1967 GT 350 REAR LEAF SPRING RATE

[CooperShelby@14]

I currently am restoring a 1967 Shelby GT 350, I have been trying to find out the correct rear leaf spring rates, various vendors sell the springs, but do not mention spring rates, they mention 4 leaf, or 4 1/2, they can drop your car 1" etc, I would like to keep my car as stock as possible, the only vendor that I found that said anything about spring rates was "Cobra Automotive" standard spring was 4 1/2 leaf 120 lb, does this sound correct?

[sg66]

4 leaf, see page 32 of 77 https://springresearch.org/pdf/volume_17.pdf

Virginia Mustang used to sell springs that looked like the originals with the rounded ends. I forget the name of the place they were sourced from but maybe Brant will see this and remember, it wasn't Eaton. I spoke with the manufacturer and they were built to 42-437 spec which was the most generic. I have a friend who owns a spring shop and de-arched them for me.

[JD]

See attached, this might help some... two versions - AM early vs AR later. The same springs were used on the GT350 and the GT 500's.

A section of one of the Ford Master Parts Catalog (MPC).  I think you need to be looking at the "Competition Handling" listings. Reposted with those listings highlighted.

Note the early version had the spring band strap with a more Round hole and the later with the square hole.  Also, ends of spring leaves are not square but a kind-of rounded. 

There are a number of threads on this site regarding the finishes on all of the different components that make up these rear spring assemblies as well.

[Bob Gaines]

I currently am restoring a 1967 Shelby GT 350, I have been trying to find out the correct rear leaf spring rates, various vendors sell the springs, but do not mention spring rates, they mention 4 leaf, or 4 1/2, they can drop your car 1" etc, I would like to keep my car as stock as possible, the only vendor that I found that said anything about spring rates was "Cobra Automotive" standard spring was 4 1/2 leaf 120 lb, does this sound correct?

Keeping your 67 GT350 as stock as possible is a multi faceted statement. You can have a part that functions like stock but does not look like what came on the car from the factory. Cobra Automotive sells mainly track oriented performance parts. The pictures online confirm a more squared off end of the spring leaf's different then what came on the car. The Detroit Eaton springs look the factory part in shape however they sit high and have to be de arched somewhat to comply with factory height. They also come painted with thick black paint that is a pain to be stripped and the band clamps have to be replaced to match factory but they are available. Since Virginia Mustang retired Detroit Eaton (not the same Eaton CO that made springs for Ford) is the go to replacement. Typically the bottom marked date coded AM or AR plate is repurposed onto the new springs for historical reasons.     

[Road Reptile]

Hi to all,
Just to add to the excellent responces from Bob and J.D. If you look on the chart provided the initial build had lighter rated springs (AM stamping 625 lb.)After mid November they were AR stamped and rated 665 lb. This should give you proper info to get replacements if you really need them. Originals can be rebuilt and often are.
May suggest talking to a spring shop as a next step....wouldn't want the car to end up looking like a 4x4.
Regards R.R.

[TA Coupe]

I don't know where the chart above is geting their weight ratings from, but 600 plus pound Springs would be for the front, not the Rear. I have some narrow leaf Trans Am Springs rated at 210 on my car and you can barely push down on the back end. Here's an example of leaf springs from Eaton. 114 and 135lb rating.

Product Lookup by vehicle https://share.google/mZA7FMUG0y4ekEnM1

       Roy

[Road Reptile]

Hi again,
The Ford spring rating is representing total capacity. The Eaton chart shows lbs. Per inch thus the difference. Can be confusing yet it is still done this way by Ford.
Hope this explains it simply.
R.R.

[vtgt500]

I'm doing a build now with new leaf springs. The leaves were shear cut to length with heavy burrs.  Also, the spring pack was dip painted, ugh. Usually within a year rust bleeds from between the leaves and looks like crap.  My solution was to disassemble. Media blast to bright, clean metal. File deburr ends.  Prime and paint with Polane. Lathe turn new bushings from black Delrin. Lathe polish, heavy wall, stainless hyd tubing for slip fit, sleeves within the bushings.  Assemble bushings and sleeves with silicon grease.  Obviously, lube the anti squeak pads too. The ride difference is very noticeably improved on all my builds.

[FL SAAC]

I'm doing a build now with new leaf springs. The leaves were shear cut to length with heavy burrs.  Also, the spring pack was dip painted, ugh. Usually within a year rust bleeds from between the leaves and looks like crap.  My solution was to disassemble. Media blast to bright, clean metal. File deburr ends.  Prime and paint with Polane. Lathe turn new bushings from black Delrin. Lathe polish, heavy wall, stainless hyd tubing for slip fit, sleeves within the bushings.  Assemble bushings and sleeves with silicon grease.  Obviously, lube the anti squeak pads too. The ride difference is very noticeably improved on all my builds.

That's quite a thorough and methodical process I must say. Great job

[Bob Gaines]

I'm doing a build now with new leaf springs. The leaves were shear cut to length with heavy burrs.  Also, the spring pack was dip painted, ugh. Usually within a year rust bleeds from between the leaves and looks like crap.  My solution was to disassemble. Media blast to bright, clean metal. File deburr ends.  Prime and paint with Polane. Lathe turn new bushings from black Delrin. Lathe polish, heavy wall, stainless hyd tubing for slip fit, sleeves within the bushings.  Assemble bushings and sleeves with silicon grease.  Obviously, lube the anti squeak pads too. The ride difference is very noticeably improved on all my builds.

For clarification this a great description of how to modify a rear leaf and make it better then stock. It is a great contribution in that context. With that said for those reading who may be new to trying to keep their car as stock as possible like the original poster of this thread intended, those techniques although good for a modification are not what you want. 

[vtgt500]

I, and obviously most others truly appreciate concours as a benchmark for originality. My'68 was an example of period hot rodding. Purchased in '77 sported, Hi Jackers, Thrush side pipes, headers, Lakewood traction bars, Super Shifter, big fat tires and everything.  Today, is more subdued, but a hell of a lot faster.  On the upside, the marginally used, original tires, wheels, hubcaps, steering wheel, and emission controls were squirreled away.

[sg66]

Found the place Brant and VA Mustang used to source correct looking springs from. Worth a call to see who they supply to now https://www.johnrspring.com/leafsprings.html