Alternator Mounting: SAE Pad Mount
- A-1 Auto Electric
- Jun 10
- 1 min read
The SAE stationary pad-mount standard for heavy-duty engines utilizes a six-hole bracket configuration to maximize versatility. This layout allows a single engine bracket to support both the short-pad and long-pad alternator designs used across the commercial vehicle industry. By integrating six holes into the mounting point, fleet operators can easily upgrade or swap alternators without replacing the underlying engine hardware.
The six holes on the engine bracket are arranged in three parallel pairs. The front pair is located closest to the drive belt and has a fixed horizontal spacing of 190 millimeters. Because precise belt and pulley alignment is critical, the alternator housing must always secure tightly to these front holes first.
The remaining four holes on the bracket accommodate the two different housing lengths. The middle pair creates a short-pad mounting spread of 108 millimeters (4.25 inches), which is the standard footprint for traditional brush-type alternators like the Delco Remy 22SI. The rear pair creates a long-pad mounting spread of 126 millimeters (4.97 inches). This longer configuration supports larger, high-output, brushless alternators like the Delco Remy 35SI, which require a wider base to manage increased torque and vibration.
While the engine bracket features six holes, the alternator itself only utilizes four bolts. To simplify installation, the rear holes on the alternator housing are drilled slightly larger than the front holes. This deliberate clearance allowance gives the installer enough flexibility to slide and align the rear of the alternator into the correct bracket holes before final torque is applied.
Why Alternator Pad Mount Holes are Different By Delco Remy