I do not know that measurement, right off hand.
There is a spare ’84 Gran Fury 8¼” differential, with springs still attached to it, deep within my garage – but it is not readily accessible.
The spring perches do have a larger hole in them (from top of my head, apx. 1-3/16”, or so - but I wouldn't go by that number) which will need to be addressed before using the spring plates – or you will not have any method of keeping rear differential square with rest of car, otherwise.
There are three different methods I have seen about correcting this is:
- Cut out some steel plate - a round disk (or square and round the corners) and weld into place, then drill a hole in the middle.
- Go to hardware store and find a flat steel washer of same diameter (or slightly smaller) and weld in place.
- Find a captive washer nut (shoulder nut) from auto salvage/local pull-a-part, etc., that can be obtained in the same approximate size. The nuts have some depth to them and sometimes can be placed in the hole (upside down) and sometimes will reside there without a need to weld in place (still a good idea, though – if you have access to a welder).
Sorry, I don’t have the measurement readily accessible, nor do I have access to get a measurement anytime soon.
That said, there is a couple of people who might have a differential readily accessible to get a measurement for you.
These are names on top of my head – and I’m sure there are others: F_Body_Deconstructor_Jim, Slant6Billy and/or Gator).
BudW