A nice looking wagon you have there!
Before I get started, I have a question for you:
I’m guessing you do not intend on using the 9¼” differential already in the vehicle?
Is that differential use 6-lug or 5-lugs?
I would like to see pictures of how the differential is attached to the leaf springs. I suspect good news there – but not sure, yet.
Your Questions:
What is the rear end width and center to center on the leaf springs?
FMJ-bodies all use the same differentials measurements (for 7¼” and 8¼”). All station wagons use 8¼” – but apparently yours does not, any longer.
They measure 54.340” from backing plate (or flange) to backing plate.
44.46” perch center to perch center
In B and C-Bodies, 8¼” and 9¼” differentials use the same propeller shaft length (which are 1.6” shorter than 7¼” propeller shafts are).
8¼” (and 9¼”) U-joint center is 11.69” from center of axle shaft.
Change the rear to an 8 3/4
A ’65-70 B-body 8¾ differential will “almost” drop right in. Just about anything else will need to be modified (ie: shortened or lengthened) to make fit.
All ’65-70 B-bodies have perch center to perch center of 44.0” (0.230” difference per side)
Backing plate (flange) to backing plate distance are:
‘65-67 B-body 54.250”
’68-69 B-body 54.936”
’70 B-body 54.906”
Any of the 3 will fit.
For bigger tires – I think the ’65-67 version might be better. For track racing, I suspect the wider differentials might be better.
FMJ’s have an ISO-clamp (ie: rubber plates) system that isolates the differential from the leaf springs. The rubber plates are not that great for performance applications. The large “U” shape part of ISO-clamp is prong to breaking and leaving one stranded, when it does break.
Several here has installed Poly spring mounts/pads and have been happy with them.
I recommend using the older spring shock plates (which would be used on 8¾” to begin with) and just eliminate any ISO-Clamp troubles.
Also, I “suspect” the older shock plates might already be used, maybe (which is why I wanted a picture of the area).
Are the springs A-body length? I'd like to change to super stock springs.
Most F-body Station Wagons (but not all) came with 5-leaf rear springs – which seem to do well on performance applications (for FMJ’s).
Leaf spring specs: (front segment / rear segment / total length)
’60-76 A-body 20 / 35 / 55”
’76-89 FMJ-body 24 / 34 / 58”
’70-74 E-body 22 / 35 / 57”
’62-65 B-body 21 / 35 / 56”
’66-79 B-body 22 / 36 / 58”
(Early) Dakota 24 / 32 / 56”
MP Super Stock 20 / 36 / 56”
A person might be able to purchase or fabricate new front leaf spring brackets to use the Super Stock Springs.
I recommend trying the original 5-leaf springs and getting them re-arched, first (if it has 5-leaf springs, that is). If not happy with performance, then try to make the S.S.’s one fit.
Some people has had good luck using Dakota springs. Note: I’ve not tried S.S. or Dakota springs (yet) so can’t comment - other than measurements.
Do they make polyurethane or solid mounts for the front K member?
Mentioned earlier – but to recap. FFI sells aluminum (solid) K-frame mounts. MP made some cast iron ones back in the day, but they are hard to find (and extra heavy). One or two people make Poly mounts. I hadn’t heard anything bad from any of them. If you are planning on racing the car (strip or track) I would recommend the aluminum ones. If mostly to get groceries in, then Poly might be recommended.
I have a set of FFI ones – Very nice and light, but pricy.
‘73’ish and up B-body, R-body and FMJ K-frame mounts are the same.
Note: if you are planning on changing the engine out, I might recommend you drop the engine/transmission/K-frame down as an assy (or more correctly said by raising the body up). That way headers (if used) install is easier. Also change out those K-frame mounts at same time.
BudW
