Boss 302 TransAm big caliper brackets

[427street]

The Boss 302/TransAm racing T-Bird big brake caliper bracket dilemma,
Or
The big brake caliper bracket eureka moment at the turn of the century!

Is that a long enough title?

Anyway. After posting some spare parts I had on the shelf for many years for the Boss 302/TransAm racing T-Bird big brake set-up, I got a lot of questions asking if I had all the parts for the set-up.

So I went looking through more boxes and crates.

I am a sick person. I have parts for parts that I didn't know even needed parts. Parts I didn't even know/remember I had, when I got them or where I got them from. Too many projects under the bridge. Well under the bridge is where I found more boxes. Sort of.

But enough about my neurosies.

The part everyone considers the holy grail of the Boss 302 TransAm big brake set-up is the T-Bird big caliper bracket that attaches to the 1970 Mustang drum brake big spindle setup.

Well guess what? I don't have those brackets. Surprise. Surprise.

But what I have is the result of the big brake caliper bracket eureka moment at the turn of the century, OK, the late 1990's early 2000's.

In the 1990's I was helping a good friend build up a 1970 Mustang as a Boss 302 clone for "club racing" and test session fun at Willow Springs. Being a clone build and a low budget project to boot, parts were scrounged from friends, back yards, and wreckers. But the big brake caliper bracket proved elusive. This may have been before Cobra Automotive offered a bracket, or maybe we just didn't want to spend the money.

But we had the internet. And luckily we stumbled on some Ford/Mustang website where this very problem was being kicked around. Was the big brake caliper OEM from Ford the only solution?

Disclaimer! I am not taking credit for the following innovative and imaginative solution. My old notes say a website poster with the handle "1RadRod" came up with this.

The genesis of the Boss 302 big brake caliper kit is well known. Kar Kraft, Bud Moore and others scoured the Ford parts book and came up with the solution and Ford Racing/Kar Kraft Engineering came up with a new caliper bracket. But was it new? Unique to thisTransAm application for sure. But the design concept – was it new?

Perhaps not.

If you compare the Boss 302 big caliper bracket with a 1965 to 1967 Mustang regular production caliper bracket they are remarkably similar. In fact the same where it attaches to the spindle, but different for the spacing of the caliper mount pedestals – wider apart for the bigger T-Bird calipers.  Were the big caliper brackets thicker or stronger. I don't think so, but I don't know for sure. Seems to me there would be more stress risers in the big caliper bracket with those caliper pedestals hanging out there.

See pic 1 below as an attachment(I still can't figure out how to insert a pic into this text)

So what was "1RatRod"s solution?

A simple but effective use of steel bar stock commonly found in any shop. (or McMaster Carr ).

A ½" thick by 1.25" wide by 6" long steel bar "bridge" was fabricated and drilled (see pics) that attached to the caliper bosses on the existing spot faced surface using the existing 9/16" tapped bosses in the caliper.
Then a 5/8" thick by 1" wide by approx. 3.75" long "bridge support" was fabricated and drilled to match the narrower 65-67 Mustang regular production caliper bracket 7/16" holes mounting holes. (see pic 2 below)

The two are then welded together to form a very rigid "T" shaped "bridge bracket". (see pic 3 below)

The caliper does not need to be spot faced on the back side of the caliper threaded attachment bosses since the OEM T-Bird caliper attaching face is used as originally purposed. (see pic 4 below)

In fact, any fine tuning to centering the caliper (in and out) on the rotor can be done with shims.

And the "bridge bracket" can be sized/positioned to accommodate the positioning of the original 68 T-Bird rotor on the inside of the hub (as we did) or the Coleman rotor/hat assy on the outside of the hub. It's just a matter of sizing the steel bars and positioning the "bridge bracket" relative to the attachment bosses on the stock Mustang caliper bracket.

Easy ( a couple of hours work), cheap ( about $25 for 4 pieces of 6"bar stock from McMaster Carr) and strong.

This solution worked just fine.

Eloquent in its simplicity.

I'm interested in your comments.

But let me go make some popcorn made before the comments start flying.

Cheers
Greg

PS. I'll be posting the complete set up I have for sale in the SAAC classifieds.

[427street]

It's been pointed out that I made a could of typos and labelled a pic incorrectly.

The OEM Mustang 4 piston caliper brackets were from 1965-1967.

I have corrected the text and the pic correctly labelled is attached below.

Thanks for looking.

Cheers
Greg

[CSX4781]

I noticed that by doing it the way you did,  you eliminated the need to drill out the threads on the calipers, which means they can be used as purchased. Very cool, good engineering!

Dave

[shelbydoug]

Before I go and sound like I am criticizing you, I will admit that I just made similar "adapters" to fit these on my Pantera.

Having said that, when I did my 68 GT350, I wanted the "T/A" bracket. Not a jabonga bracket.

What's jabonga? That's the noise the car makes as it drives down the street. 


The bracket that Cobra Automotive is selling right now, is not the bracket that the sold me. The one I purchased for $600, was cnc cut out of billet and is a clone of the original KK parts.

That satisfied my lusting.


In the case of my '68, I have 10 spokes on it. Wanna' hear a "story" about what had to be done to fit those on with no interference? Of course you don't. So for the moment I won't antagonize you with it. Maybe later if my med's don't kick in?


In all cases, the amount of unsprung weight being added is about 95% caused by the size of the 1.25 thick rotors.

Here's something actually I am adding of interest. There IS a SoCal Company that decided to cast up some of the "Big Ford Calipers" in aluminum.

About a day after they decided not to sell them any more, I found them and tried to buy a pair. No dice. They were not concerned that I was threatening them with a nuclear detonation. They must get that all day long the way I figure it?


In speaking to Mr.Gillis, he seems to think that there are or were Ford aluminum versions with XE casting numbers on them that he saw at Nicholson's?

[427street]

Hi shelbydoug. Thanks for sharing your experience.

I don't remember any jabonga-ing going down the street, just a loud exhaust!

I understand that there were wheel fitment problems, especially with the older 10 spokes (minilites?) but the newer ones have more clearance on the inside of the wheel and aren't a problem.

Also, the caliper/rotor configuration in your pics appear to be a one piece rotor/hat and mounted on the outside of the hub.

I believe the original Boss 302 Trans/Am big brake setup used the 1968 T-bird one piece rotor /hat and was mounted on the inside of the hub which gave it more rotor/caliper offset to the inside and didn't have a wheel clearance problem.

At least that's what I recall reading on very old posts. But I am getting old you know.

The set-up I've shown has the rotor mounted on the inside of the hub. I'll post some pics later.

Cheers
Greg

[427street]

Hi again shelbydoug.

I do remember quite a bit of chatter about 15 ofr 20 years ago here on the forum about aluminum calipers. But as you said. Didn't go anywhwere.

Those rotors and calipers are HEAVY. We used an old caliper that I'm sure had been used as a boat anchor (based on the rust inside) to test fit everything up at the time.

Cheers
Greg

[shelbydoug]

The calipers aren't particularly heavy but the rotors are.

I think the differences in weight between the stock calipers and T-bird is 5 v 7.
The rotors, that's a different story, but you have doubled the mass.

In both of my installations, the rotors are installed in the stock locations, behind the hubs. The '68 just has more shims between the hub and the rotor then normally.


Wheels. In my case, I went through a set of calipers, grinding them down too much and they holed through looking for clearance for an original 67 Shelby 15x7 Ten spoke wheel.

What I wound up with in the front were a pair of the current "repro's" from Branda which really look identical to the originals but are machined on the inside of the wheel to give maximum clearance.

With that wheel, a kissed edge of the caliper and a1/8" spacer, I just clear.


The Pantera is much less problematic since it looks like Campagnolo had brake clearance consideration built into the wheels from the beginning.

The only short commings on the Pantera swap is there is no "big spindle" for them and the caliper mounting to the upright is only an M12.


Sorry I can't remember the name of the SoCal "Classic Brake Company" (maybe that's it?) that had made up a batch in aluminum.

In that thread that you reference someone here seemed to be familiar with them and said the castings were not exactly the same and had at least one addition flange cast in which might or might not interfere with the entire concept of the swap.

When I inquired with the brake company they admitted they had made them but withdrew them for concern of casting porosity and the market was too small to be worth correcting the issues for them.


As I said about caliper weights, when I did an "engineering review" upon completion, I just didn't see significant value in pressing for aluminum calipers especially considering the original Ford design is a "thin casting design" to begin with and changing from iron to aluminum would be reducing the strength of the caliper and considering the stresses the caliper COULD be put under risking failure, it wasn't worth additional effort to go that way, unless of course the aluminum calipers just happened to fall into my lap. 



Funny you should mention mounting the hat over or behind the hub. Current thinking, especially in a scenario where it would be advantageous to have a quick change assembly, mounting the rotor over the hub would be a superior approach in my view.

As a matter of fact, that is exactly what we are going through now with the rear of the Pantera.
We've run into just a little bit of a snag with this concept of doing it on a KK idea of finding something already made in large quantity and applying it just like this big brake scenario for the T/A cars way back when.

However, these silly I - Talians insisted on machining the od of the hubs to 5.9". The proximity of the center line of the lug studs to the edge of the flange apparently bothered them a bit and they put an addition bit on meat on the outsides.

The Pantera flanges do not seem to be a hard steel forging. They look more like a softer cast iron alloy so there may have been some engineering consideration in providing more meat for the lug studs?

So that kind of eliminates using something with a hat id made to sit over a Mustang hub and puts us into the relhm of custom made. Not the way to go. But I'm still working on that.


Incidentally, I went with a Lincoln Versailles rear axle with discs and a parking brake.

The Pantera in the rear so far is the stock solid rotor with a Tesla EPM and 67 Mustang front discs.

The 65 Mustang front rotor does fit the rear of the Pantera (as well as the front) but all of a sudden became a one piece with hub. Go figure?

So the brake set up on my GT350 RESEMBLES the T/A cars and my Pantera RESEMBLES the factory Group 4 brakes. Porterfield R4S pads all around.

[TA Coupe]

Another thing to keep in mind is that the TA setup could use either T bird or Galaxie rotors and the hat height was different so there were 2 different brackets with the only difference being the height of the mounting towers. If you have the tall one it can easily be machined shorter. I forget which rotor has the short or tall hat.

       Roy

[TA Coupe]

You can get a much lighter 2 piece rotor and hat assembly from Cobra Automotive if you're worried about weight:
https://store.cobraautomotive.com/productimage.php?product_id=211

       Roy

[shelbydoug]

The CURRENT listings show all the "Big Ford/Mercury/Lincoln" rotors are the same part.

The only difference that I have come across is that they were originally listed as 12" x 1.25". Now they are 11-3/4" od. So I don't know if they ever actually measured 12" od or if that is just a nominal dimension, like a 2x4 not measuring 2" x 4"?

I know that the calipers are the same so the only way now to cross reference this would be if there was a different mounting bracket between vehicles?

[427street]

Hi Doug. The OEM NOS T-Bird rotors I have had sitting on the shelf all these years are a full 12 inches in diameter. I believe the aftermarket rotors came in at 11.75 inches

Cheers
Greg

[shelbydoug]

Hi Doug. The OEM NOS T-Bird rotors I have had sitting on the shelf all these years are a full 12 inches in diameter. I believe the aftermarket rotors came in at 11.75 inches

Cheers
Greg

They have Ford id numbers on them?

[427street]

Hi Doug. You got me on that one.

There are absolutely no markings of any kind on the rotors. Ford sold them back then as a rotor/hub assembly I think.

I found one of the 68 T-Bird hubs (haven't found the other yet) and it has Kelsey Hayes markings and numbers on it.

Didn't Kelsey Hayes make a lot of Ford brake stuff back then?

Cheers
Greg

[shelbydoug]

Hi Doug. You got me on that one.

There are absolutely no markings of any kind on the rotors. Ford sold them back then as a rotor/hub assembly I think.

I found one of the 68 T-Bird hubs (haven't found the other yet) and it has Kelsey Hayes markings and numbers on it.

Didn't Kelsey Hayes make a lot of Ford brake stuff back then?

Cheers
Greg

Yes K-H was the largest supplier. There MAY be some Ford Foundry castings on them but personally I've never seen those. Someone closer to the race programs at the time might know more about that?

NOT that there are those who are going to claim that THEY have original production line set ups and they have fomoco on them and a Ford engineering number but you never know?

Certainly the KK kit most likely was being made up of parts through the Ford Service Parts program which would be what walk ins off of the street would have purchased?


Having been to Vintage racing and hearing that cars went through three and four sets of brakes in practice makes me wonder about KK not having the foresight or compulsion to mount the hat on the outside of the wheel hubs for faster change overs?

What I find interesting about the big brakes is that they are much smoother and easier to prevent from locking up in a panic stop then the regular smaller production brakes are.


In looking through the descriptions of the replacement rotors, they are still refered to as 12"od.

Now, a question that I have is considering the production numbers on the big Ford rotors and the Mustang rotors, a manufacturer is going to tell me that there is more volume in the big Fords and there is enough demand to keep them in the original "just rotor" configuration and separate hubs and there isn't enough demand for the Mustangs? I would have thought it would be the other way around?

[427street]

Thanks Doug. So I guess I shouldn't call my rotors OEM NOS, although they may be.

Cheers
Greg