Inside the
rear drums.
Separate steel shoes and linings, a hollow cylinder with slotted piston ends, retaining washer and clip, and a bracket, screw/wedge and tappets replace the former solid mechanism cues. Two spring references now end at explicit shoe-web eyes. These expose assembly relationships without simulating brake operation.
Left rear mechanism
Right rear mechanism
Factory roles and component comparisons
Factory parts PDF p. 148 distinguishes the GAN6-154101-on 37H8804/5 plates, GBS625 shoes and GWC1129 cylinder from earlier plate/shoe/GWC1102 branches. It lists separate 17H7613 Belleville washer and 17H7622 circlip, 17H7618 tappets and 17H7619 wedge, handed 17H7947/48 cylinder-end springs, 17H7621 lower springs and handed handbrake lever/boot roles. These are reference roles, not identification of the installed parts.
Mini Spares’ GWC1129 component photograph and specification support a twin-ended cylinder with slotted piston tips and an 11/16 inch (17.4625 mm) bore comparison. That supplier dimension does not become a measured bore or prove the fitted cylinder, nor does the Mini application define the Midget brake installation. The supplier’s 17H7618 tappet description and photograph support separate tappets meeting the screw/wedge in a bracket; all modeled sections and tapers remain estimates.
Mounting relationships now visible
Separate backplate interfaces
The factory drawing distinguishes the handbrake slot from the round cylinder mount. The former combined opening is replaced by a 20 × 25 mm slot at Y70/Z−23, a cylinder opening of radius7.5 mm at Y68/Z0 and a bleed opening of radius3.5 mm at Y76/Z12. All are wheel-relative construction coordinates, not factory drilling dimensions. Only the two backplate meshes change in the existing hub source; thirty other hub meshes remain identical.
Cylinder, shoes and retention
The barrel/pistons/boots shift 6 mm outward from the old cue to the retained shoe-web plane, while the inlet tip stays at u−35/Y68/Z0. The mounting neck passes through the plate with separate unloaded Belleville and open clip roles. Piston slots receive the thin web envelope; seal fit, stroke, pressure channels and loaded contacts are absent. No fitted hydraulic splice is verified.
Adjuster and return springs
The bracket is open across the tappet axis. A smooth square-drive screw and conical wedge remain separate from the two tappets. Upper/lower unloaded coil and hook envelopes terminate at explicit web holes. These show roles and source relationships; taper, travel, spring hooks/handing, preload and adjustment settings remain unverified.
External handbrake boundary retained
The existing external lever, boot and bored rod-eye stations stay unchanged, as do all thirteen external handbrake source meshes. A verified internal shoe-expansion linkage has not been constructed. The separate slot does not prove lever movement, leverage ratio, shoe contact or the remote body crossing.
Reference geometry and source contacts
The nominal drum bore remains 177.8 mm. Lining outer arcs use that contour for illustration, without running clearance or wear inference. Every new profile, width, slot, hole, axial station, spring shape and interface fit is estimated. No new direct owner brake dimensions or fitted identities are applied. Existing photographs remain owner evidence; the previous evidence review did not establish a calibrated hidden brake-internal survey.
| Left source comparison (right mirrored) | Positive contact mm³ |
|---|---|
| left shoe front connected web rim and spring eyes / wheel cylinder two slotted piston envelopes | 24.0034 |
| left shoe front nominal contour lining / wheel cylinder two slotted piston envelopes | 0.065 |
| left shoe rear connected web rim and spring eyes / wheel cylinder two slotted piston envelopes | 24.0034 |
| left shoe rear nominal contour lining / wheel cylinder two slotted piston envelopes | 0.065 |
| left wheel cylinder hollow barrel neck and bleed boss / wheel cylinder two unloaded open boots | 395.841 |
| left adjuster open bracket and backplate neck / adjuster unthreaded square drive and conical wedge | 1.1547 |
| left adjuster front tappet and estimated wedge face / shoe front connected web rim and spring eyes | 0.8937 |
| left adjuster rear tappet and estimated wedge face / shoe rear connected web rim and spring eyes | 0.8937 |
This limited static sample covers mechanism pairs and the retained backplate. Positive contacts are reconstruction discrepancies, not evidence of damage or interference on the car. It does not certify the full axle, drum, wheel, spring or moving linkage envelope. The existing hub O-ring/gasket/shaft contacts remain documented separately in the hub study.
The offsets separate groups for inspection. They do not release spring energy, operate hydraulics, adjust shoes, establish drum/shoe withdrawal or provide a verified replacement procedure. Applicable fitted identities, handing, pressure seals/passages, loaded contacts, internal handbrake expansion, support, bleeding and adjustment procedures remain unresolved.
Native exports
Checks cover valid source solids and STEP round-trip, distinct backplate passages and source-preservation boundaries. Viewer checks cover source ownership, metric placement, bore/material witnesses, isolation and declared separation. They validate drawing consistency, not fitted brake function.