Brembo GT Hardware Packs – Bolt Kits for Floating 2-Piece Rotors
On 2-piece Brembo Gran Turismo (GT) rotors, the cast iron friction ring is not rigidly bolted to the aluminium hat (bell) but is floating. The connection is made by special bushings (bobbins) with bolts, washers and springs. You get these parts as a Brembo hardware pack, matched to the rotor size.
What Is the Floating Mount For?
A 2-piece rotor consists of a cast iron friction ring and a lightweight aluminium hat. This saves unsprung and rotating weight. The biggest advantage, however, is the floating mount itself: the friction ring can expand with heat independently of the hat, so it stays flat and true.
The bushing (bobbin) has three jobs:
- Connect: it joins the friction ring to the aluminium hat.
- Transmit braking torque: under braking it transfers the torque from the ring to the hat.
- Allow expansion: under thermal stress the ring can expand radially, which prevents the disc from warping.
Important Notice from Brembo
The coupling between hat, ring and bushing has been carefully engineered by Brembo. The tolerances of all components and the correct tightening torque are defined to prevent performance and comfort problems. Always use only the genuine Brembo hardware specified for your rotor.
Bushing Types (a, b, c and d)
Round Bobbin – Types a and b
The bobbin and hat fit together in a round fixing hole. Under braking, the torque is transmitted from the ring to the hat through the bobbin. The load is carried by the surface that touches the fixing hole.
- Type a: with 12 mm bolt
- Type b: with 16 mm bolt
Bobbin with Flat Surface – Types c and d
The bobbin and hat fit together on a flat surface. The braking torque is again transmitted through the bobbin, but over a much larger area than with types a and b. Under high load the surface pressure is therefore lower, which gives a longer service life. This design is used on larger and thicker rotors.
Anti-Rattle Springs
Brembo uses special springs in the drive elements that slightly preload the assembly and prevent noise from the braking system. Depending on the application, springs are fitted on all drive elements or in an alternating sequence. Bushings without springs may move slightly in the axial direction. This is intended and a basic requirement of the floating mount.
Which Hardware Pack Fits Which Rotor?
The bushing type depends on the rotor. According to the Brembo catalogue, thinner rotors use round bobbins (type a/b), while rotors from 34 mm thickness use bobbins with a flat surface (type c/d).
| Hardware pack | Compatible rotor sizes | Bushing type |
|---|---|---|
| 105715930 (105.7159.30) |
Ø 328 x 28 mm, Ø 345 x 28 mm, Ø 380 x 28 mm, Ø 330 x 34 mm | round (type a/b) |
| 105715931 (105.7159.31) |
Ø 320 x 28 mm | round (type a/b) |
| 105715932 (105.7159.32) |
Ø 332 x 32 mm, Ø 355 x 32 mm, Ø 365 x 29 mm, Ø 380 x 32 mm | round (type a/b) |
| 105715935 (105.7159.35) |
Ø 365 x 34 mm, Ø 380 x 34 mm | flat surface (type c/d) |
| 105715936 (105.7159.36) |
Ø 405 x 34 mm, Ø 412 x 38 mm | flat surface (type c/d) |
| 105715937 (105.7159.37) |
Ø 405 x 36 mm | flat surface (type c/d) |
Quantity: One hardware pack is for one rotor. For a complete axle (left + right) you need 2 packs.
Tip: Always replace the hardware together with the friction ring. This ensures the new rotor sits securely and rattle-free with the correct tolerances.
Installation Instructions & Technical Documentation
- Rotor replacement instructions: Brembo instructions for brake rotor replacement (PDF)
- Brembo GT installation manual: Brembo installation manual for the Gran Turismo kit (PDF)
Expert Advice & Support
Not sure which hardware pack fits your rotor? Send us your vehicle, kit number or rotor part number and we will be happy to check compatibility for you: Contact us now.
