Brake problems - left brake does nothing then locks up

[pn_day]

Dear all,

(With apologies for English. I've included an attempted translation from DeepL below)

I recently modified the brakes in my Alleweder using the tips from the thread on optimising brakes - now the cables go from underneath and are shorter. I also added "da tilla" and some new clamps from the exotic Swiss velomobile store, and renewed the brake inners (outers still looked absolutely fine, and were only 3 years old).

However, since doing that I've had difficulties getting the left and right brake to be even. Before I made any changes, both brakes were even, but didn't ever apply enough force to lock the front wheels. I now have enough force that I can lock both wheels - but it doesn't happen progressively.

Now it feels like the left brake doesn't do anything until I pull harder on the tiller brake lever, then suddenly the left brake locks. The right is working perfectly.

What could be wrong? Does anyone have any ideas of what I could look for?

Many thanks for any help you can offer,
Phil

--

Liebe alle

Ich habe vor kurzem die Bremsen in meinem Alleweder modifiziert, indem ich die Tipps aus dem Thread über die Optimierung der Bremsen verwendet habe - jetzt gehen die Kabel von unten und sind kürzer. Außerdem habe ich "da tilla" und einige neue Schellen aus dem exotischen Schweizer Velomobil-Laden eingebaut und die Bremsinnenseiten erneuert (die Außenseiten sahen noch absolut in Ordnung aus und waren nur 3 Jahre alt).


Seither habe ich allerdings Schwierigkeiten, die linke und rechte Bremse gleichmäßig zu betätigen. Bevor ich Änderungen vornahm, waren beide Bremsen gleichmäßig, aber es wurde nie genug Kraft aufgebracht, um die Vorderräder zu blockieren. Jetzt habe ich so viel Kraft, dass ich beide Räder blockieren kann - aber es geschieht nicht progressiv.

Jetzt fühlt es sich so an, als ob die linke Bremse nichts tut, bis ich fester am Bremshebel der Deichsel ziehe, dann blockiert die linke Bremse plötzlich. Die rechte funktioniert einwandfrei.

Was könnte falsch sein? Hat jemand eine Idee, wonach ich suchen könnte?

Vielen Dank für jede Hilfe, die Sie anbieten können,
Phil

Übersetzt mit www.DeepL.com/Translator (kostenlose Version)

 

[Christoph Moder]

What could be wrong? Does anyone have any ideas of what I could look for?

The brake pads are worn, so the self-reinforcing one gets pulled to the drum, but the spring is to weak to pull it back.

Either put a shim under the brake shoe (= the rectangular thing sitting on the brake pad); any thin piece of metal or whatever will do. Or replace the brake pads (although they are still more than thick enough).

 

[Beinarbeit]

self-reinforcing

-amplifying?

 

[pn_day]

@Christoph Moder You might be right - I'm no expert. However, the brake pads don't show much sign of being worn, and both pads/shoes seem to move as expected when tested without the wheel on.

I've attached a few photos in case somebody can see what I might have done wrong! (2 showing the left side, 2 showing the right, and 1 showing the tiller)

Thanks.

Right side


Left side


Tiller

 

[spargelix]

It looks like the brake cable has to corner to get to the brake arm.

 

[pn_day]

Yes it does slightly - due to the bolts that hold the steering arm to the strut. I didn't want to use smaller bolts with flatter heads in case of failure - this takes a lot of weight!

 

[pn_day]

Photo of the slight bend on brake cable is attached

 

[pn_day]

I'm wondering if I should revert to having the brake cables enter from above - as going from below does force a bend as noticed by @spargelix

What do people think?

 

[spargelix]

Maybe the angle ist small, but the edge ist sharp.

 

[pn_day]

I think you are right. Thanks for the help. I'll try routing the cables from above to avoid this bend - but keep the lengths shorter to try and keep the improved brake performance. Thanks to @spargelix, @Christoph Moder, @Beinarbeit for the fast help.
Phil

 

[spargelix]

Maybe it is possible to fit the flexy hose direcly in the lower bolt and to mount the adjuster to the upper one.

 

[panicmechanic]

Gute Idee, aber eigentlich braucht es doch da unten keine Verstellung, wenn "da tilla" montiert ist.

 

[pn_day]

I'm using the adjusters as they hold well in the base of the Sturmey Archer plate - the other piece I had moved too much.
I think I'll try going back to routing from above and see if this fixes the issue. Thanks

 

[Uli_]

To be honest I think you have too many and too tight turns in your cables. Remember that the friction is governed by angle of turns and radius of turns much more than by length.
My guess would be that you have a slight link in you left inner cable that sticks against some tight turn in the outer one and only gives with sufficient pressure .
That' s as much as I can tell from the data given.

 

[Ralsch]

That should be easy to check by moving the cable by hand without the lever attached.
Maybe something to look into: Are you sure that the „nose“ of the excenter (the thing which presses the brake shoes into the hub, dont know the exact term even in German) is on the upper side?
Otherwise, the brake power is reduced and the brake power is not linear. Shouldn‘t lead to a blocked wgheel, though. Normally…

 

[tieflieger]

When u pull on the cable, the arm goes further down, and the angle gets sharper. With that it gets more likely, the arm sticks. If possible it might help to angle the flexible noodle a bit more inline with the cablepull.

It might also be that the pivotaxle in the brakeplate. The part on wich that black arm rotates, can get a bit sticky. It helps to oil that very carefully. Do not spill oil on the pads.

 

[TimB]

How many km have you accumulated @pn_day ? You might have too much play in the axle of the break lever and Brake pad fixing bolt.
Does the brake lock up once and then behave normally? Can you provoke the locking on the first braking after roling backwards with brakes applied?
Then you will need a new Brake Plate set from S&A.

Regards,

Tim