I've got a GTS De Dion with GTS shocks and I'm trying to set it up so that I can mount my rear diff with the drive shafts parallel to the floor. My question being, I have a stool on the front end of the chassis with the engine sat in place and axle stands on each end of the De Dion, I then sat on the back end and the trailing arms aren't parallel to the chassis. Should they be? How do I mount the diff properly if not?
Cheers all

The trailing arms should be parrallel to the chassis when the car is fully built and on it's wheels with the correct spring settings etc etc........in an ideal world.

The easiest way to do it is to estimate how much ground clearence you are going to have, then measure where the centre of your wheels are going to be, and work out your diff position from there.

I'll do a pic, it's worth a thousand words you know, when i get time and e-mail to you.

Ah yeah I get you. Wasn't overly sure if the trailing arm stuff was vital, just don't want the weight coming off the car when hitting a bump and the arms bouncing off the chassis. The diff height should be, I suppose, half the rolling radius of a wheel so as to keep the drive shafts parallel. Cheers John.
Was thinking of 15" wheels, anyone know the rolling radius of them?

That depends on what size tyres you are going to use,

205/50's are 590mm diameter
195/50's are 574mm diameter.

I've been thinking this through (dangerous I know!) if I mount the diff/shafts central to the wheel, but the trailing arms are not parallel with the floor then the axle wil not be parallel and so will force the driveshafts t slope downwards. Am I just worrying too much about all this?

Depends what ride height you want. IIRC with the trailing arms parallel on my GTS you get about 4" ground clearance at the back of the car. Mine was well high until i would the spring seats down to let the back end down...

David