FAN CLUTCH INFO FOR YOUR BUICK GS
Over the years I have made a personal list of fan clutches that can be used on the 455 powered GS. Info is from various sources plus my own personal experience. You can see that many are identical specs, I have no doubt there are only a couple of manufacturers and everyone just puts their name on the box.
Not going to get into a debate about fixed fans vs clutch fans vs electric fans, everyone has their reason for using what they use, this list is just meant to provide some info for those who wish to use clutch fans.
Clutches listed by part number, standard (S), heavy duty (HD), severe duty (SD), fan height, pilot hole depth, pilot hole diameter, then notes/comments
Pilot hole depth less than .75” inch usually requires cutting shaft on waterpump shorter with die grinder or drilling out clutch. When cutting water pump shaft don’t overheat it or you may damage the seal. Take your time.
Pilot hole diameter was originally 0.63”. Some clutches come with 0.75” holes and supply a bushing to fit the 0.63” as well. This works ok.
Most fan heights are 1.51 or 1.63, on a factory 455 GS of 71/72 vintage with the long water pump (ie, A/C or HD cooling) this puts the fan almost completely inside the shroud which is not ideal but works. Make sure shroud is mounted/centered properly or you could have contact with larger fans (20”). Standard (short) pump and 1.51 fan height puts the fan half in/half out of shroud which is perfect. Only two clutches have short fan height, the Hayden 2765 and Hayden 2947 at 1.09” which would put the fan half in/half out on long water pump 455 cars. Have not tried them yet.
A lot of these are not originally for our GS cars. Applications (when known) are posted to help source parts.
If your thermostatic clutch engages too early (cool), you can modify them by unclipping the coil, straighten it out with pliers, then rebend about 3/16” shorter, trim off the excess witha die grinder., and re-clip the end. The shorter coil will delay the opening to a higher temp (some clutches end up pretty close to rad) so it won’t be constantly roaring, which is great for cooling, but sounds crappy and loads things up. Please note this can ruin the clutch if you take off too much or bend something so be prepared for that if you plan on playing :)
On another note, Hayden and others make some very good 6 bladed fans for these clutches. The Hayden 3619 is a six bladed 19" dia oem style fan as an example. Don’t get all wrapped up with the 7 blade 18” stuff... if you can’t find one, the new fans have wider chords and good design, they flow a tremendous amount of air. No worries about cracks and bent blades either. Don’t forget the 71/72 HD cooling/AC/Stage 1 cars originally used a 5 blade 20” fan. Larger fans turning slower are more efficient than smaller fans turning faster. Hayden and Flex-A-Lite used to make a 20" 6 blade clutch fan, they are no longer available, currently 19" seems to be the largest diameter.
Some of these may not be available anymore. I’ve had great luck with Hayden and Four Seasons.
One final note. the 1.09 fan height fans are a bitch to install. You can't just put them right on on due to the limited space, as you won't be able to get the nut in between the clutch hub and the stud if the fan clutch is even halfway seated. Can't use shorter studs or there won't be enough thread to be in safety with the nuts tight. Also I haven't been able to find slightly longer studs (ie, maybe 1/8" longer is about you could go) which would help. You need to just barely hang the clutch on the shaft (of course you pre-fitted to make sure it seats properly, right?), start each nut 1/2 turn, then once all 4 are started you can slowly run them on while sliding the clutch in as you go. If you tighten one nut all the way you will jam up the others. Aftemarket nuts sometimes have the threads starting quite deep inside the nut edge, you want something that has threads right there or you will really be in for a party!
As of June 2020 RockAuto is a great source for fan clutches.
AC Delco 15-4320 SD (no info)
AC Delco 15-4216 (GM p/n is 12306568) (no info)
AC Delco 15-4949 (no info)
GM12529772 (HD, not sure on sizing, rpm, temp, 85 Olds diesel)
Airtex 2797TA (no info)(same as Hayden 2797?)
Everco A8198 S, 1.51" fan, 1.03 pilot, .63 dia, (works great)
Everco A8189 HD, 1.63 fan, .63 pilot, .63/.75 dia (bushing)
Everco A5570 SD, 1.63" fan, .63 pilot, .63 dia
Four Seasons 36952 S 1.53” fan, 1.03 deep, .63 dia (Rock Auto) (GS spec’d) (identical to Hayden 2705)
Four Seasons 36956 HD 1.62”fan , .63 pilot, .63-.75 dia (bushing) (Rock Auto)
Four Seasons 36704 SD 1.63” fan, .63 pilot, .63 dia (Rock Auto)
Hayden 2705 S, 1.53” fan, 1.03 pilot, .63 dia, (Rock Auto) (GS spec’d) (identical to FS 36952)
Hayden 2765 S 1.09” fan, .56 pilot .63/.75 dia (bushing) (Rock auto)
Hayden 2747 HD 1.62”fan, .63 pilot, .63/.75 dia (Rock Auto)
Hayden 2797 SD 1.63”fan, .63 pilot, .63 dia “noisy” (after coil mod excellent, 190 degrees)(Rock Auto)
Hayden 2947 HD 1.09” fan .56 pilot .63/.75 dia (bushing) (Rock Auto)
Imperial 215045 SD, ?? fan, .63 pilot, .63 dia (same as Napa 271301?) (85 Chev 3/4ton, 350)
Imperial 215046 HD, ??fan, .63 pilot, .63 dia (pics show busing so .75 as well?) (85 Chev 3/4ton, 350)
Murray 271301 (same as NAPA 271301?) (no info)
NAPA 271305 S 1.51” fan, 1.03 pilot, .63 dia
NAPA 271303 HD 1.63” fan, .63 pilot, .63/.75 dia (bushing)
NAPA 271301 SD 1.63” fan, .63 pilot, .63 dia, (85Chev 3/4ton 454, low temp) (same as Hayden 2797?) (excellent)
TRW FC 135 –no info
-Tim
Updated Sept 2020