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Modification Modification
Car: Ford | Fiesta | CX (Mk3) | All Derivatives | Hatchback

Mondeo Mk2 Servo

I find standard Mk3 Fiesta brakes lacking in terms of both power and feel. Stepping in to a Mk3 after driving a more modern car can now take some getting used to, especially if larger than standard Calipers are fitted. Mechanically, RHD cars are at a disadvantage due to the link-bar arrangement which introduces further pedal movement due to its bushes which have some degree of tolerance. LHD models have a direct Pedal-to-Servo Arrangement like most modern cars.

There are several options which I identified for improving pedal feel with larger capacity brakes (e.g. Cosworth or ST170:

Of all these options replacement of the Servo and MC (Master Cylinder) will represent the largest improvement to pedal feel, and an increase in Master Cylinder size will permit the fitment of larger Calipers without the usual resultant sacrifice of increased pedal travel.

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The optimum Size of MC bore is calculated based on variables including Pedal Ratio, Brake calliper size, Brake Caliper leverage, Dynamic Axle weight and more. The non-scientific method is to fit a MC from a similar car to that which your modified brakes have come from. In my case, I was using Cosworth brakes which are identical in piston volume to the Mondeo V6.

Master Cylinder and Servo Information

FWD Ford models manufactured between the 80's late 00's tend to feature a similar arrangement for mounting the Servo and Master Cylinder which makes adapting another servo a reasonably straight-forward task. There are many options to choose from, including Escorts, Ka's, and later Fiestas.

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Mk3 Fiestas come with several Master Cylinder sizes:

  • 20.6mm - Mk3 non-sport models without ABS
  • 22.22mm - Mk3 Sport models and ABS equipped vehicles;
  • 22.Xmm - Mk3.5 non-sport models without ABS;
  • 23.80mm - Mk3.5 Sport models and ABS equipped vehicles.

The Mk5 Escort Servo/Master Cylinder has been used for some time when fitting larger Calipers but I wanted to improve on that and fit something newer. I chose to replace my MC with much larger 2001 Mk2 Mondeo Servo and non-ABS (4 outlet) 25mm Alloy MC taken from scrapped Mondeo (I also cut the Monedo brake pipes to leave the fittings in the MC). This is improved from the earlier Mk1 cast iron master cylinder. This setup will provide additional pedal assistance and increased capacity to support larger brakes.

Mounting the Master Cylinder and Servo

Start by removing the existing Master Cylinder and Servo and draining the system of fluid.

Mk3.5 Ghia Freshen Up Mk3.5 Ghia Freshen Up

The Mondeo Servo is considerably larger than the Mk3 (right0 and just clears the Fuel Pressure Regulator on my CVH-type Inlet Manifold.
Please take measurements of your chosen servo before work commences to ensure it will fit your particular Engine bay.

Mk3.5 Ghia Freshen Up Mk3.5 Ghia Freshen Up

Ford change the mounting bolt pattern depending on the vehicle and this is the first area requiring modification. I made a template of the Mondeo bolt pattern and transferred this to my Fiesta mounting bracket (left), then drilled the new bolt pattern using a 10mm bit

If mounting to a Mk3.5 with PAS, ensure that the (flimsy!) reinforcement bracket is also re-drilled to suit (far left – see the second bracket behind the servo bracket).

Mk3.5 Ghia Freshen Up

The Mondeo Servo shares the same pivot mount diameter and split pin arrangement as the Fiesta, I find it easier to mount the pivot bush and split pin first (right), then pull the entire assembly forward until the Servo dowels can be inserted into the Fiesta mounting bracket.

Once mounted, tighten the four mounting nuts and check pedal operation.

Plumbing

Mk3.5 Ghia Freshen Up

The Fiesta uses M10 fittings in the MC, but the Mondeo uses M10 for one circuit and M13 for the other (left), meaning the Fiesta lines must be converted. The OEM lines are made from a material which is much harder then the Kunifer 'bunding' tube available from most Automotive outlets, and I found it nearly impossible to re-flare two of the Fiesta pipes to add the Mondeo M13 fittings I'd got with the MC.

Mk3.5 Ghia Freshen Up

I ended up making new Brake Pipes for one of the front corners to add the M13 Male fitting, and modifying the opposite side rear corner to add the same. The rear brake lines on the Mk3 have couplings down in the steering rack area, which means (thankfully!) the entire line doesn't require replacing, only the MC to connector section!

I carefully bent all pipes, including the Mk3 lines I didn't modify, and used clips kept from the Mondeo to tidy the installation (right).

Mk3.5 Ghia Freshen Up

The image left shows one of the new front pipes in the wheelhouse area, the original Fiesta/Mondeo fittings can be re-used providing they are in good condition.

Mk3.5 Ghia Freshen Up

I mounted the bias valves in the rear wheelarches (right)at the end of the brake pipes, this is beacause 1 bank of the Master Cylinder outlets are different sizes to the M10 threads in the bias valves.

Fluid Reservoir

Mk3.5 Ghia Freshen Up

The Mondeo MC Reservoir features exactly the same thread and cap diameter as the Mk3 meaning the Fiesta cap can be re-used. I checked the depth of the cap before fitting to ensure that the low fluid sensor would be operating within the correct fluid range - it was (left). The Mondeo sensor is integral with the Reservoir itself and features the same style 3 pin AMP connector as the Fiesta, it can be used providing enough slack is made available in the Fiesta loom.

Mk3.5 Ghia Freshen Up

The final modification is to blank off the Mondeo Hydraulic Clutch feed line. For this I used an old sawn-off M10 bolt (right). The Fiesta vaccum hose can be carefully rearranged to fit the Mondeo MC.

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Mk3.5 Ghia Freshen Up

Whilst the brake fluid was drained I took the opportunity to replace all of the brake hoses. Take note that post 95 brake calipers feature a convex seat where pre-95 are concave (left).

I fitted Mk5 Fiesta calipers to the car and so I fitted Mk5 hoses, front and rear. These are compatible with the Mk3 pipes have have the correct post-95 style fitting at the caliper end.

Bleeding the System

It can be tricky to bleed an entirely new, or opened, brake system. It is advised to 'Bench Bleed' the MC before fitment. This is performed by fitting the Reservoir and manually pumping the MC in a vice until fluid is ejected from each port. I do not perform a Bench-Bleed but instead use a pressurised bleeding system to great effect; these are available from most well-stocked Automotive outlets. I recommend the 'pump' variety rather than those which use air from the spare wheel.

© Mark Stewart, Friday 4th December 2009
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