Jun 042013

An almost standard replacement for the front suspension lower ball joint is the later sealed for life units. Less so is fitting a modern upper ball joint as it requires the case hardened wishbone to be machined to fit. If wear occurs in the upper ball joint, it is often as a result of wear in the wishbone’s ball joint seat, which becomes more oval in shape.

After a lot of deliberation, I opted to change the upper ball joints as well, using a kit from CMC as the local machine shop agreed to do the necessary milling of the wishbones.

I was less convinced of their ability when the kit was taken round and thought it wise to seek someone else to do the work. The instructions suggest annealing by heating the wishbones to cherry red and allowing it to cool slowly. All the larger firms weren’t interested and the independent machinists were few and far between.

The components of the CMC ball joint kit, including the mystery small nylon washerIn my hour of need I turned to E-Type International Rescue – McLaren’s Skunk Work team. There was some bemusement as to why the kit contained a pack of 9 shims rather than machining the wishbones correctly.

Also the brevity of the instructions had not explained the need for a small nylon washer in the setup.

After a few discussions it was decided that a grease nipple inserted into the cover plate would protrude below the plate. So the kit included a nylon spacer and a similar depth of shims to allow for the depth of the nipple below the cover plate. Ideally the plate should have been designed accordingly rather than requiring shimming and therefore additional machining.

The wishbone was media blaster before profile milling to match the shape of the nylon ball joint cupThe ball joint bores were profile milled with a ball-ended tool around the circumference, progressively stepping down after each revolution until it had cut to the required parallel depth.

At which point the wishbones were machined to match the curvature of the green nylon ball joint cup by reducing the circumference with each step down.

I’m really pleased as I had precious little chance of fitting newer ball joints without their help. I now owe several loans of the car … once it’s finished!

The completed wishbone and new ball joint awaiting fitting of the circlip

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