Anatomy of a failed hydro caliper

[Brucey]

one of the internet Gurus suggested using Silicon grease, applying to the piston and then pushing fully in when exercising during a brake service. I am replacing a leaking M515 (I think at the weekend), replacing with M6000 this weekend . This a real problem for commuting. I have lost 3 Callipers over the last 2 winters. Avid's didn't fair an better, I had always assumed down to my ham fisted servicing, but Now I am wondering

oddly enough I was having a conversation with a mechanic in an LBS about silicone grease just yesterday; I suggested that for commuter bikes, applying this to the extended piston would be one of the few things that would be easy to do and might do some good rather than harm.

I am currently looking into what silicone grease to use. I used to have some meant for vacuum systems (made by Dow Corning) and I'm sure that would do the job but it is quite pricey. There are also silicone greases meant for plumbing (these use food grade thickeners, if used on potable water supplies, so might behave differently) and there are special silicone greases meant for car brakes, e.g. I think Sealey make something like this.

I know that the Dow Corning stuff doesn't melt (I tried it; if you heat it up it just sits there and eventually turns to, er, sand) and doesn't migrate easily either. The other stuff I'm not so sure about.

All suggestions for a suitable product welcome.

cheers

[Jezrant]

take two...

[Jezrant]

Hi,

That's the solution to lining the pockets of garage owners. Hydraulic brake fluid only needs to be changed if it's contaminated.

Rowlocks!
A litre of fluid and less than one hour is not going to kill the bank.
In my experience on motorcycles and cars, keeping three cars on the road for decades / doing all my own work for mot's for 40 years..........never employed a mechanic.........means that fluid system parts barely give trouble at all.

I will admit that motorcycles and modern bicycles may need better than yearly maintenance for sure.

If you want to be a bit more penny pinching then change brake fluid as per manufactures recommended periods which will be 2-3 years.

Important, some especially older steel car slave cylinders will need changing anyway periodically every five years depending on how used and where you live.

Manufactures recommend changing slave and master seals as a maintenance periodically.
All I am saying is that changing brake fluid (not silicone, I know nothing of this as I never use it) eliminates most of brake fluid problems.

How do you know its contaminated................................?

I keep cars for decades but if you can afford changing car every 3 years for new then you will never get your hands dirty.

Garage the car and do 2000 miles a year and you might never have a problem, put car in garage when its dry, how many of us do that.

Rowlocks yourself. You've been throwing away your money, mate. Next time you go into your friendly local garage, ask them to test your brake fluid. Or since you've been doing all your car maintenance yourself for decades, buy a little tester and do it yourself. It ain't complicated. If the moisture content is lower than 3%, your brake fluid is fine. I change mine when it needs it, but hey, you want to change it every year, that's your business. You also then have to dispose of it somewhere, responsibly.

Sorry Brucey, got a bit off track there.

[NUKe]

I am currently looking into what silicone grease to use. I used to have some meant for vacuum systems (made by Dow Corning) and I'm sure that would do the job but it is quite pricey. There are also silicone greases meant for plumbing (these use food grade thickeners, if used on potable water supplies, so might behave differently) and there are special silicone greases meant for car brakes, e.g. I think Sealey make something like this.


All suggestions for a suitable product welcome.

cheers

Mine is ICI Silicone grease I know nothing else about it other than I have had it for years, cant remember why I got it. Although it was with a load of hydraulic pipes I had for a job long forgotton when I found it again.

[Jezrant]

one of the internet Gurus suggested using Silicon grease, applying to the piston and then pushing fully in when exercising during a brake service. I am replacing a leaking M515 (I think at the weekend), replacing with M6000 this weekend . This a real problem for commuting. I have lost 3 Callipers over the last 2 winters. Avid's didn't fair an better, I had always assumed down to my ham fisted servicing, but Now I am wondering.

I can see a good case against hydraulic disc brakes for year-round commuting if the route involves roads that have salt on them in the winter. Out of curiosity, if you were buying another bike for commuting, would you get one with hydraulic disc brakes again?

[NUKe]

one of the internet Gurus suggested using Silicon grease, applying to the piston and then pushing fully in when exercising during a brake service. I am replacing a leaking M515 (I think at the weekend), replacing with M6000 this weekend . This a real problem for commuting. I have lost 3 Callipers over the last 2 winters. Avid's didn't fair an better, I had always assumed down to my ham fisted servicing, but Now I am wondering.

I can see a good case against hydraulic disc brakes for year-round commuting if the route involves roads that have salt on them in the winter. Out of curiosity, if you were buying another bike for commuting, would you get one with hydraulic disc brakes again?

Yes I would.The advantage of disc on a recumbent out weigh the disadvantages I just need to devise a service routine. I might consider a top end mechanical such as bb5's.

[Brucey]

well a trip to my local independent tool shop produced a 500g tin of the sealey silicone grease for about £15. Initial impressions are favourable; a 'button' of grease stands up 1/2" above the filler plate and it shows absolutely no signs of separation, i.e. no oil has bled out sideways from the grease.

The grease is aimed at lubrication of push-fit joints in drain pipes etc, not for potable water, so is likely to have the same thickeners as are found in vacuum greases etc (rather than food grade ones). There is no smell, the grease is immiscible with water, and when heated the grease burns before it melts, which is exactly what I wanted; this means it is unlikely to migrate from (say) pad backings onto the friction material in use.

It is (roughly) #2 viscosity, and is not unlike Vaseline to handle, maybe a touch less stringy.

Obviously it can only act as a physical barrier to water; it is otherwise inert so there is no chemistry to help fight corrosion per se. I may also experiment with using it at vulnerable cable entries, seat pins, and so forth.

It occurs to me that the seal groove will trap water and this will help foster corrosion. The BR-615 caliper shows clear signs of this having happened. It may be possible to cut a slot or to drill a tiny hole into the air side of the seal groove so that water is less likely to be trapped. However it isn't clear whether the seal itself will be damaged by being pressed up against the slot/hole, (which it will be every time the brake is used).

Other thoughts I have had include that it may be possible to shroud the caliper better. However in the case of the rear disc, it seems likely that it will pick up road spray from the front wheel, and drag it through the caliper body. Other than shrouding the disc itself, there is not much that you can do to prevent this, I think.

cheers

[Brucey]

re mechanical discs such as BB5 or BB7. These do not modulate quite as well as hydro discs no matter what you do with them, and good cables (and maintenance thereof) are essential. Mechanically they are (in conrast to spykes/spyres) so simple that they are unlikely to give you any real trouble provided you are prepared to do some basic maintenance on them at intervals.

I suspect that in some uses, the maintenance intervals for some mechanical calipers are not far different from the intervals at which some hydro disc calipers might need to be replaced due to corrosion.

In use you need to adjust the pads with a mechanical disc but at least this means you are able to keep track of the pad wear; folk often wear hydro disc pads down to nothing and don't notice. A Brucey top tip is to set the brake up with new pads, and then make a mark on the red adjuster wheel and the caliper body, eg using permanent marker pen. When the mark has done one full turn to get the adjustment back again, then exactly 1mm is worn from the fixed pad and replacement is nearly due.

There are three points that need regular attention on BB5 and BB7 calipers

1) The fixed pad adjuster. The threads on this need to be lubricated with copper grease (or maybe silicon grease) so that it doesn't seize. If it starts to seize, before you wreck the torx fitting (which is in aluminium and is not super-strong) then remove the red wheel and use a full hex socket on it. Also try tapping the metal part of the FPA with a small hammer (e.g. via the socket) so that it is more likely to free itself.

2) the balls and ramps. There are three balls that ride on ramps and provide the axial movement that gives the braking action. This part of the caliper body doesn't seem to get as hot as the FPA but even so there is a chance that the grease might melt. Even so a grease loaded up with MoS2 etc is probably the best choice here, because the loadings are very high.

3) general corrosion; salt water corrosion will take the paint off the caliper and will cause corrosion in all kinds of daft places, like in the return spring which is under the LH rubber boot. Obviously all screw threads (adjusters, pinch bolts etc) might corrode if they are not kept treated with anti-seize.

Just for fun I have taken several BB5 calipers that were headed for the scrap and rebuilt them; most just needed a bit of grease/TLC and new pads. WIth BB5, it makes more sense than usual to use sintered pads; all weather use with organic type pads can result in very high wear rates, because the pad wear area is smaller than with a lot of other brakes.

BTW on a trike, are the calipers not mounted facing in opposite directions? Does this not cause uneven pad wear on one side with some hydro brakes? The reason I ask this is that the piston bores are offset w.r.t. to the pad backing slots and this is intended to work properly if the disc sweeps through the caliper in one direction only.

cheers

[NATURAL ANKLING]

Hi,
Picture of my M/Cycle front calliper, is cast aluminium, stored out side, changed fluid but apart from that, no other maintenance, was badly corroded, like the bracket in pic.

I have not popped piston but imagine that its an "O" ring in a groove.
This design eliminates corrosion on inner bore, the plastic (whether its a plastic piston or metal shrouded in plastic I don't know exactly until its apart) must bear on the bore and O ring and touch fluid.

Its an off road bike which has seen much green lanning all year round and has always been stored out side since new, probably over 15 years old, only ever changed the fluid..........

[Brucey]

that piston looks very long, so it is possible that there are two seals in the caliper body; one that holds the fluid back and another to keep the water away from the main seal, if you see what I mean.

It also looks like the bike has not seen a lot of road salt; the plated parts are still bright and the caliper body is not corroding too badly.

FWIW motorcycles tend to drive water out of their brakes in use; higher airspeeds and higher temperatures do the trick.

cheers

[NATURAL ANKLING]

Hi,
You should of seen it before I started.
Cleaned the calliper of corrosion.
The bright pin is sleeved with a rubber bellows and holds grease.
Will take apart tomorrow to reveal what's inside.
Plastic piston.....?

[NATURAL ANKLING]

Hi,
Pictures as promised-

[Brucey]

that looks like two seals, as I hypothesised?

Quite a nice design that; but imagine a grease nipple between the seals, and adding a bit of silicone grease at intervals...

cheers

[NATURAL ANKLING]

Hi,
What about Twin pot floating calliper design, opposed pistons always sound nice, but pistons can be outboard not limited by space? (like the calliper I posted and many car designs) and you remove sealing the halves with O ring.
The single or twin pot with floating calliper and sliding pins is a well trusted design, even some mechanical single pot designs use this idea.

OK so mechanical ones probably are more reliable through winter.

I have been using cheap Zoom mechanical callipers on bottom end bikes, the rear works well but the front is liable to wear pads uneven, not helped the calliper opening up when used.
These bottom end callipers have similar performance to V brakes and in winter fall to about 50% of dry performance as do V brakes.
I think that simple fixed calliper mechanical discs are simpler to maintain than V as you do not have to worry about setting up pads and balancing arms.
I know your not a fan of discs.

[Brucey]

.....I know your not a fan of discs....

that is not quite true; I have disc brakes on cars, motorcycles, and several bicycles.

What I'm not a fan of is the assumption that disc brakes are the best sort of brakes to have on any particular sort of bicycle; very often this is not the case, or not always the case, and/or can completely alter the fundamental nature of the way the bike rides. All brakes have strengths and weaknesses; seldom do these enter as they should into people's thought processes when they are selecting bikes and brakes; often folk make their mind up about these things (in a highly irrational fashion) before doing anything else.

For example I visited the campag website recently and the way they have structured it betrays this thought process exactly; when you start to look at their products, the first choice you make is from four options; disc/rim brakes and mechanical/electric shifting. This choice is (for no reason that I can see) put ahead of your budget and how many gears you want, that kind of thing....

FWIW twin pot sliding calipers (or even single pot sliding calipers on cars) work very well for their intended usage. I don't think that there is much about them that translates to bicycles though.

cheers