Knowledge shared with others will result in Progress.
The AC Cobra Replica Site
People that have visited this page from 20-Dec.-03
Revised at 14 - June.-2007
There are several design considerations for a good working clutch.
1– It should Works!
2- Pedal force. (You want to have as low as possible)
3– Travel of T/O bearings. (Should be enough to engage the clutch)
3– Travel of the pedal. (Not to much to get easy live)
4– Stroke of Cylinders. (Should be check for the proper selection )
5– Cylinder selection. (Just that, select the correct one)
I have made and Excel Spread Sheet that will help you to setup your Clutch.
Please read before you DOWNLOAD (at the bottom of the page)
There are two basic type of clutch setups. Those are related to the Fork design.
Type “1” is the one that has the pivot point at the middle.
Type “2” is the one that has the pivot point at the edge.
How to use the spread sheet:
The grey cells are the calculated results with formulas. (Don’t touch it)
Red cell is a base information that will fit 99% of the Clutches.
Yellow cells are the cell where you can play and put your specific information.
At the left side, in grey cells, I have put the GM information as a reference of this particular example. But FORD guys will be also have the same information.
The important thing here is the “T/O bearing stroke” RED cell, this 11 mm apply to 99% of the clutches. Don’t tell me that your clutch is different!!!!!! Just use 11 mm.
The people that use other type of clutches, know about it and they don’t need to use this information page.
How to work with:
1- First select that work sheet that fits your fork, Type “1” or “2”
2- Put the amounts of Kg that are required for your clutch (F4) most of the clutches are around 180 Kg when we talk of a clutch diameter of 11”
3- Measure your fork dimensions A and B (Check the drawing)
4- Now you can fill the cells with the dimensions A and B
5- Measure the pedal and fill the cells C and D
6- Select the diameter of the cylinders, Master and Slave. Indicate at the yellow cells the
diameter of the cylinder in Inch. There is a table below with the most popular diameters.
7- Now become the most difficult part, evaluate the results and make the decision.
Lets see if I can help you.
All the important information is located at the box “HOW MUCH”
- Pedal Travel
To long will be annoying, try to keep it under 100 mm
- Pedal Force
Here is one of the most important things, make it as low as possible, if you can achieve 15 Kg consider as done.
If you want to see how much you can handle use the next trick. Take a bath room scale and find a place to seat that is equivalent to your seat position with good support of you back. Support the bath room scale like it is you pedal. Now push the scale with you feet and read what you can and please select what you want for a city traffic.
As reference “Can you hold the force for a minute?” that is OK but if you get tired from holding the force don’t select that.
Everything above 25 Kg becomes very heavy!!!!!!!!!
- Master Stroke
This is the result of all the input information and you should check that your selected master cylinder can handle this length.
- Slave Stroke
This is also a result of all the input information. Off course you need to check that your selected cylinder should be capable to achieve that.
This is a difficult point to have a design that fits all drivers satisfaction.
In a Cobra you have several problems related to the space.
Length of driver.
Length of the “foot well”
Position of pedals.
Dash board high.
Size of feet.
Position of the steer.
And more that you can think about.
The automobile industry has spend lots of money to make a compromise design so there is a guide for us.
Go to you daily drive car and check the position of the pedals, make measurements and try to copy the situation.
Most of the cars has a recessed area at the gas pedal, or you can say an elevated area at the clutch pedal.
I have solved my ergonomics by elevate the bottom of the feet rest position by 25 mm.
Just put a wooden plate, of 25 mm thickness, under the carpet and check if you like.
This is an easy trick to make, just try it!!!!!!!!!
OK the promised Excel Spread Sheet.