14 bolt brake drum question

[scrap--metal]

Do these look like the 11" or 13" drums?

The guys says they came off of a '76 3/4 ton single wheel 14 bolt rear end with 9,300 original miles. It got a disc brake upgrade, so he's unloading these parts.

If they're the correct diameter for my truck, what would be a fair offer? They are powder coated...

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I have yet to get inside my rear brake drums, but based on the heavy rust eating away at the external fins I'm guessing that they're on borrowed time.

 

[SquareRoot]

Hard to tell from that pic. Worse yet, without measuring the inside diameter you can't know how much life is left on them. Worse than that, they are powdercoated. Might make them look better but defeats the purpose of those heat dissipating fins. I would keep looking if it were me.

 

[fast 99]

Should say on the edge max diameter 13.080 or something similar. There are also different width shoes and different offset for floater and non-floater within a 13" diameter.

Agree powder coating is a very bad idea on drums. Pass on those.

 

[squaredeal91]

Those kinda look like the drums to the non floating rear axle

 

[Bennyt]

Do these look like the 11" or 13" drums?

The guys says they came off of a '76 3/4 ton single wheel 14 bolt rear end with 9,300 original miles. It got a disc brake upgrade, so he's unloading these parts.

If they're the correct diameter for my truck, what would be a fair offer? They are powder coated...

I have yet to get inside my rear brake drums, but based on the heavy rust eating away at the external fins I'm guessing that they're on borrowed time.

If he went with a disc conversion, is he selling the entire brake package with backing plates, shoes, wheel cylinders, etc? If all that looks good and its the correct size (diameter and width, and hub mounting), and it all looks like 9000 miles on it, I'd offer $50 for the complete brake package. Stock parts aren't that expensive for drum stuff from Rockauto and almost zero demand for used stuff.

The powdercoat doesn't bother me as I powdercoat most of my brake parts on builds. Drums only do about 30% of the braking and don't get that hot unless you are towing and dragging the brakes a lot, and the powdercoat would burn off if it was an issue. Maybe 200 degrees in heavy use compared to 400+ in a disc.

Heavy rusting on your stock drums may not mean anything at all, you'd have to throw them in the ocean for quite a few years to see any significant material degradation. As long as they

 

[scrap--metal]

Thanks for the feedback guys. My K20 is not used for towing, just hauling stuff and hunting, so I'm not too concerned about heat dissipation in the rear drums. I agree that powder coating will reduce the ability to cool the drums to some extent, but it's not like we're talking about an aluminum heat sink. If I was hauling car trailers and such, doing real 3/4 ton stuff, I'd be more concerned about that aspect.

There are also different width shoes and different offset for floater and non-floater within a 13" diameter.

He's going to measure the drums this evening, including the depth, and get back to me.

If he went with a disc conversion, is he selling the entire brake package with backing plates, shoes, wheel cylinders, etc? If all that looks good and its the correct size (diameter and width, and hub mounting), and it all looks like 9000 miles on it, I'd offer $50 for the complete brake package. Stock parts aren't that expensive for drum stuff from Rockauto and almost zero demand for used stuff.

The powdercoat doesn't bother me as I powdercoat most of my brake parts on builds. Drums only do about 30% of the braking and don't get that hot unless you are towing and dragging the brakes a lot, and the powdercoat would burn off if it was an issue. Maybe 200 degrees in heavy use compared to 400+ in a disc.

Heavy rusting on your stock drums may not mean anything at all, you'd have to throw them in the ocean for quite a few years to see any significant material degradation. As long as they

I asked the seller about the backing plates, and he has those too. Thanks for that suggestion. I think $50 sounds like a good offer if all the parts match up to what I need. I can't touch a pair of drums for under $150, so the cost savings makes sense to me even if the powder coating is somewhat undesirable.

I'll see if I can snap a picture this evening to show you an example of "significant material degradation". My K20 came from WI...

Thanks everybody!

 

[Bennyt]

I think you have a 50/50 chance of these drums fitting. On the '76 it should have had the drum behind the hub and the 80's had the drum in front of 14BFF but I do believe even though backing plate and hubs were different, everything else was the same parts. The early 14BFF is more commonly swapped to disc because of the amount of time it takes to work on brakes as you have to pull the axle/ hub.

 

[OldBlueDually]

@scrap--metal here is a pic from a while back on my dually-----originally a single rear 76 GMC full float, 14 bolt corporate---with a dually conversion done to it, so drums should be the same.

Mine look like crap, but they are actually quite new with very little wear. I think someone replaced them, barely drove the truck, then parked it--the MN rust did the rest.

Those drums you show look a little different and no center hub. Like @Bennyt mentioned, the axles had to come completely out of the rear-end to get these off.

I happened to have this picture in my build thread

 

[scrap--metal]

I think you have a 50/50 chance of these drums fitting. On the '76 it should have had the drum behind the hub and the 80's had the drum in front of 14BFF but I do believe even though backing plate and hubs were different, everything else was the same parts.

Those drums you show look a little different and no center hub. Like @Bennyt mentioned, the axles had to come completely out of the rear-end to get these off.

Thanks for the info! I'll have to look things over more closely on my truck. I haven't taken the rear wheels off this one since I bought it, so I have some learning to do. I've been in many 10 bolts, but the 14's are still new to me.

 

[scrap--metal]

I'm pretty sure I have the smaller 11" brake drums. See the picture below; wheels are 16" for reference. I'm guessing my ability to use the 13" set up that's for sale, including backing plates, depends on whether my drums sit in front of or behind the hubs. Does that sound correct?

The picture below shows the "significant material degradation" I previously referred to. Some of the cast fins are missing. @Bennyt I can promise you these weren't in the ocean.

Maybe the hub location can be determined from the pic below as well? Again, IDK jack about these 14 bolts yet. I plan to take a peak inside the drums this Saturday if things go as planned.

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[sickchev]

Here is some pictures of my 11s off my FF 3/4 ton 1979 c20.
I purchased new drums from a parts store for $120 per drum.

https://www.autozone.com/brakes-and-traction-control/brake-drum-front/p/duralast-brake-drum-8847/22004_0_0

Full build thread will all the brake rebuild part number can be located here: https://www.gmsquarebody.com/threads/1979-c20-long-bed.37512/page-3

 

[scrap--metal]

Here is some pictures of my 11s off my FF 3/4 ton 1979 c20.

Thank you for the pictures, and the links.

I have a better understanding of how the drums and hubs go together now. A picture's worth 1000 words...

I believe my hubs/drums look like @sickchev example pictures above. With that being said, could it be possible to swap the hubs from my 11" drums to the 13" drums that are for sale? The 13" drums obviously don't have any hubs in them. I'm thinking this would be dependent on the drums having the same height/depth so the axle position is not changed.

 

[RaisedK5]

I swapped from 11 to 13 on mine. Only issues I ran into were differences in e-brake cable attachment and I needed longer studs b/c the 13" drums were thicker than the 11s. The e-brake cables were b/c I had an early 70s 11 inch set up and went to a later 80s 13" set up and at some point they started using that crossover dealio for the cables so they both ran to the driver side. I just found a couple short cables that would fit the backing plates at the junkyard and adjusted the frame mounting so it would pull them enough.

 

[Bextreme04]

Also, for all things 14 bolt... this is pretty much considered THE resource: http://www.billavista.com/tech/Articles/14-Bolt_Bible/index.html