69/70 Rear Leaf Springs

[The Old Ranger]

As a long time owner of a 70 GT500 (since 1981), I have often thought about why the
69/70 Shelbys received special rear leaf springs.  And how do they compare to regular Mustang springs? Does anybody know the answer(s)?
Tom

[papa scoops]

all fords received different springs. it depended on options such as auto/stick, type of suspension, ac or no ac, ht or convert etc. it had to do with weight distribution as much as handeling. if you can find an original (not updated) ford mpc, you can see all the different combos, weights, color stripes and so on. most were superceeded by a spring or 2 it really didn't matter much about ride height (minimal at best) I tried to raise the  back of my 68 gt 350 using 500 convert, ac springs heavyiest listed, didn't change any thing. think of axle weight also, for the purpose of braking. phred

[Special Ed]

69 shelbys (except for the very early cars) had  unique s9ms 4 leaf 2 wrap rear springs then c9zx springs (and they look the same as s9ms) started showing up later in the year . I put them side by side & dont see a difference just engineering # change & both show up on gt350 & 500  4-speed &auto fastback & vert  & a/c cars.

[papa scoops]

true, but the spring rates are different (not by much)

[69 GT350 Vert]

On a similar train of thought, I wonder why only the 1969/70 GT350 was equipped with the 9984 coded rear axle.  It wasn't shared with any other mustang or cougar based upon my research, which may be faulty.   

[Special Ed]

I think the 69 shelby unique leaf spring had something to do with the new f-60-15 tires that were supposed to be standard on  the new 69 shelbys & the fact that previous shelbys (except for 68s) had some kind of rear traction help. The 69 shelby 2  leaf spring wrap never had a wrap on the bottom leaf & it was a straight leaf with no curve (kinda like a slapper bar type) vs regular mustang 3 wraps & the bottom leaf had a wrap. I think the s9ms # change to c9zx # was same spring just a running change like 69 b9 parts started out with kkx#s then went to c9zx#s same parts just changed to a regular ford #.

[J_Speegle]

On a similar train of thought, I wonder why only the 1969/70 GT350 was equipped with the 9984 coded rear axle.  It wasn't shared with any other mustang or cougar based upon my research, which may be faulty.   

I have at least one 69 M Code Mach I with a 3 speed manual buildsheet, with that same rear end code

Not allot of stripped down Mach I's out there and that may have got in the way of finding other examples

[69 GT350 Vert]

On a similar train of thought, I wonder why only the 1969/70 GT350 was equipped with the 9984 coded rear axle.  It wasn't shared with any other mustang or cougar based upon my research, which may be faulty.   

I have at least one 69 M Code Mach I with a 3 speed manual buildsheet, with that same rear end code

Not allot of stripped down Mach I's out there and that may have got in the way of finding other examples

Interesting.  Do you know if the bottom leaf on that Mach 1 has the S9MS identifier on it or the 5RS68(as on my GT350)? 

[Coralsnake]

Pretty sure the S9MS spring is unique to Shelbys as it was installed by AOSmith, not Ford assembly.

It has a lower load rate than most other Mustang rear springs.

[Bob Gaines]

Pretty sure the S9MS spring is unique to Shelbys as it was installed by AOSmith, not Ford assembly.

It has a lower load rate than most other Mustang rear springs.

You can be sure it is 69/70 Shelby unique.

[Bob Gaines]

On a similar train of thought, I wonder why only the 1969/70 GT350 was equipped with the 9984 coded rear axle.  It wasn't shared with any other mustang or cougar based upon my research, which may be faulty.   

I have at least one 69 M Code Mach I with a 3 speed manual buildsheet, with that same rear end code

Not allot of stripped down Mach I's out there and that may have got in the way of finding other examples

Interesting.  Do you know if the bottom leaf on that Mach 1 has the S9MS identifier on it or the 5RS68(as on my GT350)?

Are you implying that the M code Mach I also used that same 5RS68 leaf spring?

[J_Speegle]

On a similar train of thought, I wonder why only the 1969/70 GT350 was equipped with the 9984 coded rear axle.  It wasn't shared with any other mustang or cougar based upon my research, which may be faulty.   

I have at least one 69 M Code Mach I with a 3 speed manual buildsheet, with that same rear end code

Not allot of stripped down Mach I's out there and that may have got in the way of finding other examples

Interesting.  Do you know if the bottom leaf on that Mach 1 has the S9MS identifier on it or the 5RS68(as on my GT350)?

It would not have had the Shelby springs. Rear axle code has nothing to do with rear springs that were assigned and installed in the car. Two different things.

[69 GT350 Vert]

Thanks for the clarification that the springs are not correlated to rear axle code.  I didn't know that.  I always thought that the rear springs were part of the rear axle assembly. 

The axle code chart I read on dead nuts on website said the 9984 code was exclusive to the shelby.  Since a Mach 1 was found with the 9984 coded axle, I guess that is not true.  Just wondering what is different about the 9984 axle that caused Ford to create a separate code for it.  I always thought it was for the leaf springs, but that isn't the case based upon the responses.   

[J_Speegle]

Thanks for the clarification that the springs are not correlated to rear axle code.  I didn't know that.  I always thought that the rear springs were part of the rear axle assembly. 

Ford designed allot of different rearends and to keep track of everything they had to assign them each their own codes. Things like housing differences, axle spline count, carrier used, yoke used, pinion retainer used, axle snubbers or no axle snubber, axle ratio,  brake line attachment location and many many more details  all come into play and by changing one a different coded axle assembly was needed.  Sterling plant assembled these as a unit, marked and labeled each then sent them off to the car assembly plants based on need and orders. Springs and all the attaching hardware came from other different suppliers to the plant.  If the rearend and leaf springs had been a single subassembly there would be no reason to list the axle and the rear springs separately on the buildsheet

Just looking at 69 Mustangs there were at least 19 RPO combinations/different axle codes possible. Each different from one another so when you ask  "Just wondering what is different about the 9984 axle that caused Ford to create a separate code for it. " you would have to choose which other of the 19 you wanted to compare it too.

[Dennis Y]

Would Eaton have the specifications for these springs?