How-To Model A Bucket Re-creation Project: Disc Brake Adaption

Falcon rotors and Commodore calipers to early Ford stub axles

The fitting of disc brakes onto early Ford stub axles is a swap that has been done many times in many different ways. One of the most popular methods favoured when fitting disc brakes like this first became popular was to use XR-XT Falcon solid discs and hubs with adaptors to allow the bearings to fit the early Ford stub axles. My ’30 Model A pickup has these brakes and they have been doing great service for 30 years. I also used a set on the front axle fitted under my ’32 Ford hiboy roadster project that still languishes in storage (I will get back to it one day).

A natural update for this swap was to opt for the XW-XY discs when they became readily available and they were a better performing brake, thanks to their vented rotors. This swap is still popular today and that’s what I decided would best suit the Model A bucket project. Yes, there are more modern variations available, but I thought the XY option best reflected the period style this bucket is designed to emulate.

When I mocked up the front end in the bucket I used a pair of stock, round back ’37-’39 Ford stub axles, complete with their original steering arms. Everyone knows the steering arms need to be modified if you are using a dropped axle, but I decided against doing that at this stage. Instead I removed the stub axles from my ’32 hiboy project because they were the same type, but their stock steering arms had already been removed. The use of hairpin front radius rods on the bucket means I need dropped steering arms anyway, so this way I could just buy aftermarket dropped steering arms and bolt them straight on (or so I thought). The spindles on these stub axles were also modified and fitted with the bearing adaptors to suit the XR Falcon hubs and solid disc rotors, exactly what is also required for the XY rotors I am using this time. Gary Wright at Early Hot Rod Parts supplied me with another set of these adaptors so that I can fit discs to my stock spindles that can be modified in a similar manner to that described here and then fitted back onto the ’32 front end. This swap also requires that the outer end of the spindle be shortened by ½ an inch (25mm) and the threaded section run on the same amount to suit the Falcon bearing spacing in the hub. The outer bearing landing needs to be machined inwards by the same amount, for the same reason. All these modifications had already been done on my hiboy spindles.

Since the earlier XR-XT discs and the XW-XY Falcon rotors in their stock configuration bolt to their hubs, and you can buy brand new XW- XY type disc rotors, my first instinct was to simply buy a set of the vented rotors and bolt them to the XR-XT hubs of which I have about five sets. Wrong! I now know XR-XT hubs are different to XW-XY hubs – the XR-XT hubs have two bolt circles, one for attaching the rotors and the second for the wheel studs, on XW-XY hubs there is only one bolt circle as the wheel studs are also used to retain the rotors on the hubs.

It’s worth noting here that a more popular version of this swap uses XF Falcon type rotors and hubs that use a larger inner bearing than the XR-XW versions, but otherwise the adaptors and process is identical. The XF inner bearings are actually only larger on the inside diameter so the adaptor is only different in that section – the outer bearings and inner seals are the same and the spindle needs to be machined inward the same amount for the outer bearing location.

However, in the process of researching and learning all these important facts I also found a really nice way around the different hub problem. In searching for replacement XW-XY vented rotors I discovered that RDA Brakes supply a brand new one-piece rotor and hub assembly that incorporates the original XW-XY bearing sizes. You can simply fit new bearings and races into these brand new assemblies and slip them straight onto the modified spindle in the same manner as the XF Falcon version! Perfect! What’s more, they aren’t expensive, retailing from RDA distributors for around $190.00-$215.00 per pair. An added bonus is that they have a very nice passivated finished, even inside the vented area of the rotors, no greasy protectant to remove and they won’t go rusty while you are putting your project car together. RDA Brakes have distributors all over Australia.

Having discovered and purchased these new hub and rotor assemblies I couldn’t wait to fit the bearings and slide them onto my early Ford stubs and get on with making caliper mounts.

When it comes to calipers for this particular brake swap it is also popular to use VB-VS Commodore type calipers thanks to their compact size, attractive appearance and simple, parallel two-bolt mounting design. Depending on what model your calipers are from they also feature a ribbed design (VR-VS) that can be polished if you are seeking that look, or a smoother design without the ribbing. Mine are the smoother design and came to me from Hugh Nally in Tasmania who supplied them with new kits fitted, ready for use, because he’s a good friend and he just happened to have some “in stock”. If you opt for the ribbed VR-VS type you need to know that they have a different mounting bracket (see sidebar on page 44) that needs minor modification to suit this swap.

For caliper mounts I wanted something that looked tidy and suited the style of this project. My end vision for the car is to have a clean, tidy appearance and, while not a full-on show car, to exhibit suitable detail in the areas that count, especially front end appearance. That’s why I elected to use stainless steel hairpin radius rods and polished front end accessories. In keeping with that theme I decided it would be good to make my caliper mounts out of stainless steel that could be polished and to make them the same size as the disc rotors to hide the bare surface of the disc where the pads engage.