Being a year round rider, bike maintenance becomes a serious responsibility in order to keep a reliable and top performing machine. Hubs are one of the most important pieces of equipment found on a bike and subject to marginal lubrication conditions. These exist anytime lubricant (in the case of most hubs) grease, is contaminated by water or dirt. After running Shimano XT through Axle hubs (QR 15) for a few years, and then most recently having a set of the MT 55 29er wheels, I noticed a serious flaw in the integrity of the non-brake side bearing seal. Shimano hubs consist of separable (adjustable) angular contact ball bearings protected by in most cases a contact lip seal and labyrinth style non-contact seal/shield. A labyrinth seal provides a tortuous path for potential contaminants to follow before they reach the lubricant and other critical components and do this my providing a close clearance, non-contact seal. The pros are marginal sealing provided with no deal drag, the cons are marginal sealing. Hubs can be designed to be sealed with much more positive contact through increased seal lip pressure, but the resulting drag and wear from the seal lip on the contact surfaces would not be acceptable to the discerning rider.
With this article focusing on the Shimano XT and MT 55 front hub seal upgrade, I will discuss the sealing arrangement on those hubs. (Exploded View of the MT 55 front hub can be found here:http://bike.shimano.com/media/techdocs/content/cycle/SI/Wheel/MTB/SI_4SE0A/SI-4SE0A-003-ENG_t_v1_m56577569830765346.pdf)
The non-brake side of these hubs has a non-serviceable lip seal retained by an anodized silver aluminum ring. The first pic shows the new v-ring and the standard hub. This seal is very exposed to the outside world and is the only means of protection for the bearing on this side. The next picture shows the removal of the lock ring and bearing cone with a 23 and 24 mm cone wrench. I am doing this just to show how the hubs are sealed, and if you want to, you can repack your wheel bearings. This is not necessary to install the v-ring seal.
There is a small black spacer ring on this side that has a tendency fall off during wheel changes if you are not aware it is there, it only held on with a small o-ring. If this falls off on the trail during a flat repair, you are going to have trouble re-installing the wheel properly as it will not sit in the drop out on the fork securely.
The picture on the upper left shows the small spacer ring. Keep track of this anytime you remove your front wheel!
The next picture shows the seal exposed and the grime that can accumulate between the seal and the retainer ring. The new v-ring eliminates this problem and protects the inner seal.
The loose ball bearings are loosely held in place by a polyamide plastic cage and can fall out unless enough grease is present to “stick” them in place. I use a light Phils grease or proper Shimano hub grease as per the OEM recommendations.
With the non-brake side locknut and bearing cone removed, the axle can slide out on the brake side as shown in the picture to the left. You can see the polished ball inner race and the labyrinth outer bearing shield. This covers the inner lip seal and provides another measure of protection that is not found on the non-brake side seal.
Brake side labyrinth ring and bearing race shown cleaned up:
Brake side bearing lip seal and ball bearings/cage:
With the hub reassembled and the bearings full of clean grease, the v-ring can be installed as shown in the pic below. It is a simple procedure, using hands only, no tools, stretch the v-ring over the lock nut and cone on the non-brake side and rotate so that the seal lop is smooth and sits up against the anodized ring. The edge of the v-ring should be flush against the outer edge of the cone lock nut.
Installation complete, Install the wheel, enjoy better sealing!