Four different sets of rear springs have been used throughout the production of the Jaguar XK. All springs were of the semi-elliptical type and consisted of 7 bended leaves, the strength and thickness of which varied over the years.

Typical XK rear suspension spring

1. XK 120

1.1. The XK 120 started with rear suspension leaf springs (Jaguar part number C3661) which consisted of 3 leaves 7/32″ thick and 4 leaves 3/16″ thick.

1.2. With the introduction of the XK 120 Special Equipment (SE or MC) models the road springs became stiffer by increasing the number of 7/32″ thick leaves from 3 to 5 and reducing the 3/16″ thick leaves from 4 to 2. This second version leaf spring was now coded C5721.

1.3. This new spring became the standard for all XK120s by November 1952 from chassis numbers 661040/673320 and 669003/680397 onwards till the end of production.

2. XK140

2.1. All XK140s had the same set of springs which was in fact the continued XK120 SE version with code C5721.

3. XK150

3.1. The XK150 received an updated spring coded C13006 which was basically the continued XK120/XK140 set of leaf springs (C5721) but with a different mounting to the chassis with new rubber bushes and also rubber buttons at the end of the springs.

3.2. Because of the increasing kerb weight of the XK150 July 1958 saw the introduction of the fourth version of rear suspension leaf springs coded C14476 . The differences were twofold: one of the 7/32″ thick leaves was replaced by a stiffer ¼“ thick leaf and a nylon sheet (Jaguar name: “Interleaf”) was placed between the top and the second leaf. This meant that next to the ¼“ thick leaf there were now only 4 leaves 7/32″ thick and 2 leaves 3/16″ thick. This set of springs was interchangeable with the previous version C13006.

Leaf spring composition:

 

XK 120 (SE) and XK 140		XK 150 (S)
C3661	C5721	C13006	C14476
			1 leaf ¼“ thick
3 leaves 7/32” thick	5 leaves 7/32” thick	5 leaves 7/32” thick	4 leaves 7/32” thick
4 leaves 3/16” thick	2 leaves 3/16” thick	2 leaves 3/16” thick	2 leaves 3/16” thick

External markings:

Next to the part number and date code the manufacturers name and logo is stamped on the lower leaf spring. The company logo shows the words “Registered Trade Mark” and a horse head, followed by the name Wm E. Cary Ltd.

The three examples below show a XK 120 spring from 1953, a XK 140 spring from 1954 and a (original) replacement leaf for the XK 120/140 from 1962.

  

Replacement springs

As the leaf springs lose their strength over the years the car body drops sometimes up to 2 inches. But also leafs may break after some decades. Replacements are available and can be used without too many problems.

The finish of most replacement springs is not up to the same level as the original ones: e.g. no tapered ends of the leaves and many burrs. In addition the brackets that hold the leaf package together sometimes have some “play” which is not the case with the original springs. It may be worthwhile to disassemble these new springs and rework the spring ends and use new brackets with a better fit.

 Bracket holding leaves

As the original product code and manufacturers logo is stamped in the lower leaf and this leaf has the lowest contribution to the overall stiffness of the complete spring, it is a nice idea to re-use that leaf in the new spring assembly. It requires to remove the aforementioned brackets that hold the leaves together which allows you at the same time to add the nylon “Interleaves” between the top and second leaf (or even more if you want). Any good quality nylon 0.3 to 0.5 mm thick sheet will do. Other similar strong and durable or wear-resistant plastic can be used as well.

Manufacturer of original Jaguar leaf springs.

The original supplier of the leaf springs is the company William E. Cary Ltd of Manchester. This company supplied to various car manufacturers, not only the leaf springs but also torsion springs and other stampings. See also the adds below.

   Advertisements of 1951 and 1954