This guide captures ‘bygone’ advice on how to dismantle and examine differential components on an MGB
It is part of my series on MGB Differential Rebuild.
Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.
Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.
Step By Step – Dismantle The Differential
Begin by removing the universal joint (UJ) flange retaining nut using a socket wrench and a tool which will prevent the flange itself from rotating.
There is a BL tool manufactured for this job (18G 34 A) but it is easy to fabricate a tool and improvise.
The pinion flange can now be tapped out gently using a soft-faced mallet, and its oil seal can be prised out carefully with a screwdriver and discarded.
Now remove all the crown wheel retaining bolts.
The crown wheel can then be removed by tapping it off the differential carrier with a softfaced mallet. Drift out the concealed roll pin which locates the pinion pin and then withdraw the pinion pin from the casing
Now rotate the differential wheels until the pinions are opposite the apertures in the differential cage (first pic below) and lift out the pinions together with the thrust washers which are located behind them (second pic below).
The differential wheels can then also be lifted out, together with their thrust washers. Take care that none of these components are interchanged and make a note of their relative positions.
The differential inner bearing races can be removed using a two-legged bearing puller (originally achieved using or BL service tool 18G 47 C, together with adaptor 18G 47 AK and plug 18G 47 AR)
Fit the tool to the differential assembly so that you can clamp the protruding lip of the tool’s flange firmly in a vice. Have an assistant hold the differential assembly while the handle of the tool is turned clockwise and the differential cage is pushed out of each inner bearing race.
Alternatively, it is possible to drive the bearing races off using a hammer and a drift but great care should be taken not to damage any of the components.
Finally, remove the pinion shaft bearing in a large press.
Step By Step – Examine The Differential
A thorough examination of all the differential components should be made after cleaning them in a proprietary degreasant such as Pioneer or Gunk, in order to determine which parts require replacement.
Check all bearing rollers and races for wear or scoring and purchase replacements for any bearings which appear to be suspect.
It is generally a good idea to replace all the bearings while the unit is dismantled, since they are relatively cheap and it is false economy to compromise on repairs of this nature.
The teeth of the crown wheel and pinion should be checked carefully for general wear and particularly for pitting, scoring and chipping.
These two components must be replaced as a factory-matched pair if they appear to be defective.
The differential wheels should be checked for similar signs of wear and all thrust washers should be examined for scoring or pitting.
A new pinion oil seal must be fitted at the re-assembly stage and so must a new collapsible pinion spacer.
To complete this overhaul it is also advisable to replace the axle-shaft seals and bearings as a matter of course.
MGB Diff Parts on eBay
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