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Soft Brake Fix Weirdness
Angry Date Late May 2025
By Ren Withnell
I've done this a few times. And for the most part it's worked. But I DO NOT understand how or why and that bothers me...
You've had the brakes apart (again) because the goddam poopy things were dirty and seized and binding and generally being absolutely rubbish (again). Goodness knows how much time I've spent dealing with brakes that are prone to giving up at the first sign of rain/dirt/salt/age.
You've spent an hour separating the sliders. Another hour wire wheeling the sliders into something that resembles a slider once more. You've finally accepted the pitting on the pistons is too bad and waited a week and spent a small fortune on new pistons and seals. You've scraped and blasted and cleaned and dried the calliper body so much your hands are bleeding.
Nah, nah it'll be fine, plenty of life left in that.
Come out you little swines!!
With the callipers rebuilt you ensure the sliders are sliding, the pistons haven't nipped or twisted the seals, and you've checked the threads for the banjo bolt and bleed nipple are intact. You affix the calliper and brake line, fill the master with fresh DOT4 from yet another newly opened bottle. You bleed and bleed and after a while there's the feeling of "a brake" at the lever.
Woohoo!...? The lever is soft and spongy. Not to worry keep on bleeding, there'll be an iddy biddy bubble of air somewhere. Bleed and bleed, top up the master, bleed and bleed. It's a bit better but it still doesn't feel right. Bleed and bleed, top up the master, bleed and bleed. It's a bit better but it still doesn't feel right. Bleed and bleed, top up the master, bleed and bleed. It's a bit better but it still doesn't feel right.
Natch. Check the banjo bolts for a weep. Check the bleed nipple. Get cross. Throw tools around the shed. Realise you've just broken an expensive side panel in your anger. Get even angrier. Stomp inside, make a brew, sit on the settee and cry. You wish you'd just spent the money and gone to a real mechanic not a feckless halfwit called Ren who ALWAYS messes everything up because he's a tight arsed pillock.
After an hour of self loathing and doom laden thoughts you recall that trick. You go outside and use a zip tie to pull the lever to the bars (or a huge weight on the foot lever). It can't work. With your total and complete understanding of how a master cylinder works putting a load, a strain, pressurising the brake fluid overnight still makes absolutely no sense at all.
All you are doing is pushing/pulling/holding the brake lever. When you do this the master cylinder is "disconnected" via a seal from the brake line and the calliper. Any air in the brake line or the calliper has NOWHERE TO GO. This MUST be a fact because if there was somewhere for the air to go - then the brake fluid would be going the same way too and you'd have a leak.
Everything you'll ever need to know about brakes - right there.
You lie in bed at night while promising to get yourself a car, give up this stupid motorcycling nonsense, keep warm and dry, have space to carry more than a spare t-shirt and your phone, gain access to affordable parts designed to last more than 30,000 miles, not have to carry a helmet everywhere you go, and just be a normal human being that pays people to do what they're good at.
The next morning you go to the bike, release the zip tie (or remove the weight) and lo! The lever is firm and effective, the brakes are working a treat, all is well with the world, you love motorcycles more than life itself and you, yes YOU are a mechanical GENIUS!!! I'll put gaffer tape on that broken side panel it'll be reet.
OK genius - explain how this works then.
The only possible, reasonable explanation I can come up with is - and it's not a good explanation - this. The pressure overnight somehow causes the air to be "absorbed" by the brake fluid - much as deep sea divers get nitrogen absorbed into their body. When the pressure on a diver is released this causes The Bends which can be fatal. When the pressure on the lever is released somehow the absorbed air is released at the top of the system into the bowl above the master cylinder?
I dunno. It's as simple as that.
Addendum.
I've just asked ChatGPT - I think its answer also makes sense?
What Happens When You Hold the Brake Lever Down? When you pull and hold the brake lever (usually zip-tied to the handlebar overnight):
Pressure is applied to the system: The lever pressurizes the brake fluid, slightly compressing any trapped air bubbles.
Bubbles migrate: Under pressure, tiny air bubbles can combine into larger ones. These larger bubbles are more buoyant and more likely to float upward toward the master cylinder or reservoir.
Micro-leaks get sealed: In some cases, very small leaks or gaps (like at the banjo bolt washers) can seal better under constant pressure.
Surface tension is broken: Tiny bubbles clinging to internal surfaces (like hoses or calliper bores) might detach and rise when the system is under steady pressure.
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Reader's Comments
Bogger said :-
Nah mate you're just inept.
Well someone had to say it?
Bogger
17/06/2025 11:32:28 UTC
Bogger said :-
On a serious note. Brakes can be infuriating. The Piaggio Beverley I had was a nightmare to keep the brakes fettled and working for a couple of weeks.
The materials they used were useless. Very, very poor.
In fact poor build quality and materials ruined a very capable and fast scooter.
Bogger
17/06/2025 18:14:53 UTC
Ren - The Ed¹ said :-
You do know you're not supposed to use motorcycles or scooters in anything other than warm dry weather? You're supposed to be in a Mediterranean country under glorious sunshine not riding through the grimy gritty roads of North West England in the rain. I can imagine even the cheapest of brakes can last a "reasonable" length of time as long as the don't get dirty or wet.
I keep on thinking "there's a market for a brake for motorcycles where the brake is designed and built to cope with awful weather and winter salt etc etc". I have visions of "Ren's Brakes" where we create drop in replacements that feature rubber boots and stainless steel and simple mechanisms. Then I remember most riders only ride in nice weather anyhow. I'd spend a million tooling up only to sell 1,000 callipers worldwide.
18/06/2025 08:00:37 UTC
ROD¹ said :-
Ren, Buy second hand clippers from a breakers and rebuild them over winter. When the weather improves swap the callipers over and then rebuild the other set at your leisure and repeat the next year.
Alternatively strip and clean the brakes around mid February and again when the weather picks up. As you say, it's the winter riding which causes the problems.
I think that the ChatGPT explanation is feasible.
18/06/2025 09:19:25 UTC
Ian Soady¹ said :-
I've always pooh-poohed the cable tie method as well, however I can see some vague logic in that chatgpt answer.
All weather brake? Like this?
18/06/2025 09:53:43 UTC
Ren - The Ed¹ said :-
As bogger stated ROD it's not just a case of once or twice a year, my brakes seem to require a dose of looking at quite regularly. It seems to be quite variable, 5 or 6 months then every month - probably due to the level of riding I'm doing at that time and the weather conditions. I do have a spare front brake calliper...
Ian - I've had drum brakes on many bikes over the years although most are single leading shoe not twin leading shoe as pictured. These are not without issue too. Where the lever passes through the drum plate to the shoes is prone to seizing up and I've had front brake cables freeze solid in deepest winter. That is an "interesting" experience. However drums are a much simpler solution and shoes seem to last forever, they can lack power though.
18/06/2025 10:24:26 UTC
ROD¹ said :-
Although it was over 50 years ago, and memories can get distorted over time. I had a duetto twin leading shoe brake on my 650 BSA. I remember this brake being very powerful but lacked feel. The brake worked as soon as the brake lever was touched and did not have any progression.
On a visit to Eddy Dow's shop in Banbury (the then importer of the brake system) I was told that this brake was designed for racing and basically it was either on or off.
The solution was to back off one of the shoes so that the shoes wouldn't bite at the same time, or take the brakes apart and reprofile the shoes with a file to make them more progressive.
This brake then seemed very good, BUT at this time I had not experienced disc brakes and the tyre technology was more basic back then.
18/06/2025 11:02:37 UTC
Ian Soady¹ said :-
The brake I pictured (Triumph 8" TLS on the B'Zuki) is powerful and progressive but haven't tested its fade resistance. I'm not sure it's actually better than the SLS item on the Norton which is a similar diameter.
Remember diisc brakes in the 70s which refused to work in the wet till the wheel had done a couple of revolutions by which time you were heaving on the lever with all your strength and the wheel locked? We do have it easier these days in many ways.
18/06/2025 11:38:25 UTC
Ian Soady¹ said :-
Oh, re Rod's snatch brake - these brakes were often fitted with Ferodo AM4 linings. These gave very good fade resistance and friction but as you say were very grabby especially for the first use when the drums might have a light coating of rust. Apparently the material was designed for milk floats.....
19/06/2025 11:37:01 UTC
nab301 said :-
Ren when you mention that you bleed , and bleed the brakes what method are you using? If you're talking (non ABS system) about forcing air downhill towards the bleed nipple , don't bother , push the caliper pistons in fully and hold them there with a suitable piece of timber, then just tap the brake lever rapidly , a steady stream of bubbles should appear in the reservoir ( air naturally moves up) , if not maybe crack open the upper banjo to release a large airlock , retighten, and brakes should bleed as above in minutes .
Basic ABS systems may require a suitable hand vacuum pump and other systems may require the ABS pump to be "activated" . As mentioned previously , I did rebuild and bleed an Enfield Himalayan system successfully with the vacuum pump method in minutes.
Tapping / flexing the hydraulic lines can help release any air bubbles too.
I spent years with an Enfield twin leading shoe front brake setting it up correctly , using different linings , bedding in and checking with chalk , all was a waste of time .
The best brake was obtained with a £10 set of shoes purchased on Ebay but as with all the others was never consistent , the brake issues were solved in minutes with a disc brake conversion .... braking has since been excellent , consistent, and strangely never seized !
Nigel
20/06/2025 14:03:53 UTC
Ian Soady¹ said :-
The hardest system I had to bleed was the Moto Guzzi V50 with its linked brakes. The pipe run was such that there was always a bit of trapped air. I bought a cheap vacuum pump from ebay and that sorted it out.
I like the sound of your method Nigel but all my bikes have drums now. No doubt in the future I'll be lured to the dark side again.
20/06/2025 16:16:59 UTC
Upt'North ¹ said :-
Just catching up with this chat. I can't answer your question re holding the lever in overnight Ed but it does work from experience.
I'm with Nigel too and "tapping" the lever. Although I wouldn't describe it as tapping, using my delicate sausages I move/apply the lever by an almost imperceptible amount constantly and rapidly for a few minutes or the trigger finger kicks in. Leave the cap off and watch the little bubbly beggars rise and die.
Bleeding non linked ABS systems hasn't been an issue. Bleed once. Activate ABS. Change underwear. Bleed again.
Upt.
22/06/2025 13:42:10 UTC
Ren - The Ed¹ said :-
I've had no REAL problem bleeding the brakes on the CB500X Nigel - but don't let that get in the way of making a point. I have not tried the tapping method before so when (not if) I'm struggling next time I'll give it a go.
I presume the only way to activate the ABS Upt' is to simply grab a handful of brake? In which case yes fresh underpants will be required. I can activate the rear just fine but grabbing a handful of front goes against EVERYTHING motorcycling has taught me over the years.
23/06/2025 08:44:27 UTC
Upt'North ¹ said :-
Yes it's a bottle tester. And yes against every ounce of self preservation about 50 years of motorcycling instills into ones being.
It is strange how easily a front will lock when snatched. It's all about weight transference innit, or lack of it. When I say lock I mean activate the ABS.
One of the best training tips ever placed into my noggin is always lightly brake with the front first, then as soon as weight transference commences apply the rear also along with more front brake. In normal riding I can't remember locking a wheel in years, with or without ABS.
Is it weight or is it mass? Ed'll know.
Upt.
23/06/2025 12:43:56 UTC
Ren - The Ed¹ said :-
You always have the same mass even if you are "weightless" in space. Weight is how much a gravitational well is affecting your mass. You mass might be 100kg, if it is it is always 100kg. Here on earth the scales would show 100kg meaning your weight is 100kg, on the moon the same scales would show about 17kg so your weight on the moon is 17kg. But your mass on earth, or the space station, or on the moon is still 100kg.
Imagine you and your bike's combined mass is 300kg. Imagine then you bump into a stationary car at 10kmh (about 6mph). The force you hit the car with is 300kg at 10kmh. Now imagine you are floating through space on your bike and you bump into the Tesla that SpaceX put up there. If you are moving directly towards the Tesla at 10kmh (relative to the Tesla's trajectory) you will hit the Tesla with a force of 300kg at 10kmh - even though you are "weightless".
But here on earth we tend to use mass and weight to mean the same thing.
24/06/2025 08:14:05 UTC
Ian Soady¹ said :-
Very nice & concise explanation Ren. Your erudition is showing......
24/06/2025 10:18:54 UTC
Ren - The Ed¹ said :-
I had to google "erudition"...
24/06/2025 12:29:27 UTC
Upt'North ¹ said :-
Our leader ain't half smart....
No he ain't, he really ain't.
Ta me duck.
Upt and edumicated. But what if it's a Bedford TK and not a Tesla?
24/06/2025 13:01:28 UTC
Ren - The Ed¹ said :-
Well I don't know the specific mass of the Bedford TK nor the Tesla. The force you collide with the vehicle, either the Bedford TK or the Tesla, would still be the same. What would change depending on the mass of the vehicle is how much you move the vehicle - the greater the mass the less influence you would have on its trajectory.
Recently mankind intentionally crashed a small spacecraft into an asteroid. While the spacecraft was, relatively speaking, "small" compared to the mass of the asteroid the crash did alter the asteroid's trajectory - a small amount. However a small movement in the right place of the asteroid's trajectory can lead to a large change in it's orbit.
One has to wonder why you would place a Bedford TK into space? Mind you - you can also ask the same question for a Tesla. Marketing - that's why. I doubt Bedford has (had) the fiscal resources or the expertise with which to place a TK into orbit. The TK would have rusted away during transportation to the launch pad anyhow.
24/06/2025 13:39:10 UTC
Snod said :-
I always wondered if the zip tie trick just crushes the pads against the disc, and the pistons against the pads, squeezing any grease and muck out the way and that's why it feels better afterwards. I mean brakes always take a little while to bed back in after being rebuilt so maybe it's a bit like that?
Of course we could avoid seized calipers with hydraulic drum brakes, self adjusting, the large cast wheels we now have would be a better heatsink than a few spokes.. all talked about in the UMG about 40 years ago and still no closer to existing! So, like Ren, I have to rebuild my horrible cheap Kawasaki calipers twice a year. And there's one either end because of fashion.
26/06/2025 01:00:35 UTC
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