Lew,
You are absolutely correct. You need the bearing spacer properly shimmed to
allow a tight stub axle nut to increase the effective diameter of the stub
axles when using tapered roller bearings on an old MG. Use of tapered
rollers and a shimmed spacer with properly torqued stub axle nut gives you
the same stub axle strength as the original ball bearing installation. But
tapered rollers are better bearings.
Same applies to pinion tapered rollers, you must have the bearing spacer
properly shimmed to get a slight preload on the bearings with a tight (
about 100 ft-lbs torque ?? ) pinion flange nut. If you have no spacer, you
can't tighten the pinion flange nut and the unit will likely fail. The MMM
Technical Topic does call for fabrication of a new sleeve ( read bearing
spacer ) and/or spacers to give a slight preload on the tapered baearings.
Unfortunately the MMM Technical Topic leaves a bit up to the experience of
installer as there is no mention of the importance of a tight pinion nut. A
tight pinion nut is a requirement.
Bob Grunau
Bob,
I seem to remember a discussion a while back on converting to tapered
bearings on front stub axles. The theory was that if you do so, it was
apparent suicide to not use a spacer between the inner and outer bearings.
Apparently the stub axle wasn't up to the job of carrying the load without
the spacer.
I wonder if the same principle applies here. If one were to convert to
tapered bearings in the diff pinion without a suitable spacer to transfer
the load, would this be inviting failure?
Cheers,
Lew Palmer
-
The most recent Fall 2005, page 17, issue of the NAMMM newsletter has a
Technical Topic on the conversion of MMM pinion bearings to taperted
rollers. Great advice.
I decided to check the pinion bearings on PA-0531 to see if they were OK as
I have had a load of experience with failed pinion bearings on MG TCs. The
design is very similar. Sure enough, the PA front pinion bearing had the
brass cage holding the balls broken and the front balls were very seriously
pitted. Extended further use would have caused a complete failure of the
thrust bearing. So do your MMM car a favour and check the front pinion
bearings. If any doubt, change to tapered rollers. More work but a bullet
proof repair.
In the case of PA-0531 I replaced the double row thrust bearing with a
double row steel caged ball bearing SKF-3305. For some reason, the diff was
not the same as a standard PA and did not have the long pinion
sleeve/housing. Maybe a Morris diff?? So converting to tapered rollers was
not an option.
Bob Grunau
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