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Issue with disc brake conversion on a 9"

Fishnbeer

The dude abides
Joined
Jun 8, 2020
Member Number
1907
Messages
409
Loc
CA
Hey guys, just joined up here. Looks like the 'other place' is a barren wasteland now.

I am working on an early bronco and going from drums to disc. I went with the BC bronco kit. Their design mounts the rotor to the inboard side of the axle flange and the wheel studs secure the rotors to the flange. The issue I have is the knurled part of the studs will not press into the holes on the axle shafts, the hole diameter is too small (or the stud is too big). They are not ford shafts, I am running 31 spline dutchman chromo shafts.

i called up bc broncos and they sent me a second set of studs but they are exactly the same. I know the studs they use are made by dorman. So I d/l the dorman catalog and went through all the studs they make and I concluded they dont make a stud that will work for what I got.

So I am wondering if it is possible to drill out the stud holes on the larger to take this stud? They are chrome moly but I dont know what grade, how hard, etc. Should I pull them and take them to a machine shop? Ditch this kit and put drums on? Im kinda stuck here

thanks
 

'84 Bronco II

El Chingón
Joined
May 19, 2020
Member Number
293
Messages
1,239
Loc
NM
It should be no problem to drill the holes out on the shafts, you just need to figure out what size hole you need for a proper press fit. If you have a solid drill press and a good drill bit (Cobalt or carbide), you should be able to do it yourself fairly painlessly, but if you don't, or feel uncomfortable, if shouldn't be a very expensive machining job.

I think the best answer though is to just buy the correct size wheel studs for your shafts. What size are the stud holes currently in your shafts, and what size (or part number) are the studs BC sent you?
 

Fishnbeer

The dude abides
Joined
Jun 8, 2020
Member Number
1907
Messages
409
Loc
CA
Well I wanted to just find the right stud because that is the easiest option, but I went through the whole dorman catalog and did not find what I need. Then I looked through ARP and they have something that looks close but I dont think it will work.

The studs that I got are dorman part # 610-273. Their site lists the knurled section as .625" diameter. I cant find my damn micrometer right now, but the holes on the flange are slightly larger than .500 (threads are 1/2"-20)

I did some googlin' and searchin on youtube and it looks like it is a fairly common thing to drill holes in the hub flange. Some guys do it to install larger diameter studs and some do it for a new bolt pattern. I am a little worried about torching all my bits and possible drilling the holes out too big. I think I am just going to take the shafts, rotors and studs to a machine shop and have them take care of everything.
 

Phil

The Thrill
CAL4
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May 20, 2020
Member Number
754
Messages
78
Loc
West Sac CA
Dude if your shafts are threaded 1/2-20, and the lug studs you want to run are 1/2-20, why not just run thread-in lug studs? Drill out nothing.
 

Fishnbeer

The dude abides
Joined
Jun 8, 2020
Member Number
1907
Messages
409
Loc
CA
Sorry if that came out wrong... hub flanges are not threaded. I was referring to the threads on the studs. Hub flanges have holes slightly larger than 1/2"...
 

'84 Bronco II

El Chingón
Joined
May 19, 2020
Member Number
293
Messages
1,239
Loc
NM

Fishnbeer

The dude abides
Joined
Jun 8, 2020
Member Number
1907
Messages
409
Loc
CA
A picture might help here. The stud I need is not as common because it has a shoulder where the rotor sits and then the splined section starts. Its not a regular stud where splines meet the head. I just cant find a stud like this with the same size shoulder (I think 21/32 for the shoulder where the rotor sits) and spline diameter closer to 1/2". In the entire dorman catalog there are maybe 5 studs that are this style. There is an ARP stud that looks close but I dont want to buy $75 studs and have it not work out...

photo8242.jpg
 

Fishnbeer

The dude abides
Joined
Jun 8, 2020
Member Number
1907
Messages
409
Loc
CA
Well I decided to take a stab at it. I drilled a 9/16" hole in some 3/8 plate and it was a nice tight fit for the studs I had. So I swapped the belts on the drill press to run as slow as possible, used some 90w for cutting oil and applied light pressure. I imagined it being super tough stuff and impossible to drill, but was not too bad.

photo8663.jpg
 
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