I read a story once that Donald Healey, designer of the Austin Healey 100-4 up through the 3000 would periodically wander through the assembly line and when he found that the welders were only making seam welds on the firewall-to-cowl every four inches he would give them hell and tell them to continuously weld it all around because he designed it that way for strength. Probably, when he left and the line supervisor and Mfg. Eng. found out and then told the welder to go back to the alternate 4" welds to save time (Having been a Mfg. Eng. once, I totally believe this).
HOWEVER! None of the cars with continuous cowl welds exhibit "scuttle shake", while all of those with alternate 4" welds do. Everyone doing ground-up rebuilds check for those welds and complete them if they find the alternate 4" ones. It really tightens the car up.
Just an interesting tidbit from one of my Healey books.
That aside, I'm just curious if supporting the rear of the car better will affect the shakiness. The front is supported just behind the front wheels and then with the additional support just ahead of the gas tank (a bracket to the top of the front beam) so it has quite a bit of body support and relatively short torque arms for any vibrational effects.
The rear, on the other hand, has, solely, a big (almost 3 feet long and 2 feet wide) 2" X 2" boxed-frame hoop holding things up which is only supported at the very front, just behind the doors with a step-up joint and no additional bracing. This allows everything to move vertically so I want to brace it from the transmission mounting bolts at the rear of the horns. I also want to look at possible corner bracing for the hoop, but that may not be practical - or necessary, we'll see.
Original Post