3D-printed polyurethane rear diff bushes (Cerbera)
This page covers a DIY approach to replacing the rear differential mount bushes on a TVR Cerbera using polyurethane cast into 3D-printed PLA moulds. It documents a second attempt at the process, where three usable bushes were produced and fitted to the car along with the diff itself.
This is an experimental, owner-engineered repair rather than a manufacturer-approved procedure. Diff and suspension bushes are safety-related — if you copy this approach, verify materials, hardness (Shore A) and dimensions against the originals, and inspect regularly.
What’s being made
Section titled “What’s being made”The Cerbera rear differential is mounted to the chassis through rubber-bonded bushes. When the rubber perishes or the bonds fail, the diff moves under load — causing clonks, driveline shunt and uneven tyre wear. Aftermarket polyurethane replacements exist, but they can also be cast at home if you have the mould geometry.
The approach here:
- Model the bush in CAD, then design a two-part (or multi-part) PLA mould around it on a 3D printer.
- Mix a two-part polyurethane casting resin and pour it into the mould around a metal inner sleeve (and outer where required).
- Allow a long, undisturbed cure.
- Split or peel the PLA mould away from the cured bush.
- Press the finished bush into the diff mount and reinstall.
Three bushes were made for this job: two main diff mount bushes and a rear top-hat bush.
Lessons from round 2
Section titled “Lessons from round 2”The first attempt produced bushes that were dimensionally off and under-cured. Changes made for round 2:
| Area | Round 1 problem | Round 2 change |
|---|---|---|
| Mould design | Tight tolerances, hard to release | Redesigned for easier separation |
| Mix | Slightly off ratio, soft cure | Fresh, carefully measured mix |
| Cure time | Rushed | Extended undisturbed cure |
| Yield | Marginal | Three usable bushes |
Fitting notes
Section titled “Fitting notes”Fitting the new bushes into the diff mounts required pressing/squeezing them home — the second one in particular was a struggle, which is normal for poly bushes (they don’t compress as easily as rubber). A smear of silicone or rubber grease on the outer face helps them slide in without tearing.
The rear top-hat bush is the small one that locates the back of the diff; it goes in last before the diff is offered back up to the chassis.
Wrestling the diff back into the car is a two-person job. The unit is heavy, awkward, and the mounting holes need to line up in three planes at once. A transmission jack or trolley jack with a cradle makes it much more controllable than balancing it on a bottle jack.
While the rear of the car was apart, fuel and brake lines in the same area were inspected and tidied up — worth doing whenever the diff is out, as access is never better.
Cautions
Section titled “Cautions”- Polyurethane hardness (Shore A) matters: too hard transmits vibration and load into the chassis mounts; too soft and the diff still moves. OE-equivalent poly bushes are typically in the 80–95 Shore A range — confirm against a known-good aftermarket part before casting.
- Home-cast bushes have no traceable batch data. Inspect after the first short drive, then again after a longer run, for cracking, extrusion or movement.
- Check diff oil level and pinion/output seals before refitting — far easier now than later.
- Torque all diff mount fasteners to the manufacturer’s specification (see the Cerbera torque settings reference) and use fresh locking hardware where specified.
See also
Section titled “See also”Compiled from a community video build log (Matt Green / 16vmini, 2026) — always verify dimensions, materials and torque values against the original manufacturer’s specification before relying on home-cast suspension or driveline components.