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Drum Brake Hub, wear liner press fit assembly

kineticmx

Aluminum
Joined
Mar 10, 2014
Location
United States, CT
Been working on machining replacement motorcycle hubs this past year. Lots of learning in the process, current conundrum is brake liners. Securely fixing a steel brake drum liner inside of an aluminum hub without it shifting during use. Brake drum ID is roughly 3.55", been turning steel wear rings out of 1020 DOM tubing. ID bored, OD turned, OD straight knurled to transmit braking torque. So liner ring ID 3.55" ID x OD 3.75" x .95" length. Press fit into 6061 billet hub. Straight Knurl prevents spinning, press fit should keep it in position. Good brake performance, however after hours of use SOME of the brake liners are shifting out of pressed position axially: IE; no longer bottomed in bored hub pocket, slowly shifting out of the hub. Small Screws installed into liner through OD, aka mechanical retainer, have been the current fix for hub liners moving. But there has to be a better way. Any resources on pressing a knurled bushing/shaft into a hub? More interference? Liner OD is a slip fit to the bore before it is knurled. Increase interference fit before knurl? How have the OEM's designed these for 100+ years? Straight knurl + press fit is new to me.

Using 5/8" 30 tooth straight knurl about .030 knurl depth (per lathe wear offset, gives full form knurl), it increases the part diameter significantly, hence my question, how are knurls factored into a press fit assembly.

Appreciate any input, need to get this assembly process reliable, I believe interference should be adequate, just don't know how to calculate these fits pre assembly.
 

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
You shrink fit in ally...any press just shaves the ally....knurl even worse,when the points all break away......anyhoo,tiny brake...minibike?......steel is no good for drums either ,use cast iron.
 

mjk

Titanium
Joined
Oct 20, 2005
Location
Wilmington DE USA
Just a thought, once the heat from braking is transmitted to the aluminum, it will expand faster than the steel.
I would think a closer fit without a knurl and pinning would be the way to go.
Fortunately the brake shoes will blend the pins as the liner wears
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Best solution is to machine your liners (Ductil Iron) with a flange on either the OD or iD depending on the outer drum setup...
Flange on the OD,,,flange is on the outboard end of the drum and fits flat to the face of the drum Use screws of rivets through the flange into the drum outer face.....

Inboard flange: Flange is on the inside inner surface of the liner....seats to the inner wall of the drum...similar to the OD setup but on the opposite side of the liner...rivet or screw flange to drum face....

Lots of early drum brake Italian racing and street cars (Osca, Maserati,Ferrari etc) used the fanged drum setup for iron liners on alloy drums....
Have done a number of replacements on these....need lots of shrink on the liner to keep it tight in service.
Might want to have a look here.....

https://www.practicalmachinist.com/...r-diameter-work-361987/?highlight=Brake+Drums

Cheers Ross
 

plastikdreams

Diamond
Joined
May 31, 2011
Location
upstate nj
We have a 3m product at work we call set it and forget it...it cures at like 250 and doesn't think of coming apart until over 1000°f...if interested I'll get the name of it when I go to work in the morrow.
 








 
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