Brake servo sourcing — community notes
This page summarises a PistonHeads forum discussion about sourcing the brake servo fitted to the TVR Cerbera, Griffith and Chimaera (and shared in spirit with several S Series cars). It is intended as a quick orientation when planning a servo replacement; see also Brake servo TRW PSA328 — cross-reference and donor vehicles and the brake servo replacement guide.
The servo TVR used
Section titled “The servo TVR used”The servo factory-fitted to the Cerbera, Griffith and Chimaera is the TRW PSA 328, originally a Ford Fiesta Mk3 component. It carries a number of part numbers depending on supplier and era.
| Brand | Part number |
|---|---|
| TRW | PSA 328 |
| Bosch | 0 986 485 090 |
| Ford | 6186400 |
| Ford | 89FB2005BC |
All of the above refer to the same unit. The Ford part has been discontinued for many years, and stock at TVR specialists has steadily dried up. Reproduction servos sold through online marketplaces have a poor reputation on the forums and are not recommended for a safety-critical component.
Why people look at alternatives
Section titled “Why people look at alternatives”With new-old-stock units increasingly hard to find, owners have considered fitting a servo from another car. The usual approach is to use a unit with a remote fluid reservoir piped to the master cylinder, which is common on more modern vehicles and gets around the rather specific reservoir position on the TVR.
Any substitute needs to match the original closely enough to bolt in and to give correct pedal feel and travel. The forum consensus is that the following dimensions are the ones that matter:
| Measurement | Why it matters |
|---|---|
| Diaphragm diameter | Sets the assistance ratio and overall servo size in the engine bay |
| Mounting stud pattern | TVR uses an offset four-stud arrangement (two closer to centre, two further out) |
| Pushrod length to brake pedal | Determines pedal height and free play; the clevis end can be remade if the thread differs |
| Pushrod-to-master-cylinder gap | Critical for correct master cylinder operation — too little and the brakes can bind, too much and pedal travel is lost |
Practical advice from the thread
Section titled “Practical advice from the thread”- If you find a genuine TRW or Bosch unit at a sensible price, grab it — they are getting rarer every year.
- Treat unbranded reproductions with suspicion; the brake servo is not a place to save money.
- For an alternative donor servo, measure the original carefully before ordering anything. A matching diaphragm diameter and stud pattern is the starting point; the pushrod can often be adapted.
- Remote-reservoir conversions are feasible but mean planning where the reservoir and feed pipe will live in the TVR engine bay.
Safety note
Section titled “Safety note”The brake servo is a critical safety component. Any substitute must give correct pedal feel, full master cylinder travel and the correct pushrod gap, and must be securely mounted. If in doubt, have the installation checked by a TVR specialist before driving the car.
Compiled from a PistonHeads forum discussion — always verify part numbers and dimensions against your own car before purchasing.