Custom Sierra 4×4 Uprights

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I’ve started to make my own front uprights.

The CAD has taken a while, plus I have had to do some extra research into suspension geometry.

A lot of people seem to know about Ackermann Geometry, but the well known image of the two lines intersecting at the rear axle does not take into account caster, camber or steering axis inclination.

Ackermann Angle

In the above shot there is zero steering axis inclination and zero caster. (Let’s ignore camber for now)

Caster

Caster Angle

Steering Axis Inclination

Steering Axis Inclination

Bump Steer

The ‘classic’ ackermann angle aerial view also doesn’t mention that the steering rack ball joint needs to proportionally at the same height as the track rod end, ball joint to avoid bump steer.

Bump Steer

 

Realistically, when viewed from above you would be able to see both the upper and lower A Arm ball joints simultaneously.

Once any of the above are introduced, Ackermann Geometry becomes an artform. The intersection point at the rear axle would only be at the centre of the axle at normal ride height with zero bounce or body roll. Therefore, I have made all of my calculation for a stationary vehicle. ‘True’ Ackermann geometry can only exist whilst the vehicle is not moving.

Ackermann Angle
Ackermann Angle

I intend to use 5 stud Granada 4×4 front wheel flanges and Sierra Rear Hub Carriers. Ignoring the different number of splines, the front wheel flanges are very similar to the rear. However, to make the front flanges correctly fit the rear hub carriers I will need to remove a little material in the lathe. There is a small lip that fits inside a rubber grease seal. The seals are different from front to rear.

My only worry is the 4×4 Granada 5 stud wheel flanges are ultra rare. I’ve been building this car for 3 years and the ones I have are the only ones that have ever been listed on ebay. Specialist breakers laugh when you ask whether they have any. The local Ford dealer look them up on an old microfiche and said they couldn’t find a part number. If I knacker them, I will have to get some scratch built.

Sierra 4x4 Custom Uprights

The calliper flange will be machined away. A new flange will be added directly to the new upright. The plan is to use a combination of lightweight after-market callipers and Audi two piece discs. The above shot shows how I’d construct them using steel. I would use a different design for aluminium.

I have just bought a milling machine, so I haven’t decided whether I will machine the new uprights from single blocks of T6 aluminium or construct them in steel from several pieces like at the rear.

If I were to go the aluminium route, I could go for some after-market aluminium hub carriers or I could integrate them into the uprights.

Sierra Hub Carriers

It seems crazy to spend the best part of £200 on custom hubs then instantly cut them up so at the moment I leaning towards steel.

That’s unless some cheap aluminium turns up.

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