Author Topic: strange problem with cable disc  (Read 1697 times)

Blodwyn Pig

  • what a nice chap
strange problem with cable disc
« on: February 25, 2020, 06:41:56 pm »
Olive is fitted with TRP  Spyres,  and the front is quite good, but the back is ...adequate. Cable was starting to bind internally,so I fitted a new inner. Went off for a winter weekend in atrocious weather, and a couple of weeks later, the rear was binding again but working quite well. So I tipped the bike on its end, pulled the lever in hard, and squirted liberal amounts of lube down the cable  hole in the lever. This freed it up nicely, so I put the bike away.   

next morning, I went out on the bike , and woah!!!!!!!!  NO  rear brake.  I pulled the lever almost to the bars, and it barely slowed the bike at all. So, I cleaned the disc with cleaner, and took out the pads, and sanded them, and put back, ....... nothing  . So i went for a ride thinking they needed bedding in again.....nothing.  Came back, swapped pads for another  good pair.........nothing ???

So I put my flat bars  on, with the mtb hydro calipers and levers, and reused the first set of pads. took it for a spin, and from the first dab, it had NO problem locking up the rear wheel on dry tarmac.   Before i couldn't even skid on wet grass.

Whats going on???    Only thing I can think of is the excessive lube, has somehow softened the  internals of the outer cable, so that it is now like a squidgy thing. Must say the hydros really are something else, even tho they are 16 years old, and ne'er been touched.

I will have to get some compresionless outers,  but I doubt they will come close to the Hydros.

Kim

  • Timelord
Re: strange problem with cable disc
« Reply #1 on: February 25, 2020, 06:44:00 pm »
Maybe try some new outers that aren't full of crud / lubricant?
Careful, Kim. Your sarcasm's showing...

Re: strange problem with cable disc
« Reply #2 on: February 25, 2020, 08:27:51 pm »
squirting lube into cables which are starting to bind is a stopgap/sticking plaster  repair IMHO. The chances are that the cable is starting to corrode (even stainless inners can corrode under anaerobic conditions such as are seen inside a long cable outer).   The cable run to a rear (chainstay mounted) disc brake is very often a spectacularly poor arrangement that is vulnerable to water ingress; the cable housing is often not protected at the ends and  has a low point in it so that water will simply pool in the outer and cause trouble.

Long Bowden cables need to be perfect in order to transmit force efficiently; every 90 degree bend can rob you of about 25% force, even in a good cable. 

[If you try an experiment to rate your cables, just coil up a cable and see how many turns you can get before the cable binds so much it can't be pulled.  IME very good cables will allow up to three full turns, but corroded ones may bind solid in less than one full turn.]

So I'd suggest installing new cables and outers. Lubricate them well, protect the ends from water ingress, and think about at least installing a drain point/lube point so that the cables can be maintained. 

cheers

Re: strange problem with cable disc
« Reply #3 on: February 25, 2020, 08:29:19 pm »
First thing I'd do is work out if it's the brake or the cable.  My TRP brake won't stay adjusted, whatever cable is on it, though it's usually over a period of days rather than hours.

FifeingEejit

  • Not Small
Re: strange problem with cable disc
« Reply #4 on: February 25, 2020, 08:58:58 pm »
The steps I see missing are checking that the pads actually contact the disc when operated from the lever, and then operating them manually at the caliper and seeing if there is contact and to what extent there is (i.e. does it stop a spinning wheel and how well)

If the lever is going to the bars with no actuation, then presumably the bar end of the cable is being pulled the same amount, various things cause different pull at the caliper though, slightly loose clamp bolts are annoying in the dark.

Re: strange problem with cable disc
« Reply #5 on: February 25, 2020, 09:00:47 pm »
The chances are that the cable is starting to corrode (even stainless inners can corrode under anaerobic conditions such as are seen inside a long cable outer).

Excuse my ignorance but my understanding is that all corrosion is about the forming of oxides. Anaerobic means a process that occurs without oxygen. So how do oxides form if no oxygen is present?

That excludes the thought that the cable outer is not airtight and therefore oxygen is present along its length.
If you don’t make time for exercise now, sooner or later you’ll need to make time for ill health.

LittleWheelsandBig

  • Whimsy Rider
Re: strange problem with cable disc
« Reply #6 on: February 25, 2020, 09:10:37 pm »
Corrosion is a lot more complicated than that. Anaerobic corrosion is a thing, as is macrocell corrosion and a few other variants that behave in unexpected ways.

https://corrosion.ksc.nasa.gov/Corrosion/FormsOf is a pretty good guide that includes some esoteric types of corrosion.

If the supply of oxygen (e.g. percolating through gunge) is slower than it is consumed, anaerobic conditions can be created pretty quickly.
Wheel meet again, don't know where, don't know when...

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #7 on: February 25, 2020, 10:13:49 pm »
The function of the calliper , and thus the gripping of the disc, was just as it was before the lube. The disc flexs a bit. It's as if I've sprayed polish on the disc, but obviously I haven't . I seems to me that the lube has softened the casing of the outer, thus robbing it of its strength.

quixoticgeek

  • Mostly Harmless
Re: strange problem with cable disc
« Reply #8 on: February 25, 2020, 11:03:33 pm »


I see no mention of adjusting the pads, did you use a 3mm allen key in the 2 screws to move the pads in a little? It doesn't need too much to move the pads in and improve stopping power.

One thing to also consider is if the caliper is properly aligned. Loosen off the two bolts holding the caliper to the bike, squeeze the brake lever, hold it squeezed, tighten the screws.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

bludger

  • Randonneur and bargain hunter
Re: strange problem with cable disc
« Reply #9 on: February 26, 2020, 12:34:09 am »
I last had this with my spyres. The problem was that the 'arm' was not positioned correctly to give suitable stopping power onto the rotor via actuation of the pistons.

See illustration D1 https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.trpbrakes.com/userfiles/file/SPYRE_Final_053113%25281%2529.pdf&ved=2ahUKEwjr7-7y--3nAhWNUcAKHedYCIAQFjAEegQIBxAB&usg=AOvVaw0EPodKl90ZcaPcgpbH8GPj

No matter how finely dialled in the pad position is, the 'arm' has to be configured correctly too!
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Re: strange problem with cable disc
« Reply #10 on: February 26, 2020, 12:43:29 am »
The function of the calliper , and thus the gripping of the disc, was just as it was before the lube. The disc flexs a bit. It's as if I've sprayed polish on the disc, but obviously I haven't . I seems to me that the lube has softened the casing of the outer, thus robbing it of its strength.

some spray lubes can soften the liners in some cables, which is bad news. But if the cable was practically seized before you used the spray lube, it is extremely unlikely to have suddenly become 'lovely' simply because it (probably only just) moves; it is much more likely still to be crap. Remember that the cable is meant to transmit force and only a fraction of the effort you apply at the lever end gets to the other end even in a good cable. In a bad cable it can seem to be alright (e.g. move fairly easily under light load) but be virtually useless at transmitting the high loads required for the brake to work properly.

 It is also possible for lube to leak out of the bottom end of a brake cable and contaminate both the disc and pads.

If the disc appears to flex with a spyre brake then it is almost certain that the pads are not adjusted correctly as QG suggests. This will also make the braking action rubbish. Spyres have the nasty habit of the pad adjusters self-adjusting as you ride.

Re corrosion, as LWaB says it is complicated. Stainless steels are only 'stainless' provided the oxygen potential is high enough to maintain a passive film of Cr oxide over the surface of the steel.  If the oxygen potential isn't high enough (eg in anaerobic conditions) then the material does not have this film any longer and is liable to be subject to all kinds of corrosive attack. I've pulled quite a few stainless inner cables out of cable runs with a low point in them and the cables have been black in colour, and so rotten (and they even smell rotten BTW) they don't even come out in one piece. This condition starts when the cable fills up with water; that and a bit of chafing is all it takes.

cheers

Re: strange problem with cable disc
« Reply #11 on: February 26, 2020, 06:37:59 am »
Similar issues with my rear Spyre. I replaced with new Shimano ‘treated’ cables and outer. Inner was fine. Outer was corroded right by the brake mechanism.

I see a design fault in that on my Spa Cycles Elan, the cable end points up, channeling water down the outer.

This time I have sealed the end with a blob of grease and the little rubber Durex that comes standard. It’s something for me to keep a close eye on. As a gardener I can completely link in with anaerobic corrosion mentioned upthread.

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #12 on: February 27, 2020, 12:59:10 pm »
I couldn't get on with the flat bars, after 2 rides, so but the droops etc back on. Cleaned rear caliper, opened it wide, and cleaned the pistons, as far as I could, and a light smear of some oil on them. Lubed the cable at the bottom end again, re fitted the pads from the hydros, and re set the arm, and pads. it feels better , although I've not been out due to weather, but it does feel  better whist tying to push it. I've ordered a TRP cable set, with compressionless outer, also some in line cable oilers.  BUT ......''I have an idea!!''.............

https://winstanleysbikes.co.uk/media/catalog/product/cache/afad95d7734d2fa6d0a8ba78597182b7/f/4/prod_17654.jpg

What about these little jobbies, they even come in 1 1/2" ( 38mm ) Olive's downtube dia.  Was thinking a pair of these, top and bottom, and because they are slotted, easy peasy cable lubing at the caliper end.    Is there any reason NOT to use these on Discs, that normally have full length outer.  Should eliminate most of the flex.   Also should the lower short outer cable get corroded, t'would be a small matter to cut a short length to fit without stripping the whole bike down... thoughts?...

ps, I know they are black, but 5 mins in a small bowl of caustic soda, and they will be mostly very silver indeed. ;D

Re: strange problem with cable disc
« Reply #13 on: February 27, 2020, 01:15:32 pm »
hmm, I think they will always struggle to find a balance between gripping the tube well enough that they won't ever slide along it, and crushing the living daylights out of a thin-walled tube. Brake cable loads can reach over 300lbs, and your safety may depend on those parts....

I'd also note that the lower one will present a fine path for water to get into the cable; water runs down gear cables and if it is set low enough it will be right in the path of all the crud sprayed from the front wheel.

An inline oiler (just behind the BB seems like a good place) is going to work better and be easier/safer to install, I'd have said.

cheers

Kim

  • Timelord
Re: strange problem with cable disc
« Reply #14 on: February 27, 2020, 01:31:50 pm »
I'd also note that the lower one will present a fine path for water to get into the cable; water runs down gear cables and if it is set low enough it will be right in the path of all the crud sprayed from the front wheel.

OTOH, as with a typical gear cable run, it's a lot easier to replace that lower short length of outer than it is to replace a fully enclosed run.
Careful, Kim. Your sarcasm's showing...

FifeingEejit

  • Not Small
Re: strange problem with cable disc
« Reply #15 on: February 27, 2020, 02:47:30 pm »
The function of the calliper , and thus the gripping of the disc, was just as it was before the lube. The disc flexs a bit. It's as if I've sprayed polish on the disc, but obviously I haven't . I seems to me that the lube has softened the casing of the outer, thus robbing it of its strength.

So the caliper itself works fine, it's just the mechanical pull on the calipers actuator is insufficient?

Re: strange problem with cable disc
« Reply #16 on: February 27, 2020, 04:50:37 pm »
I'd also note that the lower one will present a fine path for water to get into the cable; water runs down gear cables and if it is set low enough it will be right in the path of all the crud sprayed from the front wheel.

OTOH, as with a typical gear cable run, it's a lot easier to replace that lower short length of outer than it is to replace a fully enclosed run.

well yes, except if a cable oiler is fitted near the low point in the run, it'll again be a case of replacing a short outer length if things go pear shaped, presumably.

There is one advantage to a bare run with slotted guides though; you can usually unhook the cable housing from the slotted guides and delouse the cable in a few minutes.  However in this case I'd plump for the cable oiler instead.

 Cheers

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #17 on: February 27, 2020, 05:18:14 pm »
Ah! what about a cunning plan Baldrick.   Fit both cable stops, thread the cable thro the first one, cut a length of outer to go between the stops, thread cable thro' this , then thro the second stop.    Exposed length of inner is now protected, BUT its not compressing at all when brake is applied.    ;)

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #18 on: February 27, 2020, 05:20:28 pm »
The function of the calliper , and thus the gripping of the disc, was just as it was before the lube. The disc flexs a bit. It's as if I've sprayed polish on the disc, but obviously I haven't . I seems to me that the lube has softened the casing of the outer, thus robbing it of its strength.

So the caliper itself works fine, it's just the mechanical pull on the calipers actuator is insufficient?

meaning totally useless......yes. All was working fine, its as if the outer was made on sponge.  Not tried riding the re-jig yet, cable oilers have arrived.

Kim

  • Timelord
Re: strange problem with cable disc
« Reply #19 on: February 27, 2020, 07:41:51 pm »
Has the outer been damaged somehow?  I've had them split at an anchor point after being bent sharply in bikes-on-trains and recumbent-trike-snagging-cable-on-undergrowth incidents, but the inner cable holds them together so it isn't entirely obvious that there's damage until you discover that it's squidgy and/or full of gunge and decide to replace it.
Careful, Kim. Your sarcasm's showing...

Re: strange problem with cable disc
« Reply #20 on: February 27, 2020, 08:02:36 pm »
Ah! what about a cunning plan Baldrick.   Fit both cable stops, thread the cable thro the first one, cut a length of outer to go between the stops, thread cable thro' this , then thro the second stop.    Exposed length of inner is now protected, BUT its not compressing at all when brake is applied.    ;)

the joints would still need to be sealed somehow to prevent water ingress; by contrast in-line oilers are normally a tight fit on the housing and the chances of stuff leaking in where they are fitted are pretty slim, especially if you use them as intended.

FWIW the amount of compression in dead straight housing is usually tiny; it is curved housing which generates most squish. Also I'd be surprised if that was really the problem with the old cable; my more likely that simple crud, corrosion and friction, mainly on the corners caused the problem.

cheers

Re: strange problem with cable disc
« Reply #21 on: February 29, 2020, 04:46:41 pm »
It sounds like your outer cable is nackered!
When you replace it with the 'compressionless' one from TRP I think you'll notice a big difference.

Let us know how you get on.

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #22 on: March 02, 2020, 12:04:14 pm »
IMG_1142 by mark tilley, on Flickr

IMG_1143 by mark tilley, on Flickr

TRP cable set and cable oilers arrived and fitted. The cable set came with flexible spiral wound section about 4" long, with a built in ferrule, for te h/bar bend, but I CBA to strip off all the tape etc, so cut the extg outer just where it comes out, and put 2 oilers there, then non compressible outer. On the rear I added the 3rd oiler as shown with a short section of spiral wound to finish off , with a ferrule. Et Voila.

Big question, DID IT MAKE A DIFFERENCE.........pardon...

Well the answer is a most definate yes.  The Spyres were never that good, even when new, but now, well totally different. I have never been able to lock the rear wheel, in the wet, without using the front to the max.   Now I can easily lock the rear on its own in the wet,even just going thro a puddle,  on a dry road, I can lock it up.  Also i can lock up the rear on a dry road, with a little help from the front. BUT , thats not the point, because you don't want it to lock up at all,really. So they are just right.

Hydraulic ( 16 yo)   F  12/10    R  12/10

Spyres   ( before)    F  6 /10    R    2/10

Spyres    ( after)     F   9/10    R     9/10

Bearing in mind that they can be too good, and possible catch you out.  (had a little 'whoops' moment yesterday when someone pulled out, and I grabbed a handful of rear brake)  ::-) 

So if your brakes are carp, try these, £18 cable set, and £7 for 3 cable oilers.  Also makes outer replacement easier in future.

Re: strange problem with cable disc
« Reply #23 on: March 08, 2020, 02:21:47 pm »
No difference for me  :-\  I bought a set of these  compressionless TRP cables and fitted yesterday, went out for a ride today and found them to be no different from the Shimano cables they replaced.

Back brake does very little at all apart from slowing me down very slowly, no locking or good grip coming to a stop, front brake provides that.

So disappointing that after replacing both inner and outers i found no improvement on what i had on before.
Mind of a cyclist, body of a dart player.

LittleWheelsandBig

  • Whimsy Rider
Re: strange problem with cable disc
« Reply #24 on: March 08, 2020, 02:28:19 pm »
No contamination of pads, etc?
Wheel meet again, don't know where, don't know when...