How To Assemble A Differential On An MGB

How to assemble a differential on an MGB

This guide captures ‘bygone’ advice on how to assemble a differential on an MGB

It is part of my series on MGB Differential Rebuild.

Go here for all my Classic Car Maintenance DIY Guides or visit SCOTTYS Technical Library and Supplier Library 

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 – Assemble a Differential on An MGB

Great care must be taken during the re-assembly procedure in order to ensure that all adjustments are made correctly and that the noise level of the rear axle assembly will be kept to a minimum.

Begin by measuring the inside and outside of each pinion thrust washer (as shown below) and compare the measure­ments to find out if there is any wear which would indicate that the washers must be replaced.

Note you can buy replacement thrust washer sized shim kits to help overcome water problems.

Check the Pinion Thrust Washer on an MGB Differential
In order to check the pinion thrust washers for wear, use a micrometer to measure the thickness at the outer edge
Differential Thrust Washer Measurment on an MGB
Now measure the thickness at the inner edge and compare the reading with the one taken at the outer edge of the washer

Now fit the differential wheels, the pinion wheels and their respective washers by reversing the dismantling procedure.

Align the pinion pin with the hole in the differential cage and use a small drift to drive the retaining roll pin into its position.

Bolt the crown wheel to the differential cage and then use a torque wrench to tighten the bolts to 8.3 to 8.9 kg/m (60 to 65lb/ft) (as shown below).

Fitting a crown wheel to its carrier on an MGB Differential
Use a torque wrench to bolt the crown wheel to the carrier assembly and tighten them to 8.3 to 8.9 kg/m (60 to 65 lbs/ft)

Now it will be necessary to use a dial indicator to measure the run-out of the crown wheel as it is rotated (as shown below).

Measure Crown Wheel End Float on an MGB
Mount a dial indicator gauge on the casing in this way and position the probe so the crown wheel run-out can be checked

Mount the gauge on the differential casing so that its probe just comes into contact with the edge of the crown wheel then turn the wheel and check that the run-out does not exceed 0.05 mm (0.002in).

If the measurement exceeds this figure, the crown wheel should be removed and checked for dirt or metal filings on the mounting face.

Alter the position of the crown wheel on the differential cage by matching up the holes in the crown wheel with different bolt holes in the cage assembly until the correct alignment is achieved.

When you are satisfied that the run-out is correct, the bolt torque should be re-checked. If after adjustment, the run-out is still excessive, a new crown wheel and pinion must be fitted.

What Next ?

Head back to MGB Differential Rebuild to select the next stage instructions.

MGB Diff Parts on eBay

Dial Test Indicators on eBay

Micrometers on eBay

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