57 PW Brake Drum Dia.Tolerances

[Resto Ray]

Hello,

I would like to have my 4 drums resurfaced, what are the tolerances I have to work with? They are 14'' drums.

Thank you,

Ray

[W_A_Watson_II]

Per the Army's TM 9-1808B
Diameter of new Drum = 14-1/8 in.
Thickness of new shoe lining = 1/4 in.
Drum wear limit = .020 in.

[Resto Ray]

Per the Army's TM 9-1808B
Diameter of new Drum = 14-1/8 in.
Thickness of new shoe lining = 1/4 in.
Drum wear limit = .020 in.

Hmm..about 1/32 of play-doesn't leave much room for improvement:(
Thank you for the prompt reply and the additional info!

Who is the best source and price for shoes in the USA? I have VPW prices. Being from Canada its a 30% premium do to our CND dollar dropping like a rock, before shipping.

[Frank Irons]

The manual I have, TM9-8031-1, lists the wear limit of the drum at 14.220" If you have your drums machined make sure they are on the hubs when it's done and also tell the machinist to take as little material as possible off.

Frank

[W_A_Watson_II]

Frank's information on turning on the hub is indeed the smart way, his manual is likely a later updated and is good to know (TM 9-1808B was 11/1943). There are also brake pads with a slightly thicker lining available to help on those drums that have been turned to the maximum limit.

[Greg Coffin]

Unless the drums are out of round or somehow damaged, I would not turn them. New shoes will break-in after a short while. And oversize friction material is available for oversize drums.

[Resto Ray]

I'm finally getting around to completing the axles rebuilt as well as having the drums machined-(9 months after my original question...sigh). I was looking for some best practices before bringing the hubs and drum assemblies to the machinist.

Would it be best to paint the hubs and drums before of after the machining? Hi temp paint on both?

I know the hubs need to be matched with the drum, after machining can I take them apart as long as they are index and put back in the same position?

Should I press in the new bearing races before or after machining? I would be of the thinking that it should be prior?? Though I'm concerned they may be damaged from the machining jig??

Thank you

[Frank Irons]

I'm finally getting around to completing the axles rebuilt as well as having the drums machined-(9 months after my original question...sigh). I was looking for some best practices before bringing the hubs and drum assemblies to the machinist.

Would it be best to paint the hubs and drums before of after the machining? Hi temp paint on both?

I know the hubs need to be matched with the drum, after machining can I take them apart as long as they are index and put back in the same position?

Should I press in the new bearing races before or after machining? I would be of the thinking that it should be prior?? Though I'm concerned they may be damaged from the machining jig??

Thank you

You could paint before or after machining, I do it after. Drums can be removed once the machining is done, they will go back on only one way. I leave the old cups in for machining as the turning will generate a lot of cast iron dust which must be thoroughly cleaned out before you install your new cups and cones.

As Greg pointed out above, unless your drums are really bad I would not turn them. Finding a good shop that will take the minimum material off till clean up is important. Most shops want to take one pass and be done.

Frank

[wayneh]

turning drums

Ray: I had my brakes lined while I waited in Baltimore Maryland at a place called Friction Material Services. They re-line things like elevator brakes and bus/truck brakes. They did it for less than I could buy them for online but I could not buy the 20 over linings.

Regarding turning the drums. The toe/heal adjustments on are brakes are critical if you expect to get a decent pedal and not have it sink half way to the floor before it stops. To do that, the distance between the drum and shoe is very critical. The books give specs, but the bottom line is they should just start to drag. All four, not just one or two!

Now if the drums are worn or the pads are worn don't expect the cam to make up the difference. They won't, and you will never get the proper clearance and hence never get the right pedal. What I am saying is if you must buy shoes from the internet, get the 20 over shoes.

On turning the drums. OEM drums need to be turned if you expect to adjust the shoes and have even drag without high or low spots. You have to leave the bearing race in to do that, but you remove the bearing and seals. Most important though is to thoroughly clean the mating surface between the drum and hub. If you leave old paint, rust, scale it will never run true. When I first started hanging out at the machine shop I thought they were having me do busy work wire brushing rotors and drums before we turned them. It turns out that 0.001" of paint or rust gets multiplied because the drums are so huge, so make sure those mating surfaces are clean and the drum is tightened to spec with the lug nuts, not just the screws when you turn them.

I had a chance to check out two other PW brake systems this past weekend. Both were horrible compared to mine. But I worked hard to find nearly OEM drums and I used new shoes.

Now bleeding them is easy too, but forget about having your wife or GF pump the brakes while you bleed them, that is not the most effective way to do that today.

Wayne

[Resto Ray]

Thanks for the tips guys!
I'm going to clean the grease and grime before handing it over to the machinist. I will literally have him knock down the outside grove from the brake pad wear on the drums and explicitly tell him to surface machine any unevenness but to not oversize past 14.145 as a max wear limit isn't much room at all:(

Sounds like power bleeding is the only option for effective functioning brake.

I was not aware of a thicker lining option-darn. Having the pedal press to the floors isn't an option as this is a nut and bolt resto and want to operate just as well as the weekend efforts going in to this:)


**I purchased my new brake pads from DC Truck Parts-always great service.

[Resto Ray]

Ok. My drums and hubs have been prepped for machining and sitting at my local machine shop-a one man show. He's particular and we've been going back and forth. Initial dia measurement are 14.200 on three and 14.220 on another.

He wants to be as close as perfect as possible. Pushing the dia to 14.250 was suggested by VPW-if absolutely necessary. Any thoughts with new stocks shoes at 14.250. My machinist discussed oversized shoes at .020 over. (Locating some a whole different story here in Canada) May have to send mine to Baltimore Maryland as suggested:(

My machinist, has asked me to measure the dia of the new .250 shoes when installed on the truck at there maximum adjustment. Do any of you have this figure by chance? He wants to to get all the numbers in front of him to look at the best option.

Bob as also offered to arch the new shoes.