Notes: This guide isn’t approved by Shimano. In this disposable age, these BB units are seen as disposable rather than serviceable. Hence the do not disassemble instructions. Care and patience is required at all stages. Rushing the job may lead to damaged or broken component parts or personal injury. Work in a well lit and ventilated environment. Latex gloves and eye protection are recommended.
Tools required: 5mm Allen Key; Torque Wrench; Shimano HollowTech II Bottom Bracket Spanner (Shimano TL-FC32 or Park BBT-9); HollowTech II Bottom Bracket Lockring Tool (Shimano TL-FC16); Two Blades; High quality water-repellant grease; GT85 or similar light lubricant; Toothbrush; lint-free cloth; rag or paper towel; A4 paper.
This service guide is applicable to any of the new Shimano Hollowtech II external bottom brackets. This design is shared by XTR, XT, LX, Dura Ace and Ultegra and will undoubtedly trickle further down the groupset range. This technique has not been tested on similarly designed products (e.g. Race Face).
Using a sharp blade carefully lift the outer plastic shield. Care is required here not to damage the lip seal that sits around the periphery inside of the alloy bearing body. Once one side has been lifted insert a second blade and move it to the opposite side (see picture).
Remove the outer plastic shield by using the blades to extract it from the alloy casing. Use the blades to lever the bearing shield from the body. Be careful not to cut yourself as some force is required to do this. Once the shield is removed use a blade to delicately remove the large lip seal (pictured).
The bearings are protected by a standard metal core rubber bearing cover (pictured). This is similar to that found on all bearings. The amount of filth that accumulates behind the bearing shield gives and indication of just how good the exterior lip seal and outer shield is.
If the inside is really filthty at this point use a rag to clean off any excessive debris and use a light lubricant such as GT85 to reveal the bearing cover edges. Using the point of a blade carefully lift and remove the bearing cover to expose the bearings. Take care not to bend or damage the bearing cover.
With the bearing cover removed the state of the bearings will become apparent. As with servicing any bearings if things look really bad at this stage it may not be possible to save them and a new unit may be required. If the bearings are shot, it time for a new unit.
It may only be possible to judge the state of the bearings after cleaning. Use a high quality citrus based degreaser and a toothbrush to clean the bearings. Several applications may be required. After degreasing flush the bearings with GT85 to remove any trace of the degreaser.
If the bearings have been freed up, then continue and clean each of the other components in a similar way. It is useful to create a clean area using white paper to avoid contaminating the bearings between cleaning and before reassembly. Once all the components have been cleaned, repack the bearings.
Shimano’s Dura Ace grease is purpose suited to this task, but other alternatives exist. Water repellant greases are preferable. Overpack the bearings as refitting the bearing covers will force grease though the bearing. Press the bearing covers back into place and clean up the excess grease with a lint free cloth.
With both sides of the unit cleaned and regreased, reassemble the units. The application of some careful force is required to ensure that the outer bearing shields do not become damaged as the plastic is quite brittle. If the service is successful it will substantially increase the life and reduce the cost of running the excellent new Hollowtech II cranksets.