A recent milestone for the restoration of the 1963 FHC is the completion of the independent rear suspension aka the IRS. The IRS on the Etype was an improvement over the solid axle design of the XK-120/140/150 series cars. It is “independent” in the sense that each wheel can respond to suspension movements independently from the other one. Theoretically this will allow the car to corner better, especially on uneven pavement surfaces. Here is a 3D cutaway drawing that was penned in 1961 for Autocar magazine.
The driven halfshaft, over top of a rigid link, forms a parallelogram that allows the hub/roadwheel assembly to move up and down with minimal camber change. Twin spring/damper units control the vertical movement, as well as supporting the weight of the car. A trailing arm that attaches forward under the body serves to locate the assembly in the fore/aft position. A small anti-sway bar is used to increase the roll stiffness.
Another feature of the design was the use of disc brakes mounted “inboard” just adjacent to the differential. This design reduces unsprung weight at the wheels, although making work on the brakes much more difficult from an access standpoint.
Finally, not visible in the cutaway drawing, was a mechanical limited slip device in the differential that allows power to be delivered to a single roadwheel if the other one is slipping for any reason.
So at the end of the day, a rather complex sub-assembly, certainly not cheap to build, but adding much cachet to the Etype’s sporting image when released in 1961.
Here is a photo of the exploded parts drawing in the SPC.
As you can see, there are quite a few small parts involved.
Last year, I had Dick Maury at Coventry West rebuild the differential. Last winter, I started to restore the entire IRS as a good cold weather project in my heated shop. This job was not on the hurry up list and it has taken me a year to get done. I will not attempt to discuss the details of the assembly work. It is daunting but a doable task for a home mechanic. If you need some good on-line technical assistance, I would recommend this web page. This fellow has really gone above and beyond in documenting the various steps required.
I would also point out that my effort included the installation of new stock springs and SNG Barratt’s new line of reproduction dampers. So in effect, I went with the original suspension characteristics that this Etype was born with, with no attempt to make any “upgrades”. One exception, visible, is that I installed a remote bleeder kit. All bearings, u-joints, trailing arm bushings, wheel spline drives, brake discs, brake pads, and brake pistons are new. I also had to source a new bracket to hold the mechansim that activates the parking brakes, as the original had gone missing from my box of parts. I set the camber per the workshop manual to -3/4 degrees.
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