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1970 Cadillac convertible top rattle under med to heavy throttle

Started by Scot Minesinger, August 19, 2013, 11:50:00 PM

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Scot Minesinger

I put this post in before. 

Top down no rattle, guessing it is due to weight on sheet metal body below folding top mechanism.

Top up and pressing gas down a bit and the rattle is there.  It is not the top mechanism.  It is not the trunk torsion springs.  It is not in the passenger compartment.  It sounds like fuel or break lines but that is not it.  Exhaust is clear of the body.  Anyone have this problem and cure it?

Thanks,

Scot
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Scot Minesinger

I should add that this rattling/tapping noise is in the back for sure.  Car in park and fast idle after start up and the noise is there.  I have ridden in back seat with someone else driving and it is coming from right below where convertible top folds down into.  The noise is not from front of car, motor mounts are relatively new and it is not fan shroud.  The noise is loud and could easily be heard with top down.  Seems it is definitely a torque or higher throttle issue.  The car has dual exhaust from before I bought the car, and I'm going to look into that a little more (seems a non-original thing not always completely thought thru is often the route of problems).  This is very difficult and I have been after it for years.  It is not a killer because the car is most often driven top down anyway, but would like to cure rattle.  At highway speed top up it is there but greatly diminished due to other wind/road noise.  Any further ideas will be helpful.  I will check my motor mounts anyway
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Scot Minesinger

Art,

Good thought on the mufflers, never thought of a baffle inside the muffler coming loose.  The brake lines and fuel lines are so secure the whole car could be vibrated to death and those would be unharmed.

I will go under car with top down and see if I still here noise too, that is a good idea - get close to the noise.

Thanks,

Scot
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Scot Minesinger

Finally found the trouble.  The rear bumper bolt was rattling against body of car inside trunk.  The nuts that screw on to the 3/8" carriage bolt threads(head in rear bumper) that anchor the top section of the bumper to the body of the car were not tight enough and the rubber washers were worn out.  The rear bumper actually joins the frame to the body and these rubber washers are important.  Replaced them with nicer rubber washers and re-torqued nuts.  Now the car is quiet. 
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

66 Eldo

Reminds me of a problem my dad had with his 70 SDV that he bought new. It had a similar clunking sound that sounded like a tire iron being dropped in the trunk under acceleration from a stop light. But only when it RAINED.  I was just a kid but I remember the sound vividly but also being aware enough to know the car was not breaking traction. He had the dealer look at it countless times, they switched tires and tried everything. Never found the problem.