[gto4evr]

Hey guys, I'm setting a friends 68 goat with AC right. currently he's got an 11 bolt cover/pump on there with the 128 pulley from the 70 setup on the water pump. when I put the 68 timing cover on there it's going to shorten up the water pump neck when it goes to the shorter 8 bolt pump. Everything is stock on the car with factory rad and shroud and that fan with the clutch is just about out of the hole now with the current setup. Once I put that 68 pump on there it's going to come out of the shroud all the way. I've got a 75 parts book saying that they used the same fan clutch from 64 out. doesn't seem right to me, I'd expect that fan clutch for a 68 to have a longer neck to push the fan in deeper. no way they used a spacer between the clutch and the wp.

I could swear I came across info somewhere out there on the web that there were different fan clutches for various years but of course I can't find anything on it now. Not sure if GM just consolidated it all into one number for ease of inventory or what. by 75. anyone have any insight on this?

anyone with a correct 68 (still running 8 bolt cover) with a fan clutch and stock shroud that can show a pic or take a measurement of where the fan's sitting for me?

Thanks,
Dennis

[dataway]

I can measure the fan clutch neck if you want. Not in the car so I can't show you how it fits in the shroud. The 68 clutch I have does have a bit of a neck on it, without running down to the shop I'd say about 1 inch of shaft showing before it gets to the mounting flange. Yes, no spacer that I have ever seen on an AC car.

[68ragtop]

in 68 is the clutch to water pump held by bolts, or studs? I see many pictures with studs, but the assembly manual shows bolts.

Any ideas? Thanks, 68RT

[dataway]

Bolts on mine. I've never personally encountered a pump flange with studs.

[68ragtop]

What style bolt heads? are they std, or do they usually have the star pattern like the water pump, PS pump, etc. Not that you can really see the front of them, but I have both styles on hand.

[dataway]

Mine have the recessed star pattern. Considering the application they are probably pretty high quality bolts.

[68ragtop]

I recently got a nice clean Eaton clutch from a friend, I was cleaning it up & realizing it seems to be engaged full time. (as if it was hot) The one I have now is new, but a typical universal where you can see the bolts through the universal bolt pattern slots. That bugs me, would like to find one that fits the Pontiac bolt pattern.

[dataway]

I ordered an Hayden clutch off Rock Auto ... has the universal mount also ... it's the one most people use ( 2747 ?). Every clutch they sell has the slotted mount.

The shafts are one piece ... so I don't think there is a way to graft on mount from an OEM clutch. Might be some NOS examples out there. Seems like the proper four hole mounts disappeared about 30 years ago.

[kk68]

Originally Posted by gto4evr

anyone with a correct 68 (still running 8 bolt cover) with a fan clutch and stock shroud that can show a pic or take a measurement of where the fan's sitting for me?

Thanks,
Dennis

Meant to respond to this awhile back. Took the attached pic from mine and measured the visible fan clutch shaft between pulley and fan at 1.5 inches.

[68ragtop]

Thinking more about the clutch fan & how it works......

If the clutch is not loose, meaning has no lateral or axial movement but is tight where it feels engaged, is it possible it was either removed after it was hot & not run again, or stored the wrong way where the viscous fluid got into the internal veins & no way to return? I know these are always supposed to be stored clutch side down, but I have never really understood how improper storage can ruin a good clutch. Unless it can leak out & down the shaft?

Can anyone elaborate?

About the only thing I "think" I understand is a valve opens as the thermal spring rotates allowing the fluid to enter the veins to lock it up, & then returns when the spring contracts & closes the valve.

[dataway]

I suppose one could have a faulty or damaged thermostat spring?

How hard is it to turn? They certainly don't free wheel when they are disengaged, specially a new one. They will turn by hand, but it's not like you can spin one up.

I've never had the balls to do the "rolled up newspaper" test. Mine pushes a lot of air even when dead cold ... but not the hurricane you get when one is hot and locked up.

[68ragtop]

Just seems very locked up compared to all the others I have worked around. But, I am pretty sure it was stored incorrectly before I got it. So, maybe the fluid just needs to find its way back to the front storage area. That would be cool as it looks similar to an original. Not exact by any means, but closer than the one I have now.

[dataway]

Should be able to pretty easily push it around with one finger. If you are having to grab hold of a blade to turn it ... then maybe some is amiss, but would probably been fine once it has had a heat cycle. There has been a ton of discussion on how these things feel engaged and disengaged.
Maybe I could make a video of some sort showing how hard/easy mine is to turn.

[68ragtop]

You don't have to do bother doing that, but I do appreciate the offer.
I am pretty familiar with them. I have a few 70s' Birds with pretty much the same type of clutch fan, I could always compare those as well to refresh my memory. Probably worth trying a heat cycle on a car so the centrifugal forces push on the fluid like it should. I would think if the clutch was in fact bad, it would likely free wheel without ever locking up as it gets hot. I am just wishful thinking right now

[dataway]

I think they usually fail to the free wheeling state ... but that typically caused by wear, lose of fluid etc.

[68ragtop]

So I had an idea last night & I chucked it up in my metal lathe. what happens is if I hold it back its initially locked up pretty good, but not solid. Same way its felt in my hands since I got it. But, once its turned a few times it gets looser & feels like any other clutch thats not locked. I can then hold it back (while wearing welding gloves) & it slips easily for as long as I want to hold it. I then took a heat gun & warmed the front to 225 ish, I could see the spring turn the fluid valve, but no change. IT never locked up. Leave it sit for 15 seconds & its stiff again until its broke loose. While I am not sure whats happening inside, it does not appear to be functioning correctly at all. My lathe only has a 10" swing, so it would have been better to have a fan bolted to it & let the blade resistance be the real test, but that would take a different setup. Was fun testing it. I am easily amused when I experiment with parts like this that I have taken for granted for decades, but never completely understood how they work. I used to have a Silverado truck that the fan would lock up & sound like a street sweeper for about 30 seconds "almost" every time I drove it. It would then release & go quiet. Did that from the day it was new. Was kinda weird, never had a car or truck do that, but it might have had an exceptionally loud fan too.

I would like to say this clutch has lost its fluid, but there is for sure some thats locks it up initially. Probably low. Once I know its toast I might open it up for curiosities sake

[dataway]

Yeah those things have always been kind of voodoo the way they work. I wonder if it needs the load of the fan on it, and to be turning, while the thermostat spring is heated.

Here is the difference I've seen when one is operating normally. Engine is cold ... open the hood, rev the engine it blows a lot of air, doesn't make a lot of noise. Open the hood and rev the engine when it's hot ... sounds like an airplane and moves a ton of air, and usually you can just see the blades flex a bit and thin out their pitch.

[gto4evr]

Originally Posted by kk68

Meant to respond to this awhile back. Took the attached pic from mine and measured the visible fan clutch shaft between pulley and fan at 1.5 inches.

(thanks for the heads up Carl, been awhile since I've been on the forum )

KK, thanks for the measurement, I'll check it out when I'm over at his house next week to see where we ended up on this.

as to bolts vs studs....I've never come across an original that had bolts holding the clutch to the WP, always been studs in my experience. Fine thread going into the pump (5/16-24) and course thread for the nuts holding the clutch to the studs (5/16-18)

most of the repop kits out there have the wrong lengths on the threaded sections as well so you have to watch for that.

[north]

Good point about how the mid year 69 pump lengthening would have advanced the clutch and fan a extra half inch into the shroud. I always assumed they just let that happen but maybe there was a part number change in the clutch to go with the new water pump. I'll have a look in my november 69 MPC and let you guys know.

[68ragtop]

My fan is just barely into the shroud. Maybe 1/2" The clutch I have been talking about above would put it another 1/8" in I really want to install the other clutch for ascetics not functionality though. I will likely try it once my car is running again. Engine hasn't been fired up in 6 or 7 years. Properly shut down last time knowing it would be a while, so no concerns there however.