1966 Electra Brake Drum Confusion

[TxBuicks]

I'm working on the brakes of my 1966 Electra Convertible.  I noticed a chunk has been taken out of one of the front brake drums.  I asked around and thought I had located one locally, so I went and got it.  When I got it home, I noticed it was different than the one I had.  All of my brake drums are like the one on the left in the picture.  Notice the fins are wider apart and it is not as tall as the one I got locally.  Not knowing what problems this would cause, I returned it for a full refund.  No big deal.  Then, at the recent BCA National meet, I located a set of brake drums that the vendor swore would fit my 1966 Electra.  They were exactly the same as the one I had given back before. They were like the one on the right in the picture.  They had more fins and were taller.  So, now I'm confused.  Can someone explain the difference in these brake drums, and what would happen if I used the drums on the right instead of trying to locate one identical to mine, like the one on the left.  If the drums on the right would work on my 1966 Electra then I will buy them from the vendor I met in Brookfield.  Thanks in advance for your help.

Edited July 21, 2017 by TxBuicks (see edit history)

[Larry Schramm]

The important thing is the size of the brake drum on the inside.  The shoe surface diameter, the diameter from the edge of the drum to the bearing race and the size of the bearing edge to the inside edge of the shoe surface, etc.  If all of those dimensions are the same the drum should work. 

 

The higher number of fins (heat sinks) should help with heat dissipation and reduce brake fade on hard braking. 

 

Also double check the outside diameter of the drum including fins to be sure that they are not so large as to interfere with any other parts.

 

Just IMO and what I would do.

Edited July 21, 2017 by Larry Schramm (see edit history)

[avgwarhawk]

The only difference I see is more fins provide more surface area to dissipate heat.  If the insides diameter and width where the shoes ride are the same as well as the race/bearing for the hub then the drum should work just fine.    

[RivNut]

It's just a difference in  years.  The 45 fin drums preceded the 90 fin drums.  I'm not sure in which year the change took place.  Other than the number of fins, they're the same.

Edited July 21, 2017 by RivNut (see edit history)

[NTX5467]

Is the original aluminum and the replacement cast iron?  Or are they both aluminum?

 

Other than the architectural "hard points" and wheel bearing size, as mentioned, the other dimension to be concerned with is the width of the friction surface, which would also relate to the width of the brake shoes.  

 

Even with a new drum, depending upon how it was warehoused, vertically or horizontally, it might be necessary to do a "truing cut" on the drum in order to get it completely round inside.  I'd wait a while after installation to do this in order than any metal "curing" that might happen with hot/cold cycles was pretty much complete.

 

NTX5467

[Beemon]

There are two different sizes, 2.25" shoes and 2.5" shoes. It looks like your 45 fin has 2.25" shoes and the 90 fin drum has 2.5" drums. I have two 45 fin drums I had gotten last year to convert to the aluminum drums, they're both 2.25". They don't have a lot of meat on them, but if I recall correctly someone relines them now. On one of them I had removed the rivets to separate the drum from the hub to see if they'd work on a stock hub, but they interfered with the stock backing plates on my 56 Buick and stuck out .25" off the hub. Both drums are worn down between the fins and the brake surface, where the backing plate rides. They are no use to me, PM me and maybe we can work something out? You can also get replacement drums over the counter, they're cast iron instead of aluminum, but is a cheaper more local fix to your problem... just need to remove the rivets that hold them to the hub.

Edited July 23, 2017 by Beemon (see edit history)

[RivNut]

From what wear is the 2.5" drum?  I checked a bunch of parts sources for the years 63 - 69 and all of them

show only 2.25" shoes for the front.

[Beemon]

I'm not sure for the 90 fin but it definitely looks too tall for a 2.25" shoe. When I was looking for Roadmaster 2.5" shoes, they didn't exist either but that's what they came with, could be the same here. 

[RivNut]

Don't let the exterior profile of the drum determine the width of the shoe.  The later 90 fin drums have a different profilr6. The first step are deeper and extend over the backing plate more.  Internally they're the same.

[avgwarhawk]

Who relines these aluminum drums? 

[Beemon]

https://www.jgrelining.com/services

[avgwarhawk]

Thank you sir!  My 60 sports aluminum drums.  May need this service one day!