[Healeys] Diff. difficulties

[Andrew Thorp]

Hi Gergo,

I'm part way through doing my BN4 diff and have found a
 few things so far. I
decided to change from the 4.11 ratio to a 3.54 
and in the process discovered
the cross-pin was damaged in the 3.54 and 
so elected to replace the whole
centre with a Quaife ATB. The Quaife 
unit has now gone back to the
manufacturer because it wasn't machined 
concentrically but that is another
saga altogether.

There are four critical adjustments in the diff:
the pinion bearing preload (set by shims behind the front bearing)
the pinion mesh depth (set by the thickness of the spacer behind the large
pinion bearing)
the side bearing preload (set by the washer thicknesses each side)
the crownwheel mesh depth. (set by the washer thicknesses each side)


My advice is to get an old-school diff rebuilder to do the setup work 
once
you have obtained the bearings and seal. They will have a hydraulic press and
a surface 
grinder to adjust the spacer thicknesses and also a stash of other
spacers to substitute. Getting a quiet diff is very much a black art 
still
and I would be very surprised to see a home-built diff give 
satisfactory
service.

Be aware of the order that the front pinion
 shims go back in, they must go
back in with the thick shims next to the
 bearing/spacer and the thin shim(s)
sandwiched between in the middle. 
If the thin shim is put against the bearing
or spacer it will be crushed
 and torn, resulting in it escaping and the
preload of the pinion 
bearings being lost. It is very important that the
pinion nut is 
tightened fully to 140lb-ft.

Re the side bearings coming in two, 
this is how they are supposed to be. You
take off the outer race and 
balls/retainer from the centre, then press the
centre onto the carrier. 
Then refit the outer parts. There is a slight lip on
the inner race to 
stop them falling off.

Only bearing brands I'd watch out for are 
chinese made ones. There are some
pretty random names of bearings out 
there but the supplier I have used AH4H
in UK assure me their bearings 
are not sourced from Asia. The prices vary
wildly so
 shop around for them- the local supplier here wants 3-4 times what
they
 sell for online for the pinion bearings but their side bearings are
about 1/4 the online price. You can Google the part numbers off the 
bearings
and come up with a few suppliers and crossover numbers.

If your axle hub bearings and seals haven't been replaced I'd suggest doing
them too at the same time.

Cheers,
Andy.