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Blueprinting Your Driveline For Optimum Clutch Engagement

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Enthusiasts with manual transmissions might know whether their clutch release mechanism is operated by cable or by a hydraulic bearing. But if it’s the latter, it’s unlikely they could tell whether the bearing operates in constant contact with the clutch fingers or intermittently—that is, operating only when the clutch pedal is depressed. More interestingly, what would lead a manufacturer of high performance hydraulic clutch bearings to adopt one style over the other? Most will tell you the intermittent style offers a greater range of adjustment and quieter operation. It also eliminates the exhausting prospect of a constantly spinning bearing.

In a Columbia, South Carolina, factory, Ram Clutches makes single and dual-disc clutch sets that transmit from 400 to 1,300 horsepower. The company has also cultivated a fine reputation for the production of hydraulic clutch release bearings. These operate on both single- and dual-disc clutches and function only when the clutch pedal is depressed. Tim Matherly, the acclaimed NMRA Real Street Mustang racer says, “The regular hydraulic release bearings that run constantly have a tendency to chirp. But on the higher horsepower cars, if you’re looking for quality, Ram has the best option and they’re quiet.”

First, install the fittings in the bearing housing. The best way to seal the fittings is by applying Teflon tape to the male threads. Do not use liquid sealants as they will leak. Then install the fittings in the bearing housing, using a 7/16-inch wrench to tighten them.

High-performance release bearings that operate only when the clutch pedal is depressed have 0.800-inch of potential travel. More importantly they should be positioned with the correct gap when the pedal is not depressed; that is, the gap between the contact face of the release bearing and the clutch fingers. Excessive gap causes improper release; inadequate gap can cause the bearing to over-travel and collide with the snap ring, or cause slippage as the clutch wears and the fingers move back, making contact with the bearing.

Again, use Teflon on the two-piece bleed fitting. The bleeder line, which is the shorter of the two lines fitted to the bearing housing, will be installed on the top port of the housing to ensure efficient bleeding.

Single-disc clutches operate best with a gap of 0.150-inch while dual-disc sets require a gap of around 0.200-inch. Because the clutch fingers automatically travel toward the release bearing as the friction disc/s wear, an additional clearance of 0.050-inch is assigned to the dual-disc arrangement.

To establish the correct longitudinal position of the release bearing on the input shaft, three measurements are required. The first measurement represents the distance between the crankshaft flange and the rear-machined face of the engine block.

That’s all fine and well, but how do you know when they’re operating with the correct gap? As we know, the entire clutch mechanism is concealed within the bell housing and therefore not visible. However, Southern Performance Specialists, located in Sugar Hill, Georgia, just north of Atlanta, regularly performs the operation and show us in the following series of pictures how it’s accomplished.

To establish the correct longitudinal position of the release bearing on the input shaft, three measurements are required. The first measurement represents the distance between the crankshaft flange and the rear-machined face of the engine block.

 

The second measurement establishes the height of the clutch. First, ensure the clutch is fully bolted-down to the flywheel. Next, place a straight bar across the clutch fingers and measure down through the fingers and center hub of the disc to the back flange of the flywheel. If the back flange of the flywheel is recessed, set it on a pedestal to obtain a true measurement.

 

Again, remember to deduct the thickness of the straight bar and record the clutch height dimension (3.050-inch) on the set-up diagram.

 

Install the stud on the guide collar and secure the guide collar to the bell housing. The stud prevents the bearing from rotating. Next, slide the bearing over the collar to establish the third measurement, which is the dimension from the face of the hydraulic release bearing and the bell housing mounting flange.

 

Remember to deduct the thickness of the straight bar and record the amount (3.650-inch). To calculate the third measurement, simply add dimensions A (0.300-inch) and C (3.050-inch) and subtract this sum from dimension B, which indicates that the bearing when fully retracted is positioned 0.300-inch from the clutch fingers.

 

Typically, Ram aims for a 0.200-inch gap on dual-disc and 0.150-inch on single-disc installations. So to reduce the bearing gap, remove the bearing and place the appropriate amount of cone-shape shims behind it. Some of the shims provided measure approximately 0.100-inch, others measure 0.045-inch.

 

Finally, place the straight bar across the bell housing flange once again and re-measure. If the gap is acceptable install the hydraulic lines—the bleeder fitting resides on the top line—the remaining line routes to the master cylinder.

 

 

Next, check the length of the drive stud with the bearing fully extended. The stud must not come in contact with the clutch cover. Push the bearing out to its full extension and fit it back on the stud with the appropriate shims beneath it. If the stud protrudes through the bearing housing and threatens contact with clutch cover, shorten the drive stud.

 

Finally, there’s good reason to consider inserting a pedal adjuster in the hydraulic line just before the master cylinder. Hydraulic bearings often engage high on the travel stroke of the clutch pedal, which can be uncomfortable. Conveniently, the pedal adjuster enables you to place the pedal mid-travel or, in fact, any clutch engagement position you’d prefer. Usually, the pedal adjuster mounts on the firewall or fender well.

 

Sources

Ram Clutches

(803) 788-6034

www.RamClutches.com

 

SPS Engines

Sugar Hill, Georgia

(678) 482-0866

www.SouthernPerformanceSystems.com


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