Drilling rear drums

[AlaskaJeff]

So I am in the process of swapping out the center section on my 8.75 rear axle from a 741 case 3.23 open to a 489 case 3.73 sure grip unit. I also acquired a set of a-body BBP axles that I would like to put in so I can get rid of the SBP to BBP spacers/adapters that are currently on my street driven Duster. I would like to swap out backing plates and all associated brake components from 1 3/4" to 2 1/2" brakes BUT it's just not in the budget at this time. Can I just drill out my current 10" SBP drums to BBP and be on my way? I know it's not ideal but it should work for the time being. Or am I missing something?

 

[33IMP]

Depends on if your axles have the big brake offset, or the small brake A-body offset. If the offset is the same as your small pattern axles, you should be good with just drilling your drums.

 

[AlaskaJeff]

Depends on if your axles have the big brake offset, or the small brake A-body offset. If the offset is the same as your small pattern axles, you should be good with just drilling your drums.

I'm not sure about the offset you speak of. How can I tell? From what I can see they were stock SBP axles that were drilled for BBP. There are 2 sets of lug stud holes with the BBP ones filled with studs.

 

[33IMP]

Those just look like redrilled stock axles, rather than aftermarket axles with the big pattern, intended for the big brakes. So basically you are stuck with the small brakes, but drilling the drums is all you need to do.
The offset is the difference between the wheel mount flange and the flange that the retainer bolts to. It's different between the big brakes and a bodies. The backing plates are different too.

 

[AlaskaJeff]

Those just look like redrilled stock axles, rather than aftermarket axles with the big pattern, intended for the big brakes. So basically you are stuck with the small brakes, but drilling the drums is all you need to do.
The offset is the difference between the wheel mount flange and the flange that the retainer bolts to. It's different between the big brakes and a bodies. The backing plates are different too.

They do appear to be stock axles from what I've researched. I have been out of the Mopar muscle game for decades and have forgotten most of what I knew when I was a 20 something back in the 80s Thanks.

 

[doug 371]

You must use your original backing plates, shoes and drums. Did they use 7/16 or 1/2 inch studs?

 

[AlaskaJeff]

You must use your original backing plates, shoes and drums. Did they use 7/16 or 1/2 inch studs?

I figured as much. I am pretty sure the BBP axles I've got have 1/2" studs. I never thought to confirm. Something to check for sure. Thanks.

 

[Syleng1]

And to answer the original question. “Yes” you can drill your original drums but my suggestion is to drill them in between the factory holes and not oblong the originals. Knock your current studs out of the axle and center it and mark holes and drill. My 72 Demon has Mosier axles at the 5x 4.500” 1/2” studs but set up for factory brake backseat so the original drums work. Machine shop did the holes for me.

 

[AlaskaJeff]

And to answer the original question. “Yes” you can drill your original drums but my suggestion is to drill them in between the factory holes and not oblong the originals. Knock your current studs out of the axle and center it and mark holes and drill. My 72 Demon has Mosier axles at the 5x 4.500” 1/2” studs but set up for factory brake backseat so the original drums work. Machine shop did the holes for me.

The deed is DONE! Not machine shop perfect but they will work. I checked and the replacement axles and they have 7/16" studs. So I am going to upgrade them to 1/2" before installation. And a look at the spacers I was using.
Are the axle lug studs pressed in? Can I knock them out myself or should I let a machine shop R & R them?

 

[33IMP]

Knock em out yourself. Put a standard lug nut on, flat side out, leave it proud a little on the stud, and whack away.
I doubt they will be usable in your axles.

Wait. Are you talking about the studs in the adapter, or the axles?
I'd knock em out of the adapter, have the axle ones pressed out, BUT ONLY after I found some 1/2" studs with the same knurl.

 

[AlaskaJeff]

I remember changing out lug studs back in the 80's on my 67 Barracuda. after breaking off 2 studs and realizing the drivers side was still LH threaded!!
Since the studs currently in the axles are 7/16" and I'll be replacing them with 1/2" will the holes need to be enlarged to accept the larger studs?

 

[33IMP]

Press out one stud (or knock out) and measure the existing knurl, then try to find a 1/2" version with the same (or maybe plus a few thousandths) knurl. Think Dorman catalog. Dr Diff also might have the part number you need.

 

[Daves69]

...........I'll be replacing them with 1/2" will the holes need to be enlarged to accept the larger studs?

FWIW, this is what my stock '69 re-drilled flanges for 1/2" studs look like. The old 7/16" holes were filled.
You'll get pretty close to the O.D. with press-in studs. These studs are 1/2" X 2" screw ins...........

My Moser re-drilled direct replacement axles have a larger diameter and thicker flange on them with press ins.........

 

[4mulas]

I remember changing out lug studs back in the 80's on my 67 Barracuda. after breaking off 2 studs and realizing the drivers side was still LH threaded!!
Since the studs currently in the axles are 7/16" and I'll be replacing them with 1/2" will the holes need to be enlarged to accept the larger studs?

I wouldn’t do that. if you do the holes will be very close to the flange on the axle. Plus if you want Cragar’s etc.. the 1/2 mag nut won’t fit in the bore hole of the wheel. Ie: standard 1/2 mag nuts have a .68 shank thickness and the 7/16 nut has a shank thickness of .61 inch. You won’t fit the shank of the 1/2 nut into the wheel

 

[Heywodja]

I have a set of the Moser axles, and some re-drilled drums that I just took out of my dart

 

[65Val]

Also, I would get the old holes in the axles welded up, for added strength.

 

[AlaskaJeff]

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