Raging_Bulls

Hi all.

I'm a reasonable mechanic when it comes to MTB stuff, but never worked with drum brakes.
As a result I feel like it might be time to ask for advice.

I just put an old MTB back on the road to learn its ins and outs before I do a full-on restoration. The bike uses quite large drum brakes (alledgedly made by Sachs) and hasn't been ridden in about 5-10 years (based on the condition it was in when it arrived here).
It rides and shifts ok, but the brakes are plain dangerous.

When I use the front brake, it does slow the bike down a bit (10-0 MPH in about 5 seconds). However I can't use that brake just to scrub off some speed because the brake stays on when I release the lever.
In fact letting go of the lever will loosen up the cable to the point where it can free itself from the arm that's on the drum. When that happens, the cable can get in between the spokes and I could have a major problem on my hand.
Bringing the bike to a standstill will still leave the brakes on, but if I move it backward a little (even 1/16" will suffice), the drum's arm just snaps free again.
The arm requires a lot of force to pull, but releases ok.
Before I mess the brakes up even more, does this sound familiar and are there any parts I need to check?



Also, the rear brake lacks any kind of braking power. 10-0 MPH takes about 10 seconds on that one, and I'm really squeezing the lever as hard as I can. Any tips to restore some power?

fietsbob

see if cable is binding in the housing..

Internally there is just a cam that spreads the brake shoes out,
and return coil springs bringing them back together..

Automobile drum brakes in miniature.

IDK what levers you use.. try V brake levers for their greater cable pull length.

[I use old campag road levers , with my Mustache bars on the bike that has drum brake hubs]

(its my icy road studded tire old mountain bike.. )

UK made Sturmey archer Elite sealed bearing ..

to snappy up the return on a lever that did not have
it's own return spring, I put a coil spring around the cable between the cam turning lever
and the adjusting barrel/cable stop..

spring came from the hardware store ..

Airburst

I had exactly the problem you describe with a Sturmey-Archer drum brake. A mechanic at my LBS, who had previously worked as an automotive mechanic, explained the problem. Basically, it's due to what's known as the servo effect. Basically, because of the way drum brakes work, they are partially self-assisting - the more force the brake shoe is exerting to slow the drum down, the harder it gets pushed against the drum. This does not occur on disc brakes (or rim brakes, which are functionally discs in this sense) because the pad movement is completely perpendicular to the direction of the braking force, whereas on drum brakes, it isn't.

As the shoes in a Sturmey-Archer drum brake wear, the servo effect increases due to the way the pivots are set up. The problem I had was that the brake shoes were worn to the point that the servo effect was enough to jam the shoes into the drum. Obviously reversing the direction of the force on the brake (i.e. by moving the bike backwards) doesn't remove the servo effect, but because the shoes have always worn in the forward direction, the servo effect is no stronger than normal when the bike is moved backwards, and the spring can compensate.

Basically, the shoes may be worn out. I might be able to tell from a picture of them if they are. If they are and you can't find a replacement set of shoes and you still want/need to keep the drum brakes, I'd recommend this as a replacement. Spare sets of brake shoes are available for all of Sturmey-Archer's drum brakes.

Edit: As for the rear brake, new cable/housing would be my first suggestion, followed by possibly sanding the brake shoes to remove any glaze from the surface, and maybe also cleaning out the drum with automotive brake cleaner. Try and keep the brake cleaner away from the bearings and your skin, as it'll dissolve the grease in the wheel bearings and may irritiate your skin.

FBinNY 

Airburst explained one possible cause, but there's another likely possibility, especially if an older more worn brake doesn't release even after a full stop.

The arm rotates an oval (sort of) cam between the shoes spreading them apart. Normally you never reach the tops of the oval, or the arm would rotate past that. When you release the lever, springs on the shoes pull them together rotating the cam back with a sort of wedging action.

But with shoe and/or cam wear, the cam rotates farther, getting very near the top. That means the the wedge angle is flatter, and with wear can be nearly flat, so there's not enough wedging action to push the cam back. The usual fix is new shoes and sometimes a new cam, but new shoes for the British made brakes are very hard to come by (at least here in the states, so you may be SOL.

If you're a fairly skilled mechanic, open it up, check for wear at the key points, and cross your fingers if anything is worn out.

Raging_Bulls

Thanks for the replies so far.

@ Airburst : I took some pics. Click them to enlarge.
From the camera's point of view, the normal rotation of the wheel would be clockwise.












As for changing hubs etc, I'm afraid that's impossible.
The drum brake itself is attached to the fork, and the wheel has a bespoke hub due to being mounted on one side only. It's a prehistoric Lefty really.

EDIT : Just pulled the lever all the way to the handlebar, and the cam doesn't rotate more than 30°. So that's not going to be the problem. It must indeed be the brake pads themselves that are sticking to the drum.

Airburst

Those shoes do look rather thin compared to the ones on my Sturmey-Archer, I'd say they could be worn. Whichever of the theories is correct, both the problems are caused by worn brake shoes, so you may be in trouble, unless SA can save the day again with this single-side mounted drum brake hub and some ingenious bodging.

On an unrelated note, have you got a picture of the whole bike? It sounds intriguing...

fietsbob

Leading edge of those brake shoes is thinner from wear.

does look like there could be a tiny bit of lubrication added to that cam ..

Greenspeed in Australia has a lot of those single sided hubs on their recumbent trikes .

Raging_Bulls

Thanks for the Greenspeed hint, Fietsbob. I'll look into them.


Not too sure on the Sturmey Archer hub, but it might be worth looking into.
If the brakes need replacing indeed, I think my best bet would be to just measure the inside diameter of the drum and contact manufacturers in an attempt to find shoes that could fit.


oh, and as for the whole bike :








It's a 1990 Laïti Mono. French design. I only just took delivery of it yesterday and plan to restore it over the winter.
Even on the French biking forums there is very little info on these things.

Airburst

Wow, that's not a design I've ever seen before!

All I can really say is good luck finding replacement shoes, the manufacturer must've intended for them to be replaced if they wore out, so presumeably they made spares at one point. I suppose they're the sort of thing a really old bike shop might have a couple of sets of lying around in a box somewhere. There's a shop around here like that, they have all these old parts from a load of bike shops that gave them their old stock and have been very helpful to me in the past when I was looking for vintage parts, if you can find a shop like that near you, you may be in with a chance.

Also, I suggest you post a thread on that bike in the Classics and Vintage forum, there may be someone over there who can help you, and if not, they'll certainly appreciate the interesting design!

Bill Kapaun

I would disassemble and lube the cam/bushing.

I don't have a clue about this brake specifically, but see if the top "pin" rotates. It might be slightly elliptical to give you brake pad adjustment.
If nothing else, you could shim it slightly with a piece of aluminum cut from a soda can.

EDIT: Possibly flipping the brake shoes might change things? (maybe worse?)

fietsbob

wonder if Mike Burrows consulted on that? he has long
been on the single sided monostay, 1 blade fork, thing..

Mike is British, he might have solutions to offer ..
particularly the freewheel being on opposite sides
of the Monostay from the hub, in back..

Raging_Bulls

It looks like someone already did that with the front-facing pad.
Based on what I've learned about drum brakes in the past 30 minutes, both pads should be worn at the bottom (where the cam is). The rear one is worn there indeed, but the front one appears worn at the top.

I'll flip the rear one around and tomorrow I'll see if that helped. (it's 1AM here, so a little late for a bike ride)

krome

It is possible to buy brake shoe material and re-line old brake shoes. McMaster-Carr sells brake lining in the US. I'm sure there are other sources. Sometimes brake lining is riveted on, sometimes an adhesive is used. This is used for unobtainium parts.

FBinNY 

One step might be to test the action of the mechanism outside of the drum. If it's perfectly smooth and opens instantly, fit it to the drum and see if it changes, then it's a matter of seeing what is different.

One possibility (pure speculation) is that with the wear toward the ends, that the curvature of the shoes, isn't matched to the drum anymore, and the end of the shoes flex open a bit. That changes the pivot to pivot distance, and there may be a wear pattern where the shoe engages the end of the arm.

I once worked on a friends hub with then identical problem, and also similarly worn shoes. As I remember we couldn't get the cam off to examine it, and got it working as well as we could with cleaning and lubrication, and in the end gave up and fitted a helper spring to push the arm back so it would open. I worked better, but was never right again, and my friend found a slightly used hub and transferred the guts into his wheel.

Kimmo 

Wow, cool bike!

Fingers crossed you resolve this deal-breaker...

Raging_Bulls

Time for a little update.

I went to one of those old-fashioned shops today, where they receive old abandoned bikes and either break them down or fix them up and sell them.
We took the wheels off and went for a rummage in the warehouse. The biggest Sturmey Archer shoes were quite a bit smaller and narrower than these. These really are the size you'd expect on a Honda Camino or similar moped.

I took the brakes apart and checked everything. The arm's pivot has been lubricated and moves freely, the cam is in good condition, the drums themselves seem okay ... but after reassembly the problem persisted.
The culprits seem to be the pads, so Airburst's initial thought was bang on. The shop's owner actually came to the same conclusion as soon as I showed him how the brake behaved.

On the plus side, I found an engraved brand name on the backplate of the drums. It reads "Excelioo".
A Google session reveals 1 post from someone who bought out the stock of an old bike shop and was selling a bunch of hubs, including 1 Excelioo 5-speed hub with brake. It's a different type and only one hub, so it's no good for me.
It would appear that Excelioo was one of those obscure brands that folded shortly after this bike was built and is now completely forgotten.
I guess the only viable option is to send the shoes off to a specialist, who can put new pads on them.

When I first saw a picture of this bike, I knew I was going to be in serious trouble if I bought it. This restoration is going to be one hell of a ride.

fietsbob

"Excelioo", as a trade name does send mixed messages..

Exceli-Loo trips off the tongue easily..

jim p

Just as a test. You could cut an index card in the shape of the brake pad and tape it to the brake shoe. Then assemble the hub and see if the brake would release. If the brake releases this might reaffirm that the pads are too worn. If the brake still wont release, then maybe the pads are not the problem.

wroomwroomoops

I would like to know more about this. I now have a number of drum-braked bikes, both front and rear wheels. One of the front wheels has a drum brake that's rather old and I'm willing to learn how to re-line these brake shoes.

krome

I don't have any personal experience with either re-lining or getting them re-lined. I worked with a guy who had an old forklift, he had them done somewhere. I don't know if it was a local vendor who did it, or a local vendor who sent them off to be done. I had thought that I'd come across the lining material at McMaster-Carr, and I looked there again before I posted to be sure. They might have adhesives for linings as well.

I was told that if the shoe has had any contact with the drum and the associated wear, that the vendors who re-line brake shoes will not accept them. This might be due to some regulatory laws regarding motor vehicles however. As you are looking to re-line bicycle brakes, this may not be an issue.*

You may want to check on some antique car forums, if you are looking for more details on doing the process yourself. It doesn't look like it would be too difficult, just make sure you have the appropriate materials. You might need a jig to clamp the material securely while the adhesive sets up. I think you can even rivet lining to pads that had been adhesively bonded before. Holes are drilled and the lining is counterbored to accomodate a rivet.

Edit: *this might be an issue with shoes that have had the base material worn away. Simply re-lining a shoe that is worn, may throw off the geometry enough that the brake might not work correctly if re-lined.

wroomwroomoops

Claro.


Many thanks!

Raging_Bulls

I'll do the index card test shortly, but either way the brakes will need to be re-lined. I'd rather have that done by a pro, just to put my mind at ease.

When braking softly, the front brake releases just fine. Only when you pull the lever further, the arm doesn't return.
A return spring would be a good temporary fix, but even then the braking will be marginal with these pads. I don't plan to do rolling stoppies, but it would be nice if I could do an emergency stop when necessary. Right now it feels like I'm riding a fixie with a freewheel.

dddd

Very cool bike there!

I was holding out much hope that basic lubrication would help, or that one spring had merely failed (sigh).

I'm assuming you can get those shoes re-lined, and they'll perhaps want to know the exact ID of the drum to determine the lining thickness, maybe even want to have the backing plate assembly at hand.

Good luck with it, and hoping the braking power comes up to a contemporary level!

dedhed

Seeing as your across the pond.

https://www.saftek.co.uk/vintage/saftekservices.html

badmother

I remember re lining the brake shoeson my car when I was young. I would not drill holes in a brake shoe that is not pre drilled, I would worry about weakening it. I would look at old books for auto repair, I am sure they describe the process. I have somebody sleeping on my sofa just now so I do not want to go and search trough the bookshelf.

I was also thinking about peopel restoring motorbikes and cars. Must be forums where they chat just like we discuss bikes.

Just make sure the drums are not worn out. Can cause the brakeshoes to lock to the drum becouse of not being able to return after being spread out too far. Kind of feel I am missing some knowledge of the right woords here..