PLEASE NOTE THIS RELATES TO MG MIDGET & AUSTIN HEALEY SPRITE
This advice should be considered as a mix between my experience, having changed a few, and documentation around that provides such advice. It should not be considered as Finite, Complete or Manufacturers Advice.
There are some points to consider first, mainly that these cars did not use tapered roller bearings from the factory. Instead they used ball bearings that are designed for thrust in one direction. The stub shaft by itself did not provide adequate support for the inner bearing races so a bearing spacer is used. The bearing spacer fixes the two inner bearing races to the stub shaft once torque is applied to the nut. Arguably, this bearing spacer set up is also to increase strength of the stub axle. If you think about it, once the nut is tightened, there is basically a tube around the stub shaft consisting of the two bearings inner races, and the bearing spacer. They are all squeezed together by the nut on one side and the face of the stub shaft on the other. The above has been subject of much debate but lets assume the spacer does add strength.
However the problem with using the bearing spacer is that all parts in the stack up must have very tight machined tolerances. The hubs, the spacer and the bearings themselves all must be manufactured virtually identically to one another, regardless of the manufacture of each component to end up with the correct endplay of the hub. If even one of these components was off by as little as .002”, it could result in the bearing being excessively preloaded, having excessive end float, or the bearing actually being damaged by simply tightening the nut. If more than one part was out of this tight tolerance range, the problems only grow.
You may notice when installing a front hub assembly onto the stub axle that there is a problem, there are two things you could do to correct it.
- If the bearing is tight (too much preload) when assembled, you should shim in-between the outer bearing and the bearing spacer.
- If the bearing had excessive end play (>.004”), you could remove material from one end
of the spacer.
Either way it requires pushing one of the bearings out of the hub, which also ruins the bearing. None of this information is in the factory manual.
You can start to see how the stack up of these parts is problematic if all parts are not machined nearly perfect.
The main benefit to switching to a tapered roller bearing aside from the ease of maintenance and the above difficulties is the ability to correctly set hub endplay without destroying perfectly good bearings in the process.
Only the outer races are pressed into the hub in a tapered bearing set up. The rollers, cage and inner race are not a part of it and therefore can be removed separately. This is important because it gives access to the bearing spacer (for shimming or trimming) without having to knock a bearing out of the hub.
What this means is that the tolerance between the hub, bearings, and spacer is much less of an issue because there is a relatively easy means of correcting it.
In most cases the assembly will require shims between the outer bearing and the bearing spacer.
Now it is a widely debated subject as to whether you need the bearing spacers at all, particularly as there are several other cars that do not use a spacer with tapered bearings. Some say put them in the bin. Obviously I cannot give such advice and you could not argue against it providing additionally strength, However be prepared to be patient and methodical in setting these bearings up correctly.
The instructions below only cover the installation of tapered roller bearings. You will may need a workshop manual to use as a guide for disassembly of the other parts e.g. brakes etc. You will most likely need shim kit MOSS 263-508 to complete the install of the tapered roller bearings. These are the same shims used for MGB front wheel bearings. It is worth reading and understanding these instructions before starting
- On level ground, chock the rear wheels, set the parking brake and put the transmission in 1st gear. Lift and support the front end of the car with jack stands. Remove the front wheels.
- Using a workshop manual for guidance, remove the hub assembly.
- Remove the bearings from the hub. This will require a drift or punch and a hammer as the bearing are pressed into the hub.
- Clean the hub and all related parts to get them ready for reassembly.
- Using a bearing driver and a hammer or press, install both inner and outer bearing races into the hub. Make sure both races are seated all the way down.
- Pictures of inner and outer race beds
- You may need to remove a little material from the small end, outside radius of the factory bearing spacer so that it doesn’t interfere with the outer bearing cage. Only the outer corner of the small side of the spacer needs to be taken off. Not all spacers need this modification. To determine if your spacers need modification:
- Set the outer bearing on a flat surface, big dimeter down, small diameter up. Only the inner race should be touching the flat surface. See below:
- Hold the race firm to the table and give the bearing a spin to get a feel for how it spins free.
- Fit the small end of the bearing spacer to the inner race of the bearing.
- Hold the bearing spacer against the bearing, pinning the inner race to the table, and try to spin the bearing. If the bearing will not spin freely, it’s because the cage of the bearing is in contact with the spacer. If the bearing still spends freely, your spacer doesn’t need any material removed; skip to main step 8
- Remove the outer corner of the spacer where it was touching the bearing cage using a file, grinder, belt sander, etc. You can see below a before and after.
- Clean the spacer thoroughly before fitting it back up with the bearing. You do not want abrasive debris in the bearing.
- Repeat the above adjustment and checking processes until the bearing spins freely with the spacer pinning the inner race firmly to the table.
- Tip: The rollers and cage of the bearing will be pushed away from the bearing spacer when assembled on the car, so don’t get carried away with material removal. You can remove enough material from the spacer for it to clear the bearing race in less than a minute on a belt sander or bench grinder.Before any grease is applied to the bearings, you must install the entire hub and bearing assembly dry to set the bearing preload/end float. Do not include the seal at this point. Clean and lube the spindle to aid with bearing fitment. Install the parts onto the spindle in the following order from LEFT TO RIGHT .
- Inner bearing
- Inner bearing spacer ring
- Bearing spacer – factory part not provided in kitHub
- Outer bearing
- Stock keyed washer
- Castle nut provided with roller bearing kit. The factory nut will not allow the cotter pin to fit. Do not tighten the nut at this time, just finger tight will do.
- Spin the hub as you slowly begin to torque the nut to 46ft. lbs. If the hub starts to build resistance as you torque the nut; stop torqueing the nut. Shims are required. Move on to the section of instructions labeled ‘SHIMMING THE BEARINGS’ The resistance of the bearing as the nut is tightened is called bearing preload. Having to add shims is the most typical scenario.
- If you are able to achieve 46ft. lbs. of torque on the nut and the hub spins freely, check the hub endplay. It should fall between zero clearance and .004”. If the end play is looser than .004”, the bearing spacer stack will need to be shortened. Move on to the section of instructions labeled ‘SHORTENING THE BEARING SPACER STACK.’ Most vehicles do not need this procedure.
- If you are able to achieve 46-65 ft. lbs. on the nut and the hub end play is .000”-.004”, you are lucky and no further fitment is required. Move on to the section of the instructions labeled ‘FINAL ASSEMBLY.’
SHIMMING THE BEARINGS
- Remove the castle nut, keyed washer and outer bearing.
- Install .020” worth of shims from shim kit 263- 508 between the bearing spacer and the outer bearing.
- Reinstall the outer bearing, keyed washer and castle nut.
- Begin to tighten the nut and check for preload. If preload still is felt before the torque spec on the nut is reached, repeat this step, adding shims until the nut can be fully torqued and there is zero preload on the bearing. The goal is to set the bearing preload to zero and have the endplay between .000” and .004” with the castle nut torqued down to 46-65 ft. lbs. You will need to try a few combinations of varying thickness shims to meet this goal.
- Caution: Excessive bearing preload or end float (tight or loose bearings), will cause excessive wear and premature bearing failure. Below shows where the shims go
SHORTENING THE BEARING SPACER STACK
The easiest way to shorten the stack is to remove the inner bearing spacer ring so that the bearing spacer sits directly against the inner race of inner bearing. However this will cause the spacer to contact the inner bearing cage. Follow step 6 of these instructions except: use the inner bearing and remove material from the large side outer radius of the bearing spacer to gain the necessary clearance. Once you have removed the ring and filed the spacer for clearance, you will need to shim the bearings. See the section of these instructions called ‘SHIMMING THE BEARINGS.’ You may find you need another pack of shims to attain proper bearing set up.
Remove all the parts from the spindle. Clean everything once again for final assembly.
- Pack both bearings with grease.
- Install the inner bearing into the hub.
- Install the dust seal into the hub.
- Install the hub, inner bearing, seal assembly onto the stub shaft.
- Install the inner bearing spacer ring.
- Install the bearing spacer.
- Install the shims if required.
- Install keyed washer.
- Install nut and torque to 46ft. lbs.
- Install the cotter pin through the castle nut and stub shaft. If the nut doesn’t line up with the either of the holes in the stub shaft; tighten the nut until it does. Do not exceed 65 ft. lbs. If the cotter pin will not fit, make sure you are using the castle nut provided in this kit and not the vehicles stock castle nut.
- Double check the hub still spins freely. The grease will provide more resistance to spinning than the dry fit up, but the hub should still easily turn by hand. If the hub is difficult to turn, a shim may have been left out. The cause of this must be addressed before moving on. If necessary, disassemble and clean all parts and start over at step 1.
- If the hub still spins easily, check the hub endplay. Again, you may have less endplay than with the dry fit up but that is OK. The hub just needs to spin freely and have less than .004” endplay.
- Finally, install the grease cap. Do not pack the cap full of grease. The grease packed into the bearings is adequate and will expand. The cap provides and area for it to go.
- The installation of the tapered roller bearing is complete. Hold onto any extra wheel bearing shims. They could provide adjustment down the road if the hub endplay ever exceeds .004” limit.
SERVICE & MAINTENANCE
Now that you have setup the bearings, service is very easy just as long as you keep track of all the parts (especially the shims). Repacking the bearings is a breeze. The rear grease seal must be removed from the hub but if done carefully, it can be reused. Set up correctly and serviced occasionally, they will last a very long time.