The Stovebolt Site Forums The Shop Area Engine Shop 261/235 Distributor Question

Seeking advice from the GURUs..... I am playing with a GMC 302...... still getting acquainted to the engine...... this civilian motor came from a large grain truck from the West circa 1959..... it is a replacement motor factory clearly stamped 302 BUT no serial number......block has raised cast numbers...from memory 2324004 which indicates a 1958 to 62 run......

My 2403 looks very similar to the spare 235/261 dizzy....same cap same rotor...... BUT no vacuum advance. I will strip it down for in depth cleaning........ why do I need to install a vacuum advance??????.... will be used in a restored 4x4 with 4 speed synchro. Am I right in assuming that this 2403 would/possibly be different inside..... weight/springs calibrated for the 302 and a similar 261 dizzy with the vacuum advance would be slightly different although it fits the block????....... assuming that this is why Delco had so many models that had been tricked for specific engines....... or was it a marketing ploy????

Thanks for the education!!!!!

I don't understand "My 2403". Is that a number from a distributor? Below is a page from 1955.2-1960 GMC Master Parts Book listing all distributors used in GMC gasoline engines. The only one used in 302 engines was 1112414 which replaced 1112411. So same weights and springs 248, 270 and 302.

The same book shows vacuum advance units used on 100 series (1/2 ton) thru 300 series (2 ton) and some 340 series trucks. Larger trucks did not use a vacuum advance unit.

Vacuum advance units may provide better gas mileage and maybe cooler running in high vacuum situations. Big trucks didn't use them because they were mostly driven pedal to the metal.

I have a mid 50's Chevy high cap distributor in my GMC 228 and I plan to use it in my 302 if I ever get it running and installed.

Yes - the "2403" is 1112403 part number on the distributor.

The distributors with no vacuum advance were used in heavy truck applications where the gas mileage gain with a few more degrees of spark advance at light throttle was not a consideration. 1 1/2 and 2 ton Chevy rigs and heavier capacity GMC's seldom if ever ran at part throttle or less where enough vacuum to operate the advance can was available, so there was no need to have that function on them.

By Moderator: I separated this post out of an existing thread to start a new thread. It’s always better to start a new thread rather than piggybacking on to an existing one, so replies can be custom tailored to your issue.