Making a Clutch Install a One Man Job

Use a cutoff bolt with a slot cut in it.

Making a clutch installation a one man job might be as easy as some bolts with the heads cutoff. This trick will work for installing the flywheel as well as the pressure plate which is also called the cover assembly.

Check this YouTube video out HERE to see what we mean.

Where this really helps is on flywheels and clutch covers that weigh a lot. If you put these two studs at roughly 10 o'clock and 2 o'clock then you can slide the flywheel or clutch cover on these studs and then start the other bolts without fear of dropping.

You fingers and feet will thank you. If you're not wearing steel toed boots (and that still may not keep you from injury) and you drop a flywheel or pressure plate on your feet....well we don't have to describe how that might turn out.

Of course, in order to truly make this a one man job you may still need a transmission jack and a car lift.

Torin TRA4053 Pedestal Transmission Jack - 1/2 Ton Capacity

Torin QJY230C 2 Post Lift - 7,000 Lbs., Symmetric Base Plate Chain Drive 

 

Ways to Increase Clutch Torque Capacity

There are a few simple ways to increase torque capacity in a clutch system.

1) Add friction surfaces. Instead of just one disc, two or three disc clutches are sometimes used.

2) Increase the coefficient of friction of the friction material. The following materials are often used: organic (.25), carbon/kevlar (.28), kevlar (.36), ceramic (.38)  and steel/feramic (.40). As the coefficient is increased clutch grab or chatter might occur.

3) The spring/diaphragm pressure is increased in the cover assembly (a.k.a. pressure plate). The clutch pedal effort will usually increase.

4) A larger mean radius (r) is used. This is also called the radius of gyration. This means generally a larger diameter disc, cover assembly (pressure plate), and flywheel but can sometimes mean that the inside radius of the lining is increased which would give a larger mean radius without changing the overall diameter.

          r = mean effective radius of lining in feet [(inside radius + outside radius) ÷ 2]

Sometimes a combination of all four are used. For example, an Eaton (aka Spicer) clutch for a large 18 wheeler truck can have two discs that have ceramic button discs that are 15-1/2" in diameter with a 2,000 lb cover assembly clamp load.

Related Pages:

Calculating Clutch Torque Capacity 

Clutch Torque Calculator

How a Clutch Works

This is a good video that shows how a clutch system works. It shows the overall view and then how each component works.

Troubleshooting - Clutch Slipping

Trouble: CLUTCH SLIPPING

Probable Cause:

1. Worn clutch facings
2. No free travel at pedal
3. Grease or oil on facings
4. Linkage adjusted improperly
5. Weak or broken pressure springs
6. Distorted pressure plate
7. Throwout bearing (aka release bearing) riding release levers
8. Pressure plate binding on studs
9. Clutch parts binding
10. Release mechanism binding
11. Overloaded clutch 

Flywheel Hotspots

Calculating Clutch Torque Capacity

Clutch Disc with Organic Friction Material

Let's talk about torque and how the torque handling ability is calculated for an automotive clutch.

The formula looks like this:

Torque Capacity (lb-ft) = F ● Rg ● N ●µ

The torque capacity of a clutch can be calculated if the following four values are known.

1) F = Clamp load applied by the cover assembly in pounds (lb).
2) Rg = The mean radius, or radius of gyration, of the friction material in feet (ft).
3) N = The number of friction surfaces, one disc has two surfaces.
4) µ = The coefficient of friction of the facing material.

Let's go through them in order.

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First of all, the clamp load applied by the cover assembly will be something that the manufacturer or distributor will have to give you. This number can range from (but is not limited to) 800 lb. to 3,200 lb. For our import car example we will use 950 lb. Special equipment is needed to calculate this number. Contact the company you bought your clutch from as they should be able to tell you the clamp load number for the cover assembly in your particular vehicle.

The second variable is the mean radius of the of the friction material in feet. This is also known as the radius of gyration. At first glance it might sound simple to calculate but it actually involves a few steps. I will go through an example of how to calculate it. The first thing you need to do is measure the outside diameter of your clutch disc (a.k.a. driven disc) in inches.

Then measure the inside diameter of the clutch disc (at the edge of the friction surface) in inches. The Radius of Gyration in Feet = Square Root of (Outer Radius in Feet Squared + Inner Radius in Feet Squared / 2) .
Note that this formula says RADIUS of gyration in FEET. Remember that your diameter numbers will have to be coverted from inches to feet and then divided by two to get the RADIUS in FEET.

For example, if you have a clutch disc with facing that has outer and inner diameters of 8.35" x 5.91" respectively, then that would translate into radii in feet of 0.348' x 0.246' respectively. Then we plug these numbers into the radius of gyration equation. The Radius of Gyration in Feet = Square Root of (0.348' squared + 0.246' squared / 2). The final number for this example would be 0.30 ft.

That pretty much takes care of the complicated stuff. Next you would need to know the number of friction surfaces. 1 disc = 2 surfaces, 2 discs = 4 surfaces, 3 discs = 6 surfaces...... You get the idea. The example here will have 1 disc (N= 2 surfaces).

The last number you will need to know is the coefficient of friction of the disc's facing material. In general, the following numbers can be used for most automotive clutches if you just know the basic material the friction is made of:

Stock Organic Facing Material = 0.25
Carbon/Kevlar Material = 0.28
Kevlar Material = 0.36
Ceramic Material = 0.38
Steel Material = .40

Coefficient of Friction numbers can vary from manufacturer to manufacturer but these numbers are well within reason for the types of material listed and should also provide a slight safety factor which means that each material might have a slightly higher coefficient of friction at lower operating temperatures. Our example will use a stock coefficient of friction of 0.25.

These 4 values can now be entered into the formula and multiplied to determine the torque capacity of this particular import car system.

Clampload = 950 lb.
Mean radius in feet = .30 ft.
Number of friction surfaces = 2
Coefficient of friction .25 (organic facings)


950 lb. ● .30 ft. ● 2 ● .25 = 142.5 lb-ft


As mentioned earlier, this value includes a designed in safety factor that is in excess of the expected maximum engine torque.

If you don't feel like calculating this on your own use our handy clutch torque calculator found HERE.



Related Page:

Clutch Torque Calculator

The Friction Zone and Multiple Clutch Manufacturer Designs

Figure 1 - Friction Zone

The friction zone is the range of driver control from a totally released clutch to full engagement of the clutch. It is used to start a vehicle in motion from a standing start both forward and reverse. This directly determines proper clutch feel and function in addition to the ability of it to transmit power from the engine to the drivetrain. During this time the driver must be in control of the vehicle, not a chattering clutch in control of the vehicle. This is when chatter would occur, and it interferes with the ability to totally control vehicle speed and position.

Figure 1 at right represents the pressure plate just beginning to touch and compress the friction material facings and the marcel cushion springs in between them. This compressible section along with the friction material creates what many refer to as the “Friction Zone”.


Form, Fit & Function

Figure 2 -  Variations of Cover Assembly Designs
of the Same Part Number

Figure 3 - Lever to Table Dimension

One of the issues customers are often confused about is why the parts removed do not look like the ones being supplied in the new clutch set. Take a look at one of the most popular applications, the Ford Ranger. Due to the popularity of this range of trucks, almost every company that manufactures clutches in the world offers a cover assembly for this application. This allows for a lot of potential confusion in the field when a customer attempts to match the old to the new. Take a look at the examples in Figure 2.

The collection in the image shows seven different part numbers from six different countries. One other variation is not shown so that would make it 8 variations for this one application!

How does this affect the customer, countermen and installer? Only two of the pressure plates (aka cover assemblies) look alike. The others are all built from the standard designs that these various companies like to use. All of them fit the flywheel and all work within their respective designs and specifications, but most of them would raise an eyebrow or two at the counter. This is where the fun usually begins.

 Out comes the 12” ruler, tape measure or even a pencil as a gauge. The customer and countermen should be truly commended for trying to figure this part out, but it cannot be done on the counter by comparing measurements of un-installed clutches. The cover assembly must be correctly mounted to a flywheel using either a new clutch disc or precision steel gage blocks like used on a clutch testing table in a lab.

Then the clutch should be cycled (engaged and disengaged) several times. Only after cycling, can one accurately check the Lever to Table dimension or diaphragm spring lever tip height (see Figure 3) and plate lift at the specified release travel and see if the system releases. Note that the plate lift at the specified release travel is not a published number.

One would have to tear this setup down and set up the other seven systems and repeat the entire process to get true comparison numbers. If the customer has any doubts about the fitment of parts please do not hesitate to call the tech line at the company from which you bough the part. They can provide you with all the information you need to verify a part and save you lots of time.

The only bench comparison that is possible to measure is the inside diameter (ID) and outside diameter (OD) of the pressure plate casting. Also, it is possible to compare the bolt pattern and dowel pin pattern. Even this simple comparison can cause confusion due to staggered or offset dowel pin patterns (i.e. Nissan, Honda and Toyota).

Do not forget that GM, Ford and Dodge often use 2 or 3 smaller bolt holes that act as pilot holes for special shoulder bolts. One of the easiest ways to compare confusing bolt or dowel pin patterns would be to trace the pattern on a piece of cardboard using a fine point pen or pencil. Note that dowel pin holes are usually evenly spaced between the bolt holes, or adjacent to the bolt holes. Once traced, place the cover being compared on the pattern and rotate the clutch to find the matching pattern.

Clutches can be very confusing to understand and it can only help the process if the parts do the best possible job in terms of function. It is a real plus when they match Form and Fit at the same time.