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  Chicagoland MG Club:Tech Tips

Master Cylinder Rebuild - 1974-1/2 to 1980

A leaflet from a Lockheed cylinder rebuild kit:


Tachbrook Road, Leamington Spa.
Warwickshire, England. CV31 3ER

This repair kit contains two types of secondary cup to suit master cylinders having slightly different internal design. The original type was a wide secondary cup fitted to the piston shape as shown below.

New design cylinders use a marrow secondary seal with a chamfered lip and a modified piston groove.
Visual indication that these new parts have been fitted is provided by a small round hole in the master cylinder identification tag. Ensure that the correct secondary cup for the type master cylinder being serviced id fitted.
Discard the unused secondary cup.
Two of the remaining cups are identical and these are fitted on top of the new piston washers over the projecting piston noses, as illustrated below (main cup).

The remaining thinner 'reverse' cup is seated into the secondary piston groove with the lip facing in the direction as shown. Before final assembly lubricate the cylinder bore, pistons and seals with brake fluid.

Depending on the brake system design then master cylinder may be fitted with a pressure failure warning switch operated by a pressure differential piston assembly.


In order to service both the latest and earlier design of pressure differential piston assemblies this repair kit also contains four 'O' ring type rubber seals
The smaller pair of 'O' ring seals are used with the new type pistons assembly, fitted as shown. Insert the piston after first ensuring that the plastic spacer is positioned at the bottom of the bore. When the piston nose passes into the spacer the 'O' ring in the end groove 'assembly' position is pushed into its 'operating' position, see illustration.
The larger pair of rubber "O" rings are fitted to the original design piston assembly, as shown, no spacer is used with this type of piston.
Before final assembly lubricate the cylinder bore, piston and 'O' ring seals with new brake fluid.
Always renew the copper washer when refitting the end plug to the assembly. Torque the plug to 40-45Nm (30-33lbf.ft.).

Photos courtesy of Walter Szempruch

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