TVR brake servo cross-reference (Cerbera, Griffith, Chimaera)
The brake servo (vacuum booster) fitted to the TVR Cerbera, Griffith and Chimaera — and commonly seen on the S Series — is a Ford-sourced unit shared with the Mk3 Fiesta. It has long been discontinued by Ford and stocks at TVR specialists are now thin, so this page gathers the part numbers and the key dimensions you’d need if substituting an alternative.
Information here is drawn from a PistonHeads Cerbera forum discussion (“servo options”). Treat it as a starting point for research, not a verified fitment list — always confirm against the unit on your own car before ordering.
Part number cross-reference
Section titled “Part number cross-reference”The same servo carries several manufacturer and supplier numbers. Any of the following should refer to the same physical unit:
| Brand / source | Part number | Notes |
|---|---|---|
| TRW | PSA 328 | Most commonly quoted reference |
| Bosch | 0 986 485 090 | Bosch service number |
| Ford | 6186400 | Ford part number |
| Ford | 89FB2005BC | Ford finis / casting reference |
| Donor vehicle | Ford Fiesta Mk3 | Original application |
Reproduction units have appeared from Far East suppliers (AliExpress and similar). Forum opinion on these is poor — quality is reportedly well below the original TRW/Bosch part, and given the servo’s safety-critical role they are not recommended.
Substituting a different servo
Section titled “Substituting a different servo”A workable alternative on cars where the original is unobtainable is to fit a different servo with a remote fluid reservoir piped to the master cylinder, as is normal practice on many modern vehicles. The main packaging issue is finding somewhere sensible for the reservoir to live, since the original setup is integrated.
Before committing to a substitute, measure the existing installation. The dimensions that matter are:
| Dimension | Why it matters |
|---|---|
| Diaphragm diameter | Determines assist (boost) ratio; wrong size changes pedal feel and effort |
| Mounting stud pattern | Cerbera/Griffith/Chimaera uses an offset four-stud pattern (two studs closer to centre, two further out) — the bulkhead must match or be re-drilled |
| Pushrod length (servo to pedal) | Sets pedal height and travel; the clevis end can usually be re-threaded, so overall length is the key figure |
| Pushrod-to-master-cylinder gap | Critical — too much gap loses pedal travel, too little can hold the master cylinder partially applied and overheat/drag the brakes |
Cautions
Section titled “Cautions”The brake servo is a safety-critical component. If you fit anything other than a like-for-like replacement:
- Bench-test the master cylinder and servo before road use.
- Verify the pushrod-to-master-cylinder clearance to the master cylinder manufacturer’s specification — do not guess.
- Bleed the system thoroughly and check for any tendency of the brakes to bind after release.
- If in any doubt, have the work checked by a competent brake specialist.
See also the related page on brake servo and master cylinder replacement for the practical removal and refit procedure.
Compiled from a PistonHeads Cerbera forum thread (“servo options”) — always verify part numbers and fitment against your own car before ordering, and treat brake work as safety-critical.