Reducing rear chassis flex & twist with tub on.

[Bfg]

1 hour ago, Rockie51 said:

I have occasionally pondered about making a single piece transmission and handbrake cable cover with flanges on both ends bolted to the firewall at the front and the bulkhead at the back as well as the floor. Ideally in carbon fibre (!!!) which is why I will never do it. In theory, it would improve both beam and torsional strength. Anyone?

Bi-direction glass is very much cheaper, a little easier to work than carbon-fibre and its strength or weight penalty for such an application would be negligible.  Carbon fibre composites excel in tensile-strength-to-weight application, and as a spirally-wound closed tube they also work very well in compression ..such as for a mast or a spinnaker pole, They also work very well for variations of the tube, ie. aerofoils (wind vanes &/or rudder blades) but where its edge fastening to a semi-rigid structure is via flanges and a number of localised pins, ie. screw / bolts / rivets - then these flexible connections tend to override most other advantages.  Continuous seam bonding is the obvious answer but is less practical when you need to work on your car's gearbox.  The flange can, to a limited extent, be made thicker but you'll find there's then a lack of space for the screw heads, so a continuous steel plate placed to sandwich the flanges is a better proposition.  

I'm quite used to working with composites - but I opted to adapt a steel TR3 gearbox cover for my TR4A < here >.   It's securely fastened all the way around and at its rear edge - it's screwed directly to the original (built-in, steel ) transmission tunnel.  That combined with a few other mods, such as six extra body-chassis mounts, I'm very happy with the result in its tighter fit, the lack of noise and fumes, and also structurally. . .

 

^ I made it in two halves (plus a couple of locally removable access covers). The front-rear split is some 4" forward of the gear-change. That's so the rear section (over the overdrive and its solenoid, the gearbox mount, and the propshaft UJ) could be lifted off without disturbing the forward section or its fastenings in the foot-wells and around the bulkhead.  This photo shows it mostly fitted but, at this conjuncture - without the screws I used to fasten the front and rear halves together, or the screws into the driveshaft tunnel.  It was made so the standard dashboard brace / H-frame would fit, but I've happily discarded that.

Pete

 

 

Edited February 3, 2023 by Bfg

[Malbaby]

BFG......Never owned a TR3, and was unaware of their steel gearbox cover....I like the idea, but where to find one in Australia 

A pity that the shape of the tunnel is so complex, making it difficult to custom make.

Edited February 4, 2023 by Malbaby

[ianc]

I would not be happy to discard the H brace - it is there for a good reason. 

The sidescreen TRs were prone to scuttle shake, and the H frame casting on the TR4 overcomes that problem.

Ian Cornish