High-performance engine installed- Check. Close-ratio Tremec T56 installed- check. Clutch fully operational- nope. Well that isn’t good, it is kind of hard to put 650hp to the ground when your clutch won’t engage or disengage when you operate the clutch pedal. Unlike a mechanically-operated clutch, most modern manual transmissions require hydraulic release bearings, and if you are not close enough, you may as well be a mile off. Installing the American Powertrain Hydramax hydraulic release is not difficult, in fact it is pretty easy, but it does require some math.
The relationship between the clutch diaphragm and the release bearing is the key to a properly adjusted hydraulic set up. The release bearing should ride the diaphragm without putting pressure on the fingers, but also should not be too far away. It is pretty easy to install the bearing where it is either too close (clutch is always disengaged) or too far (clutch won’t disengage). Because these installations are not stock, you have to figure out this relationship on your own. Don’t worry, it isn’t difficult.
What you need:
- Scratch paper
- Straight edge
- Calipers or ruler that reads to .001
- Partially-assembled drivetrain.
To start the process, the engine must be assembled with the flywheel and pressure plate. The clutch does not have to be installed at this point, because it doesn’t matter; but if you want to do everything at once, install the clutch with an alignment tool in place. Additionally, the bellhousing must be installed on the engine as well. Begin by placing the straight edge across the center of the opening in the bell housing. Use a ruler or measuring tape to determine the resting depth of the diaphragm, this measurement is taken off of the fingers themselves where the release bearing rides. Take this measurement in three places and write the results down on the scratch paper.
Moving on to the transmission, the center alignment dowel must be installed, along with the Hydramax bearing with the notch locked onto the dowel in the fully seated position. Use a straight edge on the transmission, running across mounting surface for the bellhousing. Measure from the transmission mating surface to the face of the bearing where it rides on the diaphragm. Measure in three places and record the results.
The two sets of measurements provide the variables needed for the final calculation using the following formula. This equation will tell you how many shims are needed to achieve the proper air gap between the bearing and the diaphragm. The recommended air gap is .150-.200”, you can have as little as .100” (absolute minimum), but try to stay inside the recommended range. It is possible on some GM applications to not have enough room to get to even the .100”. If this is the case, you may have to shim the actual transmission from the bell housing using washers or spacer. This is due to the shallow nature of the GM bell housing design. There are 3 shim thicknesses for the big 3. Mopar uses .063, GM uses .090 and Ford uses .057. The conical shape of the GM shims creates the .090 thickness, even though the metal used to create the shim is not that thick.
Bell facing to clutch diaphragm – minus Bearing Face to Trans bell face – minus .150 / .090 = Number of shims
For example: Bell to diaphragm= 2.450, bearing to trans mount face= 2.125
2.450 – 2.125 – .150 / .090 = 1.94
This means your application needs 2 shims, which yields an air gap of .180”, which is perfectly acceptable.
For GM T56, Tremec Magnum, and Viper 6-speeds, American Powertrain recommends the following procedure for measurements:
Install the clutch and pressure plate to the flywheel on the engine. Place the straight edge across the fingers of the diaphragm and measure from the inside edge to the block mating surface. Record this measurement as A.
Next, install the Hydramax bearing retainer base with guide pin to the transmission and load the bearing onto the retainer, with the guide pin in position on the bearing. Install the bellhousing to the transmission. Place a straight edge across the bellhousing and measure to the bearing face. Record this measurement as B.
Using the formula below, calculate the number of shims. A block plate for a scattershield can be factored in by adding the thickness to measurement B.
B-A-.150 / .090 = # of shims
Once you have determined the number of shims, count them up and stack them behind the release bearing on the transmission shaft, install the bearing, and mate the engine to the transmission. It is that simple. Before you mate the trans to the engine, lube the o-ring on the inside of the bearing base with a little DOT 3 brake fluid.
To demonstrate the process, we installed a HydraMax hydraulic release bearing system on a GM LS- series engine with a Muncie 4-speed (mechanical linkage with an LS is not a simple proposition) which was being installed into a 1969 Chevelle. Setting up the bearing was simple, and the results yielded a smooth clutch without any hiccups.
The process begins by mounting the flywheel to the engine. We torqued the bolts to spec.
The clutch does not have to be installed if this is a mockup, but if it is the final install, make sure it is in there. Be sure to put the clutch in using the correct orientation.
Use an alignment tool to keep the clutch in position.
Next, the diaphragm is installed to the flywheel. There may be multiple bolt patterns on the flywheel, so you might have to find the right holes and line it up.
Use a couple of bolts to secure the bellhousing and then use a straight edge and ruler or caliper to measure the depth of the transmission mounting pad to the diaphragm fingers. Measure in 3 different places and note each measurement. This is measurement A.
The hydraulic release bearing mounts on a stud in the transmission. The American Powertrain kit comes with several studs to match the threads from the front bearing cover. Remove one bolt and match the threads.
Then the stud is installed into the transmission. Don’t forget to use medium threadlocker on the threads and bend the retaining tabs back over the hex on the stud.
The Hydramax bearing slides over the input shaft and locks in place on the stud, this is a free-floating unit, it does get bolted down.
Now measure the height of the release bearing to the transmission mounting flange. Make sure
that you measure to the top of the bearing. This is measurement B.
Using the formula, we determined we need 2 shims: (A – B)-.150”/.090 will determine the number of shims required. For example, 2.45-2.125- .150/.090 = 1.9 shims, so you use 2 shims. You can run as little gap as .100”, but .150 to .200 is optimum. Stack up the shims and install them behind the bearing.
At this point, the bellhousing is removed from the engine and bolted to the transmission using new grade 8 bolts.
Each hydraulic line threads onto the bearing and the line ran out of the bellhousing through the clutch fork hole. The lines are secured with a wire clamp.
Finally, the engine and trans are mated together and ready for installation in the vehicle.
Written By: Jefferson Bryant
Red Dirt Rodz
4518 Braxton Ln
Stillwater, OK 74074
350 Transport Dr
Cookeville, TN 38506