Just wondering: how much damage can a stuck fan clutch do ?

[LaGuardia]

As you may already know, my Eagle is sitting *again*, with a shot water pump. Parts should arrive early next week and (as per the previous post) repairing should be quite easy. Or so I hope.

But now let me share my recent thoughts about this thing. Searching for the cause of the pump seizure, I found that my fan clutch was stuck. In fact, it's as if it isn't there at all. The fan is actually one piece with the pulley.

It spins at the engine's RPM (applying all the pulleys and belts ratios, of course).

So this probably caused the pump to work under a severe overload, especially during long highway trips.

The problem is that it's been like this since I bought the car (at least). Three years and more of fan speed craze.

Then I had another problem, that only today I thought could be related: I noticed that the RPM is always a bit too high, compared to the car's speed. Say, at 65mph, RPM reaches the 3.000 notch (or a bit lower, assuming the tach isn't properly a precision tool).

I also posted about this thing some time ago: at first we thought about something dragging (brakes ?), then I supposed I had some strange transmission option or modification (trailer towing gears ?).

But now I wonder (and that's the point of this post): could it all be just fan related ?

Another clue is that things got worse (from this point of view) when I replaced the belts: so maybe before replacing, when the fan and pump couldn't catch up with the engine speed the old and dry belts just "slipped", giving some relief to the system ?

I know, I'll have the full answer (and hopefully a like-new, well-behaving Eagle) only when I'll be done replacing the fan clutch and pump, but, just for curiosity, what d'ya all think about this ?

[LaGuardia]

No no, I think I've messed up things a bit.

Reading my own writing I understood that there's something wrong in my assumptions.

The clutch operates on the fan speed ONLY, so the pump wouldn't be affected by its failure.

Some extra drag could result from this, though.

Or am I wrong again ?

I am doing something I don't usually do: I'm writing at the same time I think. No good thing. It's like talking with myself...

[68AMXGOPAC]

I agree, the fan clutch is not related to your Tach rpm reading.I also think ( unless it is a bad bearing in the fan clutch ) wich may cause an imbalance and wear on the pump bearings , that the fan issue and water pump may not be related. I also have to assume you checked the fan to pulley bolts ?? ( I should know better to ask ) .

Most older cars ,like my 68AMx didn't have a clutch fan, and ran fine, and it didn't effect the water pump. Is a clutch type fan simply for less drag and improved mpg. ?

[LaGuardia]

Well, maybe the pump just failed because it had to... as far as I know it was never replaced, and a 30 years old thing is supposed to fail at some point...

Another chance is maybe I overtightened the belt when I replaced it and the two things together did the job.

Who knows ? I'll replace everything, then the truth will be unveiled !

[BenM]

As to the RPMs, have you checked your gear ratio?

The most obvious way is the metal tag on the front differential bolts, but there is a stamp on the passenger side of the rear axle next to the center cover, where it has been machined flat.

The 2.35 didn't appear until 1982 in America, which is the gear most of us have with automatics. the 2.73 was common on standards, with higher ratios for the "High Altitude" and "Towing" packages.

You could have a 3.08, 3.31, or 3.54. I'm betting a 3.54.

(I guess you'll have to convert dots & commas)

[LaGuardia]

Ben, good clue, thank you !

I'm going to check this out tonight. I guess it's good to know exactly which gears I have...

BTW, just in case I had a 3.54, what would I need to convert to, say, a 2.73 ?

[carguy87]

If by chance you have the 3.54's, you would have to change to a different axle in the rear and diff. in the front. The AMC 15's only held up to the 3.08's and the one holding the 3.54's is a bit larger.

[BenM]

Not the whole axle, just the carrier in the back axle. Check over in the axle section, but the hangup for most people is the special 2.35 front parts, which you don't have. For all other combinations, parts should be available to make the change you want.