My LT1 in my 69 seems to building pressure somewhere. When driving sometimes i will here a squeek. when hearing this squeek if i shut the engine off i will here a whistle where pressure is releasing for 5-10 seconds. Can this be crankcase pressure, and should i have a breather cap on the valve cover. the sqeek is coming from the seal rubbing on the hub that holds the harmonic balancer on. Took it off and polished the small groves out of it. Better but not fixed. Seems to only squeek when i get the whistle. Anyone else seen or heard of this before.

take a close look at the rubber hose that connects the pcv valve to the throttle body.They degrade with oil and split..perhaps acting like a reed.Its a quick inspection.

So you think you are building pressure in the crank case?

Do you have a pcv of any sort, breather or anything to let the pressure out?

yes i have a pvc valve in the valve cover, put don't know if it's good enough. Order a valve cover breather and new pvc to try yesterday. don't know if pressure is coming from crank case or not. Seems to do it when engine is hot. but still doesn't do it every time. The reason i thought it might be crank case pressure is because the squeek is definetly coming from the seal rubbing the harmonic balancer hub. When ever i hear the sqeek if i shut down the motor i hear the pressure release whislte. If its not sqeeking i shut down the motor i don't hear any pressure release.

Next time it squeaks try this:
Pull the oil filler cap, that would release any pressure in the crank case.
If the squeak is still there grab some water in a spray bottle (wd40 will work but you might get some on your belts) and spray around until it stops. There is the source of your squeak. Replace or adjust as needed.

I'll try that next time (pulling the filler cap). Far as the squeek i know exactly where it's coming from. But don't know what causing it. I can spray lube on it and it will stop for a while but then comes back. Thinking maybe heat or pressure making the seal push out against the hub making it squeek. New vented fill cap and pvc was shipped yesterday, If pressure is from crank case this should help. Thanks for the help. I'll keep you posted.

I still don't get why you think pressure is causing the noise.
Try replacing the seal and making sure everything is right down there.

every time i here the squeek i shut down the motor, i hear the pressure release. If no squeek i shut the down the motor i don't any any pressure release. I know it don't make sense to me either but that the way it's been doing. Seal appears to be good, no leaks, and what i can see show no damage. Plus to cange i have to pull engine, or at least drop the pan to get timing cover off.

make sure the noise isnt coming from the cooling system at the lower rad hose. try running it once with the rad cap loose.

If a whistle is present, then you might spray the area down with soap, 409, Simple Green, etc., and look for bubbles.

Tryed running with rad. cap loose, coolant overfilled overflow, ran on the ground. Will try soapy water but might be difficult, whistle only lasts 5-10 seconds after shutting it down. Vented valve cover pvc and oil fill cap came in today. will put them on tonight and see if they help the next time i drive it. Thanks for the suggestions.

It look's like my whistle problem is gone. I put a breather oil fill cap on. and drove it over 250 miles and no whistle or squeek. Thanks for the help.

problem solved, the breather oil fill cap seems to have taken care of the problems, have drivesn almost 400 miles since no sqeek or whistle yet. Thanks for the help.