Tim
Good to hear from you.
I have a 79 and a 65 Spitfire. On each car I have done major
differential and real axle work. Partly needed on account of their age,
and partly needed on account of DPO neglect and abuse.
Rich is right, and I ran into the same problem: If you are getting a
growling noise, it could be one or other of the axles. The inner
bearing on the axle hub behind the brake plate is prone to failure. It
is poorly designed where the bearing runs directly on the axle shaft,
not a true bearing surface. This arrangement really isn't so bad, since
it functions more for alignment than weight bearing, however, there is
no grease fitting to service it. Instead the cars were built with
little plugs you had to remove, then install a fitting, then grease,
then replace plug. Dumb. Without the presence of a grease fitting or
extensive knowledge of the fine print in the service manuals, one would
never know to grease those bearings. Disassembly of the hubs to replace
the bearings is almost impossible on your own. The forces required will
bend and damage the lug flange unless you have the right shop tools.
Again, these parts to so small they don't survive well when serviced
improperly.
Also, you may have universal joint failure on the inner end of the
shaft. Since the Spit uses comparatively microscopic u-joints, there is
no room for grease fittings, so they don't get serviced. If they are
old, they may be very troublesome to remove from the yokes. I left the
last set a a machine shop to remove. It was worth the 35 bucks.
Now, as far the differential unit itself is concerned, these cars came
with three different ones over the years (aside from the ratios). You
need to check for number of splines on the output shafts and input
shafts, and also the size of the flanges. The Victoria British catalog
has good illustrations of the different units.
If you swap one out, it should bolt into your car just fine, but the
driveshaft flange may not be the right size to match your driveshaft.
Also, the fore/aft location of the front flange plane may be slightly
different as well. This may be what some people run into problems with
the drive shafts not being the right length. The correct shaft
according to the book may not actually fit if someone has already
changed the differential.
The cost for differential bearings and seals is about $120 and
installation and setup is about the same. If your gears are OK,
replacing these parts is the way to go. If the bearings are OK too,
just replacing the seals is fine. The output shaft bearings should be
replaced with the seals, since the bearing removal necessary for seal
replacement can be quite abusive on the bearing. Those bearings are
standard size and inexpensive. BTW, it is almost impossible to get the
bearings off yourself. You should take them to an automotive machine
shop that has a small enough pinch clamp to do the job. Otherwise the
shafts can be ruined. On the earlier differentials, the pinion shaft
seal can be replaced successfully with just retorquing the pinion nut to
its exact location prior to removal. I have done this with success on
three on three different units. On the later differentials with the
collapsible spacer I don't think you will enjoy such easy results.
A third source for your noise could be the driveshaft. On my 65 the
driveshaft showed no external signs of failure such as lateral play in
the u-joints or broken u-joint cups, but when I dismantled it, the rear
joint was very dry and many of the needles were disintegrated causing
terrible noise and balance problems. On both cars I have replaced the
drive shafts with custom built units. Any good local driveshaft shop
can do this. The cost is a fraction of the catalog replacement price,
and you get a better result. On the later cars the front carden joint
is non serviceable because of the rubber boot. Just replace the drive
shaft with a custom built one. I think I paid about $100 for a custom
built shaft with the ujoints installed. Although I had to bring in some
flanges.
All the best,
Brian
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