In listed GM transmissions, severe wear of the TCC regulator valve bore from the OE valve allows regulated converter apply pressure to exhaust. This is a primary cause for a TCC-related 1870 slip code and overheated converters. Exhausting apply pressure also diminishes line pressure, which results in burnt clutches. Excessive wear at the isolator valve bore reduces TCC apply pressure. Sonnax isolator sleeve kit 77754-ISO in combination with Sonnax TCC regulator valve kit 77754-03K or 77754-04K allows you to restore hydraulic integrity of the apply circuit. Sleeve is manufactured from highly wear-resistant aluminum to provide full support for the valve and prevent side loading.