Gm 298mm early design bearing failure
Another popular topic frequently brought up by members is how to prevent premature bearing failure on GM 298mm early design bearings.
This is the two-piece design, as shown in photo A, which after rebuild frequently returns broken or shattered. This leads to catastrophic converter failure and many unhappy customers.
It has amazed many of us that this bearing may last 100,000 miles or more brand new or only 5,000 miles after rebuild. Question: Why the difference in performance, and what went wrong?
The answer seems to allude most rebuilders, although the solution is quite clear and simple. During impeller hub removal it appears that the inside diameter of the bearing location hole is bored oversized. This dimension needs to be held no larger than 1.525 inches and no smaller than 1.510 inches (Photo B).
This provides an accurate bearing location and will not allow the bearing to interfere with the stator or stator support shaft. It is also noted that you should always provide a .025 radius on the inside diameter to provide clearance for the bearing to set flat.
If the inside diameter is larger than the pilot diameter, located inside the impeller hub, a quick trip around your vertical welder will fill the void.
Afterwards machine the diameter to the proper size. Recheck with a bearing for proper fit. Always replace the bearing race located on top of the stator in addition to the new bearing. This will assure you proper bearing performance and will meet your expectations along with your customers’ needs.
It has been a misbelief that this bearing is somehow inferior to the later design. This simply is not true. You can now rebuild this converter with complete confidence that the bearing will not fail. We hope this solves your issue.
Found in issue 08, 2004