TVR brake servo replacement (S Series, Griffith, Chimaera, Cerbera)
This guide covers replacing the brake servo and master cylinder on TVR’s wedge-era and ‘big cat’ cars — S Series, Griffith, Chimaera and Cerbera. Like most of the running gear, the braking system is a parts-bin job built around Ford Fiesta Mk2/Mk3 components, which is good news for parts availability but does mean later cars use a different layout to early S Series cars.
⚠️ Brakes are safety-critical. Torque fasteners to the manufacturer’s spec, use new clevis pins and split pins, bleed thoroughly and pressure-test the system before driving. If you’re not confident, hand the job to a specialist.
Which setup do I have?
Section titled “Which setup do I have?”There are two distinct factory arrangements, and many S Series cars have been converted to the later layout when the original Saab master cylinder became unobtainable.
| Feature | Early S Series | Later (Griffith / Chimaera / Cerbera) |
|---|---|---|
| Servo | Ford Fiesta Mk3 | Ford Fiesta Mk3 (rotated 90°) |
| Master cylinder | Saab, remote reservoir | Ford Fiesta Mk3, integral reservoir |
| Reservoir | Bulkhead-mounted, two rubber feed pipes | Bolted to master cylinder |
| Master cyl. bolt pattern | Saab | 90° offset from Saab |
On early S cars the remote reservoir feeds the master cylinder via two rubber tubes that run above the right-hand exhaust manifold — these must be heat-shielded or they perish and weep fluid onto a hot pipe.
Servo part numbers
Section titled “Servo part numbers”The same Ford Fiesta Mk2/Mk3 servo (1983–1997) is used across the range. Common cross-references:
| Supplier | Part number |
|---|---|
| TRW | PSA328 |
| Bosch | 0 986 485 090 |
| Ford | 6186400 |
| Ford | 89FB2005BC |
| Girling | 4110328 |
See also the dedicated brake servo PSA328 cross-reference page for donor vehicles.
Master cylinder
Section titled “Master cylinder”Use the Ford Fiesta XR2 or 1.6i Ghia master cylinder. Two bore sizes were fitted from the factory — TVR needs the larger 22 mm bore (this is what the 4.2 Cerbera was set up for, and it’s what the rest of the range uses too). Note that the mounting holes are oriented 90° away from the Saab item, which is why a conversion needs the bulkhead redrilling.
Reservoir options
Section titled “Reservoir options”| Application | Reservoir |
|---|---|
| Early S (original) | Saab 74470810 — no longer available new |
| Later cars / S conversion | Ford Fiesta Mk3 integral |
| Alternative | Ford Escort Mk2 reservoir |
The Saab low-fluid warning sender in the reservoir cap can usually be transferred onto the Ford reservoir, or you can source a Ford loom connector and use the Ford sender instead.
Common failure mode
Section titled “Common failure mode”Because the later servo sits with its underside exposed in the engine bay, road dirt and water collect on it and the steel can corrode through. In extreme cases the diaphragm perforates or the two halves of the servo can separate under braking — inspect underneath the servo at every service and replace if you find rust scabs or pinholes.
Converting an early S to the Ford master cylinder
Section titled “Converting an early S to the Ford master cylinder”Because the Ford master cylinder is rotated 90° relative to the Saab one, four new bulkhead holes are required. The old and new holes overlap by only a few millimetres, which makes this the fiddly part of the job.
Bulkhead hole positions
Section titled “Bulkhead hole positions”| Hole pair | Original spacing (Saab) | New spacing (Ford) | Direction to move |
|---|---|---|---|
| First diametric pair | 102 mm | 90 mm | Inward (closer together) |
| Second diametric pair | 90 mm | 102 mm | Outward (further apart) |
| Hole diameter | — | 8 mm | — |
The centre-to-centre offset between an old hole and its new neighbour is only 6 mm, so the new hole centre sits just 2 mm clear of the old hole’s edge.
If your existing holes have been opened up to 10 mm (very common), the new centre will land right on the old edge. The practical fix is to file the inner holes outward by 6 mm and the outer holes inward by 6 mm to form ovals, then bolt the new servo through with large penny washers and a smear of sealant to keep the bulkhead watertight.
Clevis pin and pedal
Section titled “Clevis pin and pedal”| Item | Old (Saab/early) | New (Ford) |
|---|---|---|
| Clevis pin diameter | 8 mm | 10 mm |
| Brake pedal hole | 8 mm | Drill out to 10 mm |
Brake pipework
Section titled “Brake pipework”The outlet ports on the Ford master cylinder sit roughly 45° further around than on the Saab unit, so the ends of the two front brake pipes need to be carefully re-formed (or remade) to line up. Don’t crank tight bends into existing pipe — if in doubt, make up new ones from Kunifer.
Recommended fitting sequence
Section titled “Recommended fitting sequence”- Paint the new master cylinder before fitting. Pattern replacements rust very quickly in a TVR engine bay.
- Disconnect the steering column at the upper UJ for vastly better access to the bulkhead.
- Vacuum the brake fluid out of the reservoir before disconnecting any pipes — much less mess and no fluid running down painted panels.
- Fit the servo, master cylinder and reservoir; reconnect pipework; reconnect the clevis to the brake pedal with a new split pin.
- Bleed the brakes starting from the nearside rear (furthest from the master cylinder), then offside rear, nearside front, offside front. Pressure-bleed if you can — the Fiesta master cylinder can be reluctant to self-prime.
- With the engine off, pump the pedal until it goes hard, then start the engine — the pedal should drop noticeably as the servo pulls vacuum. Check every joint for weeps before road testing gently.
Related pages
Section titled “Related pages”- TVR brake servo cross-reference (Cerbera, Griffith, Chimaera)
- Brake servo TRW PSA328 — donor vehicles
- Cerbera torque settings
Compiled from a community workshop guide by Andrew C (andrewc.org.uk) — always verify against the original source and your own car before relying on it.