'71 C60 belt number

[Joe G.]

Hi everyone. I tried searching the archives for this answer and apologize if it has been covered before. I am planning on replacing the belts on my late '71 LS5 car and I want to make sure I order the correct one for the AC system. Looking at the AIM in the C60 section, page C2, there is a revision listed on 12-23-70 that changes from belt 3969948 to 3999272. Just wanted to make sure I am reading this correctly. Is 3999272 the correct one? Thanks for the input.

[Joe L.]

Re: '71 C60 belt number

Joe-----

It depends upon when your car was built. You say "late" but not how late. Keep in mind that the 12-23-70 revision date is when the change was made to the drawing; it's NOT the date that the assembly plant actually changed the part actually installed. That probably didn't occur until, at least, early March, 1971. It might have occurred even later than that, depending upon how much of an inventory of the 3969948 the plant had. SERVICE inventory of the 3969948 did not run out until October, 1971 so that WEAKLY implies that there may have been a considerable inventory of the 3969948 "in the system".

The GM #3969948 was a belt of 15/32" width and 46-1/4" length.

The GM #3999272 was a belt of 15/32" width and 45-3/4" length.

My GUESS would be that if your car was built in the period of February to May, 1971, it could have had either belt. If it was built after May, 1971, it would very likely have the 3999272 belt.

[Joe G.]

Re: '71 C60 belt number

Thanks Joe for the informative response. You answered a lot of my sub-questions, such as when the parts actually went into use after a revision date. The car serial number is 20,992 with an estimated build date of July 10, 1971 and Protecto o plate date of July 15. As a side note, looking at different things on the car it does have a couple of 72 parts intermixed.

I just measured the existing Gates ES3 8455 belt with a thread and the O.D. looks like 45 3/4". The adjusting bolt is right in the center of the slot. So there is room to go either way. Wait, I just took a closer look at the adjustment slot and there is telltale evidence that the bolt was cinched down lower in the slot at one time, or that a longer belt had been on it.
Joe