Worthwhile mod?

[gjz30075]

I don't think I've seen a discussion on this particular mod. This was done by a good friend of mine many years ago to alleviate the cracking you see in pic showing......the cracking. Now, granted, the crossmember shown with all the welds is pretty beat up but I'm not sure how it gets that way. Any ideas here?

Anyway, does gussetting the gearbox mount as shown really help? Certainly can't hurt.

[Galwaylotus]

Of course it helps. A triangulated joint is much stronger and stiffer than a cantilever joint.

[oldelanman]

I don't think I've seen a discussion on this particular mod. This was done by a good friend of mine many years ago to alleviate the cracking you see in pic showing......the cracking. Now, granted, the crossmember shown with all the welds is pretty beat up but I'm not sure how it gets that way. Any ideas here?

Anyway, does gussetting the gearbox mount as shown really help? Certainly can't hurt.

My crossmember has not been modified and it has gussets exactly like the ones shown on your mod although on mine they are fully welded along the edges and yours are tack welded. I thought they were all like that but maybe it was a mod on later cars.

As for the damage to yours - from the amount of deformation around the bolt holes it looks like the hardware may have been loose. Other possible causes could be failed gearbox rubber mount, missing spacers between mount and crossmember or failed propshaft U/J all leading to excessive vibration transmitted to the crossmember and consequent failure. I would have thought though that you would have felt that before it resulted in damage.

Regards,

[gjz30075]

Roger, the beat up mount was not something I had on the car. It came with a box of bits. I agree, something odd should have been felt before it got to this stage.

[Galwaylotus]

To understand why a gusset will work, think of the part without gussets. Imagine each bend/corner as a hinge rather than a stiff joint. Now apply the gusset and you can see that the hinge won't bend. The load is taken in tension and compression rather than bending.

[garyeanderson]

These changes to the cross member bracket are what I would call a factory mod,

Some previous stuff on gearbox mounts from before
elan-f15/early-late-gearbox-tailshaft-housings-and-mounts-t19281.html

some more on the gearbox cross member

upper photo
Top is an early S2 gearbox cross member and mount (no braces)
Later cross member
Later cross member with gearbox mount

Lower picture
mounts spacings are different, the early cross member has been drilled to accept the later mount by a previous owner.

r

[GrUmPyBoDgEr]

I wasn't aware that this was a known weak point on Elan chassis/frame parts.
The G/Box bracket from Spyder seems to be designed in a similar way to the Lotus part & I feel sure that they would have done a re-design if they had felt it necessary.

It would appear that the cracked bracket that is illustrated has been subjected to abnormal loads.

Normally if a part fails the best solution is to use thicker or stronger material.

The bend radii in the Lotus bracket, the flanges & material thickness are IMHO more than adequate to transmit bending loads that the bracket could be subjected to.

To be blunt the suggested modification just moves the bending loads further outwards to another area.
Admittedly the bracket a that point is a bit wider & therefore stronger to some extent but it still represents a cantilever at that point even though the rest of the bracket has been "triangulated".
The modification could be further improved if additional side flanges were also added to the underside of that bracket.

The quality of the welding on that cracked bracket reminded me of my old welding instructor when I was an apprentice.


Cheers
John