The spring is part nr. 30977, a conical compression spring made of .032"
dia. music wire.
The small end is .554" OD and the large end is .680" OD, overall length 1.5"
with 7 coils, spring rate approx. 2-3 lbs to compress down solid.
I checked a few spring winding companies which do custom winding, and it
would be an easy enough spring to make as a custom order, but they usually
have a minimum order quantity of 100.
The only spring company I fould that carries an assortment of springs in
stock was Associated Spring.
None of theirs are an exactly exact match, but the one that comes closest is
I think this one would work fine and is made of stainless steel, but the
small end would have to be spread out a bit to fit on the cup filler.
The rubber cup is 1-1/8" dia. I went to Auto-Zone and they had no listing
for any drum braked Jags and no way to find cups by size, so I guessed
“Let’s try 1965 Ford Fairlane” and it came up 1-1/8". '65 Mustang and Falcon
are also 1-1/8 and the rebuild kit came with 2 cups & 2 boots for $3.79,
Brakeware #66818. The cup is right and the boot fits over the cylinder, but
the boot ID is smaller than our originals so is hard to get on the piston,
looks like it is made to fit a 5/16 or 3/8 shaft where ours are 5/8". I may
go back and try a few Chevy and Dodge kits and see if they have bigger IDs.