Originally Posted by BerniesVette

My '79 was a numbers matching car until I pulled the TH350 and installed the 5 speed and it has 3:55 rear gears. In fact, many 79s have had tranny swaps because of the high RPMs they were turning at cruising speeds. Since yours runs at 2400 RPM and doesn't have the higher temps should tell you that lowering RPMs by as much as 1000 RPMs has a tremendous effect on helping to keep the temps lower in our C3s. Trial and error by many of us have proved that we can keep these cars running at more reasonable temps than many are experiencing.
Bernie

Originally Posted by jdunne

ESU,i posted a lot earlier,i don't remember anyone suggesting to you a simple thing to check;make sure that your hoses aren't collapsing under pressure at speed and restricting the coolant flow back to the radiator,you will recall that they have the spring thingy inside them to stop that happening.that might explain why the prob is occuring at speed and not slower....can also happen as the hoses get older....i see in the pics that yours are sheathed in braided metal.....if you have already checked this please accept my apologies....john in sunny australia:cheers: :cool:

Originally Posted by BerniesVette

I have 3:55 rear diff gears in my '79. The primary reason for the high RPM. If we were running 3:08s the RPM would be significantly lower. The stock clutch fan kicks out around 2800 RPM; too soon with a big rear diff gear. Newer cars run lower diff gears and overdrive trannies helps keep the engine running at a more managable rpm at lower speeds when the air flow thru the rad is less and the fan needs to be working. I have gone thru this and after pulling thec rad several times, playing with electric and stock fans, t-stats and transmissions I finally found what my car likes. It runs less than 180 under any circumstance unless I'm sitting in traffic, it still doesn't go over 190. At 90 MPH it actually runs too cool and I still have the copper/brass radiator installed. Imagine how efficient it will be be when I switch to an aluminum rad and Mark VIII electric fan over the winter. There can't be that much difference from one '79 to the next.
Cory, I will wind up in Nags Head then travel back to the Raliegh area, then to the Blueridge Parkway. Wish I could get to NY to visit; I carried a badge for 5 years after Viet Nam and I would love to hear your story.
Bernie

Originally Posted by ESU

I dont know, I would imagine it's the rear end gears, probably 3.73, maybe u have 3.08. Just a guess not sure really. Maybe someone else can shed light on it.
ESU

Originally Posted by ESU

Couldnt remember whether it should or shouldnt spin freely.Yeah a lot of input but where DO I go from here??? I'll drop a few bux on the supposedly hi flow t-stat or maybe even rig my fan for direct drive. They're both cheap enuf and easy to do but I'm not holding my breath that they'll work. I am intrigued by the fan thing though, if the clutch I have disengages at @ 2800 rpm's and my problems surface shortly after that who knows, maybe there is a correlation. Guess for now it's just drive it at 65 or less. As always I'm up for suggestions.
ESU

Originally Posted by Capt. Ron

ESU. your RPM's are consistant with mine, seems like if you double the RPM's you get pretty close to your MPH. I am thinking of stopping by the bone yard and finding a used fan clutch to modify as locked in all the time. I was just a little worried about how many RPM's would be too much for the fan.

Originally Posted by dwncchs

Cory on the direct drive fan-you are relying on that for a test not permanent-correct?That 7 blade at 5000 RPM is not intended -hence the factory slipping it at 3500-I think if direct helps then the electric would be the way to go.I like one wired automatic and the other wired manual- for driver control- or at least one wired so you can turn it on when you want.PS how was the movie?

Originally Posted by rihwoods

Here is a chart...check your tire diameter.....quick check assuming your speedo is correct...

http://www.corvetteactioncenter.com/...gearcombo.html

Originally Posted by ESU

Have no idea what diameter my tires are, 255/60/15 or what rpms at 60 , usually only worried about 65 or 70. I'll check the rear for those numbers,
ESU

Originally Posted by rihwoods

Your tires are 27" diameter.. (I tach about 3300+ RPM at 70...almost 3000 at 60..

Originally Posted by rihwoods

Two choices...remove spring completely which "locks" clutch...or...
rotate spring to next slot....which would change calibration of valve..

When spring heats up,it expands turning clutch valve...so by rotating spring..it gets "smaller" and does not expand as much when it heats up....this was explained to me by a local GM tech who has removed springs in clutch fans to "Lock" them..I'm going to see a radiator shop owner this morning who I'm told knows a bunch about clutch fans and see what he knows..

All I want out of this is a clutch fan that will disengage at 3500 RPM like my old GM version...
Rich

Originally Posted by ESU

5000 rpms on direct connect I guess would be a problem. If done it would be just a test and see what happens from there. I only considered it because it would be a cheap and easy fix that could be reversed also.
Movie was good, a few of my friends were in it, two were featured prominently in the movie, if you see it you'll understand my screen name. My unit (ESU) lost 14 of the 23 NYPD officers killed on 9-11. Kind of brought old wounds back to the surface a little but it was a good thing. Kept my mind off the car.
Cory

Originally Posted by ESU

That translates to @3.73 for me.

Originally Posted by dwncchs

Check this site out the non-thermal type might work.http://www.haydenauto.com/fce2.htmedit-Maybe not that free wheeling sounds bad unless it will wait until after 3000--be nice if it was adjustable to RPM---edit- http://www.haydenauto.com/severeduty.htm -here is their severe duty clutch this is just like the GM#343721 which was their biggest for the Corvette that they offered it changed to #88961768 but I have not seen it after it changed numbers-Delco mkaes a #15-4259 which is non-thermal type _I actually have this one on the shelf but it looks just like the Hayden one.edit-OK I also have a #343721 on the shelf and like Rich said it does have 2 position retainer for the spring-it looks like you can put in 2 positions and you can rotate it around as many time as you want-it appears so-maybe once you go around your just repeating the same valve position.

Originally Posted by dwncchs

Cory you might want to try what Rich has been talking about "if" your spring is the wind up type it will be easy to do and the fan would be less likely to over rev.When the term lockup is used I dont think it actually locks-these fans are filled with silicone and are fluid drive and the spring only controls a valve which allows the fluid to drive more or less--------going back to the "if" some of these fans have flat bimetalic springs which you cant change