70-72 LT-1 Harmonic Balancer

[Jeff B.]

Is the GM Performance 88960604 balancer the current replacement for the original part number 3947712?
From what I can tell the GM 3947712 was discontinued and replaced by GM 6272224 and then replaced by GM 12555879 which I can't find and possibly discontinued as well.

My original damper's rubber ring has a section which has moved about an 1/8 inch rearward (where the rubber comes together) and has started rubbing the timing cover. Am I better off sending my original out to be rebuilt or buying a new 88960604 from GM Performance? Thanks in advance.

Jeff

[Joe L.]

Re: 70-72 LT-1 Harmonic Balancer

Is the GM Performance 88960604 balancer the current replacement for the original part number 3947712?
From what I can tell the GM 3947712 was discontinued and replaced by GM 6272224 and then replaced by GM 12555879 which I can't find and possibly discontinued as well.

My original damper's rubber ring has a section which has moved about an 1/8 inch rearward (where the rubber comes together) and has started rubbing the timing cover. Am I better off sending my original out to be rebuilt or buying a new 88960604 from GM Performance? Thanks in advance.

Jeff

Jeff------


Yes, the 88960604 is the current "iteration" of the 1970-72 LT-1 balancer (as well as 1969-70 L-46 and 1973-80 L-82). Just how it differs from the original I do not know. However, I believe that one difference involves the embossment of degree marks around about 90 degrees of the perimeter of the ring. This is the same as the 12555879 but NOT the same as the 3947712 and 6272224. Your best bet might be having your balancer rebuilt by a reputable rebuilder like the Damper Doc.

[Jeff B.]

Re: 70-72 LT-1 Harmonic Balancer

Joe,

Thanks for the information. I pulled my damper last night to send out for rebuild- I was impressed with the knowledge and experience from a phone conversation with David with Dale Manufacturing in Oregon. My late June build 1972 LT-1 has the GM 6272224 balancer on it. The stampings on the front side are "2224 B2F" and the casting number of the hub on the backside is 3942538. I am assuming the B2F is the date code for the assembly- can you shed any light on this code?

Jeff

[David L.]

Re: 70-72 LT-1 Harmonic Balancer

Jeff,

You are right about the date code ("B2F" = Feb. 1972). I do not know what the letter "F" means but it might represent manufacturer. I have collected several Chevrolet balancers over the years.
"7704" and "B9F" (Feb. 1969)
"4684" and "E8F" (May 1968)
"2223" and "J1F" (Sept. 1971)
"7706" and "J8F" (Sept. 1968)
66 Chev. 327 w/"T0521HAR" on engine pad, balancer stamped only "E6F" (May 1966) without the 4-digit part number.

None of my 1965 and older balancers have any code stampings.

I believe that the date code stampings were first appeared in 1966 and the 4-digit part number (last 4 digits of the 7-digit part number) was added maybe a year later.

I also have a couple of balancers with different codes which I have not totally decoded.
"7701" and "1S0" from 1971 block "K0217CGC" and "1 B 12" (Feb. 12, 1971) casting date
"7704" and "AS0" from 1970 Monte Carlo

Dave

[Jeff B.]

Re: 70-72 LT-1 Harmonic Balancer

Thanks Dave for your help with the dates!