Author Topic: strange problem with cable disc  (Read 1698 times)

Re: strange problem with cable disc
« Reply #25 on: March 08, 2020, 02:34:59 pm »
No contamination of pads, etc?

New pads put on and discs thoroughly degreased.
Mind of a cyclist, body of a dart player.

LittleWheelsandBig

  • Whimsy Rider
Re: strange problem with cable disc
« Reply #26 on: March 08, 2020, 02:51:21 pm »
Thoroughly bedded in?

If the discs are the same size, have you tried swapping them?
Wheel meet again, don't know where, don't know when...

Re: strange problem with cable disc
« Reply #27 on: March 08, 2020, 02:55:11 pm »
How long was the ride? New pads sometimes need to wear a little to conform to the shape of the rotor.

(though IME drop bar cable discs are an exercise in frustration that's only ended by You Know What)

Re: strange problem with cable disc
« Reply #28 on: March 08, 2020, 03:01:18 pm »
Thoroughly bedded in?

If the discs are the same size, have you tried swapping them?

Discs are 160 front and 140 rear. Can’t swap due to fitment at rear. Out for 80k in all weathers today but all stopping coming from front pads. I’ve yet to find a combo of pads/discs/cables that work well on the rear.
Mind of a cyclist, body of a dart player.

zigzag

  • unfuckwithable
Re: strange problem with cable disc
« Reply #29 on: March 08, 2020, 03:43:03 pm »
i've had good luck with several models of cable disc brakes, therefore imo there should be a solution. if outer cables are cut clean and square, inner cables lightly lubed, rotor clean and true/straight, caliper in line with the rotor, bolts secure, pads bedded in - there is no reason for the brakes to feel weak.

Re: strange problem with cable disc
« Reply #30 on: March 08, 2020, 06:12:23 pm »
need to know type of disc, type of pads, type of inner cable, type/amount of lube on inner cable, state of wear of disc, caliper type, brake lever type, whether the whole outer was changed (or just the visible bit), amongst other things. Also if the caliper is old, new, and/or has been overhauled recently and/or the caliper alignment checked/reset.

FWIW degreasing used discs is not always sufficient; if they have been contaminated with (say) chain lube, even in small quantities, it can bake on to the discs to make a kind of varnish, which degreaser won't necessarily remove, but that will degrade brake performance. In at least one LBS near me, if the discs are suspected of being contaminated that way, they are usually replaced if the brake shows the slightest signs of weakness and this kind of contamination is suspected.

The small rear disc will be (assuming the brake track is 15mm wide) about 125/145ths as powerful as a 160mm disc,  i.e. about 15% less..  Likewise if there is a mismatch between the brake lever and the caliper then the brake power might be less than normal.  These things are liable to be overlooked in a front brake, but once the added cable losses in rear brake are factored in, the rear brake can be pretty rubbish when compared with the front.

cheers

Re: strange problem with cable disc
« Reply #31 on: March 08, 2020, 07:08:51 pm »
Disc is an Ice Tech rotor, less than a year old, pads are Shimano B01S, cables are the TRP compressionless set bought from Merlin, full replacement of outer and inner, 105 5800 lever and TRP spyre calliper.

Complete overhaul of the bike yesterday, new cassette, chain, chainrings, bartape, tyres, jockey wheels, callipers removed and re centred when putting back on.

Rear brake showed no difference to the Shimano cables that I removed and binned.
Mind of a cyclist, body of a dart player.

Re: strange problem with cable disc
« Reply #32 on: March 08, 2020, 07:19:56 pm »
Disc is an Ice Tech rotor, less than a year old, pads are Shimano B01S, cables are the TRP compressionless set bought from Merlin, full replacement of outer and inner, 105 5800 lever and TRP spyre calliper.

Complete overhaul of the bike yesterday, new cassette, chain, chainrings, bartape, tyres, jockey wheels, callipers removed and re centred when putting back on.

Rear brake showed no difference to the Shimano cables that I removed and binned.
Ooooo. I bet that's disappointing.
Rust never sleeps

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #33 on: March 08, 2020, 07:35:39 pm »
well that is strange. Mine did take a few goes to fully bed in. When re fitting the new inner, I tensioned the arm until it was flush with the main body of the caliper back, then adjusted the pads to suit . Mine really are sharp.  Funny tho, went out the other day in terrible weather , lots of rain, next day rear brake was carp again, took pads out, quick wipe with sand paper ( puncture outfit) et voila,superb!

Re: strange problem with cable disc
« Reply #34 on: March 08, 2020, 08:01:40 pm »
lube on cable?


Re: strange problem with cable disc
« Reply #35 on: March 08, 2020, 08:07:52 pm »
Mind of a cyclist, body of a dart player.

Re: strange problem with cable disc
« Reply #36 on: March 09, 2020, 12:18:25 am »
that'll be your problem then.

cheers

Re: strange problem with cable disc
« Reply #37 on: March 09, 2020, 05:44:03 am »
that'll be your problem then.

cheers

 Don't think so, No lube on front either and it works very well. Rear cable is all routed internally.
Mind of a cyclist, body of a dart player.

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #38 on: March 09, 2020, 06:44:20 am »
Lubing  the cable with gt 85 ( or summat else is imperative imho) the front is very short run so less important. This is why I fitted the cable oilers. You could do worse than buy 3 x 5 mm ones, remove inner, cut outers and fit, as I have done.  If you fitted un lubed gear cables, I'd be surprised if they indexed properly, due to friction, I even lube my gear cables, and I run friction leavers, they let me know when they are thirsty.

Re: strange problem with cable disc
« Reply #39 on: March 09, 2020, 07:26:38 am »
Lubing  the cable with gt 85 ( or summat else is imperative imho) the front is very short run so less important. This is why I fitted the cable oilers. You could do worse than buy 3 x 5 mm ones, remove inner, cut outers and fit, as I have done.  If you fitted un lubed gear cables, I'd be surprised if they indexed properly, due to friction, I even lube my gear cables, and I run friction leavers, they let me know when they are thirsty.

I never ever lube gear cables and they work perfect, I always use the optislick Shimano ones. I've never felt the need to lube any cables as all the ones I've had across 3 bikes have always worked well.
Mind of a cyclist, body of a dart player.

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #40 on: March 09, 2020, 07:29:43 am »
Ok doky,  don't lube them then.  ;)

Re: strange problem with cable disc
« Reply #41 on: March 09, 2020, 07:56:59 am »
every bend adds more places for friction to occur. The friction increases pro-rate with the tension in the cable. You can (for a while, until the coating comes off.... ::-)) get away with no lube in some gear cables (eg Optishit), mainly because they don't need much tension in them, so there isn't ever that  much friction either. 

As per my comment upthread, if you take an unlubricated cable it doesn't take many bends in it before it will stop moving altogether.  Lubricated cables are better, which is why, er, people lubricate them.

You don't believe this?  Go educate yourself.



Bottom line; you are (I estimate) likely to be losing about 2/3 of your rear brake effort in cable friction.  With a lubricated cable it might be 1/3rd losses instead, so your brake is likely to work about twice as well. Simples.  Your front brake isn't losing as much to start with (shorter run, fewer bends) but it too will work better if it is lubricated .

cheers

Re: strange problem with cable disc
« Reply #42 on: March 09, 2020, 08:16:54 am »
In 10+ years of riding I've never felt the need to lube any cables as all the ones I've had across 3 bikes have always worked well. All these years that I've put up with perfect shifting and braking too  ::-) Where have i went wrong  :facepalm:
Mind of a cyclist, body of a dart player.

Re: strange problem with cable disc
« Reply #43 on: March 09, 2020, 08:23:27 am »
your brakes are not working properly right now and that is the most likely reason. :facepalm: ::-)


Re: strange problem with cable disc
« Reply #44 on: March 09, 2020, 08:46:24 am »
your brake is not working properly right now and that is the most likely reason. :facepalm: ::-)

FTFY

I give in, there's no point arguing with God  O:-)

Mind of a cyclist, body of a dart player.

Blodwyn Pig

  • what a nice chap
Re: strange problem with cable disc
« Reply #45 on: March 09, 2020, 11:41:08 am »
In 10+ years of riding I've never felt the need to lube any cables as all the ones I've had across 3 bikes have always worked well. All these years that I've put up with perfect shifting and braking too  ::-) Where have i went wrong  :facepalm:

Yebbut, before cable discs,   normal brakes (caliper, cantilever, V etc) all had cable stops on the tubes, to ...........minimise the length of thee outer, to reduce compression and friction losses, and for ease of maintenance, now we have all become uber modern, with cable discs, the outers are now full length, and some run internally,so maintenance ( ie lubing), is difficult, hence the in line oilers. But please feel free to ignore my ramblings, I've only been cycling and fettling for 45 years.

Re: strange problem with cable disc
« Reply #46 on: March 09, 2020, 12:06:11 pm »
FWIW cables vary and so does the installation.  But IME all cables benefit from some lubrication rather than none, and there are plenty which are seriously compromised without it.

A good (but annoying) case in point is when you buy SA hub brakes, they come with premade cables (for flat bars) with nipples both ends. They are, if they fit, and when lubricated correctly, good cables. But they come with no lube on them at all, which does nothing for the brake performance when the cables are new and soon means that the brakes can turn to utter rubbish if the water gets into them, as per this thread.

 I own (and use) a hydraulic cable oiler which is meant for motorcycle clutch cables etc. These days it mainly gets used on SA brake cables. Once correctly dosed they usually last for many years.

BTW in case anyone is wondering, if you can't route the SA cable with the fittings on it, or it is way too long etc, or you want to use dropped bars, you can cut one nipple off and use the (supplied) solderless nipple to terminate the cable at the brake end. It is all cleverly designed so that one of the original nipples suits a flat bar lever, and the other one (which is normally at the brake end) will fit a dropped bar lever. Neat, huh?  The SA solderless nipple itself is not to be compared with other solderless nipples; it is designed so that the cable (literally) cannot pull out of it, once it is tightened, and (in stark contrast to other solderless nipples)  I have yet to see one give any trouble whatsoever.

The usual method I use for lubing cables as they are assembled is to
a) put a smear of suitable grease on the inner ( eg Finish line Teflon; others report good results with TF2 Teflon) and
b) add oil to the inner as it is fed into the housing.

With practice this is easy to do; note that the grease and oil mix in situ and the resultant mixture doesn't drain out of the housing at any great speed, which is otherwise possible if you use oil alone.

cheers

Re: strange problem with cable disc
« Reply #47 on: March 10, 2020, 09:55:55 am »
In 10+ years of riding I've never felt the need to lube any cables as all the ones I've had across 3 bikes have always worked well. All these years that I've put up with perfect shifting and braking too  ::-) Where have i went wrong  :facepalm:

You went wrong when you asked for help/advise and when it was given you argued against it/poo-pooed it before trying it.

You believe that cables don't need lubing because...


...You never have!


TRY OILING THE CABLE if it doesn't improve the performance of the brake then come back and tell us.

When I was a teenager a friend asked me to help with his motorbike as the clutch was stiff and the brake was not working well + stiff.
His bike was immaculate clean polished shiny BUT he had NEVER oiled the cables or done any other maintenance on it.
He had your attitude about oiling cables too, until I'd fixed his bike by OILING THE CABLES.