Front Suspension – Part 1

Now the real excitement can begin as I get to attach the first components to my new chassis. Since for now, at least, I’m following the manual, the first step is to build up both corners of the front suspension. All the large components for this are supplied by AK, but you will also need 4 new ball joints (which I ordered from SNG Barratt), as well as the refurbished front hub (a topic for another blog post).

My first task was to dig through the large pile of bubble wrapped parts supplied by AK to find the top and bottom front wishbones for both sides. I will also need the four M10 x 75 bolts and nuts required to fasten the top ball joints in place and the pack of 1”1/4 x 5/8” washers (all AK supplied). Then I will need the two top and bottom fulcrum shafts from my donor parts pile and the new ball joints.

Parts required to assembly front right corner.

New Ball Joints

Before assembling anything onto the chassis, the new ball joints need to be installed into the bare wishbones. The top ball joints fit into a crevice, without any additional shims (this is different to the donor vehicle). They are secured in place by passing the supplied M10 x75 bolts through both the crevice and ball joint. These bolts are fastened in place with the pair of M10 washers and nuts. The ball joints and bolts fitted easily and there were no issues with excessive powder coating, so a nice simple job to get me started! 

Front top wishbones with new ball joints - not installed yet.

The bottom ball joint is secured in place with four ‘special bolts’ ordered from SNG. According to AK the actual dimensions of these bolts are 5/16” x 1”, although I did not verify this. To avoid these bolts coming lose I added some additional lock tight and spring washers. Whilst spring washers were used on my original donor vehicle, I have replaced these with new ones.

Components needed to install lower ball joint.

Ball joint assembled with M6 bolts for caster angle measurement installed.

Installing the Wishbones 

With the new top ball joints secured to the wishbones, they can now be fitted to the chassis using the clean fulcrum shafts from the donor vehicle. To ensure the caster angle of the front uprights is correct, the build manual suggests distributing the 1”1/4 x 5/8” washers placed between either side and in between the wishbone and the chassis. Starting with the top front wishbone, two washers are placed either side of the wishbone (same on both sides).

Front wishbone fitted to chassis. The first part which I fitted :D.

When inserting these fulcrum shafts I had no issues with excessive powder coat and the shafts slide in easily. I applied copper grease to the shafts at this stage, which in hindsight might have been a mistake as it makes this job a lot messier when it comes to removing the fulcrum shafts to redistribute the washers.

One thing I did notice was that after installing both top wishbones, and resting them along the center line of the chassis they did not align correctly. I queried this with Jon to ensure I had not already made a dreadful mistake, and he assured me this is normal. Although a little unsure, I will take his word for this is and move on.

Top front wishbones rotated inboard. Notice they do not line up along the chassis rail below

The bottom wishbones are then installed, bypassing the donor fulcrum shaft through the chassis and wishbone, whilst placing a set number of washers between the wishbone and chassis. Since the number and their location affects the angle, AK suggests the following initial order.

• bottom right wishbone, place 3 washers to the front and 1 to the rear.
• bottom left wishbone, place 4 to the front and none to the rear.

Bottom wishbone installed and supported on a trolley jack.

With the bottom fulcrum shafts installed, it was apparent that my donor shafts were a little too long. The build manual states that the length of the fulcrum shaft is dependent on the age of your donor vehicle. To compensate for this, I placed 2 additional M22 washers at the head end of the shaft to shift the shaft’s position.

Fulcrum shaft too long, before adding additional washers.

With both top and bottom wishbones installed, the next step is to secure the upright to the ball joint. The easiest way I found to achieve this was to raise the bottom wishbone with a trolley jack and whilst it was being supported, secure the bottom ball joint in place. Then the top wishbone can be rotated into place and it’s ball joint loosely attached to the upright. 

Assembled front corner. Spirit level used to ensure wishbones are level.

Setting the Caster Angle

Now comes the setting up of the caster angle. After reading other cobra builder blogs, this job appears to be either very quick or a time-consuming nightmare. The first challenge is to level the chassis by altering the location and height of the four jack stands.

Then a pair of M6 bolts (lower bolt is packed with washers) are fastened into the upright. The caster angle is then measured against these two bolts, with a target of between 6 and 8 degrees. The further challenge is to ensure that the angle is the same on both sides.

To measure the angle between the two M6 bolts, AK supply a paper gauge and suggest using this with a plumb line. I had two concerns with this approach, firstly how straight was the edge of the paper now and after I have used it a few times, and how accurately can I secure the plump line to the central mark on a thin piece of paper. I, therefore, choose to use an application downloaded on my mobile.

The angle of the upright is then altered by redistributing the number of washer’s front to back on each wishbone. This is certainly a trial and error process but didn’t actually take that long. In the end, I had the following washer distribution and an angle of 7 degrees on both sides.

• Left top: 0 to the front and 2 to the rear
• Left bottom: 3 to the front and 1 to the rear
• Right top: 2 to the front and 0 to the rear
• Right bottom: 1 to the front and 3 to the rear

With the wishbones installed, the next step is to rebuild the front hubs and finish off the front suspension.