From the umpteen questions I’ve already asked you may know that I’m building a McSorley 7+4 chassis to which I’m going to fit a DeDion rear end.

At present I’m about to weld in the upright rear tubes that form the back end of the transmission tunnel (tubes e and f) which, on the McSorley plans are spaced so that the outside dimension over the 20mm RHS tubes is 140mm which ties up with other drawings I’ve seen including the GTS W7DE chassis.

On the GTS drawing for a DeDion rear end however these tubes are set to give a dimension over the 20mm RHS tubes of 177.8mm with their diff mounting plates welded outside of these.

My diff has a mounting with of 195mm so wouldn’t fit within these plates unless I’ve misunderstood how it works (very possible).

Should I simply move the tubes further apart so that they are the same with overall as my diff (ie 195mm)? If I do this should I keep the transmission tunnel rails parallel which would mean they wouldn’t actually meet tubes e and f but simply be welded to tube O3

Any advice would be welcome.

John.

The GTS chassis (and most Locost chassis with IRS or De-dion in fact) is designed to take a 7" Sierra diff which is around 177mm accross the mounting points.

It sounds like you may have the rather large and heavy 7.5" diff, as fitted to the RWD Cosworth, XR4, Granada etc. This diff is massive overkill for most Locosts, but if you wish to fit it then you will need to modify the chassis by moving the two tubes apart as you have described.

"On the GTS drawing for a DeDion rear end however these tubes are set to give a dimension over the 20mm RHS tubes of 177.8mm with their diff mounting plates welded outside of these. "

that exactly how i did mine, and my diff slides in a treat.does sound like you have the 7.5" diff.

i suppose you could set yours to fit your diff, and if you were in the future to replace your diff with a 7" diff, you would only have to "shim it up".