Brake drums

[BTFD 3227]

Greetings all and thanks for letting me in. New here but have been reading along as a guest for a while but can’t find the information I’m in need of.

I’m working on a 55 B85F for our local Firefighters Union and need some help locating rear hydraulic brake drums. At some point the rear brakes have gotten really hot and the pass rear drum broke. The driver side is intact and can hopefully be turned out.  
Does anyone out there have or know of a source for these drums? Or an aftermarket alternative. I just need to find drums to get this old girl stopping again.

Any help would be appreciated.

[Geoff Weeks]

whoo-boy, that is going to be difficult is my guess. Look for some casting numbers on the old drum.

If one got that hot, it is likely you'll need two. Once a drum get hot, it gets hard and will not grab the lining, requiring more pressure to stop, which leads to what you see in that picture.

What is the brake size? Hopefully it is a common size.

[Geoff Weeks]

1st measure the ID of the drum, along with how wide the shoes are

Next measure the pilot diameter (red) and the bolt circle diameter (blue) and start looking for a match

Ideally you'll have a Mack # or a casting # to try and cross.

[BTFD 3227]

Yeah, I’m finding out that the hydraulic brakes on these older Mack’s are rare and rather unique. Especially the rear brakes. I’ve got a casting number off of the good drum but nothing crosses over. 
The rear shoes are 15x5 and are rare as well. 
I’m wondering if I source a set of drums without the concaved bowl, which I’m guessing is by design in case of a seal failure to stop oil from entering the drums, will there be any issues. Unless there’s a seal failure. 
which brings me to another question,,, is the inner bearing a grease bearing or oil bath? If it’s oil bath like the outer, then why is there a seal in the middle of the hub? Another topic for another day I guess.

[Geoff Weeks]

15x5 sounds small for a B85? IIRC that size may be used by wedge brakes.

I have some that have a stamped steel piece that is like your concave bowl.

I don't have a lot of Mack axle experience.

I would 1st try and get some numbers

2nd I would grab a catalog and start looking for drums that match those measurements.

[Geoff Weeks]

here is Webb's offerings, you can look up by brake diameter, you need inboard with 6 or 5/6 mounting holes, and with the pilot measured from your old drum.

https://www.webbwheel.com/webbipad/pdf_files/SD 090 - 2019 Catalog.pdf

[Geoff Weeks]

Gunite's offerings

https://www.accuridecorp.com/sites/default/files/resources/2023-08/WE1.011 Rev. 4 Gunite Brake Drum Product Catalog 8-7-23.pdf

[BTFD 3227]

Thanks Geoff 

Aftermarket seems like it may be my best option. I’ve talked to a couple of individuals up north that may or may not have drums laying around somewhere in their collection. 
 

The stamped steel piece you mentioned, is it separate from the drum and hub? How does it attach? Just wondering if something like that would solve my concern in case a seal fails. 
I need to figure out if it’s even needed. 

[Geoff Weeks]

The stamped steel mounts inside the drum, and is held in place by the same bolts that hold the drum to the hub.

It seams to be left off newer set-ups, My guess the improvement in seal tech made them obsolete.

[h67st]

16 hours ago, BTFD 3227 said:

which brings me to another question,,, is the inner bearing a grease bearing or oil bath? If it’s oil bath like the outer, then why is there a seal in the middle of the hub? Another topic for another day I guess.

The inner bearings were greased. When I built mine I omitted the center seal and made them both oil bath. As GW said, wheel seals have come a long way over the years.

[BTFD 3227]

Thanks guys.

Makes sense. I appreciate the information. 
Hopefully I can find drums now and get this old girl back on the road soon.