Front Wheel Bearings
POOR FITTING SPRIDGET FRONT WHEEL BEARINGS
To many enthusiasts who have maintained their own cars or indeed helped others to do the same, the mere mention of front wheel bearings sends most into a fit of gloom. From my own point of view I have included myself in the above mentioned group and always dreaded the MOT and the customary remark of, “bit of play in the fronts me old mate”. Those of you who have not suffered this mental turmoil will be wondering what on earth all the fuss is about? Well it is simple, when we change the front wheel bearings generally; the end result can be as much free play as when we started. This play is felt in the front wheels by ourselves and the MOT man who is not happy, and he will fail our cars at their annual inspection. Naturally there has to be an answer to this problem and indeed there is. However before we can resolve the problem we must first understand the causes of it.
The design of the Spridget front hub and bearings date’s back a long way and used the technology available at the time. Naturally by today’s standards it does seem poor but perhaps when it was designed it could have been cutting edge!! As can be seen in the original design section below, the hub consisted of 2 wheel bearings, an inner and an outer (green). These 2 bearings although different in dimensions are exactly the same type, They are a pair of 20 degree angular contact bearings installed in the hub opposite to each other. Whilst this type of bearing can support lateral side forces, it is not tolerant to over tightening of the inner race against the outer race as this will cause binding and will either suffer premature wear or more likely catastrophic failure. On the other hand the design of this type of bearing requires it to be installed in applications that POSITION the inner race against the outer race with JUST THE RIGHT AMOUNT of clearance for the balls of the bearing to run freely. Too much clearance and we will have “play” too little clearance and the bearing will overheat and fail. Just one more fact about these types of bearings is that they are designed to have lateral force in one direction only; lateral force in the other direction will simply make the bearing fall apart, and is the reason why they are installed in the hub opposing each other. It is therefore this positioning of the inner and outer races of both bearings in the hub that is critical to ensure just the right amount of clearance to have a tight wheel bearing (no play) whilst allowing enough clearance to avoid failure. How then is this achieved?
Well in layman’s terms the hub that the bearings fit into has a spacer machined into the centre. The Hub is coloured red and the machined spacer can be seen as the red bit between the 2 green outer races of the bearings. This spacer machined into the hub holds the outer races of the 2 bearings apart and sets them at a specific distance apart. Also another spacer (blue) is placed over the stub axle between the two bearings and is used to set the 2 inner races apart. The 2 spacers ought to be exactly the same length and both bearings should be what we call “face adjusted”. If all that is true then the assembly of both bearings in the hub as designed will be exactly as designed and will have already built in the exact amount of play the bearing manufacturer requires. This will be almost discernable by feel alone. However many of the bearings sold today by so called specialists are not face adjusted and are therefore not made to the same specification as he original used by BMC/Leyland and therefore do not create the correct amount of play when used with the 2 spacers. In fact bearing manufacturers no longer make the original Spridget front wheel bearings in face adjusted tolerances, so it is no surprise that they do not work correctly. The keen eyed amongst you will recognise this drawing as refering to a drum braked front hub. It is actually a drawing used for the Morris front hub bearing and therefore is drum braked, although the construction of the hub is the same for the Spridget, both drum and disk braked and also wire wheeled. The basic bearing numbers that you will buy today are 7303 and 7205, these are the basic bearings and if used with the standard Spridget set up will end up with play in the bearing. This is unacceptable but you must be clear about this problem, it is not because of poor quality of bearings, the standard bearings of today are good quality, however the problem is that they are the wrong specification!!
However this problem can also be over come by fitting 2 taper roller bearings again opposite each other. The benefit of this type of bearing is that they are tolerant of side ways pressure and therefore maybe used without the inner spacer and can be tightened against each other to remove any play and the main nut locked in the position that gives this exact position. Whilst this is fine they can also be used in the same way as the angular contact bearings, in so much as using both spacers and buying face adjusted bearings. Thus in the second method the main nut can be tighten without worry about bearing preload as the inner spacer will maintain correct spacing and the whole unit will be a stronger set up accordingly. The downside of taper rollers is that they are less efficient and have more friction than angular contact ball races and thus expected life is less and maintenance is higher.
Finally perhaps a far better option is available, and is my choice of bearing giving major advantages. On the market now is another angular contact bearing which has an increased angle of 40 degrees and gives it greater tolerance to lateral loads. Also this being a modern bearing the main advantage is that this bearing can be purchased in “face adjusted” form thus buying the slightly more expensive face adjusted bearing will ensure perfect fit in the hub and no more nightmares. The 2 numbers for the 40 degree face adjusted angular contact bearings are NSK 7303BEAT85SUN and 7205BEAT85SUN or in SKF no's 7303BECBP 7205BECBP
Don't only take my word for this here is an extract from a Spridget owner on a BBS who has suffered this very scenario
K Harris, IoW Frog+71GT
I have just rebuilt the front end of the Frog (New bushes, Springs etc)
but the straw that broke the Camels back was Wheel bearings, the new ones
supplied by a well known parts place mentioning no names, turned out to
be such a poor fit the Wheels rocked from side to side (I wouldn't insult
my MoT man by showing him a car in this state, as he is fair but that would
be taking the P**S)
New SFK Bearings fitted 7303BECBP 7205BECBP, no rocking
of the wheels side to side so should pass the MoT now, many thanks!!
Well we are all pleased about that mate.....
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FITTING BETTER (FACE ADJUSTED, 40 DEGREE) SPRIDGET FRONT WHEEL BEARINGS
On a wire wheeled disk braked car
This procedure follows the actions of changing the front wheel bearings on the passenger side front wheel (British car)
1. Remove the road wheel by jacking up the front wheel and removing the knock off, and then remove the wheel.
2. Remove the brake caliper. It is best to push back the caliper pistons
or remove the brake pads, then undo the 2 bolts at the rear of the caliper.
These 2 bolts are tab washered that need knocking back before using a 5/8th
AF socket to remove the bolts and pull the caliper away from the disk. I
generally leave the hydraulic hose connected so rather than allow the caliper
to hang on this hose it is always beneficial to support the caliper on something
thus not stressing the hose.
3. Now the hard part. Within the wire wheel hub is a large castellated nut
that holds the hub onto the axle. This is a couple of inches inside the
hub and will be locked into position by a split pin. On careful inspection
around the outside of the splined hub you should be able to locate a hole
that will line up to where the split pin locks the hub nut. Occasionally
it is possible to work inside the hub with long nosed pliers and extract
the pin through the small hole. However normally the split pin is in such
a condition that this becomes impossible. On these occasions I take a 15/16th
AF socket complete with short extension and tap it onto the hub nut. Then
with a bar undoing the nut anticlockwise will shear the split pin and allow
the hub nut to be removed.
Split pin hole Hub nut
4. Again another difficult hoping bit. You should now be able to pull the
hub assembly complete with disk off the stub axle. At times this is not
so easy and I use a copper hammer to persuade the hub to come off by tapping
at the rear of the disk. If this is really hard work it will more than likely
come off and leave the inner race and sometimes bearing on the axle shaft.
This is not a big problem and it can be removed after the hub is clear.
Hub Removal Deform and Remove Oilseal
5. With the hub off the axle, we now need to knock out the oil seal and
2 bearings from the hub. The oil seal is easily deformed with a screwdriver
and removed from the back of the hub. Now working from the rear of the hub,
with a long bar or punch you need to tap out the outer bearing from the
outside of the hub. This will normally come out very easily but will split
the bearing and leave the outer race of the bearing still locked into the
hub. Do not worry this can be removed shortly. Now working from the outside
with the same bar and technique knock out the inner bearing if it did not
come out when the hub was with drawn from the stub axle. Again it will normally
leave its outer race lodged firmly into the hub. Was that difficult? As
they say in all the great movies you aint seen nothing yet.
6. We now need to remove the 2 outer races that will be lodged inside the
hub, not an easy task it has to be said. Remember that a spacer is machined
inside the hub that both the outer races will be butted up against. At 2
points on each edge of the machined spacer, recesses are machined to allow
a tool to be placed against the outer race to permit them to be punched
out. This is extremely difficult to do with a wire hub without a decent
tool. I made one that fits and does the job that you may wish to copy, the
normal hub is a little better to get at.
Here you can see the inner bearing removed the machined
spacer in the hub and one of the indents that allow a tool to be used to
remove the bearing
7. With these driven out the hub is a bare shell and you will have recovered
the spacer that was between the two bearings over the axle, do not lose
it. You now need to check the length of this spacer and compare it to the
spacer that is machined into the hub. These should both be 1.5 inches give
or take a thou.
8. New parts are now required to fit into the stripped down hub. You will
need a new oil seal (Payen NA301) and an inner and outer bearing that are
NSK no’s 7303BEAT85SUN 7205BEAT85SUN or in SKF no's 7303BECBP 7205BECBP
New Bearings Non Thrust Face Thrust Face
9. You will notice that the 2 new bearings are different sizes. The larger
diameter bearing is the inner bearing and thus the smaller one is the outer.
Cleanliness is of vital importance when assembling the new bearings into
the hub so make sure the hub is clean before assembly. I always fit the
outer bearing first, mainly because on a wire wheeled car the outer bearing
is a long way into the hub and it is beneficial to be able to check from
the other end to ensure the bearing is fitting into the hub squarely.
10. Starting with the outer bearing first force grease (LM) into both sides
of the bearing. I tend to push grease into the bearing races and slowly
spin the bearing to ensure all the balls have a good coating. Then identify
the thrust side. When fitted this side faces towards the centre of the hub
and is identified by having a thicker outer race on it’s face, as
can be seen on the photos.
11. With this face identified drop the bearing into the hub with the thrust
face towards the centre of the hub. Making sure it remains square to the
hub start tapping it into the hub with a hammer and flat nosed punch. Alternatively
if you have a socket slightly smaller than the diameter of the outer race
then that too can be placed down the hub and it can be tapped to drive the
bearing into its seat. However what ever you use it must ONLY be used on
the face of the outer race, any hitting of the inner race or the balls themselves
will destroy the bearing. The most important part of this operation is to
ensure the bearing is driven into the hub squarely. I use a flat nosed punch
and hammer and tap the outer race of the bearing at 3 points around its
diameter. If the bearing is being driven into the hub squarely each tap
will be a small “thud” and experience allows you to feel it
push the bearing slightly. If the bearing skews as it is being driven into
the hub it will sound more like a “ring” and will stop moving.
If this occurs do not be tempted to continue knocking the bearing in, but
turn the hub over and tap the bearing back square. Again with it square,
turn the hub back over and continue knocking the bearing back into the hub.
Eventually when the bearing has been driven completely into the hub it will
seat against the spacer machined into the hub. This will be felt by the
bearing not moving into the hub when hit and the sound of the tapping becoming
a ring as opposed to a thud. Make sure you can feel the difference because
this side can be checked for being fully in by turning the hub over and
checking visually. However the opposite side bearing will need to be installed
by “feel” alone.
Here we have the outer bearing being knocked in. In the final shot the hub has been turned over and you can see the face of the bearing against the inner machined spacer.
12. Now turning the hub over and working from that side begin by filling
the hub with grease. Remember now to pop the spacer into the hub with the
tapered end facing down towards the bearing you have just fitted. Make sure
that the hub has plenty of grease around the outside of the spacer and to
the same height as the spacer.
Here is the spacer being placed in, the inner bearing in, the oil seal fitted and hub finished
13. With the inner (larger) bearing greased up and the thrust face facing
towards the centre of the hub drive the bearing into the hub exactly the
same as you have just fitted the outer bearing. Remember to hear the ring
as it sits on the spacer.
14. The final part of rebuilding the hub is to fit the oil seal. This fits
after the inner bearing. The side of the oil seal with the spring exposed
fits towards the bearing and the smooth side looks out from the hub. I always
push grease into the area where the spring sits and I also wipe grease all
around it to help it insert into the hub smoothly. Again tap it into the
hub with light hammer blows around its edge taking care to make it enter
squarely and not cause it to deform. When it is properly fitted it should
be level with the edge of the hub.
15. Hey we can now refit the hub to the front stub axle. Clean the axle
down paying particular attention to the larger diameter at the rear. This
section will be shiney and is where the oil seal runs and so should be smooth.
With a little grease on the stub axle slip the hub onto it pushing it as
far as it will go. Resist the temptation to thump it on with a hammer or
what ever as this could damage the bearings by forcing them apart. The hub
should push on easily and be far enough to fit the washer and hub nut onto
the end of the axle shaft. The washer has a tab on it that locates in a
slot on the axle at the top. With that on and the hub nut fitted, it can
be tightened up to draw the hub onto the axle. Eventually the hub nut will
become tight and should be tightened up to about 42 ft/lbs (disc braked
cars, drum brakes should be 55ft/lbs). When that occurs you then need to
see where the castle nut is sitting. The split pin hole is drilled into
the axle vertically and hopefully the castle nut will be in a position to
drop the split pin into the hole. If not either tighten the nut further
to expose the hole or slacken it slightly. As described earlier on wire
wheeled cars this hole is exposed by a larger hole in the splined hub.
Fitting the split pin is always the hardest task
16. If it is a steel wheel car then don’t forget to fit the dust cover.
Now refit the brake caliper and pop the wheel on, has the wheel got any
play? I certainly hope not!