65 GMC Front Hub Riveted to Brake Drum

[millspec]

Just like I wrote, I have a 1965 half-ton 2wd with single master cylinder pump and pray manual brakes. I was rather surprised to figure out why I couldn’t remove the brake drums on the front brakes.
At first I thought they were just stuck, so I tried backing off the adjusters. No luck. So, I decided to try removing the hub with the drum by removing the dust cap, cotter pin and nut. It came off and to my surprise, the hub is riveted to the brake drum in 3 places!
Of course, the drum is worn, so I need to replace it.
I have looked in the factory service manual, but haven’t been able to answer the questions why and can I drill out the rivets and use a regular brake drum?
The NAPA 440-1071 brake drums seem to have the extra holes for the rivets, but must they be used?


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[lizziemeister'sV6]

You don't need to rivet the front drums to your hubs. Your back drums are loose. What you do need to do is to get the proper drums for your GMC - Chevy drums are not the same as GMC. Lots of parts stores will tell you they are the same - they are not. GMC's have an offset near the lug bolt holes. Take your old drums to compare when you get new. Hopefully other GMC owners will agree with what I said. Any comments?

[millspec]

I’m not sure what you mean by offset. I compared the drum from NAPA to the current one. The hole in the center for the hub is larger on the NAPA version in order for rear axle fitment. When I place it on top of the front hub upside down, there’s about 0.125” clearance around it.
The picture shows some tabs that are bent in which the NAPA part doesn’t have. I’m not really worried about those, but is it okay for the hub hole to be larger than the hub center?
If you happen to know the correct drum part number and a source, I would greatly appreciate it.


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[millspec]

IMG_7224.jpg


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[Prowbar]

Hmm. On my 1500 they are not riveted on, just held on by the lug nuts. But the center bore is a proper fit.
I'd say that the center bore needs to be the right size.
Can't imagine why GMC would use a different drum than Chevy.

What is the diameter of your hub?

I'm looking at Rockauto for a 1965 1000 series, the drums I've looked at list a 90.5mm (3.57") center bore.



Let us know what you find.

[millspec]

Originally Posted by lizziemeister'sV6

You don't need to rivet the front drums to your hubs. Your back drums are loose. What you do need to do is to get the proper drums for your GMC - Chevy drums are not the same as GMC. Lots of parts stores will tell you they are the same - they are not. GMC's have an offset near the lug bolt holes. Take your old drums to compare when you get new. Hopefully other GMC owners will agree with what I said. Any comments?

I took a closer look and some measurements today…and I stand corrected. The center bore size is the same both front and rear at about 0.357”. Also lizziemeister’sV6 was correct about the flange being deeper. When I put the NAPA part on the rear, the drum was not deep enough to completely cover the shoes when fully seated. I would estimate the NAPA drum lacks about 0.250” or so.
They are not the same. I will look at the rock auto drums, but not sure they won’t be the same as the NAPA.
Thanks for the help.
I’ll keep you posted as to what I eventually figure out, but if anyone has any additional suggestions or information, I’m all ears.


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[Prowbar]

Ahh. Now I understand what you mean by offset. Nice job Lizziemeister!

Can you have these drums turned or is there no material left?

[millspec]

Prowbar,
I haven’t checked into machining the drums, but I hesitate to do so for a couple of reasons. First, since the hubs are riveted to the front drums, I’m not sure they can be machined without removing the rivets. This what drove my original post. Second, when I was a kid I used to work in an auto parts store. They used to turn brake drums and also used a machine to re-arc new brake shoes to match the newly machined brake drums.
If I can’t manage to find new drums, I may have to explore machining the old ones.


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[Prowbar]

I understand. Rivets can be drilled out and new rivets can be put in. They need to be removed when you install a new drum anyway.

If you have a shop that turns rotors, it would be worth asking of they can machine it with the hub still on. Maybe a good machine job wants to try it. If you put some nuts and spacers on the lug studs you should be able to reduce most of the chatter I think. Then it can be machined in as one assembly.

Remove the grease seal and wheel bearings and use a live center in the lathe to machine it.

Let us know how it goes.