions for the clutch fork. I plan to run a 428 FE and a TKO 600 with a blow proof bell. Not sure on clutch parts yet as I am a novice. I am trying to figure out what clutch fork would be used, and what the relative dimensions are from the pivot point to the slave push/pull point, and from the pivot point to the throwout bearing centerline. This will give me mechanical leverage for my calcs.

Thanks,
Mark

Edit - Thats 428 FE not 438 FE.....

[uncltodd]

Rock on, Brudda, you are 'way past me and I wish you well.

UT

[Tommy]

Mark -

Approximating the dimensions from the photo on this web site is the best I can offer.
http://4speedtoploaders.com/shopsite...sandforks.html

[patrickt]

Originally Posted by Tallguy

I do have one last question... What I can not find are the dimensions for the clutch fork. I plan to run a 438 FE and a TKO 600 with a blow proof bell... I am trying to figure out what clutch fork would be used...

I believe the TKO600 uses a standard Ford small spline fork, D0TZ-7515A. They also fit Ford Trucks 73-79 L6 so the specs should be available on line, or you could just pick one up at the local autoparts store. OR, someone here might have one sitting on the shelf and would be kind enough to measure it for you, angles and all .

[Tallguy]

Thanks guys. I'll either find a fork spec online or estimate from a pic.

It's funny how most things I can find a million websites with more info then I need, and others are just a bit to detailed with minimal info. I think it is me digging deeper than most do to understand every little detail rather than just accept it for what it is. I am an engineer if you could not guess

Mark

[767Jockey]

Mark,
I recently spent a considerable length of time on the phone with a tech at Wilwood. They make pedal assemblies, masters and slaves. Tell them what you want, and they'll gladly mix and match components to give you the min pedal travel / max action setup available. These guys know their stuff. Ring one up and talk - the guy I got was great. Good luck.

[Tallguy]

Originally Posted by 767Jockey

Mark,
I recently spent a considerable length of time on the phone with a tech at Wilwood. They make pedal assemblies, masters and slaves. Tell them what you want, and they'll gladly mix and match components to give you the min pedal travel / max action setup available. These guys know their stuff. Ring one up and talk - the guy I got was great. Good luck.

Good tip. In this age of the internet, the last thing I do is pick up the phone. I think talking to the experts is the thing to do.

Mark

[RodgerH]

Originally Posted by Tallguy

I do have one last question... What I can not find are the dimensions for the clutch fork. I plan to run a 438 FE and a TKO 600 with a blow proof bell... I am trying to figure out what clutch fork would be used....

Originally Posted by patrickt

I believe the TKO600 uses a standard Ford small spline fork, D0TZ-7515A.

Hey Mark,

I measured an extra fork I have, p/n DOTZ-7515B, which is what I used on my FE/Lakewood/TKO600. I don't know what is different from the D0TZ-7515A.

Pivot to throwout bearing centerline= 3-7/8"
Pivot to slave rod push point= 6-5/8"

Hope this helps!

Rodger (also an engineer - but retired as of yesterday! )

[patrickt]

Originally Posted by RodgerH

I measured an extra fork I have, p/n D0TZ-7515B, which is what I used on my FE/Lakewood/TKO600. I don't know what is different from the D0TZ-7515A.

Dang, didn't even know there was a D0TZ-7515B. I know there's a C8OZ-7515B that costs about five times as much and is a clip-type for the 390. Click on this link and tell me which one your 7515B looks like the most: http://www.autokrafters.com/v4/go.gn...Template=40002

[Tallguy]

Originally Posted by RodgerH

Hey Mark,

I measured an extra fork I have, p/n DOTZ-7515B, which is what I used on my FE/Lakewood/TKO600. I don't know what is different from the D0TZ-7515A.

Pivot to throwout bearing centerline= 3-7/8"
Pivot to slave rod push point= 6-5/8"

Hope this helps!

Rodger (also an engineer - but retired as of yesterday! )

First off, congratulations on your retirement! Must be a great feeling today.

Thanks so much for the fork dimensions; this is exactly what I was looking for. There is more leverage than I thought. What clutch and pressure plate did you use, and are you happy with them?

mark