Thursday, June 20, 2013

13” Front Disc Brake Installation: The Right Stuff ...... Detailing that is!

Another solid week of work yields another completed phase of the front suspension and braking system assembly.  This week, we tackled the job of assembling the entire 13” front disc brake system on the freshened drum brake front spindles and hubs and the results were exceptional.  I love working with well-engineered, solid parts that require no fiddling to make fit and/or function.  Luckily, we’re batting a thousand lately!

To begin the latest adventure, we started by cleaning up the drum brake spindles and hubs in preparation for powder coating.  As many Mustang enthusiasts have often painfully discovered, the production Mustang spindles are very roughly machined forgings with lots of raw, sharp edges that are just begging to mutilate human tissue.  At the same time, they don’t look particularly sanitary and as such, became the focus of considerable smoothing with the angle grinder and some 60-grit discs before heading off to the blast cabinet.  After a few minutes of abrasive clean-up, the spindles looked amazing and were set aside for later cleaning before powder.
On the hubs, it was necessary to turn the O.D. of the flanges down a bit in order to properly fit the re-drilled, 13” vented (Brand X) rotors.  As an aside, these rotors have a 0.480” more inboard offset in the hat area over the “Cobra” 13” rotors to allow fitment of a wider selection of wheels without the need to use wheel spacers.  By simply re-drilling the rotors to fit the Ford 5 x 4.5” bolt circle, these rotors are a simple bolt-on choice with a wide variety of feature options in the aftermarket.  We will ultimately upgrade the front rotors at a later date, but all smoke-testing will be done on the standard rotors as shown here.

Once the hub O.D. machining was complete, they received the same abrasive clean-up as the spindles and both pairs of parts were prepped and powder coated in our standard urethane satin black that we use for all of the under-car components.  Once out of the oven, the hubs and spindles looked virtually flawless and we now had a clean foundation to begin the build-up of the assembly.
Assembly of the hubs was begun first by pressing in a full complement of new wheel studs, followed by new bearing races.  Then, each hub and spindle was test fit to seat the bearings as well as verify the fit of the new spindle nut/washer & retention cage before show time.  With the hub and spindle fit verified, we moved on to the fitting of the caliper mounting brackets.

As you may have noted, the spindles and hubs we are using are from a drum brake version of the Mustang and not the original disc brake parts that were originally equipped on the 1970 Boss 302.  There are a few reasons for this that are actually quite simple:  First, the drum brake spindles have a 4-bolt pattern that retains the brake backing plates whereas the disc brake spindles use only three.  The 4-bolt flange makes for a much more stable mounting configuration for the disc brake brackets.  Secondly, the disc brake spindles have a large mounting hole in the spindle upright and an awkward hole/flange grafted onto the steering arm section that are used to mount the production disc brake caliper bracket.  With modern 13” brakes, these holes are not used with this brake combination and historically, these areas of the spindle have proven to be weak points in this design in heavy duty and racing applications.  Besides, disc brake spindles are ugly………so there.
While Street or Track apparently no longer offers the “Cobra” front caliper mounting brackets we use here, they are relatively simple, very high quality devices that install on the 4-bolt backing plate flanges and include the aluminum adapter to properly locate and anchor the production caliper bracket.  In our case, the left and right hand side adapters had to be spaced inboard by .060” on each pad to account for the differences in the production tolerance stack-up to center the caliper brackets over the rotors.  With these details covered, the adapter brackets were torqued to final spec and we were finally able to shift our attention to the final assembly of the hubs.

Since both hubs were already mocked up on the spindles, the assembly process was very simply a matter of cleaning and greasing the wheel bearing cones with bearing grease, installing the wheel seals and sliding them into place on the spindles.  The spindle nuts were installed per the factory shop manual specifications and secured with new retention cages and split keys. 
Now for the REAL excitement!  Our friends at The Right Stuff Detailing (TRSD) have been in the disc brake conversion kit business for a long time and supplied their beautiful, dual piston “Signature Series” PBR calipers in smooth, glass black powder coat finish. 

If you have never heard of The Right Stuff Detailing, take notes.  This is a fantastic company with outstanding products and customer support and their specialty is braking system conversions and components along with custom and pre-bent tubing products, and custom and pre-made e-brake cables and a host of other braking and suspension offerings.

These calipers are a smoother, cleaner version of the classic Cobra/Corvette calipers that have been so popular in the world of classic Mustang disc brake conversions, WITHOUT the gaudy casting “identifiers” tacked all over them or the need to rebuild salvage-yard cores.  Their Signature series calipers are produced to the same exacting OE level specifications as the production model calipers and can be serviced in exactly the same way and with exactly the same parts as the production versions that are now essentially unavailable.
Here again, I am very happy to report that these calipers and brackets bolted on to the spindle assembly with absolutely no drama whatsoever after installation of a fresh set of semi-metallic brake pads.  After all, with OEM-level quality on all the TRSD parts, and standard brake hardware, these calipers don’t know they are, in any way, a part of a custom brake application.

With the TRSD calipers and 13” front rotors solidly in place, we took a step back to admire the beautiful simplicity of the setup.  Almost “elegant’ I would say.  Of course, the visual aspect is enhanced by the sheer size of the rotors and the capability that comes with them.  The Night Mission Boss 302 will STOP with authority to be sure.
As a final measure, the installation of the spindle dust caps presented the next dilemma, and one I had anticipated based on past experience:  Fitting new dust caps WITHOUT beating the snot out of them and/or damaging them during installation such that they look terrible on close inspection.  I absolutely HATE the look of dinged up dust caps on custom cars and would not settle for anything but a clean installation on this project.  I know, I know…..nobody will ever see them, but that is entirely beside the point.  If I know they look terrible, it will eat me alive until I fix it.  So……needing little prodding to dust off my lathe for a project, Ted and I set about making a proper installation tool that would allow the dust caps to be installed in the hubs with minimal effort and absolutely no damage.

Since I already had a nice driver handle that was included in my bearing and seal driver kit, I figured I would make a dust cap driver that would fit that handle for ease of use.  So after a few measurements and a quick design sketch, I scoured the scrap aluminum bin in the shop and popped up with a perfect chunk of extruded 6061 aluminum rod that would work perfectly and require relatively little work to create the tool I needed.
With the South Bend 9” lathe well lubricated and warmed up (ya have to do that on 77-year-old machines), I proceeded to whittle out a driver cup that fit my drive handle perfectly and allowed the dust caps to be driven easily into the hubs with not so much as a scratch on any component.  In fact, the simple tool worked even better than expected and relieved me of the burden of worrying about how my hidden-from-human-eyes dust caps looked.  Another thousand-dollar solution to a ten-cent problem brought to you by your buddies at the Night Mission Boss 302 project!

Anyway, there you have it:  A complete and very capable “big-brake” conversion on the Boss is now in the books.  Soon, we will once again shift back to more “bodywork” type work as we set about spraying the exterior floor pan with Raptor bed liner while the weather is being so cooperative.  Thrown in there will also be a round or two of powder coating front and rear suspension components before we dive back into the engine bay for a host of filling and smoothing operations as we head into the late summer/early fall season.  In between all of that, I have plans to do the Street Rodder Tour from San Antonio, TX to Pigeon Forge, Tennessee with in early September and I am completely fired up about spending a solid week doing nothing but cruising God’s Country in a ’32 Coupe with my uncle.  Truth being what it is, I continue to learn a lot about “smelling the roses” every day.  Until next time!

Close inspection of the stock Mustang spindle will reveal a large number of rough, sharp edges that need smoothing.  We knocked these edges off and spent a good bit of time smoothing all of the other surfaces to make for a nice presentation once in powder coat.
After turning down the O.D. of the stock hubs and smoothing and powder coating them, new wheel studs were pressed in.
With the new bearing races installed, the hubs were test fit on the spindles to seat the races and make sure there were no surprises in their operation or fit.  You can also just make out the smooth surfaces of the powder coated spindle upright.
Here, the Street or Track caliper adapter brackets are test fit to the spindle.

The hubs are re-installed to test fit the entire brake system componentry.  Note the hub-centric adapter ring that is now positioned over the center of the hub to locate the rotor properly.

Test fitting the components showed that we needed to install 0.060" shims (see yellow arrow) to account for tolerance stack such that the caliper mounts would center over the rotors properly.

With all adjustments made and fit of all components verified, the adapter brackets were installed permanently with all fasteners torqued to spec with red Loctite where applicable.

Final assembly of the hubs included moly-fortified wheel bearing grease packed into new Timken bearings and buttoned up with new seals.
The 13" rotors are an impressive sight bolted to the hubs.  Plenty of braking capability in this package to be sure!

And here is the feature part!  These beautiful Signature series PBR calipers and brackets from The Right Stuff Detailing are as good as they come.  Absolute top quality and OE-level quality and reliability make these calipers extremely hard to beat.  Couple that with a clean, elegant look that is anything but gaudy, and the combination is just about perfect!

Dust cap installation can be a challenge and I particularly hate beat up dust caps on custom cars.  I decided to design and machine a dedicated driver tool that would allow the dust caps to be driven into the hubs squarely with no hint of damage.

The tool is designed to use my bearing driver handle and it worked perfect in driving the dust caps into the hubs perfectly square and undamaged.  Here, the dust cap has already been driven in .

Simple in concept, the driver simply cover the cap and drives it home using the cap flange.

A thing of simple beauty that nobody will likely ever see.  A perfectly undamaged dust cap.  As I said above, a thousand dollar solution to a ten cent problem........I'm sick.

Here are the TRSD calipers and 13" brake rotors in place in all their glory!  I absolutely love the elegant simplicity and absolute purpose this entire assembly displays.  Once all of the bare steel parts are finished in black powder coat, this will be an amazing complement to the project. 


  1. Ahhhhhhhhhhhhhhhhhhhhh...........

    Does anything more need to be said?


  2. Shiny, stopping power. Clean and functional, it's all in the details. Great looking setup! Might have to make myself one of those dust cap tools when the time comes. :)

    1. Yes indeed and thanks Grant! I am very happy with the entire setup and it is all so easy to work on. What more could I ask?

  3. The brakes are okay but that dust cap tool is AWESOME!!! :-)

  4. I'm drooling over your access to machine tools. A dust cap tool. How cool is that!? What's your rental charge? The brake set up is incredible. I particularly like that the rotor and hub are two piece and not one piece. 13" rotors and the Signature calipers should adds lots of "whoa" to all the "giddy up". Excellent!

  5. Wonderful appeal about nice shiny disc rotors and beautiful calipers being visible behind a nice set of wheels. Always a shame to hide them behind the wheels but great comfort to know you have 13" rotors that will certainly do the job.

    I have just about finished obtaining all my front end gear now with the 70 stub axles (I think) with the larger bearings. New bearings, seals, brake pads and all that stuff so got some cleanup to do and into the assembly as well....

  6. Sven, what are the ID, OD of your hub centric rings for the front rotors? I've been trying to find a set to match my 68 mustang / 2005 17" GT rims. Thanks!