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Tips and Tricks for Vintage Racers

 

DISC BRAKE TIPS

Change fluid with Castrol LMA (especially Lockheed users) or Ferodo DOT 4 Racing for severe usage, at least annually, more frequently in humid climates or if used for racing(1-2 events). DOT 5 silicone brake fluid is NOT recommended.

DO NOT use aerosol cleaners-some leave residues that promote glazing.

Continued glass beading of rotors will optimize performance.

When changing pads, always prepare the disc rotors by cleaning with an aggressive scrubbing with Scotch-Brite (steel grade) abrasive pads, 180 grit sandpaper, or glass beading (preferred) to remove boundary layer deposited by previous pads. Rinse with MEK, denatured alcohol, or acetone.

Many compounds need a heat cycle to fully cure them. You shouldn't start a race on a fresh set unless you are sure that compound doesn't require it.

Disc lightening--drilling vs. thinning: both will reduce mass and therefore heat sink capability. Some pluses for drilling.: If the holes drilled are smaller in diameter than the thickness of the disc, surface area is increased. With the right pattern, potential for warpage is decreased. Holes or slots with give the gas bubble created someplace to dissipate. Finally, the thicker disc allows the pads to sit deeper in the caliper, minimizing cocking and enhancing retraction. The down side is that it is very difficult and usually impossible to drill a pattern that will sweep the entire face of the pad, creating uneven pad and disc wear. Thinned discs need to be slotted. Grey iron rotors (vintage Norton and Triumph) should not be modified.

Check material for fit on the disc. Lockheed applications where the friction material rides out over the edge of the disc will benefit from the use of the Grimeca application-- moves material down 3mm.

 

DRUM BRAKE TIPS

Carefully inspect drum surface for grooves (obvious), crown (not so obvious), out of round and high-low spots (dial indicator). Crown often occurs with riveted linings. High-low spots commonly result when relacing hubs. There is no substitute for a freshly turned drum for premium friction materials to bed-in against. It's like putting a new piston in an old bore-never as good as with a fresh bore and hone. And you should inspect drum surface with the same critical eye. Tolerance: .002 to .004" any dimension. Up to .010 out-of-round may be tolerated.

If you are re-riveting new linings yourself, DO NOT drill out the rivets. Chisel off the peened end and drive the rivet out.

Materials currently available far exceed those previously available. Reline your shoes with a current premium compound

Keep in mind the low unit pressures required for mechanically operated drum brakes. Most linings require the higher unit pressures available hydraulically.

Very few modern materials are compatible with pressed steel drums.

Lay back leading edge of leading shoes in 1/2 inch increments to minimize initial "bite" if brake is too "grabby", especially when hot.

The expanded metal used to cover scoops is typically 15% to 23% open area. Replace them with stainless steel screens with 50% to 60% open area, tripling air flow.


Use sealed wheel bearings --grease vapor can contaminate linings. Once contaminated, they never recover.

.Lubricate backing plate components SPARINGLY with a 500F. + degree grease, such as Sta-Lube Sta-Plex Extreme Pressure, available at NAPA.  Liberally lube parts and assemble. Disassemble and carefully remove all excess grease.

Check to see how far the backplate extends into the drum. Too far in and the sides of the shoes drag on the hub, creating excessive heat. Epoxy a shim to the inside of the backplate. Not far enough, and a ridge forms where there is no contact. Bend backplate or remove material to correct.

Worn pivot shafts cause uneven actuation. Rebush if necessary.

If a stay is used, make sure it does not cock the backplate.

Always apply brake when tightening axle.

If you want to arc the linings yourself, and have access to a lathe, first mount the relined shoes on the backing plate. Turn on the lathe (300-350rpm) to .020" under drum I.D. in .010" cuts.