Viscous Drive Fan???
My '64 GT with R1 has a flex-blade fan without a viscous drive. I
read where R-Series Engines should have a viscous fan drive. Is this
something that is missing from my car and that I should reinstall? I get
a roaring sound at highway speeds that appears to be coming from up
front. Your expert input on this subject is appreciated. ...... Harv
Photo would help. My R1 does have a viscous drive clutch fan.
Can't remember ever seeing an OEM flex blade fan. Too dangerous.
FWIW, cruising down the highway, when the viscous drive engages, you'll
think you'r being straffed by a Stuka. It's even worse in an Avanti,
but in any Stude with no insulation and with a firewall which resembles
Swiss cheese, a big fan is going to be heard.
If it's a show car, yes, make it correct. If it's a driver, consider an
electric fan. The Pick'N Pull yards are full of good candidates. Look
at the big Fords/Lincolns. Get the sensor and the wiring harness
You can solve the roaring a couple of ways: 1. Get rid of the
tractor gears in the rear end to slow the engine down. 2. Install a
viscous or thermal clutch fan. OEM is OK, but is viscous ( early
technology), is costly, and does not move much air. I have an 18.25",
seven blade clutch fan from a mid 1970s-early 1980s Corvette in both
the GT and in the 56J. The GT has a Hayden "Heavy Duty" thermal clutch,
and the 56J has a Hayden "Severe Duty" thermal clutch.
It takes only a little bit of cobbo-jobbing to make a modern, thermal fan work in a Stude.
It still would be a good idea to get rid of the tractor gears, assuming
you'd like better gas mileage, cooler running, and quieter operation
Just a note, a viscous and thermal clutch is not the same.
Thermal kicks in when it gets hot, the viscous limits the rpm the fan
will turn. As noted the R series has thermal, not viscous clutch fans.
You can search in the forum for options. SI only sells a viscous
version. There are ways to adapt thermal clutches but there is no drop
in unfortunately. Dan Miller used to sell a kit to adapt a Jag thermal
clutch but he no longer offers them.
Jack, Joe & Dan, Thanks for the replies. When I got my '64
R1 GT Hawk in SB in May 2005 and drove it back here to the Detroit area I
wasn't happy with the so called tractor gears either. So, I changed
over the std 3.73 gears to new 3.31 gears and am much happier with the
engine rpm & mileage on the highway. I'm just not happy with the fan
noise. The fan on the engine is an 18.88" diameter, 6-bladed fan. If I
understand the viscous theory correctly, it will allow the actual fan to
turn at engine lower speeds and slip at higher speeds to reduce noise
and fan function due to the additional ram air cooling with the car
rolling down the highway. I'll do some more searching but will
definitely change over to a viscous or thermal type real soon. Thanks
again guys. Your shared knowledge is much appreciated. .............
Dan, I am using a 70's 7 bladed fan off of a Olds 442. It has the
original Olds thermal clutch with the bimetalic strip in the middle,
and a "flex-a-lite" spacer. It all bolted together. Ace hardware had the
grade 8 bolts. Heavy duty water pump from SI, and thats it.
Now, I read somewhere, that a thermal clutch will spin the fan at
about 91% of engine speed, cutting in at 185 degrees. A viscous drive
turns the fan at 70% of engine speed, constantly. Now, you guys living
north of the Mason-Dixon line may not need as much air as us down south
and a viscous drive might be ok. I had problems running the a/c in 110
degree heat. Now I will try the thermal clutch, and I have a Studebaker
viscous clutch from SI, slightly used for $25.00 and frt.
Thanks Chuck I have been thinking of machining a spacer since I
could not get another one from Dan Miller, but the flex-a-lite ones look
like they can do the job. I have the same setup as you do with VA AC
setup. What size spacer do you have?
Last edited by Dan White; 04-23-2012 at 10:15 PM.
The spacer is a little over an inch thick. Will measure it
tomorrow. The bolt pattern is universal, it has 4 slots radiating out
from the center. With pullies, etc, the bolts are about 2 1/4" long. Oh,
forgot to say that this setup reduced the noise by a bunch. The seven
bladed fan makes a lot less noise than the six bladed fan. And after
seeing that pic that I posted, I need to pull the fan and repaint it.
As to an electric fan, the only one that would fit on the front of the
A/C condenser is a 10" pusher. It has to clear the hood opening arm(62
GT), and the hood latch.
To: Chucks Stude,---- Does the Olds thermal clutch and the
flex-a-lite spacer have a 1" centering hole to fit the Stude water pump
hub? ( As the comparable Stude parts would) Thanks
The bad news to all this is that none of the works on a 64 Lark.
I built the Jag thermo clutch fan as mentioned, fit perfectly except it
was about 1.3 in into the radiator and that is without the spacer (the
Lark did not need it with the Jag clutch. Still looking.....
Chuck what is the diameter of the GM fan? It appears they came in 18, 18.5, 19, and 19.5 diameters.
Will measure the fan today. Yes, there is a centering hole in
both the clutch, and the back of the spacer. The front of the spacer
does not have a centering bung. I guess that I was just lucky that they
all fit together. It would seem that the fan is either 18, or 18.5, as
it takes about the same room as the 6 bladed fan, and it was 18". If you
notice from the photo, the blades are bent at the ends. There is not a
lot of extra room in that shroud.
Sorry Mark, it won't work on a Lark. And to think, all of the spacing
that I have had to do to get the fan into the shroud. The car arrived
with a 4 bladed fan, no fan clutch, and a very small spacer, and ran hot
all the time. That thing was loud, the 6 bladed fan even louder.
Chuck, mine looks very similar to yours. I ground the nipple down
on the Stude spacer till flush with the surface of the pulley hole,
then found a socket to drive into the hole in the spacer, that extended
into the backside of the fan clutch (as a pilot/centering provision).
The seven blade is definitely quiet.
I once installed a 19.5" GM, seven blade into a 56J, but I doubt more
than a 19" could fit into a GT, due to the smaller diameter of the
longer, shroud tunnel. The seven blades run quieter than four, five or
six blades for some reason.
As for thermal v. viscous, its been awhile since I read up on them, but I
recall viscous as you described above, and the oldest technology. The
bi-metal being an earlier version of thermal, but more of an on/off
switch for the clutch. The latest thermal is the spiral spring type,
that coils/uncoils as the air from the radiator heats it up/cools it
down. As the spring moves, it changes the alignment of silicone
passages/orfices inside to gradually increase/decrease the clutch
engagement. In short, its more responsive to the engine cooling needs.
The spring type is readily available, and in Normal, Heavy, and Severe
duty versions. I am guessing the different versions have to do with how
tightly the fan engages with heat.
Mark, on the Lark you may be able to use a shallower dish pulley (brand
X), drill the hole to .75", and press the water pump coupler further
back toward the pump body. For more clearance, try a fan clutch with a
shorter drive shaft (they come in various lengths). Also, it may be
possible to gain some more clearance by moving the radiator away further
somehow. Sure seems like 1.3" is too close to give up on, and maybe
combining several tricks like that may get the needed clearance.
The fan is 18.5" in diameter, and the spacer is 1.25"deep. Hope this helps. Spacer came from a junk yard.
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