AC Aceca Front Disc Brakes: Calipers, Discs and What Fits
Front disc brakes were an option on the Ace and Aceca from 1957 and standard from 1958, and they are Girling, not Dunlop. But identifying the exact calipers and discs catches owners out, because the caliper turns out to be shared with several other cars while the disc is specific to AC. Here is what fits, what does not, and how to tell what is on your car, drawn from the Girling catalogue figures that AC Owners' Club members have pieced together.
Confirm against your car
Brakes are safety-critical, and part numbers from catalogues and forums are a starting point, not gospel. Confirm any part against your own calipers and discs, and with a brake specialist or supplier, before ordering or fitting. Original cars and later conversions differ, so identify what is actually on your car first.
The calipers: Girling, and shared more widely than you'd expect
The original front calipers are Girling, not Dunlop. The earliest cars used the Girling Type 'B'; some competition cars had the alloy Type 'BR'; and over the years many cars have run the 16-series calipers, the 16B (solid) and the 16P (split).
The surprise is how widely the caliper is shared. According to the Girling catalogue, as documented by AC Owners' Club members, the Ace/Aceca front caliper carries the same part number as the 1959–61 Greyhound and the 1961/62 TR4: 64032520/1. The later 1961–63 Greyhound used the split caliper (64032602/3), and a later TR4 caliper even found its way onto some Cobras.
Importantly, the caliper mounting-hole spacing is the same as the TR's, so the caliper bodies share the same fixing pattern. (An earlier belief that the spacing differed was corrected by members working from the catalogue, a good reminder to check the source.)
The discs: specific to AC, and not interchangeable
The disc is the part that is genuinely AC-specific. The AC front disc is larger in diameter than the TR3's, where the TR3 disc is 11 inches, AC owners measure theirs at around 11.7 inches, so treat the exact figure as something to check by measuring your own. The Girling disc part number recorded up to 1961 is GB49613, and the discs were specially made for the Ace, Aceca and Greyhound.
So even though the caliper is shared, the AC disc is not interchangeable with a TR3 disc. Don't assume a Triumph disc will fit, it won't.
Fitting the shared caliper to the larger AC disc
Because the AC disc is larger in diameter, there is a fitting subtlety when using the common Girling caliper: the bottom groove of the caliper should be relieved, opened out, to clear the larger AC disc.
Crucially, do the work on the caliper, not the disc. If you machine the AC disc down in diameter to suit a caliper, the pads end up standing proud of the disc edge, overhanging where there is no disc to grip, which is both wrong and unsafe. This corrects an older piece of advice that suggested reducing the disc; the catalogue-based correction is to relieve the caliper instead.
Original, or a later conversion?
If your Aceca left Thames Ditton with disc brakes, it has the AC Girling setup, the larger AC discs and the shared-pattern Girling caliper. If the front brakes are a later conversion or upgrade, you may find Triumph-based or other parts instead. That matters when ordering: measure the disc, and look for part numbers or casting marks on the caliper, before assuming which you have.
Where to find parts
Specialists can supply and identify these parts. BG Developments manufactures a full range of Girling historic calipers to original specification and lists AC among the cars it covers; AH Spares and other Girling suppliers carry caliper components and can confirm a type from its dimensions. As always, confirm the exact part against your own car before ordering.
Beyond the front discs: other Girling brake parts
The Girling theme runs through the rest of the braking system too, and owners identifying parts find the same pattern, numbers stamped on the parts, cross-referenced through the Girling catalogue and the club's Interchangeable Parts Booklet. As documented examples: the master cylinder is a cast-iron Girling unit (one car's is stamped 3102542W), and early cars use Girling rear brake shoes carrying numbers such as GB 41540 and GB 41542, shoes also found on the Austin A70 and believed shared with the very earliest Austin-Healey 100s, which is a useful sourcing route. Part numbers changed through production, so identify by the numbers on your own parts and confirm before ordering; AH Spares and Girling specialists can help.
In short
The front brakes on a disc-braked Ace or Aceca are Girling. The caliper shares its Girling part number and mounting pattern with the TR4 and the early Greyhound (64032520/1); the disc, though, is AC-specific and larger than the TR3's, so it is not interchangeable. If you are fitting the shared caliper, relieve the caliper groove for the larger disc rather than machining the disc down, and always confirm parts against your own car.
Sources. This article draws on the Girling catalogue figures documented by owners in the AC Owners' Club community, and on specialist suppliers including BG Developments.
Brakes are safety-critical and this is a general reference, not a substitute for the workshop manual or a brake specialist. Part numbers are a starting point, confirm them against your own calipers and discs, and with a specialist, before ordering or fitting.
About the author
A lifelong classic-car enthusiast in North Yorkshire, near Thornton-le-Dale, who owns and maintains an AC Aceca, writing the single-model reference he always wished existed. Read the full bio.