Fan Clutch Testing
Burning Brakes
Joined: Oct 2006
Posts: 1,044
Likes: 0
From: Henrico VA
I've been told to mount the clutch on something and attach the fan normally to the clutch. Spin it by hand and if it goes more than two rotations, now is a good time to replace it. These things last a LONG time.
Melting Slicks
Joined: Sep 2004
Posts: 3,226
Likes: 669
From: Northeast
I always thought the 2 spins was correct but just looked in my 78 Chassis Service Manual and it states
"If the fan and clutch assembly free-wheels with no drag (revolves over 5 times when spun by hand) the clutch should be replaced.
It does make a note: testing a fan clutch by holding the small hub with one hand and rotating the aluminum housing clockwise/couterclockwise should not be considered a test by which replacement is determined.
"If the fan and clutch assembly free-wheels with no drag (revolves over 5 times when spun by hand) the clutch should be replaced.
It does make a note: testing a fan clutch by holding the small hub with one hand and rotating the aluminum housing clockwise/couterclockwise should not be considered a test by which replacement is determined.
Drifting
Joined: Sep 2006
Posts: 1,259
Likes: 2
From: MS
Gotta heat it up to full operating temperature to test it so probably best done on the car after driving.
When you shut the engine off when hot the fan should stop almost immediately and you should
feel a definite resistance when turning by hand, if not it is bad and should be replaced.
If the clutch is original, it is almost surely gone.
When you shut the engine off when hot the fan should stop almost immediately and you should
feel a definite resistance when turning by hand, if not it is bad and should be replaced.
If the clutch is original, it is almost surely gone.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Yes. That test is to be performed when the fan temp is beyond the point where the clutch engages. So, the engine is operated to reach normal temps (city driving would do it), then stop the car, pop the hood, turn off the ignition and count the fan revs after the engine has shut down. It should only be 1-2 revs (if the clutch is engaged).
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi NMT1957,
If you decide you need a rebuild, there are instructions around (NCRS RESTORER article) on how to do it yourself. The clutch usually needs more 'fluid', and people use the silicone lubricant that R/C cars use. (Hobby Store)
Enjoying your self?
Regards,
Alan
If you decide you need a rebuild, there are instructions around (NCRS RESTORER article) on how to do it yourself. The clutch usually needs more 'fluid', and people use the silicone lubricant that R/C cars use. (Hobby Store)
Enjoying your self?
Regards,
Alan
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 993
Likes: 44
From: Jefferson Hills PA
Alan, Thanks for the info. I didnt even know they had fluid in them...imagine that. My fan clutch seems pretty tight, but I didnt want to wait for the engine start to test it. Im going to look at the NCRS site and get some details. And yes Alan im enjoying every minute of this restoration. It seems to get more interesting as it goes. I will probably spend another 3 hours tonight cleaning and sorting bolts in my quest for all originals. I would like to have all bolts prepped and ready before starting the chassis assembly.
Ned
Ned
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
Actually, there are 2 types. Some are therostatically controlled--silicone grease acts as a clutch and tightens up as it gets warm, and some are just speed controlled. More or less slip at high rpm, as probably not needed when the car is moving and won' rob hp at higher rpm's.
So, the testing techniques are different. As said above the thermostatically controlled need to get hot to test.
You can ususally tell the difference in that the heat controlled type usually have a thermostat bimetal coiled spring located on the housing around the shaft.
So, the testing techniques are different. As said above the thermostatically controlled need to get hot to test.
You can ususally tell the difference in that the heat controlled type usually have a thermostat bimetal coiled spring located on the housing around the shaft.
Last edited by Sayfoo; Feb 12, 2009 at 08:47 PM.
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thanks, Dan
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
Karol is correct. All GM service manuals from the late 60s and 70s list the same test proceedure. The next test is performed with the engine at operating temp. With the engine idling, shut it off and observe the fan. If it makes more than 2 revolutions it must be replaced.
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 993
Likes: 44
From: Jefferson Hills PA
Actually, there are 2 types. Some are therostatically controlled--silicone grease acts as a clutch and tightens up as it gets warm, and some are just speed controlled. More or less slip at high rpm, as probably not needed when the car is moving and won' rob hp at higher rpm's.
So, the testing techniques are different. As said above the thermostatically controlled need to get hot to test.
You can ususally tell the difference in that the heat controlled type usually have a thermostat bimetal coiled spring located on the housing around the shaft.
So, the testing techniques are different. As said above the thermostatically controlled need to get hot to test.
You can ususally tell the difference in that the heat controlled type usually have a thermostat bimetal coiled spring located on the housing around the shaft.
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi Ned,
The tech article I was referring to is in the Spring 2007 RESTORER.
It is however for the Switzer clutch, the one with the bi-metallic bar, not the bi-metallic coil, which is an Eaton clutch.
Good Luck!
Regards,
Alan
The tech article I was referring to is in the Spring 2007 RESTORER.
It is however for the Switzer clutch, the one with the bi-metallic bar, not the bi-metallic coil, which is an Eaton clutch.
Good Luck!
Regards,
Alan
Thread Starter
Burning Brakes
Joined: Feb 2008
Posts: 993
Likes: 44
From: Jefferson Hills PA
Alan, Im going to look into the Eaton clutch and see if there is a rebuild I can do myself. Id rather rebuild it now than have to change it later after the engine is done and body on, not that that is going to happen any time soon but just trying to stay ahead of it.
Thanks, Ned
Thanks, Ned
