40 - 48 Fan Belt

[Don Boshara #594]

My '40 60S has a '48 engine. According to the '42 & '53 parts books both engines use the same balancer pulley and fan pulley. Why does the '48 call for a much narrower belt than the '40? Both belts are noisy.

[Bill Ingler #7799]

Hi Don: I can`t answer you as to why the narrow belt on the 48 verses the 40. The 48 water pump pulley can be identified from the earlier 40s pulley as the 48 water pump pulley has a star design on the pulley front verses a somewhat smooth front pulley design on 47 and earlier water pump pulley.I have never measured the width of either the 48 or an earlier pulley so the width if different might account for the difference in belt widths. What I have experienced is the Gates Green stripe belts that several of the suppliers furnish for our 40s Cads are noisy belts, at least on my 47 and 41. I call them cog belts from their design. I have switched from the Gates belt and have bought belts from McVey which are made close to the original type wrapped fabric belt. This belt has a slightly narrower width and depth, sits lower in the pulley, more so than the Gates Green Stripe, and so far both the 41 and 47 belts are quite. Another reason I think some belts are noisy is paint in the pulley valley. I was told years ago to never paint the inside of the pulley valley as this can cause noise from the belt.

[Don Boshara #594]

Thanks Bill for your imput. I may give McVey’s cloth wrapped belt a try. In saying that both belts are noisy, I meant that both widths I have tried of the fan belt are noisy. The water pump/generator belt is also a Gates Green Stripe and is quiet.

I still don’t understand why Cadillac would call for 2 different belt widths for the same pulleys, and if the narrow belt is better why not change the part number for the ‘40 in the ‘53 book. Maybe since 55 years have passed it might be a bit late to ask that question.