298mm clearance problems and solutions
When referring to clearance on any torque converter, there are many clearances to consider. Many rebuilders experience problems when trying to set the clearance on General Motor’s 298mm converter.
If the front cover has been resurfaced and/or the lockup piston has been rebonded, the clearance must be rechecked before assembly. The clutch travel clearance is critical and must be held down to lower limits. The clearances are lower or raised by changing the selective plastic conical. This is not used to adjust overall height of the converter, as many rebuilders believe.
The second clearance is turbine to impeller clearance. If the turbine thrust surface is worn (see photo), the turbine’s surface must be refinished. To make up for removed material, Sonnax offers a replacement stator cap, part number GM-WP10-OE, that replaces part number GM-WP3-OE. The improved WP10 is .030 thicker than the WP3, which solves this problem.
Finally, stack height and internal clearance can be adjusted by adding a shim between the impeller and the front bearing. Shims are available in .010, .020, and .030 increments which can be combined to obtain the necessary dimension.
Overall length should be maintained close to the higher limit, which is 5.920 inches. The lower limit should not drop below 5.870 inches.
Note: Try to avoid using more than two shims per converter. If you need to obtain higher overall length, you may need to switch to a longer impeller hub. Remember do not adjust overall height by installing a thicker conical.
Found in issue December 2004