Late model vehicles utilize a concentric hydraulic slave/release bearing that mounts on the front of the transmission to actuate the clutch system.  It is imperative that you understand how these systems work when installing a replacement or aftermarket clutch system.

The factory concentric slave utilizes a spring to keep the bearing positioned constantly on the clutch release fingers.  When the transmission is removed the spring will push the bearing out to the maximum extended position.  The distance from the bearing when it is contacting the clutch fingers to the fully extended position described above is typically .500-.600 inches.  This distance can be described as ‘preload’ and is the main factor in setting up the factory concentric slave with an aftermarket clutch system.

There are two keys to making this factory system work with your particular clutch.  One, we must determine the amount of space available in your bellhousing for a new clutch system, and two, we must take the proper measurements to determine how much preload the bearing will have.  Too much preload will not allow sufficient clearance for the clutch to wear over time and can cause interference from the bearing sleeve to the clutch disc.  Too little will not allow enough forward movement. 

DETERMINING HOW MUCH SPACE IS AVAILABLE TO FIT THE CLUTCH

TOOLS NEEDED:

18 inch straight edge or steel ruler

Minimum 6 inch, preferably 12 inch dial (vernier) calipers

DETERMINE THE CRANK FLANGE PROTRUSION

Measure the amount of the crank flange that protrudes from the back of the engine block.  This is dimension A in the diagram below.

DETERMINE THE BELLHOUSING DEPTH TO THE RELEASE BEARING

The bellhousing is attached to the transmission and the slave cylinder bolted in place to do this measurement.  Using the straight edge, lay it across the block mounting flange of the bellhousing.  Have a partner depress the slave cylinder bearing to its compressed (shortest) position.  Measure from the straight edge down to the release bearing face.  Be sure to subtract the thickness of the straight edge.  This is dimension B in the diagram below.

DO THE MATH

The space available for a clutch is the bellhousing depth measurement less the protrusion of the crank flange, less .150”- .180” minimum for bearing ‘freeplay’ or clearance (.150” for single disc clutches, .180 for dual disc clutches):

Dimension B – Dimension A  - .180” = available space

EXAMPLE:

Dimension A (crank flange protrusion):                                  .300”

Dimension B (Distance to bearing compressed):                    3.445”

Freeplay:                                                                              .150” - .180”:

3.445”(B) less  .300”(A) less .180” = 2.965” available space

DETERMINE THE SETUP HEIGHT OF YOUR CLUTCH

Measure the setup height of the clutch assembly.  Bolt the pressure plate to the flywheel with the disc so it is exactly as it would be in the car.  Set the assembly up on a flat block under the crank flange of the flywheel.  Measure from the tip of the clutch finger, down through the disc center hub, to the block that the flywheel is sitting on.  Take an average reading of 3 or 4 positions on the fingers around the clutch.   This will be Dimension C below.

Dimension C = your clutch setup height

If the clutch assembly height is within the tolerance of 2.940”, it will fit in this application.   If it is taller by .180”, the release bearing would be loaded to its maximum and leave no free play for wear of the clutch.  Now proceed below to see how to determine the bearing preload.

DETERMINE HOW MUCH PRELOAD THE RELEASE SYSTEM HAS WITH YOUR CLUTCH

This measurement is important to make sure you will have enough travel from the slave release bearing to properly disengage the clutch.  We recommend a minimum of .500” preload so that you have a minimum of .500 forward travel.  In some cases, it may be necessary to space the factory slave off the transmission to achieve this preload.

TOOLS NEEDED:

18 inch straight edge or steel ruler

Minimum 6 inch, preferably 12 inch dial (vernier) calipers

DETERMINE THE FREE LENGTH DEPTH OF THE SLAVE RELEASE BEARING

The bellhousing is attached to the transmission and the slave cylinder bolted in place to do this measurement.  Using the straight edge, lay it across the block mounting flange of the bellhousing.  Leave the release bearing in its relaxed (extended) position.  Measure from the straight edge down to the release bearing face.  Be sure to subtract the thickness of the straight edge.   This is dimension D on the diagram below.

DO THE MATH

We have already determined the other critical measurements to figure out the preload:

Dimension A – crank flange protrusion

Dimension C – Clutch setup height

(Dimension A + Dimension C) - Dimension D  = bearing preload

EXAMPLE:

Dimension A (crank flange protrusion):                                  .300”

Dimension C (clutch setup height):                                        2.940”

Dimension D (extended bearing position):                             2.575”

{ .300”(A) + 2.940”(C) } less  2.575”(D)

              3.240”           less  2.575”(D) = .665” preload

So in this case, the release bearing is preloaded .665”, which is over the .500” minimum.  If this measurement was to come up under .500”, an appropriate sized spacer would need to be placed between the bearing slave cylinder and the transmission to achieve the .500” minimum bearing preload.

Bearing setup diagram/worksheet-->

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