December 20, 1991

CIRCULAR LETTER

(c-7772)

SUBJECT:    Prohibition of Vent Fittings in Roller Bearing Backing Rings

TO:    MEMBERS AND PRIVATE CAR OWNERS

File Number: GC-WABL – TB-48

The Wheel, Axles, Bearings and Lubrication Subcommittee has found through an extensive comparative study of vented and non-vented roller bearings that there is no significant difference in grease purging tendencies, seal lip wear, or bearing operating temperature. As a result, in order to eliminate a potential point for water ingress into the bearing, vent fittings on new journal roller bearing backing rings are prohibited effective January 1, 1992. In addition, the Subcommittee also decided that, effective March 1, 1992, vented backing rings must be converted at the time of reconditioning in accordance with the attached revision to Section H – Part II, Rule 3.25.

These revisions will be incorporated in a subsequent publication of revised pages to Section H – Part II of the Manual of Standards and Recommended Practices.

Sincerely,

Leavitt A. Peterson

Vent Fitting: Check to be certain it is not clogged, hardened, or damaged. Should it be necessary to replace vent fitting, it must be renewed according to manufacturer’s instructions. It must be properly protected during painting operations.

Vent Fitting: If a backing ring is equipped with a vent fitting, the vent and/or vent cavity must be sealed and the ingress of water or other contaminants prevented. This may be accomplished through replacement of the vent fitting with a suitable plug or by sealing or plugging the cavity with the vent fitting in place. The method and material used must provide an effective and secure seal that will not interfere with the proper seating of the backing ring on the journal fillet during the mounting operation. If a silicone caulk is used, the cavity must be sufficiently clean to provide satisfactory adherence to maintain seal and retention. The sealed vent must be checked at subsequent reconditioning cycles to verify integrity.