1971 fan clutch

[Warren F.]

My assumption is that this part was installed at St. Louis assembly line, instead of at Tonawanda engine facility. Is this correct?

[Terry M.]

Re: 1971 fan clutch

You are correct. The AIM has a part number for the fan clutch -- thus it was installed at St. Louis.

[Joe L.]

Re: 1971 fan clutch

My assumption is that this part was installed at St. Louis assembly line, instead of at Tonawanda engine facility. Is this correct?

Warren-----


Also, the 1971 fan clutch, GM #3991426, was a one-year-only and Corvette-only piece. It's not something that you want to need.

[Warren F.]

Re: 1971 fan clutch

Joe,

Your statement intrigues me. Please enlighten me, as unfortunately one of my '71 Corvettes has a replacement clutch, an Eaton style, instead of the Switzer style. I have been looking for the correct one, for awhile now.

[Joe L.]

Re: 1971 fan clutch

Joe,

Your statement intrigues me. Please enlighten me, as unfortunately one of my '71 Corvettes has a replacement clutch, an Eaton style, instead of the Switzer style. I have been looking for the correct one, for awhile now.

Warren-----


Not too much intrigue about it. It's just a fairly rare piece because of limited application and model year usage. Basically, it's similar to a GM #3937771 except the hub has a 3/4" pilot hole, a 2-1/8" bolt circle and the fan mounting studs are on a 3-1/4" bolt circle. A picture of an NOS example is attached.

[Warren F.]

Re: 1971 fan clutch

Joe,

Thank you for the physical specifics, I will write those down. I knew the '70 model year and older were different size, but how is '72 model year and up different?

[Joe L.]

Re: 1971 fan clutch

Joe,

Thank you for the physical specifics, I will write those down. I knew the '70 model year and older were different size, but how is '72 model year and up different?

Warren-----


I did some further checking and re-discovered something I once knew but forgot. As it turns out, 1972 and 1973 also originally used the 3991426 fan clutch. However, what complicates this is that GM later changed the SERVICE fan clutch for 1972-73 models to GM #342720 which was the fan clutch used in PRODUCTION and original SERVICE for many 1974-E77 Corvettes without C-60. That fan clutch was replaced by GM #460742 for L1977-79 Corvettes without C-60 and also replaced the 342720 for SERVICE in November, 1978.

The strange thing is GM never cataloged any fan clutch other than the 3991426 for 1971 models. That fan clutch was discontinued in October, 1984. I have no idea why GM considered the 342720 suitable for SERVICE for 1972-73 Corvettes, but not suitable for 1971 Corvettes.

[Warren F.]

Re: 1971 fan clutch

Thanks, Joe.

[Jack H.]

Re: 1971 fan clutch

Different fans and fan clutches are called out in the AIM depending on car/engine configuration. The base SB drawing calls for a 3888366 five blade fan with either of three fan clutches: 3916139, 3916140 and 5329100. The first two are familiar Eaton coil type & Schwitzer bar type. The third PN is a Delco Remy made 'clone' of the Eaton clutch and resembles it closely.

When A/C was added to the SB, the fan and fan clutch changed PN's with the fan being a seven-blade assy. A/C equipped BB's also call out a different fan PN.

The 3991426 fan clutch Joe mentioned is called out by the AIM for BB engine use. The drawing shows this fan clutch replaced the 3937771 used in prior years on BB's at the start of production 8/18/70. That makes sense because the old '7771 clutch didn't have the big hub and wider bolt pattern necessary to mate with new water pump(s) that came on stream in 1971. So, the earlier versions of the various fan clutches would not/could not install due to their smaller hub/bolt geometry.

As Joe once pointed out to me, there HAS to be an error in the C60 section of the '71 AIM as it calls out only the 3937771 early BB fan clutch for use on AC equipped SB engines. That CAN'T be right because there's no way that version of the fan clutch would fit/mount onto the new 3991399 water pump that was introduced for '71 SB engines...

So, what's right/correct for a '71 is compounded by which engine + what options the target car has.

[Warren F.]

Re: 1971 fan clutch

Jack,

I'm looking to locate an original correct fan clutch for one of my '71 LS-6 'vettes. My orange car has thee original and my white car has a service replacement Eaton style, this fan clutch is the universal style with mutiple holes. I've located one, however it is mighty close date wise to the trim tag date, not realistically a proper dated component, but would work. I prefer to have a dated component that is pretty damn likely to have been used originally on this car, considering that I would have to have this fan clutch sent out for rebuilding, and with the price they want for it, just to purchase is quite high. It would put me into a very costly piece, so I would want a date coded component that is as close to being correct as possible.

[Mike E.]

Re: 1971 fan clutch

I picked one up for my early 71, dated August 1970, on ebay about 8 weeks ago for $125 with the original 5-blade fan.

[Joe L.]

Re: 1971 fan clutch

Jack,

I'm looking to locate an original correct fan clutch for one of my '71 LS-6 'vettes. My orange car has thee original and my white car has a service replacement Eaton style, this fan clutch is the universal style with mutiple holes. I've located one, however it is mighty close date wise to the trim tag date, not realistically a proper dated component, but would work. I prefer to have a dated component that is pretty damn likely to have been used originally on this car, considering that I would have to have this fan clutch sent out for rebuilding, and with the price they want for it, just to purchase is quite high. It would put me into a very costly piece, so I would want a date coded component that is as close to being correct as possible.

Warren-----


Does the original fan clutch on one of your cars look like the one in the photo I posted?

[Joe L.]

Re: 1971 fan clutch

Different fans and fan clutches are called out in the AIM depending on car/engine configuration. The base SB drawing calls for a 3888366 five blade fan with either of three fan clutches: 3916139, 3916140 and 5329100. The first two are familiar Eaton coil type & Schwitzer bar type. The third PN is a Delco Remy made 'clone' of the Eaton clutch and resembles it closely.

When A/C was added to the SB, the fan and fan clutch changed PN's with the fan being a seven-blade assy. A/C equipped BB's also call out a different fan PN.

The 3991426 fan clutch Joe mentioned is called out by the AIM for BB engine use. The drawing shows this fan clutch replaced the 3937771 used in prior years on BB's at the start of production 8/18/70. That makes sense because the old '7771 clutch didn't have the big hub and wider bolt pattern necessary to mate with new water pump(s) that came on stream in 1971. So, the earlier versions of the various fan clutches would not/could not install due to their smaller hub/bolt geometry.

As Joe once pointed out to me, there HAS to be an error in the C60 section of the '71 AIM as it calls out only the 3937771 early BB fan clutch for use on AC equipped SB engines. That CAN'T be right because there's no way that version of the fan clutch would fit/mount onto the new 3991399 water pump that was introduced for '71 SB engines...

So, what's right/correct for a '71 is compounded by which engine + what options the target car has.

Jack-----


The base small block 1971 could not have used the 3888366 fan blade OR either the 3916139, 3916140, or 5329100 fan clutches UNLESS it did not use the 3991399 waterpump. It would had to have used the 68-70 style waterpump and I know of know documented cases of a 1971 using that configuration waterpump.