Distributors suffer mechanical wear or electrical failures like shorts and loose wires. Parts can freeze up from rust or break from abuse. Oil, dirt and moisture can cause additional problems. There are some NOS (new old stock) distributors available for classic cars, but they are hard to find. Luckily, most distributors can be rebuilt, unless they are damaged or weathered beyond repair.
How Distributors Work
Your car’s distributor sends the flow of high-voltage electricity from your coil to each of the engine’s cylinders. The electricity moves from the coil, through the high-tension center wire, to the center tower on the distributor cap.
Inside the distributor cap is a rotating contact (rotor) that transfers the pulse from the center tower to one of the spark plug contacts inside the cap. The cables connected to each contact carry the voltage to the spark plugs. As the rotor spins, it hits each successive contact, firing one cylinder, then the next one.
The sparking action must speed up — or be advanced — as the engine runs faster. Older distributors use weights to advance the spark. Vacuum-type distributors use engine vacuum to speed the spark. Later cars adopted transistorized or electronic ignitions, often with computers controlling advance.
Rebuilding Advice From a Pro
Jeff Schlemmer of Advanced Distributor (www.advanceddistributors.com) in Shakopee, Minn., knows what goes into as first-class distributor rebuild. “Every distributor we rebuild is disassembled, cleaned and glass-bead blasted,” Jeff explained. “Then it is inspected for wear. After we fully assess the problems, we contact the car owner with a list of necessary and optional repairs.”
Jeff says repairs to an older points-type distributor can include polishing the distributor’s shaft and the cam lobes that force the contact points to open. “We seal or lubricate any parts that may rust,” Jeff pointed out. “We also reduce end play in the main shaft and cam assembly to closer-than-factory tolerances.”
According to Schlemmer, in a good rebuild, the advance weight pivots will be repaired as needed. “We grind the weight stops so that both weights seat at the same time,” said Jeff. “The seat stops are often misplaced in the initial assembly procedure, which alters the distributor’s amount of total advance.”
Jeff pointed out that shops with the proper knowledge and equipment can test a shaft for run-out and straighten it if it tests bad. Schlemmer also recommends replacing ground wires and terminal block wires whenever needed.
“When the advance assembly is held together with a clip, this can be a problem,” said Jeff. “It’s possible to modify the shaft so the whole assembly can be retained with a screw. This allows adjustment of any excessive end play. “
A rebuilder should be able to recurve a distributor to either its original advance curve or to optional high-performance specifications, says Jeff, who uses a Sun 680 distributor tester or a Snap-On Distrib-U-Scope tester for this. In fact, it was a distributor testing machine in the back of his high school auto shop that started his career. As he tells it, “The shop teacher didn't know much about it, except that it wasn’t functional.” Jeff repaired the tester’s strobe and used it to re-curve a 1967 Camaro distributor with the help of Hot Rod magazine articles.Since then, he’s been tuning every car he’s owned — plus many more owned by his customers. Working on British cars is a specialty.