69/70 Rear Leaf Springs

[Bob Gaines]

Thanks Bob. I agree on giving Virginia Mustang our business. When I bought my springs they were the only ones I was aware of that did them for a specific application and not one size fits all. NPD is local. So was Eaton so easy choice at the time. I bought the clamps from Shelby Parts a few years ago and plan on restoring mine as the ride height was still good with my old springs. Retirement project: Replace/restore as many original parts on my vert to bring it up to SAAC gold standards sans the gold stripes and underneath paint wise. My rear frame rails and floors look as good as the top side still.

Gary ,I hope that you kept your original leaf's besides the bottom plate. All of the leaf's are a different length on the S9MS set compared to a regular mustang. the only one in common is the main leaf with the bushings. Consequently a replacement set is not worth restoring unless you can do it for less plus show detailing/bottom plate then what a good replacement set would be.   

[Bob Gaines]

I found this information in a General Spring application chart.  It shows the aftermarket part number of 42-503 as the correct spring for a 69 Shelby.
I don't know if this information is accurate or not.

That would be a replacement substitute no better then the universal replacement that Ford sold for decades to fit just about all Mustangs 65-70. I have bought ones from Virginia Classic Mustang that look the same but are a little less then Eaton plus Brant is a forum contributor. Basically you get a generic replacement regardless of who you buy from.  Eaton covers their springs in a thick black paint which for a driver is fine because they will be well protected from the elements but get ready for a major amount of work trying to get all that paint off if trying to make them look close to original. Virginia's still have paint but not near as thick.   Regardless of where you get a replacement the leaf's will not all be the proper length and the bottom leaf will look different . At least compared to a assemblyline leaf .

Based on info in an older thread, the VA Mustang leaf spring is industry replacement number 42-437, which has free arch of 6.25 inches. The 42-503 spring listed by General Spring for the 69 Shelby has free arch of 3.75 inches, which would provide a lower ride height. It is likely the spring rates are also different.  Fortunately, my early original leaf springs stamped 5RS68 are not sagging.  However, the original front and rear bushings are cracked.  I should pull them off and change them, but the car rides nice as is so I haven't messed with them.

Interesting specs from the books. Based on the free arch measuring technique discussed on Eatons YouTube presentation  https://www.youtube.com/watch?v=Gz1FE4QaqZU   those posted book figures do not jive with the real world. I laid out 6 separate will used original S9MS leaf springs that I have extra and got various measurement varying from 6 1/4 to 6 9/16 . FYI I know that they are original because besides the flat bottom plate the other two leaf's are a different length compared to a regular Mustang set. I assume the variation between all of them was due to age fatigue. I also measured a pair of well used B2 leaf's that I had extra for comparison and was surprised at their 5 7/16 free height.

[shelbymann1970]

Thanks Bob. I agree on giving Virginia Mustang our business. When I bought my springs they were the only ones I was aware of that did them for a specific application and not one size fits all. NPD is local. So was Eaton so easy choice at the time. I bought the clamps from Shelby Parts a few years ago and plan on restoring mine as the ride height was still good with my old springs. Retirement project: Replace/restore as many original parts on my vert to bring it up to SAAC gold standards sans the gold stripes and underneath paint wise. My rear frame rails and floors look as good as the top side still.

Gary ,I hope that you kept your original leaf's besides the bottom plate. All of the leaf's are a different length on the S9MS set compared to a regular mustang. the only one in common is the main leaf with the bushings. Consequently a replacement set is not worth restoring unless you can do it for less plus show detailing/bottom plate then what a good replacement set would be.

I learned before I restored my car to keep all my old parts. I posted a pic of my leafs. I still have my original doors also. Original trunk lace. "original Konis...." My car was sold new on Sept 30th 1970 as per the title on the car and my Konis are date 6/70 but of course could never prove they were installed when the car was new since Claude "lost' all his paperwork on those cars(his memory failed him on what he did with them he once told me).
second pic is when new  3rd pic is 1989. The stance really hadn't changed.

[Dennis Y]

Is there any historical data on who actually manufactured the springs that A O Smith installed? Were they shipped by a Ford supplier or did A O Smith contract them?

[csxsfm]

My experience with Eaton Detroit Spring was similar to Bob's - "knew everything."   

[Coralsnake]

Were they shipped by a Ford supplier or did A O Smith contract them?

I believe some were supplied by Ford and others were actually installed by Ford.

[Dennis Y]

In regards to Eaton, like a lot of other vendors, everyone's experience can be different. I am also a member of the Fairlane Club of America and when the club president approached them years ago about getting the correct springs built for late 63 and up cars, they were very cooperative. There was only I believe a 1/2 or 3/4" difference in were the locating pin was located (had something to do with (NHRA super stock wheelbase rules). Bob supplied a sample and they matched them exactly. Like I say, every experience is different.

[Dennis Y]

So circling back around to the OP's question, can anyone provide some specs on the differences between the original Shelby springs and the replacement 42-437 Mustang springs i.e. difference in length of 2nd and 3rd leaf that was mentioned? Is there a difference in the length from the pin forward or the pin rearward on those 2 leafs compared to the Mustang spring? Length of the bottom flan leaf? Bob, your measurements of of 6 1/4 to 6 9/16 would put them in the ballpark of the 6 1/4 spec'd from Virginia and the 6 5/8 spec'd from NPD/Eaton on the 42-437 Improved Handling spring . Most of the vendors with the Improved Handling 42-437 springs quote a rate of 114 lbs. One vendor has quoted the rate on the 42-503 at 152 lbs. I called General about the 42-503 to see what the spring rate was on that spring but person was having computer issue at the time so I didn't get a number from them. I am calling them back later today to get an update. If the 152lb number is correct, that would definetley be a stiffer spring which could have something to do with the lower free arch number.

[shelbymann1970]

So circling back around to the OP's question, can anyone provide some specs on the differences between the original Shelby springs and the replacement 42-437 Mustang springs i.e. difference in length of 2nd and 3rd leaf that was mentioned? Is there a difference in the length from the pin forward or the pin rearward on those 2 leafs compared to the Mustang spring? Length of the bottom flan leaf? Bob, your measurements of of 6 1/4 to 6 9/16 would put them in the ballpark of the 6 1/4 spec'd from Virginia and the 6 5/8 spec'd from NPD/Eaton on the 42-437 Improved Handling spring . Most of the vendors with the Improved Handling 42-437 springs quote a rate of 114 lbs. One vendor has quoted the rate on the 42-503 at 152 lbs. I called General about the 42-503 to see what the spring rate was on that spring but person was having computer issue at the time so I didn't get a number from them. I am calling them back later today to get an update. If the 152lb number is correct, that would definetley be a stiffer spring which could have something to do with the lower free arch number.

Mine are buried in my attic. When I get a chance i'll pull them out but mine are for a GT350. I will not assume the same leaf lengths as a GT500. Bob?

[Bob Gaines]

So circling back around to the OP's question, can anyone provide some specs on the differences between the original Shelby springs and the replacement 42-437 Mustang springs i.e. difference in length of 2nd and 3rd leaf that was mentioned? Is there a difference in the length from the pin forward or the pin rearward on those 2 leafs compared to the Mustang spring? Length of the bottom flan leaf? Bob, your measurements of of 6 1/4 to 6 9/16 would put them in the ballpark of the 6 1/4 spec'd from Virginia and the 6 5/8 spec'd from NPD/Eaton on the 42-437 Improved Handling spring . Most of the vendors with the Improved Handling 42-437 springs quote a rate of 114 lbs. One vendor has quoted the rate on the 42-503 at 152 lbs. I called General about the 42-503 to see what the spring rate was on that spring but person was having computer issue at the time so I didn't get a number from them. I am calling them back later today to get an update. If the 152lb number is correct, that would definetley be a stiffer spring which could have something to do with the lower free arch number.

Mine are buried in my attic. When I get a chance i'll pull them out but mine are for a GT350. I will not assume the same leaf lengths as a GT500. Bob?

Same same Gary.

[Dennis Y]

General also quotes a spring rate of 152 for the 42-503.

[shelbymann1970]

the 3 "Shelby" leafs are 20", 33.5" and 44.5" approx as I'm up in an attic by myself trying to measure end to end with a tape measure on an arc.

[Dennis Y]

Found this write-up from the Boss Registry. Goes back a ways but provides some interesting information. The S9MS 5560A that is on Gary's spring matches what is shown on the chart for the Shelbys. Interesting that the spring rate is lower on the Shelby yet the load rate is higher than that of the Boss. Shame that free arch is not noted but as was mentioned, they used different parameters back then. If you use the same formula as shown for the Boss spring, the Shelby's 750/135 would mean a free arch of approximately 5.5 inches which is still short of the numbers Bob came up with but definitely better than the 3.62 for the Boss. I am going to try and enlarge the engineering drawing at work on Monday and still have it somewhat readable. We'll see what happens.

https://www.boss302.com/spring.php