Brake pad fitting issue
Deej
Posts: 3
Hi all. Firstly I'm a relative bumpy, but replacing a set of pads on my Formula R1 brakes is (or should be) within my capabilities. However, I'm encountering a problem. When I fit the pads in the rear calliper, I can't get them back on the disc.....not enough space between to do this. I've pushed the pistons as far back into the calliper as possible, but still the same problem. They're the right pads (front calliper was an easy change). Wonder what the possible issues might be.....?
deej
0
Posts
Parktools :?:SheldonBrown
I had exactly the same pro blem on my last bike. Did this myself and bobs your uncle, fanny is you aunt.
The reason that there seems to be too much fluid in your system is that it has absorbed water.
Think about it, there was enough room for pad clearance when they were new.
Just letting a bit out is just a band-aid, the real answer is to flush and bleed.
Leaving the now contaminated fluid in there will lead to all of the horror stories you here about brakes with pads rubbing/ not retracting enough and stuck pistons.
Remove pads, pump pistons out enough until you can get in there and clean them with some isopropyl alcohol, flush and bleed.
The single biggest cause of these brakes getting a bad rap is from not regularly flushing them or using wrong fluid.
Op doesn't mention having bled the brakes.
I'd say if no bleeding has been done you need to push the pistons home harder.
They have a membrane under the cap just like your bike brakes.
The water is absorbed through the seals from the atmosphere, just like a small amount of brake fluid always gets past the seals and keeps the pistons lubed.
If your system has pumped up, you either have air in the system or water.
If there is air you will have an inconsistent lever and possible loss of of lever altogether sometimes.
If there is water all that happens to make you notice is that you can't fit your new pads in just as the OP has noted.
This is why shimano developed their own proprietary mineral fluid that is not hygroscopic so it never succumbs to this problem.
Sorry mr Rookie, you'll never get a job in our workshop.
OP, flush your brakes and be rewarded with long lasting well functioning brakes or take the shortcut and slowly but surely destroy them and become one of the many complainers about censored brakes that abound on this forum.
This is such a common thing seen on the work bench, usually a bike that is not ridden much and probably has just worn out its first set of pads.
If not done properly, the next time you see the bike is when the pads are worn out again or the they won't retract or or rub and the best thing to do then is to turf them and fit some shimano's.
This is because the pistons / bore will now have corroded and the seals degraded, it is now junk.
Even if just the pistons and seals need replacing, by the time you do this, parts plus labour make up a significant portion of simply bolting on new shimano's that nearly very customer just gets the new ones.
All systems using DOT fluid will suffer from this to a more or less degree.
Shimano invented mineral oil?
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Parktools
That's why they don't require yearly flushing as any DOT based system does.
You only really need to change it when it starts to look a bit dark through contamination from wear of the internals.
They understood early on in the piece the limitations of using normal dot fluid in such a small volume system with a small resevoir and relatively large seal exposure area for the total volume of the system that dot systems would be difficult.
As have a couple of other companies that use a mineral oil of some fashion.
Next year some of these will use shimano fluid under licence as it is simply the best for low maintainence.
The lack if knowledge of how braking systems operate is simply astounding, leading to a bunch of old wives tales propagated by a bunch of people that have no idea.
99% of people have no idea how the pads self adjust for wear and believe it is some complicated thingy that happens in the master cylinder.
They follow ritualised methods of bleeding instead of understanding how the systems work and knowing the why of the different methods applied to different products.
Amazing, simply amazing.
You attack the only respondent to the thread that explains the exact mechanisms operating and how to treat it.
How can you believe that somehow a system that was working fine but can't fit new pads has magically grown new extra brake fluid to make it too full?
And you think my moisture explanation is far fetched!!!!!!
Go back to school and learn a bit of logic.
And for frocks sake stop dishing out info that will damage other people's gear.
I've not changed the dot fluid or bled my brakes in 5 years of owner ship and 1,000s of miles in all weathers and gunk. They work just fine still and are the same make as the op's
Using both proprietary and aftermarket fluids.
I think you're overthinking it.
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Parktools
Mineral oil is less hydroscopic, but has a lower boiling point in the first place, noting that when DOT first absorbs moisture it actually reduces in volume (like dissolving sugar in water reduces the volume - I remember doing that during my third year) it's only at higher concentrations does volume increase.
All in all glad I won't get a job in your (Halfords? you fit the stereotype) workshop.
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