Under the Bonnet: Spring 1995

FRONT WHEEL BEARINGS

The condition of front wheel bearings is of vital importance to your safety, but is often overlooked.

Main concerns are cleanliness, lubrication, and adjustment (where adjustment is possible). Bearings which have suffered a lack of any of these will usually need to be replaced. While reference to a good workshop manual specific to your car is essential for proper servicing and installation of these bearings, some factory manuals do present ambiguities or gloss over some operations for which the novice mechanic needs more explanation. It is these information “gaps” that this short article hopes to fill.

The first step in dealing with wheel bearings is to decide if they need any attention or not. Signs of bearing problems include noise (often sounding like bird chirps) and vibration. Front wheel bearing noise does not change intensity when accelerating or coasting, but may diminish with a light application of the brakes. The best way to check for these problems is to set the front of the car on jack stands and rotate the wheels by hand. (If you have disc brakes, ensure that the pads are not dragging on the rotors.) The wheels should rotate smoothly and quietly, with no feeling of roughness or tightness. Then, grasp the tires at top and bottom and alternately push with one hand while pulling with the other. None but the very slightest looseness, if any, should be felt.

If you have ball bearings and they pass these tests, they are almost certainly in good condition. You may, however, wish to “have a look inside” to ensure they have adequate grease for continued safe operation. If you have tapered roller bearings, I advise having a look at the outer bearings anyway, as they usually develop problems before the inner bearings do. This is very easily done on disc wheel cars, but a bit more difficult on cars fitted with wire wheels. In any case, try to avoid unnecessary removal and refitting of the bearing races in the hubs—they are press fits, and too many removal and replacement cycles will upset the tolerances required, as well as increase the probability of physical damage to the bearings and their seats in the hubs. It is a little known fact that the inner races should be slip fits on the axles to allow them to “creep.” Consult your workshop manual if you have the slightest doubt how to remove or replace bearings.

Visual inspection of bearings will sometimes show faults which are not apparent from the function tests outlined above. Reject bearings which show pits, spalls, smears, uneven wear, serious discoloration, or any other obvious signs of incorrect condition. If in doubt, replace the bearing.

Cleanliness is absolutely essential in any dealing with bearings. A tiny piece of foreign matter or a burr between a bearing race and the recess it is pressed into can cock the bearing enough to produce accelerated wear, while dirt in the bearing or its grease can quickly cause failure. Handling of bearings should be kept to a minimum – use of clean cotton or surgical gloves is recommended by bearing specialists. If it is necessary to clean a bearing, use only clean solvent, and blow dry with clean, dry, filtered compressed air. (The air from your home air compressor does contain water and other contaminants.) Do not spin bearings with compressed air – this is not only dangerous to you, but is guaranteed to ruin the bearing.

The radial ball bearings used in MG T-series and MGA present no problems as long as workshop manual instructions are followed. Problems can arise, however, with the angular contact ball bearing assemblies used in Sprites, Midgets, and early Big Healeys, as they can be installed backwards, allowing the hubs to come loose from the axles. Workshop manual instructions for these bearings state to install the sides marked “thrust” on the outer race towards the bearing spacer. This is correct if you are using new old stock factory bearings, but most bearings currently available are not marked. To further complicate things, some manuals mention bearings marked “thrust” on the inner races; bearings so marked must be installed with the “thrust” marking away from the bearing spacer.

Tapered roller bearings, unlike ball bearings, require end float adjustment. As front wheel bearings, they must not have a preload. Since methods and specifications vary considerably, please follow your workshop manual procedures and specifications. In all cases, the bearing races must be fully seated before adjustment can be performed. MGBs and later Big Healeys use spacers and shims between the inner and outer bearings to maintain the end float adjustment. While time-consuming and often frustrating to set up, once they are set, they tend to stay set. Triumphs and Jaguars, which use only the axle nut for adjustment, can be adjusted in just a few seconds, but seem to require more frequent attention.

Lubricant specifications, particularly for older cars, can be a problem when the greases specified are no longer available. In this case, use a high temperature disc brake wheel bearing grease, even on a “low temperature” drum brake car. While it could be argued that this is like using 100 octane gasoline in an engine requiring 80 octane, it will do no harm, may work better, and the cost difference is minimal. On the other hand, trying to economise by using the cheapest chassis grease you can find is definitely a false economy, as it will not do the job.

If you do not have a bearing packing tool (and you really should), the approved method to grease the bearings is to put a supply of grease in the clean and dry palm of one hand, or, better yet, use a clean cotton or surgical glove. Holding the bearing in the other clean and dry (or gloved) hand, scrape the bearing against your palm (if tapered roller bearings, scrape with the larger end), forcing the grease completely through the bearing. The bearing cups of roller bearings should be coated with grease before assembly. General practice is to partially fill the space in the hub between the two bearings, although some workshop manuals say not to do this. When in doubt, follow the manual.

The best way to prolong the life of wheel bearings (and all other components of your car) is to follow the manufacturer’s maintenance schedule found in your owner’s manual. Keep things clean and well lubricated, and your car can last almost forever.

ERRATA: In the last “Under the Bonnet” article on steering system lubrication, it was erroneously stated that oil should be used for MG TD-TF steering joints instead of the required grease. We apologize for any problems this may have caused. —Ed.

REPLACING STEERING RACK GAITERS

To replace steering rack gaiters, the outer tie rod ends and their locknuts must be removed. As reassembly of these requires careful adjustment to reestablish correct toe-in of the front tires, the trick is to somehow retain the original setting after the tie rod ends have been removed and replaced. Unfortunately, this problem is not addressed by workshop manuals.

The best trick I have heard of to get around this problem is to accurately measure with indicating calipers the distance from a fixed position on the inner tie rod end (“ball joint”) assembly to the outer tie rod end or its nut. Record the separate measurements for both sides, as they will not be exactly the same. After putting the new gaiter on the tie rod, but before securing the inner (larger) end, assemble the outer tie rod end and its nut on the tie rod to the measurements previously made. Please note that this is not advised if you are installing new tie rod ends, as they may differ slightly in length from the old ones.

—Eric Wilhelm