In the world of sports cars, muscle cars, and hot rods, some enthusiasts passionately believe these cars must have three pedals. And for many reasons, they’re not wrong. Who doesn’t enjoy the mechanical nature of a manual transmission and the feeling you get when your feet and hands are in perfect sync as you row through the gears? And with many options for aftermarket transmissions and performance clutches, there’s no reason not to have three pedals and stick in your car. To get those feel-good gear changes, several things must first be set up properly within the transmission and clutch. One of the most important things to check is the tolerances to ensure you don’t have drivability issues down the road. To get the how and why details for measuring the clutch setup we spoke with the owner/operator of Monster Clutch Company, Steve Addison.
Measuring the gap between the slave cylinder and the clutch is vital to the operation of the setup as a whole. Without the proper gap, damage to the clutch and transmission can occur.
Not Too Much, Not Too Little
“The number one thing we get calls on is how to properly and accurately measure a clutch to find out the slave cylinder gap and determine if a shim is needed,” Addison says. “There are tolerances for every part made in an engine, transmission, and clutch. These tolerances can stack and cause you issues with the setup height of the clutch and hydraulic system.” According to Addison, two primary issues can arise from either not measuring the slave cylinder gap at all or from measuring the gap incorrectly.
The first potential issue would be caused by not having enough shim in the setup. When there is not enough shim, there will be too large a gap between the slave cylinder release bearing face and the clutch diaphragm spring tips (sometimes referred to as the pressure plate fingers). In this situation, what you will experience from the driver’s seat is with the clutch pedal depressed, the clutch will not fully disengage from the flywheel. The result is that shifts will be difficult due to the residual clutch engagement.
Properly installing the clutch and flywheel is essential to getting accurate measurements for the slave cylinder gap. Here we are installing our twin-disc clutch from Monster Clutches on Project Dirty Bird.
Conversely, the second potential issue is caused when there is too large a shim in the setup. The shims serve to space the slave cylinder towards the clutch diaphragm spring tips and shorten the gap between the two. If there is too much shim in the setup the slave cylinder release bearing face can actually be in contact with the clutch diaphragm spring tips. “Too much shim in the setup is called preload,” Addison explains. “In this situation, the clutch is not fully released, or engaged, when you let off the clutch pedal. This will prematurely wear the clutch, introduce more heat, and cause excessive wear — possibly damage — to the transmission.” You can think of this situation as if you are driving with your foot partially pressing on the clutch pedal.
“Because of these potential issues, we recommend that every single time you install a clutch you measure and make sure your unit falls within the correct tolerances,” — Steve Addison, Owner/Operator Monster Clutch Company
Minding The “A”s and “B”s
Now that we’ve covered the hazards of improperly shimming the slave cylinder let’s go over the measurements you need to know and how to correctly obtain them. Before taking any measurements you need to install your clutch on the flywheel with the mounting bolts properly torqued. “To get an accurate measurement, the slave spring must be removed, and the bearing must be fully seated at the bottom of its travel resting on the slave’s base,” Addison says.
Properly measuring the two distances accurately ensures you get a correct gap distance. You can find more on this on the Monster Clutches site.
Once the clutch is bolted to the flywheel you only need two measurements, and how you get them depends on the type of transmission bellhousing you have. If you are using a transmission with a removable bellhousing such as the T56, TKO, or T5, you will attach the bellhousing to the engine and properly torque the bolts. The first measurement you need — call it “A” — is from the clutch diaphragm spring tips to the bellhousing surface that mates to the face of the transmission. The second measurement you will take — call it “B” — is from the mounting face of the transmission to the slave cylinder release bearing face. Now before you do any math, if the second measurement is longer than the first, then there is an issue that needs to be addressed.
“If there is no difference between the two measurements, or if ‘B’ is less than ‘A’, there could be a problem with clutch engagement that could result in clutch slip, premature wear, and eventually a total failure,” Addison explains. “If you’re getting this ‘positive gap’ (‘B’ is less than ‘A’), remove the bleeder screw completely and make sure the slave cylinder is fully compressed and remeasure.”
The points of measurement are a little different if you have a non-removable bellhousing, but the result is the same.
If your transmission features a non-removable bellhousing, then your measurements are slightly different but they achieve the same results. Measurement “A” will be from the bellhousing mounting surface that mates to the engine block to the face of the slave cylinder release bearing. Measurement “B” is the distance from the clutch diaphragm spring tips to the mounting surface of the engine block. Again, before doing any math, check to make sure that “B” is less than “A“.
To Shim Or Not To Shim
Let’s assume you have correctly installed the clutch and the slave cylinder is compressed fully and seated at the bottom of its travel. You’ve accurately and properly obtained measurements “A” and “B“, and after subtracting “B” from “A” you have a positive number (a negative number would mean that “B” is greater than “A” and there’s an issue). What do you do with the gap measurement? “If you come up with a measurement that is more than 0.200 inch, add an appropriately sized shim between the slave and the transmission in order to get the measurement within tolerance,” Addison says. “Here at Monster Clutches, we recommend a gap measurement no less than 0.0625 inch and no more than 0.200 inch. On our units, the ideal gap is between 0.085 inch and 0.100 inch.”
Our transmission has a removable bellhousing. Using a straightedge and calipers we can get an accurate measurement from the clutch diaphragm spring tips to the mounting face of the bellhousing.
One thing to note is that once you have your gap measurement within the acceptable range you still need to check the engagement and disengagement of the clutch. Another thing to check is the amount of travel in the slave cylinder. Damage can occur to the clutch diaphragm spring tips if the slave travels too far when the clutch pedal is pressed. Fine-tuning the gap measurement to achieve complete clutch engagement and disengagement without damaging the diaphragm spring tips may require testing various shim thicknesses to achieve the best setup.
You can see here we have our “A” and”B” measurements, and have a gap of 0.186-inch. By using Monster Clutches 0.090-inch shim from their kit we end up with a gap of 0.096 inch which is within their ideal tolerance range.
If you’ve done everything correctly up to this point and need a shim to get your gap measurement back into the correct tolerance, Monster Clutches offers a shim kit. The kit includes several precision-cut shims of various thicknesses ranging from 0.040 inch up to 0.125 inch. This allows you to fine-tune your clutch setup for optimum performance. Another option would be to have a shim made to the specific thickness you need or want. “We can make any thickness shim you can dream of,” Addison says.
The next time you need to replace or install a clutch be sure to follow the process we’ve discussed here and you’ll be rowing gears with ease. For more information on this process, as well as other aspects of clutch setup, and to order your next clutch visit Monster Clutches’ site.
