Cafe Racer Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
33 Posts
Discussion Starter #1
Anyone know the secret to setting up drum brakes? I'm a little to young I guess to have worked on a car or bike with them and have ever only done discs in the past. It seems like no matter what I do I can't get a good balance between dragging the shoes and having good stopping power and not dragging the shoes and not having good stopping power. I'm in the middle of an 82xr 250 rebuild with a rear drum brake and a 70 cb450 with front and rear drums. If slowing down were the goal I'd have these things nailed but actually stopping seems like a far off dream... Anyone have the same experience or have any tips?

Thanks dudes!
 

·
Registered
Joined
·
306 Posts
I've read the cb160 racing guys get their drum brakes relined at a place in seattle called "metal friction". that might be worth checking out!

here's the quote from www.groupwracing.com (the whole article is a great read!) :

"Have the drums turned and the brakes relined if you can - it will make a big difference. We use a brake shop in the Seattle area (Metal Friction) that relines the shoes with an industrial truck brake lining which is cheap and works well, turns the drums and radiuses the shoes. I'm sure that real roadrace lining like Ferodo would probably work better, and someone like Michael "Mercury" Morse at www.vintagebrake.com would do a great job for you."
 

·
Registered
Joined
·
1,112 Posts
quote: If slowing down were the goal I'd have these things nailed but actually stopping seems like a far off dream...
No, sounds like you about got it.



Are the shoes at all glazed? Scuff them with some sandpaper, make sure your actuating arm is set at a good angle and for your front also be sure your cable is lubed and adjusted with a balanced amount of play at the wheel and the lever.
 

·
Registered
Joined
·
3,065 Posts
The key with getting any of the vintage stuff to work well is attention to detail. Good set-up will do wonders. For brake shoes I prefer the ones JohnnyB sells here on the forum to the ferodo race compound from V.B. Speaking of Vintage Brake he has a page with drum brake set-up tips here http://www.vintagebrake.com/tips.htm here's the excerpt:

quote:DRUM BRAKE TIPS

Carefully inspect drum surface for grooves (obvious), crown (not so obvious), out of round and high-low spots (dial indicator). Crown often occurs with riveted linings. High-low spots commonly result when relacing hubs. There is no substitute for a freshly turned drum for premium friction materials to bed-in against. It's like putting a new piston in an old bore-never as good as with a fresh bore and hone. And you should inspect drum surface with the same critical eye. Tolerance: .002 to .004”" any dimension. Up to .010” out-of-round may be tolerated.

If you are re-riveting new linings yourself, DO NOT drill out the rivets. Chisel off the peened end and drive the rivet out.

Materials currently available far exceed those previously available. Reline your shoes with a current premium compound

Keep in mind the low unit pressures required for mechanically operated drum brakes. Most linings require the higher unit pressures available hydraulically.

Very few modern materials are compatible with pressed steel drums.

Lay back leading edge of leading shoes in 1/2 inch increments to minimize initial "bite" if brake is too "grabby", especially when hot.

The expanded metal used to cover scoops is typically 15% to 23% open area. Replace them with stainless steel screens with 50% to 60% open area, tripling air flow.


Use sealed wheel bearings --grease vapor can contaminate linings. Once contaminated, they never recover.

.Lubricate backing plate components SPARINGLY with a 500F. + degree grease, such as Sta-Lube Sta-Plex Extreme Pressure, available at NAPA. Liberally lube parts and assemble. Disassemble and carefully remove all excess grease.

Check to see how far the backplate extends into the drum. Too far in and the sides of the shoes drag on the hub, creating excessive heat. Epoxy a shim to the inside of the backplate. Not far enough, and a ridge forms where there is no contact. Bend backplate or remove material to correct.

Worn pivot shafts cause uneven actuation. Rebush if necessary.

If a stay is used, make sure it does not cock the backplate.

Always apply brake when tightening axle.

If you want to arc the linings yourself, and have access to a lathe, first mount the relined shoes on the backing plate. Turn on the lathe (300-350rpm) to .020" under drum I.D. in .010" cuts.
 

·
Premium Member
Joined
·
11,267 Posts
From the brakes I've worked on, the two primary factors are:

1: Secondarly linkage adjusted properly

2: Shoes arc'd to match the drum ID.

That gets you the first thing you need...maximum contact between the shoes and the drum. Next you start worring about the compound if you need more brake. Great compound won't do squat if they aren't making contact with the drum.

Using street compound...you can expect around 30 - 40% improvement in braking power just setting up the brake well, as compared to the typical poorly adjusted street bike brake. Add another 20 - 30% braking power and better race track behaviour from race compounds.
JohnnyB
 

·
Registered
Joined
·
1,898 Posts
what johnny said but i'd add to check drum condition...sometimes a rusty area can cause drag before "real" contact is made thus requiring extra clearence for drag-free running.
-parks
 

·
Premium Member
Joined
·
11,267 Posts
Yes...a round drum is important...and if you have .010" of rust...not really rust...but the effects of old rust...pitting and such. Yeah, shoes make contact there first and don't do much stopping.

On race bikes...if you run in the rain a few times with vented brakes it's important to pull the brake down and clean it up, it will get rusty.
JohnnyB
 

·
Registered
Joined
·
4,721 Posts
I agree that chucking the assembled backing plate up in a lathe

and turning them to the correct radius of a well finished surface is the most important

then comes pivot and sliding surfaces being detailed

then linkage and such

"arcing the shoes" isn't a difficult job but commonly not done

it only takes a slight mismatch to start out with brake shoes that only make 25% contact and they can take a Looooooong time to wear in and seldom ever wear in to make 100% contact when starting out so wrong initially

huge difference in effectiveness when starting out with appropriate linings on shoes matched to the drum

when compared to minimal contact area

agreed on cleaning the vented brakes too, not a bad idea to clean non vented ones from time to time

and keep the pivot and sliding surfaces properly greased
 

·
Premium Member
Joined
·
11,267 Posts
To expand on something Hack mentions above. Those "sliding" parts I've found to be more important than you'd think, and totally ignored most of the time.
When I set up a race brake I polish the edges of the cam that contact the shoe, and I polish the steel plate on the end of the shoe that contacts the cam. Then apply a light coat of grease.

The reason I do this is.... I've put together some real nice brakes, set them up perfectly...then when I installed them I found the feeling at the lever was kind of rough, a very subtle roughnes...it was ok when using full on brake...but at that point where you are just engaging the shoes to scrub off a bit of speed the lever would feel very slightly rough and catchy.

I tracked this down to rough surfaces on the cam, and a rough machined surface on the steel cam contact plate on the shoe (Aftermarket are way worse than OEM...hence I only have OEM shoes relined). So I polish both the components down close to mirror smooth (not too smooth cause I want them to hold some lubricant). Makes a big difference in how smooth the brake engages and disengages at the lever....a big plus on touchy race compound shoes.

Like Hack suggest...same at the pivots, a rough finish and no lube ends up giving the brake a grainy feel at the lever when you start to apply some force to them.
JohnnyB

PS. When you finish working on your brake the brake arm should snap back into place smartly and smoothly. When you work it with your hand you should feel it expanding the springs with smooth snapping action. Same spot every time, shouldn't need to be nudged into it's neutral position, it should find it smoothly and quickly, the same place every time.
 

·
Registered
Joined
·
4,721 Posts
nice to read some quality stuff like that on this subject

if I ever get to where I can't do my own

I'll keep you in mind
 

·
Registered
Joined
·
33 Posts
Discussion Starter #13
Thanks for all the input guys! This is really helpfull. I put the xr back together last night (I should post up some pics) its looking sweet! I swapped out the old front end for a newer fork setup with a disc brake just so I did'nt have to deal with drums. The disc setup is awesome! I did a stoppie in the driveway and the brakes weren't even bled all the way. Now maybe I can get that back brake to do something... Also, I picked up front and rear shoes from Micheal at Vintage Brake for the cb, so now that the xr is back together I can start workin on those brakes too.

I'll let you know how it goes!
 
1 - 13 of 13 Posts
Top