ClearlyLost

Hello all,
I’m new to the site and I’ve found a ton of great info. It seems like a great group. I have one issue I can’t seem to find any info on and I hope someone can help.
I have a 67 Mustang Conv’t that I just got early this summer. It had a 351w put in it before I got it I'm not sure about the trans.
My issue is that everything was fine until I did some highway driving about a month ago. Once I got to about 70 I heard a clicking noise that was a definite metal on metal sound. It was constant but would seem to get a little louder with revs of the engine. I let it sit in the driveway when I got home to find where it came from and it got more and more quiet until it went away(about 5 minutes). It has seemed to worsen as time has gone on. If I stay under about 45(this number slowly gets lower) the sound never starts but if I go over, then it will stay until I either spend a while at low speed or stop and let it sit for a while. The car runs and shifts fine. I can't tell if the noise is comming from the trans or engine. Any ideas?

Dan04COBRA

If you have a mechanics stethoscope, put it to your valve covers while you slowly rev the engine. Try to pinpoint where it's coming from.

If you don't have a steth, take a long screw driver and stick your ear to the plastic end and have a listen!

I'm going to say your knocking under load...

e40water

Or just use a piece of heater or garden hose, Ive found that works well too.

Good Luck.

Aliate X

Just possible, might be your driveshaft universal joints, people get that problem a lot. It makes the predator noise ( yes predator from the movie predator ) when you put a load on the car in a higher gear.

pichinco

You might be describing a lifter knocking. I can't remember if 351 has hydraulic lifters or not. I've seen dirty/sticky lifters do what your describing. I was able to "clean" one doing the same thing to me in a 289 by running pint of Marvel Mystery Oil w/ 4.5 quarts of normal oil for ~500 miles. I wouldn't run it any longer than that. Seemed to do the trick.

Lot of folks will describe a lifter knock as a "ticking" sound. The sound will emanate from right under you valve cover(s).

The other thing that will cause lifters to knock is low oil pressure either from a dying oil pump, or low oil level. I had an old Chevy that would knock anytime it got a quart low. Pressure gauge wouldn't show a drop in pressure, but the lifters would knock everytime.

ClearlyLost

Thanks for the help I know someone with a scope who should bring it by before the weekend. I hope that should narrow it down.