Concentric Slave Cylinder vs External Slave Cylinder
Clutch Slave Cylinders
The function of a slave cylinder is primarily controlled by the master cylinder. Slave cylinders are divided into two primary categoires: Concentric slave cylinder (CSC) and external slave cylinder.
Concentric Slave Cylinder
The CSC is mounted inside the bell housing where the release bearing retainer is normally attached. This unique design offers the following benefits: Elimination of the clutch fork and related hardware, precise release bearing travel with better alignment geometry, and closer fit to the transmission which increases flexibility in passenger compartment design. A CSS uses a large coil spring to maintain constant contact between the bearing face and diaphragm spring fingers. Therefore, no “lost travel” is required between the release bearing and diaphragm spring before the clutch pressure plate begins to disengage.
Many newer style plastic body CSC designs include plastic shipping straps attached to the plastic bushing and to the body. These straps compress the overall length of the unit during installation, which means the pushrod does not need to be compressed in order to clear the release lever. If the hydraulic system has been properly bled, the straps will break when the first stroke of the clutch pedal moves the pushrod forward. Like other suppliers, AMS offers the CSC with the angular contact bearing already attached. However, AMS was the first supplier to offer popular CSC sku’s without the release bearing. Because the clutch kit contains the release bearing, this eliminates the duplicate cost of a release bearing when both the CSC and clutch kit are installed.
(No-bearing) Concentric Slave Cylinder
Since their introduction in light truck applications in the late 1980’s, clutch release systems containing a concentric slave cylinder (CSC) have become the hydraulic system of choice in domestic applications. Not only are they reliable and easy to troubleshoot, they also eliminate the need for other parts such as the release fork, quill, and pivot linkage. In many instances, the CSC is equipped with a replaceable angular contact release bearing. Because the thrust face surface of this bearing maintains constant contact with the pressure plate diaphragm spring, the bearing may fail before the remainder of the CSC.
When installing a new clutch kit in a CSC equipped application, it’s important to always inspect the hydraulic system. If it is operating properly, simply replace the old release bearing with a new release bearing (contained in the clutch kit), along with the other components found in the kit. However, if the clutch will not release and/or the hydraulic system is leaking or will not bleed properly, a new CSC should be installed, along with a new master cylinder and clutch kit. In this instance, the technician is now forced to purchase two release bearings, one that’s contained in the kit and one that’s already attached to the new CSC.
In order to eliminate the duplicate cost of sourcing two release bearings, AMS offers the industry’s first and most comprehensive lineup of no-bearing (NB) options. Many of these NB options are among our most popular slave cylinders. What’s more, they offer a significant price reduction versus the same slave cylinder with a release bearing. Although the vehicle owner ultimately pays the price for unnecessary parts, many of the extra release bearings end up being returned to the jobber or WD. Because no paper trail exists for the sale of the extra bearing, the distributor may end up issuing an inflated credit for the bearing. All NB options are cataloged using the standard slave cylinder part number, followed by an NB suffix (i.e. S0710NB)
External Slave Cylinder
As the name implies, external slave cylinders are normally mounted on the outside of the transmission bell housing. They consist of few moving parts other than a piston, internal spring, and pushrod. A rubber boot is usually used to seal contaminants away from the moving parts. The release bearing used in this system always maintains preloaded contact with the diaphragm spring. The external end of the pushrod is normally tipped with plastic, mushroom-shaped, bushing that serves to reduce noise and eliminate surface wear on the clutch fork pushrod tip. The plastic bushing is also important because it helps determine the overall length of the rod. This exact length is very critical in the overall function of the hydraulic system.