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GT Mustang to 13" Cobra brake Avanti upgrade process


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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! :

Cobra_rotor_fitment_009a.jpg

The next step was to press out the old studs :

hubs_001a.jpg

hubs_002a.jpg

hubs_003a.jpg

Here is the studless hub :

hubs_004a.jpg

Did you know that the factory studs have NO knurl?? No wonder they tend

to strip out so easy with an impact gun!

hubs_005a.jpg

They looked SOOO ugly, I scraped them with a screw driver, and the took

them to work and used the wire wheel :

hubs_006a.jpg

hubs_007a.jpg

hubs_008a.jpg

hubs_009a.jpg

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.

Enjoy!

Tom

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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:

Rear:

rotors001a.jpg

Front:

rotors002a.jpg

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 :

rotors003a.jpg

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

rotors004a.jpg

Close up :

rotors005a.jpg

Tom

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Nice work and pics :D. Taking the time to post this work is much appreciated. It should be a quantum leap forward in improved braking and future brake service-ability.Joe M

Thanks Joe ... its certainly taking some effort to get done!

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 :

hubs_010a.jpg

Then I used my two cut old races to tap the rest of the way until the race

was against the machined step inside :

hubs_011a.jpg

hubs_012a.jpg

hubs_013a.jpg

hubs_014a.jpg

Then I pressed in the Dodge shouldered studs :

hubs_015a.jpg

hubs_016a.jpg

hubs_017a.jpg

Finished hub, waiting to go on the car :

hubs_018a.jpg

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.

cobra_install001a.jpg

cobra_install002a.jpg

Clearance for wrenches is tight, but it works :

cobra_install003a.jpg

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 :

cobra_install004a.jpg

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!).

hubs_019a.jpg

hubs_020a.jpg

hubs_021a.jpg

hubs_022a.jpg

hubs_023a.jpg

Tom

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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.

cobra_install005a.jpg

cobra_install006a.jpg

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.

cobra_install007a.jpg

cobra_install008a.jpg

cobra_install009a.jpg

cobra_install010a.jpg

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!

cobra_install011a.jpg

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.

cobra_install012a.jpg

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

cobra_install013a.jpg

cobra_install014a.jpg

cobra_install015a.jpg

Tom

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.

cobra_install016a.jpg

cobra_install017a.jpg

Hub on the passenger side spindle :

cobra_install018a.jpg

cobra_install019a.jpg

cobra_install020a.jpg

Rotor and caliper assembled :

cobra_install021a.jpg

cobra_install022a.jpg

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 :

cobra_install023a.jpg

Is this a freaking BIG brake or what? I guess I have now officially taken

away Steeltechs claim of the "biggest brakes available for Studebaker". ;)

Sorry Dave! Though yours still fit inside 15" wheels. These wont! :o

cobra_install024a.jpg

cobra_install026a.jpg

Tom

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Tom,

Those are some mighty impressive speed scrubbers! The original set up looks like tinker toys in comparison. The wheels, rotors and calipers look tremenodus on the car. Woo hoo!

So how come you need to stop so fast? ;) Do you have an equivalent upgrade in mind to connect to the accellerator pedal?

Joe M in WV

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Great job Tom! Its really coming along. On a side note - as a professional mechanic I can't stress enough that I hope there were jack stands under the frame out of the picture. You should NEVER trust a hydralic jack with your safety. I want you to be around to enjoy those brakes.

Jim

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You caught me, no there was no jack stand under the car, usually I use them, and they were only

about 6 feet away. I just didnt. If I was going under the car, I would have done it for sure, but I

wasnt under it, so I figured worst case, it will just end up on the jack.

As for needing big brakes, I needed brakes, and I figured why have what everyone else has? I

decided to share that it COULD be done, and have been asked for help in doing so. If you look

at the cost, it wasnt that much more expensive then Steeltechs 12" setup. Heck the two front

rotors costed less then one replacement Stude rotor. Both calipers were less then 200 and thats

with pads installed. Still prototyping, but its coming along. ;)

Tom

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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!

Tom

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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 :

brake_hose_mod_001a.jpg

brake_hose_mod_002a.jpg

brake_hose_mod_003a.jpg

brake_hose_mod_004a.jpg

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.

brake_hose_mod_005a.jpg

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.

front_hub_milled_001a.jpg

front_hub_milled_002a.jpg

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 :

GT_rear_disc_001a.jpg

Drilled and Slotted rotor installed :

GT_rear_disc_slotted_001a.jpg

Caliper back on, with new pads of course :

GT_rear_disc_slotted_002a.jpg

GT_rear_disc_slotted_003a.jpg

Tom

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  • 1 year later...
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! :

Cobra_rotor_fitment_009a.jpg

The next step was to press out the old studs :

hubs_001a.jpg

hubs_002a.jpg

hubs_003a.jpg

Here is the studless hub :

hubs_004a.jpg

Did you know that the factory studs have NO knurl?? No wonder they tend

to strip out so easy with an impact gun!

hubs_005a.jpg

They looked SOOO ugly, I scraped them with a screw driver, and the took

them to work and used the wire wheel :

hubs_006a.jpg

hubs_007a.jpg

hubs_008a.jpg

hubs_009a.jpg

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.

Enjoy!

Tom

Hi Tom,

May I callyou re: the Cobra brakes ?

Irvsails@webtv.net

Irv Rich

Irv83

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