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 GT Mustang to 13" Cobra brake Avanti upgrade (RP)
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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:47:21 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
The original post got archived and its apparently impossible to take
from archive. It can not be edited while archived, and my pictures
are in a new location since posting.

Originally Posted - 07/19/2006

I got a set of front brake hubs from a guy who had recently upgraded to
Turner disc brakes from his tired 4 wheel stock drums. I pressed the old
drums off the hubs, and then trial fitted the stock hub into the 13" Cobra
rotor, and it fit perfectly - that was a BIG relief! :

The next step was to press out the old studs :

Here is the studless hub :

Did you know that the factory studs have NO knurl?? No wonder they tend
to strip out so easy with an impact gun!

They looked SOOO ugly, I scraped them with a screw driver, and the took
them to work and used the wire wheel :

Thats all for now .. I had to order the new wheel bearings, seals, caps, and
also make a tool to pound out the old races. The caps I got from Pepboys
in the Help! section, but the part that slips into the hub was too long, so it
would not sit flush, hub against the crimped shoulder. I also bought the 10
Dodge wheel studs mentioned in my original article, and drilled the hub for
the interference fit for the knurl. I took two of the old bearing races, one
of the inners, & one of the outers, and had the machine shop at my work
cut a slot through one side with the chop saw. This will allow me to use as
an installer, so I dont risk damaging the new race with an out-of-control
chisel tip! I went to buy a bearing race installer kit from the local Harbor
Freight, but they were sold out! I will update this thread as I go.



'63 Avanti, zinc plated drilled & slotted 03 Mustang Cobra 13" front disc/98 GT rear brakes, 03 Cobra 17" wheels, GM alt, 97 Z28 leather seats, soon: TKO 5-spd, Ported heads w/SST full flow valves, 'R3' 276 cam, Edelbrock AFB Carb, GM HEI distributor, 8.8mm plug wires

Commander Member

2499 Posts

Posted - 03/07/2009 :  7:48:19 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
Got out there tonight and drilled the holes out in the new rotors. Thought I
would show a couple pics, the rear rotors had smaller holes, but this could
be because they are "aftermarket". Used the 5/8 drill and went to town:



Sorry about those pics, I dont know WHAT the camera was focusing in on,
it certainly WASNT the rotor. Hummm.

Here is a couple shots of how little material had to be removed from the
front rotor holes, here is one drilled through :

Here is a partial drilled hole. Not a lot to remove :

Close up :

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:50:06 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
The next step was to remove the old bearing races, & install the new ones.
I added some Loctite & then tapped the new races in until they were flush
with the hub surface. I have installed bearing races this way for years, it
just requires that you continue to hit the race in a "star pattern", like you
torque wheel studs. This keeps the race from getting stuck :

Then I used my two cut old races to tap the rest of the way until the race
was against the machined step inside :

Then I pressed in the Dodge shouldered studs :

Finished hub, waiting to go on the car :

Then I had to remove the Mustang GT rotors, calipers, & the modified hubs
to make way for the unmachined hubs. The machined hubs are going to
Michigan to go on my dads 1969 Avanti II.

Clearance for wrenches is tight, but it works :

Drained out some brake fluid. As you can see, the prototype brackets got
some extra holes, that was to rotate the caliper up, to get the bottom bolt
higher then the steering arm, so a standard wrench could be used on the
top and bottom bolt, and tightened to 85 ft lbs :

Then pack the bearings, add the new seals (Napa now carries an updated
neoprene seal, was glad to toss the old felt ones!!), bolt it on the spindle,
new cotter pin, and add the modified "Help!" dust cap (not a direct fit like a
cross reference site for Studebaker listed!).

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:51:22 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
Once the Dodge studs are in the stock Stude hub, the rotor is an easy step
of tightening the lugs on, to draw the rotor onto the shoulders.

Then, the Cobra caliper gets bolted onto the bracket. With the thickness I
chose for the bracket at the mounting point, I found the perfect length of
bolt at Ace Hardware, though the size could be picked up anywhere.

Here is a shot looking over the Cobra caliper at the lower mounting bolt,
this shows how close the extention is to the steering arm, but it works!

Here is a shot of the upper mounting bolt, again close, but it clears! These
are BIG calipers, so they have a wide spread on the bolts.

Tire back on the drivers side, now off to do the passenger side.

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:52:42 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
I thought I would show the inner hub seals from Napa, the part number is
in the picture. They are nice, because they are not felt, but are a little bit
more difficult to install on the spindle, the rubber edge doesnt slip over on
the seal surface like the felt. I finally used the nut to put pressure on the
seal, and then rotated the hub and the seal popped on.

Hub on the passenger side spindle :

Rotor and caliper assembled :

Unfortunately, I found that the passenger side GT brake hose, does not fit
on the Cobra caliper. The locating boss interferes with the block on the
hose (these are banjo fittings). Not sure how I will correct his, I have the
stainless steel braided hoses, but some prelim comparisons made me think
that the braided lines can not fit where the rubber lines are, since the dont
bend as easily as the rubber! A speed bump .... I'll figure it out!

Tire assembly back on the passenger side :

Is this a freaking BIG brake or what? I guess I have now officially taken
away Steeltech's claim of the "biggest brakes available for Studebaker".
Sorry Dave! Though yours still fit inside 15" wheels. These wont!

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:53:06 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
In my effort to keep you all informed of the good AND the bad in this mod,
here is the latest :

After getting everything together on the car, I took it for the maiden
voyage and it was pretty obvious on the first stop, that something was
not right. The pedal was pulsating pretty good. These were two "new"
hubs that I had to history for, so I did some research on the max rotor
runout thats allowable. The spec I found was .005 at the rotor, which
translates to about .002 at the hub. I checked both sides, and one was
at .007, and the other was over .010! I was able to "correct" the .007
side to .0025 by removing the rotor, and hitting the "high" side with
my trusty BFH (Big Freakin Hammer). The hub was about .003 out, and it
was only in one localized area. A couple sharp blows got me .001 out.
With the rotor back on, that translated to .0025, which is within the
.005 max (.003 preferred). The other hub was .005+ out, & it was over
a 180 degree arc. It was pretty obvious that the BFH wasnt up to the
task of correcting that much error. So off the hub went, pressed out
the studs, and brought it to work and had Bobby take .006 off the front
side. Will try it on the car when I get home (before putting the old
studs back in) and see if its within .002 (.001 preferred).

Heck, if adapting brakes was easy - everyone would be doing it!

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:54:08 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
I think I mentioned that the stock Mustang GT front hoses didnt fit the new
Cobra calipers. The problem was that the boss on the hose end, that the
banjo fitting bolt goes thru, is in a different spot on the pass side caliper.
The GT caliper has the boss in the bottom, the Cobra has it on the top on
both sides. To get the GT hose to fit, I needed to match the boss :

Here is another shot of the steel hose bracket I made. I made a drawing
for this, to make it easier to make another set.

Then I had to machine that hub, to get it right took two tries! It must have
been bent, since the pass side hub only needed a good wack to get it to be
within spec on runout. I would assume that a standard brake lathe could
be used to "true" up a hub before new bearings are installed. The other
fix would be to "true" the rotors with the hub bolted into them. I was not
able to do this, as you arent supposed to "turn" drilled and slotted rotors.

Then I went on too the rear brakes. I could have gone to Cobra rears, but
that would require modifying another set of brackets. I figured that the
GT rears were plenty fine for the 30% left to stop the Avanti. But I wanted
them to match .. so here are the drilled and slotted rears installed :

The old rotors :

Drilled and Slotted rotor installed :

Caliper back on, with new pads of course :

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Commander Member

2499 Posts

Posted - 03/07/2009 :  7:54:34 PM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
Decided since I had the gauge, I might as well check the REAR hubs to be
sure that they were in spec, I didnt FEEL any noticable pulsing with the old
rotors, so I though I was safe. Boy was I wrong. I found the pass side hub
was over .014 out! Thats crazy wobble! I dont know HOW I got away with
that before. I think it might be because I was using used rotors, and they
had a slight runout and I was lucky enough to put them on JUST right???

Regardless, I borrowed a puller, yanked the hubs, & pressed out the new
studs. These should be EASY to turn on the lathe. This wouldnt have been
a problem had I just assumed they needed to be "trued". One thing I had
thought of that could cause the rear to be SO bad. To remove the hubs,
you must use a puller that pulls on the studs, the amount of force involved
could warp the hub a couple thousands each time. This slight amount of
runout probably wont make a difference in a drum brake car, but the max
runout on a disc is .005, and the bigger the rotor, the larger the error is to
be exaggerated. Not a big issue to true up with the hub removed, but the
more material thats removed from the hub surface, the more offcenter the
rotor becomes comparied to the caliper. The calpiers are sliding, so they
with self center, but you could remove so much material, as to make the
caliper bracket interfere with the rotor! (thats a lot of material, but its the
worst case). To remedy this isnt a hug issue, some .005 shim stock could
be used between the hub and rotor to recenter. There are always ways to
get around things that dont go together smoothly (see BFH).

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Starlight Member

69 Posts

Posted - 03/08/2009 :  12:56:00 AM  Show Profile  Email Poster  Reply with Quote

As always great work and thanks for keeping us all updated on the progress with these modifications/upgrades. They sure are looking great!

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Commander Member

2499 Posts

Posted - 03/08/2009 :  01:04:59 AM  Show Profile  Email Poster  Visit sbca96's Homepage  Reply with Quote
Thanks Steve, but this is a repost (RP) of the archived article, your
positive comments are certainly welcome, just clarifying that this is
about 2 years ago (not that much else has come about since then). The
yer 2008 was a complete waste, as my wifes recovery from surgery and
the accident resulting in totalling her car all started the year. My
injuries put me behind on the Avanti, and the search for a new car to
replace her "baby". Hopefully soon I can refocus on the Avanti and do
the Cobra rear brakes to match.

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