The Lockheed single-circuit brake master cylinder is mounted to the chassis alongside the pedal box and operated by a push rod from the brake pedal lever. The TD and TF use the same Lockheed master cylinder specification throughout production, no factory production change is recorded, and the cylinder is one of the many brake components shared between the two models. As a single-circuit system the master cylinder feeds all four wheel cylinders from one bore and one fluid reservoir, which is period-correct for the era but means a single internal seal failure can affect the whole braking system; regular inspection of pedal feel, fluid level and fluid condition is important.
Cylinder, Seal Kit and Internal Components
The complete master cylinder, the seal kit (containing the internal seals only), the internal main spring and the internal circlip are all individually available, the spring and circlip are listed as separate items rather than being included in the seal kit, which is worth noting when ordering a full overhaul package. The filler cap and its rubber sealing washer are also separately available; a perished filler cap seal allows fluid to weep when the cylinder is at full level and air to enter as fluid is consumed, which is a common cause of unexplained low-fluid warnings.
Push Rod and Fork End
The push rod connects the brake pedal to the master cylinder piston. Its fork end is supplied with a left-hand-threaded lock nut, the left-hand thread prevents the fork end from working loose under the cyclic pull-and-push of normal pedal use, which would otherwise be the natural tendency with a conventional right-hand thread. A clevis pin retains the fork end on the pedal lever and is separately available, as the pin and its hole are both wear points that should be inspected during any brake service.
Mounting and Adaptor
The cylinder is bolted to the chassis by two bolts with nuts and spring washers. The master cylinder adaptor connects the cylinder outlet to the first rigid brake pipe and is sealed by two copper sealing washers, one between the adaptor and the cylinder body, and one for the cylinder plug. These washers should always be renewed when the adaptor is disturbed; copper crushes to seal and will not seal reliably a second time.
Diagnosis and Overhaul
A failing master cylinder typically manifests as a spongy pedal that does not improve with bleeding, a pedal that sinks slowly to the floor under sustained pressure (indicating internal seal bypass), or visible fluid weeping at the push rod end of the cylinder. The seal kit resolves seal failure where the bore is in serviceable condition. Bore corrosion, scoring, or pitting requires a replacement cylinder rather than reseal, as fresh seals will not survive long against a damaged bore. Use of correct DOT 4 brake fluid and routine fluid renewal every two years is the simplest defence against bore corrosion in long-term use.