[huudie]

Try adjusting the fit of the shroud when everything is cold,checking all sides.I have seen this problem before.The plastic changes shape a little when it gets cold.

[quicksilver97ta]

Is it an aftermarket shroud? A freinds 70 GTO did the same thing, he said it was the aftermarket shroud, I guess cheaper plastic, changing shape from the original mold over time and changing back once warmed up as you described. Could be the change in season affecting that plastic.

[pont3]

Have you replaced the shroud or radiator lately? A similar but incorrect shroud could cause this. I had this problem when I switched to an aftermarket four core radiator. It did not fit perfectly and distorted the shroud. Make sure the lower radiator support rubber insulators are in good shape as well as your motor mounts.

[70 Dream]

OK, thanks for everyone's ideas . . . . I really appreciate it.

Haven't had time to get out in the garage and look at it again or drive it (too busy with Christmas, now).

When I get the problem fixed, I'll report my findings here . . . .

[gotpls]

Chances are your torque converter bots have come loose. Pull the inspection plate, and you can get to all of them by just turning the motor over with a socket on the harmonic dampner bolt, and a braker bar. Good luck

[Droptop64]

I had a similar problem with a truck of mine. I was positive the noise was coming from the fan, and if I took off the belts and ran the engine, the noise went away. I couldn't see where the fan had been hitting - either on the shroud or the fan blades.
I found out the truth by painting the edges of all the blades with a nice red nail polish. (This will make your wife happy) When the blades hit, they flaked the nail polish off and you could see where the blades scuffed the shroud. Some minor trimming and repositioning took care of my problem. Acetone (or your wife's nail polish remover if you want her to be really happy) will take the remaining red off of the blade edges.

[428GTO70]

I have the exact same preoblem in my 70 GTO. I replaced the factory shroud with the repo gm shroud offered from various vendors. My factory 7 blade clutch fan hits the bottom only when in reverse or backing up at an angle. Sounds Terrible! This is with new fan clutch, new motor mounts and trans mount. My fan had been scraping on the lower passenger side of the shroud. I went to the junkyard and found another 7 blade fan off a 80's or 90's cadillac and put it in there, was a little smaller in diameter and now it never rubs. I have found that my framerails are slighly bent up under the car where the crossmember sits from people jacking in the wrong locations, I think this has caused my crossmember to sit higher than it should just slightly and thus has tilted the engine forward a bit. I havent gotten a chance to try and bend them back yet but It should help the problem.

[J_JAMNIK]

Same problem in 68 Bonneville. Hitting the bottom of the shroud with new motor and trans mounts. I also noticed that the pulley on the harmonic balancer is so close to the frame cross member that it is hard to put the belts on. I remedied the problem by making 1/4" shims and putting them between the mounts and the frame. I guess over time the frame either spreads apart or the flanges bend, lowering the engine slightly.

[unclescratch]

428gto70: Good Luck with that frame being crunched up. I've seem that to from cars that haven't had such a good life. (Junkyard clowns) Perhaps you'll post if you tackle it successfully.

[tenthta]

I had a similar noise, the water pump pulley cracked at all 4 holes and the center was broken away from the pulley itself. Noise only showed up at startup.

[70 Dream]

Thanks for all of the comments . . . . I still haven't gotten it up in the air to find out what the problem is.

If it is the body mounts, do I go ahead and replace them all while it's up in the air?

Do I want rubber or polyurethane or polygraphite?

[70 Dream]

Well, I finally got under there to take a look (finally), and it looks like 428GTO70 had the right answer.

It looked to me like the radiator support frame (that goes accross from left to right) was kind of bent upward from maybe driving over too many curbs or speed bumps (I didn't do it) and pushed the radiator and shroud up with it.

Got it up in the air, and tried bending the rail back down, but it didn't work (no way can you bend it with your hands).

I grabbed the bottom of the shroud and pulled down on it to kind of reshape it as best I could - maybe gained 1/16" clearance, if that. Anyway, I think it was enough, as the fan is no longer scraping, so I hope that works.

I am hoping the shroud does not revert back to its original shape.

BTW, the motor mounts looked like they were OK.

Thanks for everyone's ideas - that's what makes the FORUM so great . . . . !

[Droptop64]

I have had fan clutches go bad in exactly this manner. They appear fine when you give them a spin by hand, but when spun by the engine ( especially during cold operation) will tend to wobble up to 1/2" front to rear. If you have close tolerances on the fan shroud to begin with, this will most likely cause the clanging. When I've had them go bad, they have stopped the major wobbling when warmed up. Give it a visual, and check the front to rear spread of the blades (wobble)when the engine is running versus hand spinning. If in doubt as to what it really is, take the fan off and start the engine when cold.

[Bill H]

My flex fan was just scraping the bottom of the shroud, this was the result after it really hit hard.

[Robby D]

First of all, removing the fan shroud is far easier than removing the fan itself, then you can then see any scratches that will confirm beyond a doubt whether or not the noise is coming from the fan!

The crossmember goes on top of the frame.

Remove the shroud and check it for marks instead of going thru all the guesswork you have done so far. Correction of any mecanical problem is a process of elimination. If the shroud is not scratched up, that eliminates all issues of engine/trans alingment; then you can move on to the other possibilities mentioned here.

[Robby D]

So far, you have not mentioned removing the shroud to actually check if the fan is hitting it! Do that FIRST to determine whether you have an engine alignment issue or not. Correction is a process of elimination. If you have a scarred up shroud, then OK, examine mounts and bushings. Otherwise move on to other areas of the drive train.

The crossmember mounts on top of the frame.

[Robby D]

Duh, sorry about the double posts... I was a bit behind the post history, didn't realize there was a page two!!