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MG MGB Technical - Front wheel bearings - replacing

I know this has been discussed a million times but here goes. Will I need a hub puller to get the hub off or are they normally 'loose'?
Any tips on the 'end float' setting without a DTI gratefully received
Ta
Bernie
1970 CB with Wires
B Anderson

Hello Bernie,

No you do not need any extractor for that. And have somme diff. specs shims to make final adjustment. I start with original shims set-up and it is a try & error procedure.Hub must spin freely without any grab or loose...

Cheers,

Jean G.
Jean Guy Catford

Yes, they should be loose when the hub nut is undone, in fact you have to watch bits don't fall out and get lost.

For end-float setting fit the bearings dry first and without the grease seal, then use combinations of shims each one thou thicker than the last, starting with the original set and torquing to 40 ft lb minimum, until you get one set that gives no play and the next set one thou up gives just perceptible play. Then use the thinner set plus a .003 i.e. the thinnest to get the required .002 to .004 play. Then pack the bearings - pressing grease in from one side only until it oozes out the other side, if you try to speed things up by pressing it in from both sides you will trap air and get premature wear. Then fit the grease seal, groove facing into the hub. Just pack the groove with grease, not the space between the bearings.

The only time I've had to replace bearings the original set were correct for the new bearings. I may have just been lucky, but I did wonder if the bearings were manufactured to very tight tolerances which seems reasonable, and the shims were to take account of variations in the hub and spacer tube, most dimensions of which are less critical.
PaulH Solihull

Thanks Paul. Most helpful. I won't be doing it for a couple of weeks as I am on hols. But I feel a lot more comfortable with the method now.
B Anderson

Bernie-
Yes it's a frequent subject on this BBS, so let's really nail it down-

It should be noted that there are a variety of caged bearings that are available to be used as wheel bearings. While these all perform their function as thrust bearings quite well, care must be taken as to their proper installation. If incorrectly installed, the hubs may come loose from their axles, sometimes with catastrophic results, both mechanical and personal. They should always be checked to see if there is any clearance between them and the radius of the stub axle. If any clearance exists, then the radius of the inner cage of the bearing is too small and they should not be used. When the bearing radius is smaller than the radius of the stub axle, the bearing does not fit against the flange. The contact between the bearing and the flange face is designed to help support the axle load. Hence, a gap would provide a flex point which could easily lead to failure of the stub axle.

These two caged wheel bearings, although of different dimensions, are of exactly the same type. Although this type of caged wheel bearing can support lateral side forces, it is intolerant to over-tightening of the inner race against the outer race, as this will result in binding and they will consequently suffer either premature wear or, more likely, a catastrophic failure. On the other hand, the design of this type of caged bearing requires that it be installed in applications that position the inner race against the outer race with just the right amount of clearance in order for the wheel bearings to run freely. If there is too much clearance, then you will have “play”. If there is too little clearance, then the bearing will overheat and fail.

The hub into which the wheel bearings fit has an integral spacer machined into its center. This integral spacer holds the outer races of the two wheel bearings and sets them at a specific distance apart. In addition, another spacer is placed over the stub axle between the two wheel bearings and is used to set the two inner races apart. These two spacers should be measured in order to assure that they are exactly the same length, in order to assure correct alignment of the inner and outer races. Both wheel bearings must then be what is referred to as “face adjusted” with shims when installed. A “face adjusted” bearing is one that has been surface ground so that the surfaces that are in contact with the hub and the spacer are flat and parallel to each other whenever both races are in contact with the bearings as they would be when properly installed. This necessity is due to the fact that bearing manufacturers no longer make the original front wheel bearings in the necessary face-adjusted tolerances, thus it should come as no surprise that they do not fit correctly unless the appropriate thickness shims are used. Some cars were designed to use tapered wheel bearings without spacers and shims, but MGs were designed to run with them. Second-guessing university-trained engineers on safety-related items is a fool’s game.

Wheel bearings can fail for many different reasons. The least common reason for their failure is that they have become just plain worn out. In reality, very few wheel bearings run their entire life and expire from being worn out. The more common reasons for wheel bearing failure include over-loading, dirty or incorrect lubrication that includes too much or too little grease, or, if the bearing happens to fail a very short time after installation, then the most frequent reason is improper installation. If you use proper procedures, then they should have a satisfactory service life. Be sure to pack decent grease into the bearing prior to fitting. Keep the entire operation perfectly clean. It does not take much grit to start a bearing failure.

It is important to understand that the rolling elements in any rolling bearing must have a smooth race to run upon. The wheel bearings should be driven into place by using an outer race in order to push the outer race of the bearing into place. Be aware that forcing the inner race into the hub can cause it to separate from the outer race. It can be difficult to properly reassemble the bearing without damaging any of its precision components. If available, a press is logically the better alternative to driving them into place because a pushing force is preferable to that of an impact force. However, if you press, or gently tap the outer race into place, then the rolling elements cannot impact against either the inner race or the outer race (an event known as "brinelling"), therefore shortening the service life of the bearings. A future problem occurs when you wish to remove the bearings from the hub, as the easy way is to push the inner race, which then forces the rolling elements against the outer race, and thereby pushing the complete bearing out of the hub. Since this method has the potential for damaging the inner race, the rolling elements, and the outer race, of such bearings should be considered to be questionable for reinstallation unless the removal procedure has caused no brinelling of either the race or of the rolling elements.

It should be noted that it is possible to install wheel bearings in such a manner that it will lead to fracturing of the stub axle. You need to be aware of the fact that stub axles are an ideal candidate for fatigue failure that is caused by the cyclic loadings they typically see in their everyday use. Fatigue cracks will generally start at the base of the stub at the bearing shoulder (i.e. in the radius). They start at the surface at the 00 and 1800 positions (i.e., top and bottom), and then simultaneously work their way transversely across the axle inwards towards the center, with the crack growing and forming a lens shape. Eventually there will only be a narrow "eye slit" of uncracked metal remaining, at which point they let go. The problem is caused by failure to understand the design of the stub axle and, as a result, installing the assembly with incorrect torque on the wheel bearing retaining nut. The design demands that the wheel bearing retaining nut be tightened to a specified torque of 45 Ft-lbs to 70 Ft-lbs. This pre-stresses the stub axle by means of the spacer, and thus enables it to carry the suspension loadings without fracturing. If you fit the Original Equipment wheel bearing assembly, complete with its spacer, tab washer, and wheel bearing retaining nut, the stub axle will be placed under tension and the spacer will be placed under compression as the designer intended. This pre-loaded structure will then easily resist bending stresses because prior to any suspension load bending the stub axle, the load will first have to compress the spacer and / or further stretch the stub axle. Since the materials used in the stub axle and the spacer are stronger when they are respectively in tension and in compression than they are in bending, any loading that would apply bending force to the stub axle will be too weak to bend this stronger pre-loaded structure. If you reckon you know more about engineering design than the manufacturer, then leave out the spacer and shims. If you have an accident that kills others and the investigators determine that the cause was that you “failed to maintain the vehicle in a safe and roadworthy state”, not only might your insurance be automatically void, but you will have to live with the rest of the consequences as well.

Wheel bearings that have been marked “Thrust” on their outer races must always be installed with the marking facing their bearing spacer. Wheel bearings that have been marked Thrust on their inner races must always be installed with the marking facing away from their bearing spacer. Wheel bearings that have no such marking must always be installed with the thicker outer part of their outer races facing towards their bearing spacer. The wheel bearings of the MGB are adjusted by installing shims over the shaft between the inner race of the outer bearing and the steel spacer tube in order to adjust the spacing between the inner and outer wheel bearings, thus providing an exact, tight, firm fit. The torque is applied not through the rollers, but through the shims, bearing inner races, and the spacer tube, which is why it has a negligible effect on any free-play that is felt at the hub. The shimming should always be done with the pin aligned and the torque of the wheel bearing retaining nut within a range of 40 Ft-lbs to 70 Ft-lbs. The adjustment with these shims can made down to a minimum clearance of .001”. The torque specification for the wheel bearing retaining nut is 40 Ft-lbs minimum, and then tighten to the next cotter pin hole (there are two), which should happen before 70 Ft-lbs. This should not affect the end-float on the bearings, but if it does then you will just have to rejuggle and add a thousandth as you have probably squeezed some grease out of faces elsewhere. It is a bad idea to put shims between the washer and the wheel bearing. When tightening the wheel bearing retaining nut t you can shave slivers off the edges of the hole in the shim, not what you want inside your hub. Mark the wheel bearing retaining nut as to exactly what position it is in and which split pin hole is used. Once you have greased the wheel bearings and have fitted the seal, you cannot feel the end float, so the marks are critical; final assembly is by these marks. In order to check the amount of play in the wheel bearing, you ideally need a magnetic-mount dial gauge. This should be attached to the hub or the disc brake rotor and the reading then taken at the hub by pushing in and pulling out the hub on the bearing. The reading should be between .002" and .004". This must be measured with the wheel bearing retaining nut at 60 Ft-lbs, using shims to get the clearance correct. If the clearance is greater than this, remove shims in order to correct it or, ideally, replace the wheel bearings and re-shim them. I have found that the easiest way to set them is to fit a surplus of shims initially, measure the endplay (endfloat), and then calculate the thickness of shims that need to be removed in order to arrive at the correct endplay (endfloat).

When replacing the wheel bearings, dry-assemble everything first (i.e. without grease or oil) as this makes it easier to accurately set the endplay (endfloat). The order of parts on the axle is: oil seal collar, inner race of inner bearing, spacer, shims, inner race of outer bearing, bearing retaining washer, wheel bearing retaining nut. The first time that you assemble the parts onto the hub, in order to seat the outer races in the hub, leave out the shims and tighten the wheel bearing retaining nut until the wheel bearings bind. Next, fit the shims between the spacer and the outer bearing. The objective is to add or subtract shims until you get an endplay (endfloat) of .002” to .004”. Once you have got this correct, dismantle the hub, pack with grease, then refit and torque it up. Tighten the wheel bearing retaining nut until the bearings bind, This will pull the outer races fully against their locating flanges inside the hub.

Note that fitting shims between the outer bearing and the locating washer causes slivers of metal to be shaved off of the shims when the wheel bearing retaining nut is tightened, because in this position the shims are resting upon the threads of the axle. Slivers of metal are not what you want in your new bearing! Using combinations and multiples of shims will give most values in .001” increments with the exception of a few of the smaller values.

Keep combining different groupings of shims until you get two combinations of shims that ideally total only .001” apart, where the thinner combination gives no endplay (endfloat) and the thicker combination gives perceptible endplay (endfloat), i.e., +/- .001”. Use the lower combination and then add another .003” shim. This should give you the required clearance of .002” to .004”. After you have determined the correct combination of shims, remove the races and inject or press grease into only one side of the bearing! Keep going till the grease comes out the other side, and leave a bulge of grease on both sides. Do not be tempted to save time by forcing grease in from both sides, as you will trap air in the middle of the bearing and possibly cause premature failure. Fill the groove in the oil seal that faces the base of the axle shaft with grease, as well as the cavity between the oil seal and the inner bearing. Do not fill the cavity between the wheel bearings or the grease retaining cap with grease. The oil seal should be fitted to the hub with the flat side of the seal facing out from the hub and the lip of the seal facing inwards. This is to keep water off of the spring that provides the tension on the lip of the seal, so preventing it rusting, breaking, and consequently letting water and dirt in and grease out. Reassemble everything and tighten the wheel bearing retaining nut to 40 Ft-lbs, and then tighten the wheel bearing retaining nut further until one of the holes in the shaft lines up with a slot in the wheel bearing retaining nut. This should occur well before the maximum permissible torque of 70 Ft-lbs is reached. The wheel bearing retaining nut should then be locked in with a cotter pin. The system then will be firm and adjusted precisely to the clearance needed between the wheel bearings and their spacers, allowing them to spin very precisely with no play or wobble. This setup yields minimal wear to the wheel bearing over many miles. It is one of the best designs on the entire car.

Once you have the wheel bearings correctly installed, refit the wheel hubs, the disc brake rotors, and the disc brake calipers. Check to see if the rotors are properly centered inside of the calipers. If they are not properly centered, adjust the position of the caliper with shims.
Stephen Strange

Wow! Thanks Stephen Very comprehensive. I strongly suspect that the current bearing (only one side as the other side was done along with the kingpin recently.) was replaced by PBO or just tightened to take up slack! There is a bucket of 'clean' grease in the hub under the cap and I am almost willing to put money down that there was not a lot of care taken with adjustments. I'll be doing the job in a couple of weeks and I'll report back with results
Bernie
B Anderson

Bernie-
Yes, it never fails to amaze how ignorant DPO's will simply slather grease all over a wheel bearing, stick it back in, tighten it all down, and believe that they've done it right. Be thankful that the assembly didn't self-destruct while you were out on the road!
Stephen Strange

It was not far off. I had not taken the car out for a couple of weeks so with limited time (had to pick up wife with bags in other car) I 'nipped' up the road having just reassembled the back brakes and bits. All was fine and dandy, nice fast 'blow the cobwebs' run of about 10 miles, all was well until I turned into our small road when it felt like the nearside front Tyre had deflated. I limped the next 100Yds or so and jacked up the front. Nearside wheel has at least 1/4 inch movement at both top/bottom and left/right. Nothing else moves (king pin, track rod etc) that I can see so I assume the bearing(s) probably just the outer. maybe he just shimmed behind the tagged washer to take up slack. As you indicate that may not be a very bright plan!

We shall wait and see :)
B Anderson

Bernie-
At least you made it home without the wheel coming off! With that much play the bearings should be considered to be suspect at best. Your life rides on those wheel bearings, so don't take any chances on this one. Do a complete teardown and then rebuild with new bearings.
Stephen Strange

That's the plan. I am out of country for a couple of weeks but I have all the bits ready to go. Should be an interesting task
:)
B Anderson

After 15 years of annual tests and around 100k miles I suddenly had an advisory that the front offside wheel bearings were showing a bit of play. "Unlikely", I thought, probably the usual thing of young mechanics not knowing that this type of bearing assembly has to have some end-float. But as it wasn't a failure I didn't argue. Checked it myself when back home and it *did* seem a little slack. Took the grease cap off and removed the split-pin, and found the hub nut just finger-tight. Reset the shims and torqued it up and it's been fine since.

Unless something actually breaks up in which case it should be making a horrible noise, or no split-pin was fitted and the nut has come loose, I can't see why you should suddenly get so much play. It will be interesting to hear what you find.
PaulH Solihull

Have always wondered why tapered bearings require shims and the resulting end float. There must be a solid reason, but I have never found one. Sure would be easier to set the bearings without that requirement. Of course easier is not always better.
Thanks for any insight.

Pat
Patrick Callan

Taper roller bearings require shimming because unlike ball bearings where the inner and outer races and the balls are assembled in the factory the three parts are loose until assembled with the spindle and hub and the axle nut is tightened. Without the shimming you can't set the relationship between the rollers and the two races. If the nut is just left finger tight to give approximately the right relationship, the inners can spin on the spindle and weld themselves to it. In fact ball bearing inner races may need torqueing for the same reason.

As for end-float, the factory specified it, although there are some that claim that as American cars didn't have it, MGBs don't need it either. For me it's to allow for heat expansion and I'd rather do things as the factory specified.
PaulH Solihull

Paul,
Thanks. I have heard a variety of opinions about the bearings here in the States, but have never been able to get a clear explanation.
Thanks again.
Patrick Callan

Well that was interesting. Started to dismantle and discovered that I don't have a socket to fit! 1 1/4 too bit 1 too small! So what size is it?. Anyway got the pin out and found the one from moss would never go through the spline hole never the hub! anyway gave everything a shake and fond no play evident in any direction . So checked the actual hub which is ok and the spinner which was full of hard grease and crud in the in the part which buts to the wheel so cleaned it all out. Spread a bit of copper grease on the splines and thread, all back together with no play!. Bargain
B Anderson

Bernie-
The retaining nut is 1 1/8".
Stephen Strange

Thanks I thought it might be. I asked at Moss but they did not have a nut in stock that I could measure!
B Anderson

John Twist has a great Youtube video about the front hub/bearing assembly. According to him, the bearings/shims/spacer/bearing/spacer all being torqued down, in effect causing tension on the spindle, makes for a much stronger assembly over all. The shims provide the small amount of bearing play so the bearings themselves are not wearing excessively. I would be surprised that the end float was designed in to account for heat expansion. They don't get very warm under normal operation, and the hub should be functional under winter and summer driving conditions, amounting to a potential 70 degree celsius temperature range.

Here is the link to John Twists video:

http://www.youtube.com/watch?v=RJYIXZtnIiw

I apologize in advance if I am repeating something that Steven has already said in his elaborate post - I confess I didn't have the time to read it all:)
Erick Vesterback

The hub can experience a significantly higher temperature range than that from braking, and a large part of that will be transmitted into the bearings.
PaulH Solihull

This thread was discussed between 10/11/2012 and 11/12/2012

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