Robert Zirpolo writes:-
>Date: Tue, 12 Nov 1996 12:50:35 -0500
>From: Robert Zirpolo <airhedrz@mailhost.iconn.net>
>Subject: Winter project..
>I'm in the process of replacing the front disc brake rotors, wire wheel hubs
>and wheel bearings on my 72B. Anyone have any words of wisdom for an
amateur???
Well Robert, I am not the last word in MG mechanics but I can pass on to you
my experience of doing what you are planning to do, having done it myself on
5 different MGB's.
Get your new hubs and rotors, assemble them and then take them to a
reputable shop to have them turned! This may come as a surprise to have new
rotors turned, but if you want the job done right you had better plan on
doing it. Since the rotor relies on the hub for its axis of rotation, it is
advisable to have the assembly checked in a lathe and if it needs trueing up
it can be done. I had a new rotor that had almost 20 thousandths run out, it
was actually worse that the old one which alas was below the limit for
turning. Runout can cause your brake pedal to pump up and down.
Replace the wheel bearings and oil seals while the hubs are off, it just
makes sense to do this while they are off, parts are small cost relative to
the labor of pulling it all apart later.
I would also replace the caliper flex hoses and since the calipers are off,
you might think about installing new seals at the same time. Again, the
parts costs are not significant and the worst part is getting everything
torn apart if you have to do this at a later time anyway.
When you attempt this job, getting the caps out of the hubs to expose the
hub nut, is a pain. You need some sort of puller and slide hammer. I
fabricated one with a spare long nut that I got from the rear cylinder head
stud that supports the air injection rail on the 72B (part of emissions
equipment). I think the thread on the wheel bearing cap was the coarse
thread and had to tap out the end to fit. Then with the studding threaded
into that long nut, it protrudes out the hub. I then used a large washer and
a nut behind to give myself something to pry behind with a couple of
screwdrivers against the end of the hub.
Getting the split pin out was another pain in the neck. I used some needle nose
pliers, find the hole through the side of the hub to pull the pin through,
it is usually filled with grease and easy to miss.
Remove the hub nut, I think it is 1 and 3/16 inch, so you will need a socket
to do this. Remove the washer behind the nut by pulling on the disc and hub
assembly. That is assuming you have removed the caliper first! If you do not
replace the caliper hoses support the caliper while it is off, do not let it
hang on the hose.
When you have the hub and disc off, the outer bearing falls out, look for
the shim washers that are behind the outer bearing between it and the large
cylindrical spacer that fits between the inner and outer bearings on the
axil shaft. There are four sizes of shim washer that you may encounter, 3,
5, 10 and 30 thousandths thick. These can be in any combination to provide
an end float of about 4 thousandths, when the nut is tightened to the
correct torque. A dial gauge is useful but not essential.
It is a good idea before pulling it all apart, to get a feel of what the end
float is like. Grab the disc with your hands on opposite sides and try to
pull and push on it, sliding it on its axil. There should be just
perceptible movement, NO movement is not acceptable! This is what you need
to achieve when you reassemble after replacing bearings etc. just
perceptible movement. You should take careful note of what shims were used,
so that you have a starting point when you reassemble. The thin shims are
hard to detect as they all stick together with the grease. I find that
holding them between the thumb and forefinger and using a sliding action
usually separates them.
To get the inner bearing out, the oil seal must be pried out first. Then
with the oil seal and inner bearing removed the spacer can be removed. The
tapered end of the spacer goes to the outer smaller bearing, when reassembling.
If the bearings are to be replaced the outer case of the bearings must be
driven out with a suitable drift and hammer. There are recesses in the hub
casting to give access to the back edge of the bearing, in order to drive it
out.
If you don't feel confident to replace the new bearings take them to your
local shop and they will press them in. I have a press and some aluminum
discs the size of the bearings that I use to press them in.
If you do this yourself, make sure you press the outer casing of the bearing
in the correct was around!
Assembly is the reverse process as they say. Pack the bearings with a good
quality grease, put the tapered spacer in small end first then the inner
bearing, then the oil seal. Now slide the assembly back onto the axil shaft,
push slightly to get the oil seal onto the inner spacer. Now place the shims
on the shaft then the outer bearing, then the washer, note the washer has a
tab on the inside, you will find it necessary to locate this in the grove of
the axil first, like hanging the washer on the shaft.
Install the nut and torque to the spec. Now check the end float. Add or
remove shims to produce that "perceptible" axial movement. If you have
access to a dial gauge, great, if not, use your good judgement. When you are
satisfied you have it right, replace the split pin and then tap home the cap
into the hub. Make sure it seats squarely into the hub, it should not be
loose as it fits into a tapered area and needs quite a bit of force to get
it seated.
If I have forgotten something or someone on the net has a better way, feel
free to comment.
Robert if you have any questions let me know.
Good luck John Bartholomew .
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E-mail jdb70@juts.ccc.amdahl.com John Bartholomew Amdahl San Jose CA.
408-746-6361 07:00-16:00 PST. ** USUAL DISCAILMERS APPLY **
1969 MGBGT; 1974 MGB; 1976 MGB-RESTORED; 1979 MGB; 1972 MGB daily driver.
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