How do fan clutches fail?

[John F.]

Re: How do fan clutches fail?

You mean "Lefty"?
John

[Joe C.]

Re: How do fan clutches fail?

The performance profile of the clutch is guaranteed by design and the control of its constituent parts, Gerry. It's a rather complex curvalinear plane in 3-space.

One axis is RPM, the second is temperature and the third is %-slip. First, you need the design spec from either Eaton or Schwitzer. Then, you mount the fan clutch to it's specified load for proper drag (the fan PN that's called out in the fan clutch drawing/spec).

Now, you spin the input shaft using a stroboscope to verify RPM and move the stroboscope to the body of the fan clutch to get a second RPM reading. The difference in RPM is then translated into %-slip.

Do this across the RPM axis. Then, repeat the test varying temperature and making SURE you've allowed thermal equilibrium to take hold before each delta-T reading and %-slip calculation.

Finally, compare the two sets of numbers to the fan clutch drawing specification. The test is a time and instrumentation consuming B(*&^ to do! The only guy I know who fabricated a controlled environment to properly characterize fan clutch operation is Fred Oliva.

On the 'hand' method of determining good/bad, you may be able to spot a complete 'basket case' failure. But, there's no way you'll be able to verify full pass/fail conformance to spec by hand!

WAY back when, Fred Oliva put on a tech session and provided about eight fan clutches. He invited members from the audience who thought they could tell good from bad by hand to come forward and sort the eight fan clutches.

Bottom line NOBODY got it right!!! Turned out all of the samples were out of spec in one form or another...

Very well said Jack. Accurate instrumentation and test stands are required to perform any valid quantitative analysis. Fred has managed to "update" the slip/RPM/temp profile of his restorations by using mineral oil with slightly different viscosity index, probably lower, such that the fluid shear is higher at lower temperatures. He can also, at the customers' request, try to emulate the original design profile by adjusting the mineral oil VI.

[Chris E.]

Re: How do fan clutches fail?

Thanks guys, much appreciated.

[Tony S.]

Re: How do fan clutches fail?

Chris. It is pretty easy to replace the oil in an original fan clutch if you want to continue using your original. The oil can slowly leak out over time. Part of the problem with these original parts comes from a lack of use. Why don't you add oil to your fan clutch and just use it? I'll bet you'll find that adding oil and using your fan clutch will "bring it back to life". Good luck.
Tony

[Jack H.]

Re: How do fan clutches fail?

It was a LONG and interesting conversation with Fred (back when his father was still alive) on how they went about 'reverse engineering' a proceedure to 'correctly' restore these parts. At one point they hired a consultant who'd worked most of his life for Ingersol Rand's Torrington Bearing Division.

The consultant was around when these parts were originally being designed and tooled up. Fred's dad was a retired ME from IBM who was VERY savvy and he hit it off magnificently with his ex-Torrington counterpart.

What came out of that collaboration was the very special nature of BOTH the main bearing as well as the hydraulic fluid used by both Eaton and Schwitzer in the fan clutch to make the system work as it was designed to (control %-slip vs. both RPM and temperature) and to avoid premature failure...

Obtaining the 'right' hydraulic fluid as well as the bearing was NOT an easy task as both were considered 'proprietary' products by their manufacturers. If I remember correctly, Fred had to purchase in LARGE quantity to get the 'right' stuff.

[Jack H.]

Re: How do fan clutches fail?

See my comment above about the nature of both the bearing and fluid used in the fan clutch. I've always wondered how/where those who suggest 'topping off' existing fluid in a fan clutch are getting their stuff from...

[Tony S.]

Re: How do fan clutches fail?

See my comment above about the nature of both the bearing and fluid used in the fan clutch. I've always wondered how/where those who suggest 'topping off' existing fluid in a fan clutch are getting their stuff from...

From personal experience, Jack. It's easy to add fluid. I found an original fan clutch that had been sitting around and had lost some of its fluid. I found the correct fluid at a toy supply company. I removed one of the four threaded studs which opened up the cavity, added the fluid, put a little silicon on the stud and replaced the stud so that it would seal. The whole operation took about 15 minutes, and it has worked just fine ever since.

No big deal.

[John D.]

Re: How do fan clutches fail?

Here's what the performance curve looks like for the 3916139 fan clutch...

[Michael A.]

Re: How do fan clutches fail?

Giuseppe, Gerardo? I know I've been off the TDB for a long time but did I sign on to a Ferrari board by mistake?

[Joe C.]

Re: How do fan clutches fail?

Giuseppe, Gerardo? I know I've been off the TDB for a long time but did I sign on to a Ferrari board by mistake?

http://www.youtube.com/watch?v=FJj8atDGBzk

[Michael A.]

Re: How do fan clutches fail?

Yowza! I wonder how our mid-years would do on this course!

[Gerard F.]

Re: How do fan clutches fail?

Giuseppe, Gerardo? I know I've been off the TDB for a long time but did I sign on to a Ferrari board by mistake?

Mike,

Just kidding around with Joe. Maybe we will both see you in Concord this summer. Test out that course in Joe's 85 Corvette (not Ferrari).

Capice?

[Chris E.]

Re: How do fan clutches fail?

Chris. It is pretty easy to replace the oil in an original fan clutch if you want to continue using your original. The oil can slowly leak out over time. Part of the problem with these original parts comes from a lack of use. Why don't you add oil to your fan clutch and just use it? I'll bet you'll find that adding oil and using your fan clutch will "bring it back to life". Good luck.
Tony

Thanks Tony. At this point I think I'm going to leave it the way it is. I tried to fix a few small details on the car over the weekend, and in trying to fix one thing, I made something else a little worse. (e.g. scratching, discoloration, etc) I only lost 2 points when you saw the car with the fan clutch that it on it now. I don't want to risk damaging something else in an effor to regain 1 point. (I'm only figuring on picking up 1 point because the condition of my original is a little tough)

[Tommy F.]

Re: How do fan clutches fail?

I'm sorting out the last few details on my '75 coupe, and it occurred to me that there seems to be an inordinate amout of fan noise throughout the RPM range, and a very slight vibration that occurs as I run the RPM up. I thought that I remembered that unless the engine compartment was warm, the fan noise would drop out as RPM increased, and cycle back in as the radiator heated up

The clutch did leak a small amout of oil ( stored sideways ) during the rebuild, but if anything, it appears that the fan is staying coupled all of the time.

The fan does spin freely with the motor off...

Let me know what you think,

Happy Memorial Day, and God bless those who paid the ultimate price for our freedom.

[Duke W.]

Re: How do fan clutches fail?

Here's what the performance curve looks like for the 3916139 fan clutch...

...very interesting piece of data. What years/engines does this fan clutch apply to, and who took the data a plotted the curves?

Duke