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Iron horse

Front brake dragging

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Iron horse

So I have cleaned and lubed the slider pins and same with the pads retaining pin. Now much better but the front wheel still doesnt spin completely freely. I thoroughly cleaned the pistons when I put new pads in a few months back too and have cleaned again. What's the next step?

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djsb

I've got the same problem with my rear caliper after the seals and pistons where replaced recently (not by me though). Keen to find out what the problem with yours is.

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DaveM59

It never will 'spin' freely, there is always drag on a disc brake, but it shouldn't be enough to cause heat build up or pad wear. If the pistons are freely moving and are fairly easy to press back into the calliper then the rest of what you have done should make a perfectly normal brake.

If you push the pistons back in then pump them out without pads fitted ( not too far to pop out the pistons) and wipe around the exposed piston. Use a piece of 5 ply (1/4") as a stop in the centre of the calliper and apply a smear of white brake grease around them then press them back in and they should be fine.

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temp

Hi Dave, I use ACF50 instead of brake grease, should I be using a different product?

Thanks, H

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Tex
1 hour ago, temp said:

Hi Dave, I use ACF50 instead of brake grease, should I be using a different product?

Thanks, H

 

You need to be careful with that, chum. I have no idea what the ‘active ingredients’ of ACF50 are, but the rubber seals in brake callipers are best lubed with proper brake grease. 

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DaveM59

Tex, the ACF50 blurb does say it is safe on most rubbers and is a lubricant and all the other stuff we know about so I'd assume it was OK on brake callipers, just not on the pads or discs. You can apply it to wiring and switchgear so it must be fairly inert on plastics and rubber. I don't use it so never tried it on such things but it's only filling he tiny gap between piston and bore outside of the seal itself keeping the road dirt from getting in there. Time will tell but I think it should be fine.

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Mark8arker

Had the same problem with both front and back brake. Cleaned both before went on holiday.  After 2 weeks riding, thought check them before hand i bike in for a  2nd service. The front was sticking again. 

Cleaned all parts has discarded above and applied white grease to pistons ( stop rust ). Use brake cleaaner not WD40 or any over petroleum based products to protect seals. Then stripped and cleaned hand brake same time. Ask the mechanic at the dealers to check the brakes for me + how i was cleaning looking after was correct. Pick the bike up next Saturday . See what says then!

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embee

You don't really want the piston to seal contact lubricated as such. The retraction of the pistons works basically by "sticking" to the seals and slightly flexing them when the brake is applied, when released the seal then relaxes back and eases the piston off the pads. It's possible (speculating here) that the ACF is penetrating between the seal and piston and effectively preventing the "stiction" and thus you're not getting the retraction.

I use red rubber grease round the exposed parts of the pistons to ward off corrosion, but it shouldn't work its way under the seals or act as a penetrating lubricant.

Try taking the pads out, ease the pistons out a bit, clean with brake cleaner, apply RRG and ease them back in.

Edited by embee
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Iron horse

Interesting. I hadn't thought about the seals playing a part in retracting the pistons

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Trumpet

The piston seal is square, and it twists and distorts as the piston comes out. It retracts fractionally on release. Also I've read ACF50 is petroleum based and not recommended for EDPM (Brake piston) seals, or the slider rods. As said, vegetable oil based grease, or Silicone brake grease is the ontly thing recommended for a light coting on the piston sides when pushed out for cleaning.

Edited by Trumpet
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embee
57 minutes ago, Trumpet said:

…... Also I've read ACF50 is petroleum based …..

http://www.acf-50.co.uk/acro2017/ACF-50 BULK LIQUID MSDS _ 2017 _ ENGLISH.pdf

Looks like it's significant percentage of naphtha of one sort or another, the same family of stuff as white spirit, so yes a hydrocarbon base. Interestingly WD40 is also a naphtha/mineral oil based product.

Probably best not used on brake seals as Trumpet says. EPDM is "unsatisfactory" exposed to naphtha, here http://mykin.com/rubber-chemical-resistance-chart-4

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temp

Interesting stuff. But on a practical note, I have used ACF50 for years on the brake pistons without a problem.

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machinman

Pads more likely to be binding in the caliper body or on the pins in my (limited) experience.

Edited by machinman
Typo again

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Trev

Bloody front disc on my Enfield is awlays dragging, I really need to do the piston seal clean/lube thing when I get some garage time

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Andy m
16 hours ago, temp said:

Interesting stuff. But on a practical note, I have used ACF50 for years on the brake pistons without a problem.

Rubber reacts in various ways to chemical attack. Some age and crumble away, some go hard and split open, some swell and fail by blocking function or mechanically from some bit they should clear. The rate depends on concentration, dilution, location, use etc. If you put the seal in a test tube of ACF-50 it would fail the manufacturers hardness or dimension tests in a few days. In use, rain water washes it, it is probably sealing on a bit that wasn't heavily exposed etc. Just keep an eye on it and be careful where you spray. *

13 hours ago, Trev said:

Bloody front disc on my Enfield is awlays dragging, I really need to do the piston seal clean/lube thing when I get some garage time

Had to wet and dry the pins on mine. Someone in India defines a running hit as requiring a light hammer (as against the Ural spec 14lb one) . Think they were out of round as much as anything. 

 

*During the Great European Unity issues of the 1940's SOE would put Pistachio nut oil in the dastardly Huns oil. This had the triple properties of being oily and so attacking rubbers which might stand its acidic properties. Thirdly, the mild abrasion of the nut part kept exposing new surfaces to the acid or oil. You could also eat it, so not something they could really stop you having. My own experience is of lime oil. This is also oily/acidic and destroyed every known rubber we tried as pump hoses. This was a Canadian "Lager" manufacturer trying to make lager and lime by the cubic meter. I wouldn't recommend the stuff. The acid resistant hoses swelled under oil attack, the oil resistant ones crumbled under acid attack. 

 

Andy

 

 

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Trev
2 hours ago, Andy m said:

 

Had to wet and dry the pins on mine. Someone in India defines a running hit as requiring a light hammer (as against the Ural spec 14lb one) . Think they were out of round as much as anything. 

 

 I did the same to mine and thought that had cured it but it's been back for a while now, bloody annoying as makes the thing a little harder to wheel about in the garage and it can ill afford any of the miniscule power to be sapped.  Hopefully Murray's seal explanation/suggestion will sort. I picked up a braided hose for the thing at the NEC show for only a tenner so am going to strip and clean the caliper when I fit that. 

I've been out on it today and once again reminded of how much it suits crappy, cold (ish) weather and muddy leafy back lanes, wife and I enjoyed a 80 mile round trip with a coffee stop midway and warm fire when got home. I left with the fuel light just starting to flicker and returned with it full on and still fuel sloshing about, a combo of 90mpg, decent tank size and ludicrously early warning light will catch me out one day :no:

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Andy m

Did the same with the CB today and that doesn't lie. Two bars showing on the gauge, 200 on the odometer, so at least 10 on the "part used" bar, 50 on the full one and the countdown to walking after that that should be 50. I still let the voices in my head talk me into filling up at 245 (It was a supermarket). 

 

Andy

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Trumpet

EPDM seals  swell with lithium based grease. It was supposed to be red grease with added PTFE, but turned out to be WRONG. The dust seal from my rear brake actually oozed out like a Hernia :cry:

Edited by Trumpet
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makman

I bought a titanium pad pin for front caliper and it made a difference. At least it does not corrode and is easy to lube once in a while. I do strip and clean the calipers using RRG and brake cleaner.  Need to flush through the brake fluid at some point though.

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commuter

 All interesting stuff... I like to keep the brake pistons inside the caliper during autumn and winter and so routinely change the pads every autumn. During this time I thoroughly clean then lube the pins sparingly  with copperslip or graphite. That  does the trick. I never got a seized caliper on a bike or a car. As regards brake fluid I have always disregarded all advice and have used silicon fluid whenever the need arose to change seals and pistons. I have only ever changed seals and pistons on bikes and cars which have previously had their mineral oil derived brake systems neglected by previous owners/ professional servicers. Changing seals with pistons has always seemed the right thing to do since knackered pistons will ruin new seals and knackered seals will ruin good pistons. I like silicon fluid since it doesn't take paint off and doesn't attract water. I have also run systems with silicon fluid in them for many years with no negative impact and because it is not hygroscopic it doesn't need changing. I do find that it is slightly more "squashy" than DOT4. By "slightly squashy", I mean that the difference is less than comparing standard flexible brake hoses with goodridge flexible brake hoses. Someone said that some drag is always there on disc braked bikes. I agree but it can be minimised by keeping the barke systems in good fettle. If I can touch my brake discs after  an average ride, I don't have a problem, if I burn my fingers, I need to have a look at my brake system. The last time i had a problem ,I found I was absent mindedly resting my foot on the back brake and needed to adjust the pedal position down a fraction... since this was on my tiger cub , I heated up the lever with the oxyacetylene and bent it a bit.

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