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Big Twin Springer Brake Drum dimension

Moderators: Curt!, Pa

Post Sun Oct 19, 2008 5:27 pm

Posts: 11
Location: Bergen County New Jersey
Can anyone tell me what is the inner demension of a big twin springer brake drum? Ive been having a problem with with the front brake shoes barely making contact on my UL. Im using an oem brake drum and a new set of aftermarket brake shoes. Cant even use the brake as a hill holder.Any info is appreciated. Thanks
Joe E

Post Tue Oct 21, 2008 11:58 pm

Posts: 530
Location: Ogden, Utah, USA
40UL Joe: I have the same issue with my springer front. Tried new pads bonded to the original shoes with no real effect. Tried a set of new repop shoes and had about the same results. My drum is cast so I don't suspect a lot of wear on the drum. That could be a mistake on my part but I have been known to make mistakes before and I will make more as I go. Never was willing to spend the money on a new repop drum so instead I added a "shim" shaped like ] and [ to the bottom of each shoe to space them out from the cam. I made them from some aluminum scrap I had laying about. Helped a bit, not a lot but a bit. Looked at the problem again and discovered that there is a big space from the shoes to the drum at the top where they pivot. What this means is the "cam" effect is diminished. More pressure is required to enguage less shoe to drum. Please refer to my assumption about wear on the drum above. Put the backplate on an axel and put it in a vice. Then I could turn the assembly to measure it for round and the diameter. Not much joy in the results. My "fix" with the "shims" made for a rather eccentric assembly. Think elipse not circle. With the shims out I was much closer to round and a lot smaller than the drum diameter. I may need that new drum after all. Sorry I never wrote down the measurements I need to keep a journal in the garage I suspect. Maybe some one else has figured out what the dimensions should be and more important what the difference in diameters should be. My best guess at the difference in diameters would be some where around say 1/8th to 3/16 inch? That would be .1250 to .1875 inches. Maybe a bit larger? Someone here should know...I hope. From what I have heard the front brake was never very robust from the factory. Just what I heard folks not a "FACT". :) Steve
Steve H

Posts: 634
Location: Wisconsin, USA
H-D sold O/S brake shoes with a .030 thicker lining to compensate for drum wear or turning, offered for the swing arm era bikes. A local old time brake service shop may have thicker linings available.

Posts: 11
Location: Bergen County New Jersey
Thanks for the info guys.Ive found that the ID of a springer brake drum is approximately seven and a quarter inches .My brake drum is approximately this dimension.I have several springer brake sets and at least one new aftermarket brake drum. No matter what combination I try the results are the same.The crazy thing is I run the identical set up on my 56 pan and it works great!On the pan setup I am using an early set of original brake shoes(Longer).When I tried the Ul brake using another early set of shoes it would not hold.Several days ago I ordered a new dual cam brake setup from the 45 Parts Store ,complete includind their brake drum.Hope this cures the problem.
Joe E


What's missing is something that was standard procedure in drum brake overhauls for 75 years (until the EPA decided that reading the word "asbestos" on a label killed the observer).

The shoes must be arc-ground to the drum size. Find a shop with a big lathe.

If you can't find someone and don't want to use Vintage Brake (who does this), you can improve it yourself. This courtesy of John Healy:
"If you want to arc the linings yourself, and have access to a lathe, first mount the relined shoes on the backing plate. Place .015" shims between the pivot cam(s) and shoes, and turn on the lathe (300-350 rpm) to .010" under drum I.D. in .010" cuts.
Remove the wheel then adjust the levers so both shoes are touching the drum a the same time. Do this by holding one lever hard against the drum with the other lever at first loose. Then adjust the other lever until it is tight against the drum as well. Remove the backing plate. Cut strips of coarse sandpaper (perhaps 100 grit-the coarser the paper the faster the sanding action) the exact width of the working surface of the drum. Using rubber cement (Gasket Cinch or similar product) glue them into the drum working surface so that there are no gaps. Reassembly the brake backing plate with the axle in place. With the wheel axle in a large bench vise apply the brake lever while moving the wheel back and forth so as to sand the brake shoes. Occasionally remove the backing plate, check the progress, and blow out the brake dust (asbestos may be in the old lining so be careful). You may have to replace the sand paper occasionally. The progress is easy to follow and when at least 90% of the shoes working surface show sanding marks, you are done. Remove the sand paper. Clean out the rubber cement with lacquer thinner. The braking difference is amazing."

Posts: 923
Location: South Provence of FRANCE

Hi !
i have had many times the same problem with the repro front brake shoes .( wlc and B.T ONLY !!!! )

in facts : the repops are FINE !
they just have a small "default" you can easyly fix the way i show you on the drawing .
each time i did this way : the front braking was perfect !


you only have to modify the diameter about 2/3 Mms . it's NOTHING .
but these 2 or 3 millimeters will change your life .

to do the job :take measurments on an old original shoe ...

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