Rear view mirror screws, into top dash tube?

[Murd]

I have a resonant vibration from my engine at about 2100 rpm, anything that can rattle buzzes when rpm crosses that speed. The worst culprit is the body cowl above the dash where the rear view mirror mounts. I currently have it only mounted to the fibreglass, however I recall seeing that it should go into the 1” square tube below it. I pulled the mirror off the other day and there is about 1/2” between the body and the square tube, too far for the supplied mirror screws to reach. I have a feeling the tips of the screws may be hitting the steel tube and be the cause of the noise. Hen it starts to buzz, if I push it down hard it stops
Question is, should I drill into the steel tube to mount the mirror?
If so should I push the body down so it is sitting on that tube?
The screws might just be long enough if I push the body down when I install them, or most likely get some 1/4” longer. I’ll also have to open up the fibreglass holes so that the screws are just threading into the steel.

As always thanks in advance for the advice.

[rich grsc]

So if the screws are too long and touching the tube, cut them off? FFR sends a pair of spacers that go between the body and the dash hoop if you mount the mirror to the body, NEVER pull the body down to the hoop. Best thing is NOT mount the mirror on the dash, but up on the windshield frame.

[GWL]

Dark Water Customs (DWC) make a mount for the mirror that 'rich' is talking about. They are a supporting vendor here.

http://www.darkwatercustoms.com/cart.php#!/Rear-View-Mirror-Bracket/p/474064/category=185741

George

[PeteH]

I made a steel strip with 10-32 nuts welded on the bottom and bonded it under the dash, however this was easy with body off.

[j.miller]

Everything vibrates....What you have are two vibration waves crossing at 2100rpm. Your mirror happens to be susceptible to that range. Screwing the mirror to the tube underneath will change the range it is affected . It may go away, it may show up at a different rpm. DO NOT PULL THE BODY TO THE TUBE WITH THE SCREWS. The 4 basics that vibrate are tires, driveshaft, engine/trans/clutch/flywheel and engine accessories. Tires between 0-2500, engine etc. 600-3500, driveshaft 1500-5000, accessories 2000-4000......da Bat