New rear brake drums: take Chevy parts and machine them...

[jonny]

My '56 C-3B needed new rear drums, one having been welded by a previous owner and consequently cracked.

 

Anyone who's ever tried to find drums for a C series will know that they're rarer than hens' teeth, and there isn't a direct substitute. I've come up with a solution that might help. 

 

After much measuring of my old drums and digging around online, I found a drum intended for the rear of a '59 Chevy Impala (and possibly a few other vehicles besides), which had broadly similar dimensions and, with some machining, could be adapted to fit.

 

The drums are a Centric 123.62000, which cost a mere £20/$26 a piece from Rock Auto. (Shipping to the UK and import charges were another matter...!)

They have a slightly too small centre bore, the bolt circle is 4.75" rather than the 4.5" of the Dodge, and the drum is a little too deep - only by maybe 1/8" or thereabouts. But crucially, they have the correct 11" internal diameter.

 

I took these drums, plus an old drum and hub for use as a template (separated by drilling the rivets out) along to a local machine shop, who slotted the bolt holes, enlarged the centre bore and trimmed the back edge of the drums for me at a cost of £100 (about $130).

 

I also replaced the old wheel bolts with M14 studs, which are knocked into the hub. The drum now slips on to the hub and is clamped in place by the wheel studs, as on a lot of more modern vehicles.

End result was a pair of drums that fit perfectly over my rear brakes, which I fully refurbished while the drums were at the machine shop - new shoes, new cylinders, all the fittings thoroughly cleaned, and the backplates cleaned and painted.

 

Once I've finished replacing all the brake lines with cupronickel ones, I'll be able to tell you how well they work!

 

https://www.rockauto.com/en/parts/centric,12362000,drum,1744

 

Edited August 7, 2018 by jonny

[jonny]

Here's what lies behind those drums. Much nicer than the rusty, half-complete, seized, leaky and generally broken brakes that the truck arrived with.

[ggdad1951]

clever!  Might next time clock the drum a bit and have new holes drilled instead of slots...while not likely, slots COULD allow some movement off center.

[jonny]

1 hour ago, ggdad1951 said:

clever!  Might next time clock the drum a bit and have new holes drilled instead of slots...while not likely, slots COULD allow some movement off center.

I did think about that, but was concerned about taking too much material out of the drum face. An extra set of holes would mean twice as much metal removed, potentially weakening the drum.

 

To keep the drum centred I had them machine the centre bore to be accurately concentric with the friction surface, and sized to just fit on the centre of the hub. This is what keeps it centred, rather than the wheel studs.

[Merle Coggins]

1 minute ago, jonny said:

I did think about that, but was concerned about taking too much material out of the drum face. An extra set of holes would mean twice as much metal removed, potentially weakening the drum.

 

To keep the drum centred I had them machine the centre bore to be accurately concentric with the friction surface, and sized to just fit on the centre of the hub. This is what keeps it centred, rather than the wheel studs.

 

That's good. I was concerned about that too.

[Silverdome]

At work we will fill the holes with weld then redrill if we have interference issues. That usually only happens if we go from 4 to 5 or 5- to 6 hole patterns or vise versa. Otherwise we just clock them as there should not be enough pressure on that part of the drum to cause any problems.

[Todd B]

Back in the early 80’s I had a Dodge Charger and I bought magnesium wheels for it. They were actually slotted like that so you could use it on different makes. Loosened up the first time but once I torqued them probably they stayed tight. They self center themselves, I don’t see that being a problem. 

[Todd B]

Great idea by the way