Clutches, Linkages & Bellhousings for Jeep Conversions Part 4

Obtain a release bearing based on the above measurement and install it on the fork. Be advised that forks with the flat type spring require that the tips of the fork AS WELL AS THE TIPS OF THE SPRING are installed in the groove of the release bearing.

This chart shows the length of the bearing in inches. Most auto parts stores only stock a couple of these release bearings and they may not be the best ones for your swap. This chart lists five bearings by the critical “A” measurement; groove to face dimension as referred to in this article.

sm420Install the transmission on the clutch housing. The release bearing must be able to move away from the diaphragm spring approximately 1/16 to 1/8″ (this is the “free play”). At this point you should be able to move the release bearing back and forward with the fork. The bearing, when against the clutch, should leave the release fork positioned at 4 or 5 degrees LESS than a right angle with the engine centerline and allow it to be moved away from the clutch 1/16 to 1/8″. If this condition does not exists, do not install the assembly into the Jeep until it does. If not, you may need a different clutch release bearing or pivot or you may have the wrong fork.

As stated earlier in this article, if you are switching from a three-finger type to a diaphram style pressure plate, you will require a shorter throwout bearing. The inverse is, of course, true if you are going the other way.

The bearing must clear the clutch or it will turn all the time and will wear out quickly—also the clutch may slip as it may be partially released.

At this point (finally) the engine and transmission are ready for installation and hookup of linkage. Install the remaining bellhousing and transmission bolts if these parts do not have to be removed again.

The engine, transmission, and transfer case should now be installed in the Jeep. With the engine mounted, the connection of the clutch linkage can proceed.

As previously stated, when mechanical linkage was used originally on a vehicle, we advise staying with the same.

Regardless of whether the stock linkage pushed or pulled, it must do so in as straight a line as possible. This will keep friction to a minimum.On installations where the engine must be moved (such as pre-1971 CJ’s) the clutch bracket that supports the frame end of the bellcrank must be relocated. This must be to a location that will put the bellcrank at a right angle to the engine and level from side to side (parallel to the ground).

On 1972-86 CJ’s where a bracket must be made to support the Jeep clutch cross-shaft, the cross-shaft must end up at a right angle to the engine in both the vertical and horizontal planes.

The arms on either style bellcrank must be positioned for maximum mechanical advantage. This means they cannot angle more than about 35 to 40 degrees from either side of a right angle to the push (or pull) rod that they connect to. This alignment angle is established at the bellcrank and the operating rods are then modified to whatever length is required to keep the bellcrank or cross-shaft at this position with the release bearing at least 1/16″ off the three release arms of the pressure plate.

Have a helper push the clutch pedal to the floorboard and hold it there. Check the air gap between the flywheel and the clutch disc with a feeler gage. As stated previously, it should be .030″ for a diaphragm clutch and .040 to .050 for a coil spring clutch.

Release and adjust the linkage until the air gap is correct for the type of clutch being used.

Check for at least 1/16″ clearance between the clutch release arms (or diaphragm spring) and the release bearing. If the bearing face contacts the clutch with the clutch in the engaged position (not enough free play) you will have to go to the next shorter length release bearing to obtain the required air gap and free play.

Bellhousing Alignment
On any engine using a standard shift transmission, with or without an adapter, it is important to check the bellhousing locating bore location relative to the crankshaft. The potential for transmission failure or premature wear is so great, due to misalignment at this point, that no engine should be assembled without being checked. The checking procedure is quite simple. Correcting misalignment is not so simple but must be done to insure normal service from the transmission. A dial indicator is required, as well as a suitable means to mount this instrument on the engine crankshaft.

A dial indicator (right) is a device that has an arm or contact point, suitably connected to a pointer, that moves in front of a dial with markings on its face. These markings usually represent .001″ each. The purpose of a dial indicator is to measure in thousandths of an inch that can be read directly on the dial of the indicator.

To check a bellhousing, mount it on the engine it’s going to be used with, make sure there are no burrs or dirt on the block or bellhousing. All bellhousing to block bolts should be in and tight. Mount the dial indicator on the crankshaft of the engine using a suitable magnetic base attachment or mechanical clamping means. The contact point of the indicator should be touching the bore of the bellhousing. The indicator must be mounted rigidly enough so it does not move on its mounting to prevent false readings. Rotate the engine by hand with the spark plugs removed and observe the reading on the dial. Keep adjusting the dial assembly until the needle moves the least amount per rotation. When you have acheived the least amount of needle movement throught he 360 degree sweep of the indicator, this is your runout. You can then determine the direction it is offset by the movement of the needle.

The total number of thousandths misalignment of the bore relative to the crankshaft is read directly on the dial. Total runout should not exceed .007″, with .010″ being maximum. The greater the misalignment, the sooner transmission problems and failure will occur. A symptom of misalignment is unusual wear of the pilot bushing. We have checked stock Chevy bellhousings on engines that were out more than 1/32″ (.032″). Some Ford one are reportedly worse. Anything over .010″ runout must be corrected before the engine and bellhousing are put in service or you can count on pilot bushing, transmission, and clutch problems, followed by transmission failure. The simplest way to correct misalignment is to try another bellhousing or bellhousings. Machining the bellhousing is the best cure but offset dowel pins are simpler. Shims between the block and bellhousing will also work if you have the patience to use this method. Offset dowel pins are sometimes available from “speed shops.”

For Reference
The pressure plate must move about .100 to .120 of an inch to RELEASE THE DISC and provide .030 to .050 air gap between the disc and the flywheel.

  • A 9″ clutch has about a 4.5-to-1 arm or diaphragm ratio.
  • A 10.5″ clutch has about a 6-to-1 arm or diaphragm ratio.
  • An 11″ clutch has about a 6.6-to-1 arm or diaphragm ratio.

The release bearing must move away from the fingers or diaphragm sping at least 1/16″
(.0625 rounded off to .06) for freeplay.

The release fork ratio is determined as described in the release fork section.

Example: A 10.5″ clutch and a #RAGM GM release arm (2.17 ratio).

So, 0.120″ required movement multiplied by the ratio of a 10.5″ clutch equals .72″ plus .06″ movement of release bearing for freeplay equals .78 of an inch. Multiply .78″ by the ratio of the release fork (2.17″) equals 1.69″ (or 1-11/16″) of travel required where the linkage attaches. It doesn’t matter if the linkage is mechanical, cable, or hydraulic, it must be able to move the end of this arm with this pressure plate the above indicated amount in order to properly release the clutch disc.

For comparison, using the same release arm with a 9″ clutch only requires about 1-5/16″ movement while the 11″ clutch requires almost 1-7/8″ of movement — nearly 9/16″ more. It is the ratio of the pressure plate that makes this difference. This is also exactly why the hydraulic slave system on 1980 to 1986 4 cylinder CJ’s will not completely release a 10.5″ or 11″ clutch on a conversion engine. It does not have the necessary travel. In this particular Jeep both the operating and slave cylinders would have to be changed to get more travel.

However, if the slave system is engineered correctly with the proper ratios, full release can be attained with 10.5″ clutches. See the Novak #HCR3 kit.

Novak Conversions – experts in Jeep conversions since 1967