In order to ensure that the release bearings (hydraulic throwout bearings) in hydraulic clutches are measured accurately and fitted correctly, it is important to follow a detailed step-by-step guide. Below is a consolidated measurement procedure designed to help you fully understand how to perform this operation.

 Preparation tools

- I.D. Gauge: for measuring the inner diameter of the bearing.

- OD Micrometer: For measuring the bearing OD and thickness.

- Plug gauges: for measuring fit tightness or clearance.

- Vernier calipers: for measuring the dimensions of the bearing housing or other relevant parts.

- Cleaning cloths and solvents: used to clean the bearings and measuring tools to ensure the accuracy of the measurement.

 Steps for Measuring Hydraulic Throwing Bearings

 Cleaning the bearing

1. Thoroughly clean the bearing with a cleaning cloth and solvent to remove oil, dirt, and other contaminants to ensure accurate measurements.

 Measure the inside diameter

2. Using an inside diameter gauge, measure the inside diameter of the bearing after the OD micrometer has been calibrated to the reference dimension.

3. Avoid the thinning area when measuring to ensure the accuracy of the measurement results.

4. Record the measurement results and compare them with the specifications provided by the manufacturer.

 Measuring OD and thickness

5. Measure the outside diameter and thickness of the bearing using an outside diameter micrometer. 

6. if required, convert the fixed probe of the OD micrometer from a flat surface to a spherical surface to measure the bearing thickness more accurately.

7. record the measurements and compare them with the specifications provided by the manufacturer.

 Measure fit tightness or clearance

8. Use a plug gauge to measure the tightness or clearance of the fit between the bearing and the bore, as required.

9. This usually involves fitting the bearing as specified and tightening the bearing cap bolts to the specified torque, then loosening one of the bolts and measuring the clearance at the bearing cap interface with a plug gauge.

10. Record the measurements and evaluate them against the manufacturer's specifications.

 Check coaxiality (if applicable)

11. For applications requiring a high degree of coaxiality, it may be necessary to check the coaxiality of the bearing bore using a special tool such as a concentricity gauge.

12. Mount the bearing on a measuring device and use a concentricity gauge to assess the coaxiality error of the bearing bore.

 Measuring the clearance in the clutch system

1. Remove the clutch assembly: Ensure that you have access to the clutch assembly, this usually requires removing the transmission from the engine or at least accessing the bell housing.

2. locate the release bearing: after removing the clutch, place the release bearing in a sleeve or bracket, making sure it is fully seated.

3. Install the pressure plate: Place the pressure plate on the release bearing, aligning it with the flywheel. Do not fully tighten the pressure plate bolts yet.

4. Measure Clearance: Use a plug ruler to measure the clearance between the outer edge of the locating bearing and the platen fingers or the platen itself, depending on the design. Insert the plug ruler at several points on the circumference between the bearing and the platen to ensure even clearance. Record the thickness of the plug gauge that fits snugly without being too tight or too loose.

5. Make adjustments as necessary: If the clearance does not meet the manufacturer's specifications, it may be necessary to add or remove shims or adjust the position of the throwout bearing sleeve to obtain the correct clearance.

6. Finalise assembly: Once the correct clearance has been achieved, tighten the pressure plate bolts to the manufacturer's specified torque and reassemble the clutch system.

 Caution.

- Follow the manufacturer's specifications and requirements to ensure accurate and reliable measurements.

- Use appropriate measuring tools and techniques to avoid damage to the bearing or measuring tools.

- Ensure that the bearing has been thoroughly cleaned and is in the correct mounting condition before taking measurements.

- Record all measurement results and compare them with the specifications provided by the manufacturer to assess the suitability and performance of the bearing.

 Other recommendations

- Ensure that the slave cylinder is compressed: Before measuring, fully compress the slave cylinder. This may require removing the slave cylinder spring as per specific instructions or ensuring that the bearing is at the end of its travel, in contact with the base.

- Check for correct installation: Measure the clearance between the release bearing and clutch fingers to ensure it is within the manufacturer's specified limits.

- Air Gap Measurement: When installing, set the initial air gap according to the specific transmission model or manufacturer's recommendations, usually about 1/8 in. to 1/4 in.

- Equipment: Use an accurate measuring tool, such as calipers or micrometers, to ensure accuracy.

- Visual Inspection: Inspect the bearing seals and dust caps for any damage or contamination that could affect performance.

Keep in mind that exact measurements and specifications may vary from one vehicle model and manufacturer to another, so it's always a good idea to consult the manual for a particular vehicle or component before taking measurements.