Shock Tower Brace

[grannyknot]

Mark, now you have thinking about a neat little visual experiment that wouldn't be too difficult pull off.

Two pieces of sheet metal bracing secured to the top of each shock tower with cheap red dot laser pointers mounted and pointing directly at each other. Then somehow suspend a piece of thin tracing paper (perhaps mounted in a frame so that it is taught) between the two laser pointers then aline the red dots so they shine at the same point on the paper. Mount a camera and take that Z for a serious rip.

 

With luck you would be able to see the single dot separate into two dots depending on how the frame of the car was being stressed.

Vibration could play real havoc with the camera and the mounting of the pointers...

there is a way to do this just got to give it some thought.

Chris

Edited February 27, 2015 by grannyknot

[John Coffey]

Back in 2000 when I was building the Rusty Old Datsun I took the car to Bill Savage at T-Mag in Vista, CA.  T-Mag did a lot of the suspension fabrication for NPTI when they were racing the GTP cars in the late 1980s.  T-Mag also built ALL of Nissan's off-road and stadium trucks for at least 15 years during the 80's and 90s and Bill was the head of Tech for SCORE for God knows how long.

 

Anyway... we did a lot of measuring and built a finite element model of the 240Z chassis.  By far, most of the chassis stiffening efforts on the S30 should be done from the seats forward.  The firewall, roof, floor pan junction is the most flexible part of the chassis.  The biggest bang for the buck chassis stiffening improvement is a 10 point roll cage that ties the front and rear strut towers into a 8 point central safety cage.  This mod is orders of magnitude better then any combination of other modes.

 

The second biggest bang for the buck is full length, welded subframe connectors that go from the TC rod mounts to the rear subframe combined with triangulated front strut tower bracing.  Third best is a welded in roll bar but that doesn't address the front issues.  Everything else is just feel good stuff.

Edited February 27, 2015 by John Coffey

[TomoHawk]

I'm kinda surprised that no one has thought of putting a stress gauge on the strut bar to see what the forces are.  You could even put several on to measure the forces in the different directions and in different places (such as rear struts vs. floor.)  You'll need to take along a portable computer, but there are some for iPad and Android tablets (but more expensive.)

 

I think it would be very interesting indeed, to quantify the forces with and without the bracing, in stead of relying on someone's opinion.

[rossiz]

i agree that measurements would be a very interesting exercise - but the trick is measuring movement relative to what? in other words, are the tops of the rear strut towers are moving in relation to each other, or in relation to the base where they attach to the subfloor pan, or in relation to the side walls of the car. all these movements are possible and would depend on the relative stiffness of the components and how they work together.

 

i also agree that the body feels like it's twisting when, for example, you approach a driveway apron or when going over a speed bump slowly on just one side and this does seem to make the most interior panel noise. if the rear strut tower, when receiving load through the strut, leans in to the center of the car by flexing the subfloor it's attached to, then a diagonally braced connection between the two towers would make sense. 

 

reading john coffey's post brings up a different perspective though - for serious performance on a track, the stiffness of the whole chassis as a unit would be more important than trying to eliminate squeaks and rattles... i can see how connecting all 4 strut towers would do the most, although it's not a very practical approach for a street car. i've thought about the frame rails - they are definitely a little flimsy. mine are completely rust-free, and wen i put one end of the car up on stands they flex enough to change the door gaps. but that's an order of magnitude of work beyond a simple bolt-in brace.

 

the fact that datsun chose to diagonally brace the towers in a lateral fashion and shape the towers with their weak axis in the fore-aft direction suggests that these forces were considered less important. not that they got it right though...

 

a really simple test might be to simply stretch a thin wire between the tops of the rear strut towers and watch how much it sags under basic maneuvers like the driveway approach or one-sided speed bump. this might at least tell us if the car is twisting diagonally (across all 4 strut towers) or if the rear towers are acting independently.

[TomoHawk]

I hear those noises too, but to me they sound like the strut insulator, which was  the only part not replaced, because they weren't available.

[Mark Maras]

 Damn, I can't shake this train if thought of tracking 3 dimensional movement. How about this one for the rear. Brackets bolted to the shock towers that hold kitty laser toys pointing up to a bull's eye target on the headliner. Throw in an observer or a Go-Pro & see if it was all worth it.

 Now to the front towers, No tracking, just reinforcing. What if, in addition to the standard cross brace there was a vert. support from the c-brace down & attached to the bottom of the tower & then triangulated up to the center of the c-brace as close to the v-cover as one wanted. The c-brace should be beefier & could be welded, bolted or pinned. From the upper tower brkts. possibly down to the lower rad. support & back to the fire-wall. One more c-brace or diag. back by the f-wall & I think it would do it. I'm thinking this could possibly elliminate some of the vert. movement in one shock tower when you run over a speed bump with one wheel. At least I think that is what is happening. Or am I just OCD?

Mark

[Zed Head]

On the back, running a brace from each tower up the roof might offer the benefits of a roll cage.  You can go nuts thinking of all the places that might be braced better.

 

Some one on another forum even noted that their car had better, stiffer handling, when they glued the windhshield in.  And there are some that say the car gets flimsy when the floor panels are removed, implying that much load is handled there, they're not inert.  So bracing the floor panel somehow should help.  And rusty floor panels would be bad.

[Mark Maras]

When thinking about all the bracing possibilities, I was reminded of a documentary about the Crystal Cave in Mexico. Massive gypsum crystals going all directions. The cave looks to be well braced.

Mark

[TomoHawk]

That sounds like one crazy light-show, with the lasers. 

Can you work in a Disco ball too? 

 

On the serious side, something like the laser idea has been done before when I was in college.  We used a laser like Mark suggested, but with an optical sensor, like a 30mm strip of a CCD.  We used a computer (an Apple II) to record the data that could later be converted to millimeters, and finally charted.  It was only in 1 dimension then, but you can probably get a 2-dimensional sensor now. 

 

Still, I think strain gauges would be even better to measure the flex in many dimensions.  Not only in the one spot, too,  but  checking the affect of a front brace on the rear of the car.

Edited March 1, 2015 by TomoHawk

[EuroDat]

I went over to PU bushes and I have had rattles and sqeaks ever since. Im slowly finding and eliminating them. Thinking about it, I think I transfered the flex it the bushes to the frame making it flex more.

All this talk about bracing is starting to rub off on me. It might help reduce the rattles in mine and I like Carl's idea for a fire extinguisher. Mine is now where the tyre inflater should be which isn't very accessable.

Chas

[grannyknot]

Zed Head, modern windshields and the sealant they use now do make the glass a stressed member of the unibody, not sure if our old windshields could handle the strain.

 

Tomo, your idea about the stress gauges is much better then my loony laser plan, stress gauges would give us some real data,

But then I'm not racing the car, I'm happy with minor improvements.

[Carl Beck]

Factor Service Manuals - show the windshield in the 240Z's attached with adhesive..