- The Throttle Arm / Shaft / Plate assembly controls the flow of vacuum that pulls gasoline and air into the intake manifold.
- Shaft and hole wear leads to vacuum leaks around the shaft, particularly on the arm end of the shaft. The most noticeable effect is poor idle. The soft metal of the shaft tends to wear faster than the casting hole.
- To address Shaft wear, replacement Throttle Shaft Assemblies are available from your suppliers.
- To salvage old arm styles, I build up the worn area with solder and turn down.
- If Casting hole is worn, drill out hole and press in bushings. Bushings are available from your suppliers. See Throttle Shaft Bushing Drill Fixture Plate.
- The Throttle Plate is attached to shaft with 2 Oval 5-40 UNF (SAE) thread x 19/64 screws
- Use high temperature grease on throttle shaft bearing surfaces to reduce friction, wear, and small air leaks.
- Idle Adjust Fillister Screws were 1/2" long until early 30 and then 5/8". The Fillister screw threads are 8-36 UNF (SAE). Off engine, initial setting of Fillister screw should slightly open the throttle plate.
- Some castings have the throttle shaft hole drilled through the back sides of the casting. If this is the case, a brass throttle shaft end plug (PN 9581-P) should be pressed in to prevent vacuum leaks.