Saturday, 5 November 2011


A few "sub projects" are required to keep me busy whilst the engine bits are away at the machine shop and the rear springs seemed a likely first candidate.
The easy route would have been to simply purchase a new pair for around £150 but that seemed like a bit of cop out.  The car as purchased sat very nice and square, if a little low on its old springs.  Closer inspection on dismantling showed them to be almost certainly original, with stamped Jaguar part numbers, beautifully made with tapers in both planes at the ends of each leaf.  One side still had its leather gaiter in place.

Research into bringing them back to their original condition throws up some interesting information.  Over time, the steel starts to lose its temper (spring) causing a change in "set" - they sag.  The spring rate is mainly determined by the number and dimensions of the leaves, but also to a lesser extent the quality of steel and the tempering procedure.  They need to be set back to their original shape and re-tempered to put the spring back in.  Further digging turns up Brost Forge, a long established business in North London with an outstanding reputation.  They specialise in spring re-tempering and have the original manufacturers specs on a wide range of leaf springs.  The cost including new bushes is around twice that of a new pair from goodness knows where, but I guess that's the premium for originality.

They come back looking a little more curved and covered in a nasty sticky tar like substance. I put them on the lonely shelf for finished bits and give them a disdainful glance every time I pass. After a few days, my resolve to consider them finished weakens and I dismantle them and send them to my friend Max to blast off the gunge.

Further trawling of the Internet and the recollection of a conversation with an XK owning acquaintance about the cure for squeaky springs results in the following, totally ridiculous, massively time consuming, very satisfying process.
Each leaf is linished on both sides, then sanded smooth (allow on average half an hour per leaf).  Clean thoroughly and apply two thin coats of Acrylic paint.  Next you need a large sheet of High Density Polyethylene (HDPE) cut into strips to fit between each leaf.  Rub copperslip into all surfaces and re-assemble.  You have now virtually eliminated friction between the leaves making for a super smooth and silent action.  As the spring pack height has increased by up to 6mm a new centre fixing bolt and new guide brackets are made to measure.

Final job is to carefully record all dimensions and send of to Wefco in Yatton to have a new set of leather gaiters made.

Dismantled after tempering.   Assembled spring had been
 "painted" or possibly dipped in some nasty tar like substance

After initial shot blasting - Original Jaguar part numbers
clearly visible but different although actual leaves are identical

After linishing, final smooth finish created with sander.
Very time consuming job but quite satisfying

Leaves painted with thin coat of acylic matt black.
High Density Polyethylene 1mm strips between leaves.
Very thin coating of copperslip rubbed into all surfaces before
final assembly.  New guide brackets made to accommodate
 additional thickness of HDPE inserts

Finally assembled and looking more like it should.
Just needs gaiters fitting - awaiting delivery from Wefco.
Shame to cover it up!

Detail showing nicely tapered ends of leaves.  HDPE can just be seen
between each leaf
So - one spring done and one to go!