Woven Carbon Wear Characteristics

If you catch this problem before the lining is completely gone, you can find fine black particles in the oil because woven carbon material does not wear like paper linings. In fact, it can be compared to a brake pad, as the more it is applied the thinner it gets. We have seen this situation regardless of the manufacturer of the converter.

The wear pattern starts at the outside diameter because the piston is dished. On inspection of used piston linings, we have recorded the lining thickness as low as .005" on one side of the piston and .015" in other areas of the same piston. In the lower right quadrant of the piston shown in Figure 2, the lining is only .005" thick, although the lower center section is obviously thicker.

Figure 3 shows the next stage in the breakdown process. The piston was taken out of an OE unit that had never been rebuilt. Figure 4 ran 45,000 miles on a good used lining and shows the final stage of breakdown.

We can easily conclude that this wear pattern is par for the course for this material. This pattern has even been observed in units with on/off lockup apply, and especially in units where the lining takes up the end clearance, as it is almost always in contact with the cover.

General Motors allows a 20% wear factor in their remanufacturing process, which gives you a minimum thickness of .017". There also are other factors such as surface finish, cleaning process and the type of oil used. Since this lining starts out at .022" thickness, there is not a lot of room for error.

In our shop we have opted to change these linings 100% as we have a three-year, unlimited mileage warranty and it is a small price to pay for peace of mind. However, if you choose to reuse these linings, make sure you:

• Use a non-water based cleaning process such as solvent
• Maintain at least a finish of 20RA on the cover
• Reuse only linings which have the least wear possible and check the thickness in several places, accepting only pistons linings with the minimum thickness of .017"