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I just had a call from my coachbuilder friend and he says no problem: The tilt release cables are apparently easy to unhook and he suggests we go a step further and add bolts inside to make the seat and back more as one shell. He's a fireman on call and tends to think about safety.
This probably still won't measure up to the safety aspects of a single shell race seat, but it should greatly reduce the risks of injury we've been discussing.
It also saves me money I can put into a removable half-cage instead of an additional driver's race seat.
I'll report more as and when something is done, along with pics. If only one other person benefits, it's worthwhile sharing this info.
Robin, as I'm sure you can tell, I've also been giving this a lot of thought. I was going to suggest taking measures to stop the seat articulating all together as well. However, I'm not sure a couple of bolts will really suffice.
I'm not 100% sure of how the seat frame is contructed, but perhaps you could look into the possibility of getting the hinges and/or the pieices of the frame (up-right back and the base) welded together? A weld will be a lot stronger than two bolts which will cause local stress and might not be very strong.
That said, the seat will
still be inherently weak as the hinges on either side of the seat are the only points connecting the back and base together. Between these hinges there is nothing - just a gap. It is this lack of structure that makes these articulated 'bucket-style' seats weak and prone to twisting when they have harnesses threaded through them, loading the seat-back with forces it was never intended to cope with. Some sort of brace welded between the hinges might help, but it's the anchoring of the back of the seat to the base that needs beefing up.
One point to note - the second you change anything with the seat will cease to be TUV approved, so you'll need to make sure you insurance co. are aware of the modification.
I guess it depends how far you want to go with this, as very quickly it could become a lot cheaper to just buy rigid seat?