68 BB A/C Fan Blade

[Wayne M.]

Re: 68 BB A/C Fan Blade

..........As a general rule, I think that earlier 1968 big blocks used fan clutch GM #3916141. This is an Eaton-manufactured unit and has CURVED fins. It's still available today from GM, although its configuration is somewhat different than the originals of the same part number....

Joe; in your opinion, is this example, in the pics below, the '141' earlier configuration that may have been on early 1968 big blocks ? Has the slightly curved fins on the backside; the square fluid reservoir ends (rather than slightly angled, as in current GM offering). Also has the short (1.50" fan-to-w.pump flanges) non-stepped shaft. No SC date coding anywhere because it's not a Sweitzer (sp?) design.

This one has 'Eaton CK' and what looks like 'A3H' ink stamps on the face (a date code ?).

[Larry M.]

Re: 68 BB A/C Fan Blade

Wayne:

Info from my files indicates that the Eaton thermostatic fan clutches were date coded as follows:

The first letter represents the month: A=Jan, B=Feb, etc

The second number represents the day of the month. Based on some personal observations, it is possible that this number instead represents the week of the month. So the "3" could be January 3 or the third week in January.

The last letter represents the year, beginning with A for the year 1960. So "H" would be 1967.

Also, CJ and CK were supposedly not used/seen until late 1966.

I would be interested in others comments/opinions to help validate this date code interpretation. Some of this info was obtained from conversations with Fred Olivia, and some from other Forums/posts over the years.

Larry

[Joe L.]

Re: 68 BB A/C Fan Blade

Joe; in your opinion, is this example, in the pics below, the '141' earlier configuration that may have been on early 1968 big blocks ? Has the slightly curved fins on the backside; the square fluid reservoir ends (rather than slightly angled, as in current GM offering). Also has the short (1.50" fan-to-w.pump flanges) non-stepped shaft. No SC date coding anywhere because it's not a Sweitzer (sp?) design.

This one has 'Eaton CK' and what looks like 'A3H' ink stamps on the face (a date code ?).

Wayne-----


Yes, the configuration of this one is just exactly what I'd expect for an early GM #3916141, whether or not this one is actually that part number. However, I believe the "CK" broadcast code positively identifies it as the 3916141.

[Jeffrey A.]

Re: 68 BB A/C Fan Blade

Mark you mention that the clutch fan was off your L71. Was your car judged with the fan clutch on the car and if so as what level ( Chapter/ Regional or National) ? Finally how did the judging come out relative to the fan clutch you posted for me
Thanks Jeff

[Joe L.]

Re: 68 BB A/C Fan Blade

The 70 to 73 small block A/C cars continue to use the 3955182 fan blades with the square tip ends.

Grant-----


Oops, I missed this earlier. The GM #3955182 was last used for the 1970 model year. It was definitely not used for 1971-73 model Corvettes. The fan clutch mounting hub bolt circle size changed for the 1971 model year for all Corvettes due to the change in waterpumps and fan clutches. In fact, the big block with C-60 "spike-tipped" fan blade assembly used for 1970 Corvettes is not the same as the one used for 71-73, although the blade tips are the same.

[Joe T.]

Re: 68 BB A/C Fan Blade

The 3955182 fan is the C-60 fan for the 1969 big block car. Members here helped me research that a while back Its also the part number in the AIM. If you have the 1968 AIM, there should be part numbers for reference there. I was also educated that all OEM fan clutches for these years had holes as opposed to slots for the bolts, if my memory serves. I found my fan after diligent searches on this and other forums. If you do a search on the part number you want, sometimes it will lead to pay dirt...Good luck...joe

[Wayne M.]

Re: 68 BB A/C Fan Blade

Yes, this is the fan clutch I would generally expect to find on a 1968 Corvette big block. The clutch pictured is a GM #3937771. However, I believe that other fan clutches were used also. As a general rule, I think that earlier 1968 big blocks used fan clutch GM #3916141. This is an Eaton-manufactured unit and has CURVED fins. It's still available today from GM, although its configuration is somewhat different than the originals of the same part number.

I think that later 1968 Corvette big blocks used the 3937771 pictured. Just when the change occurred, I do not know, but I expect it was fairly early in the model year. In fact, there may not have been a discrete time of change; there may very well have been overlapping use.

Joe, others -- does the '68-9 TIM&JG recognize the fan clutch changes to correct inadequate cooling on early 1968's with 427 engines ?

There is a 7-page tech bulletin dated Dec 27, 1967 (# 68-T-9). This was reprinted in NCRS Restorer, Winter 1985. Unfortunately it doesn't mention fan assemblies [so I assume this was not a problem area -- ie. they weren't suggesting replacing 5-blades with 7], but it DOES refer to a new fan clutch # 3857530 (to raise the slip speed) on early '68 production with VINs prior to 01344. [I would assume that the '141' would be the type replaced].

The same TSB calls for replacement of fan shroud, fan pulley, drive belts, and lower valence panel extension, as well as cutting cooling slots in existing valence panel. [some of these apply only to real early cars, prior to VIN 00720, and some up to 002469].