rear brake caliper help please

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ReggieGasket · #1 Post by **ReggieGasket** » Mon Jun 03, 2013 2:20 pm

My rear brake caliper needs servicing I think as the pistons are difficult to move back. Also, one of the pistons has rusted where it meets the pad. I'm wondering whether it may be easier to replace it? Does the Falco share the rear caliper with other Aprilia models? Is it easy to replace a caliper (I believe it's tricky to bleed them)? Cheers

Aladinsaneuk · #2 Post by **Aladinsaneuk** » Mon Jun 03, 2013 4:08 pm

If you look in Aprilia technical section there is a guide to bleeding our hydraulics - it makes our back brakes work

Also in there is a set of posts re obtaining seals etc for servicing the calipers - iirc you source them through KTM

I would be tempted to have good clean and examination and follow the bleeding guide first

szrdave · #3 Post by **szrdave** » Mon Jun 03, 2013 5:01 pm

Hi Reggie,

As Aladinsane says, it's worth having a go at cleaning it up first. Pump each piston out (but not all the way out!) in turn, give it a good squirt of brake cleaner and clean all the brake dust and other crap off. Then push it back in, and repeat until it's moving freely.

To make life easier, pull the brake hose out of the channel under the swinging arm so you've got some room to maneuver.

The above is probably a half hour task, and will hopefully save you having to split the caliper and replace the seals.

IIRC the pistons are coated aluminium, so any rust you're seeing is probably from the back of the pad. As long as the section of the piston that travels through the seals is in good condition you're fine anyway.

Good luck!

D-Rider · #4 Post by **D-Rider** » Mon Jun 03, 2013 5:21 pm

Aladinsaneuk wrote:If you look in Aprilia technical section there is a guide to bleeding our hydraulics - it makes our back brakes work

Also in there is a set of posts re obtaining seals etc for servicing the calipers - iirc you source them through KTM

I would be tempted to have good clean and examination and follow the bleeding guide first

I believe you can actually buy a kit for the rear calliper - it's the front ones that have required the big effort in sourcing seals.

http://www.ebay.co.uk/itm/BREMBO-CALIPE ... 20c288d216

fatboy · #5 Post by **fatboy** » Mon Jun 03, 2013 6:30 pm

With the caliper off, insert a slim piece of wood between the pistons (where the disc woulld be ) Use something a bit slimmer than the disc, this stops the pistons popping out of the bore.
There is a dust boot and a seal on each piston, the dust boot should push back down to reveal piston surface,clean the crap off so you dont drag it back into the boot or seal, use an air line.
If the brake holds full pressure on the pedal then all is good
Probably

ReggieGasket · #6 Post by **ReggieGasket** » Wed Jun 05, 2013 3:53 pm

Thanks guys. Will clean to see if I can get the pistons moving correctly. The rust is odd - the piston to the right (looking from the rear) is corroded in the middle - I can push a screw driver right through it. I assume it's making a seal further back as there's no leakage.

fatboy · #7 Post by **fatboy** » Wed Jun 05, 2013 6:41 pm

Was that ' push screwdriver through the piston ? ? ?

D-Rider · #8 Post by **D-Rider** » Wed Jun 05, 2013 9:10 pm

If that's the case, there's no brake fluid in there!

Pictures please

ReggieGasket · #9 Post by **ReggieGasket** » Sun Jun 09, 2013 3:46 pm

Sorry, I need to go take a look, but the bike is back together at present (I hardly ever use the back brake

)

If the piston is solid at the end where it pushes the pad, then it's knackered. If it pushes the pad with a circle imprint then it may be OK.

Aladinsaneuk · #10 Post by **Aladinsaneuk** » Sun Jun 09, 2013 4:27 pm

Try reading "a twist of the wrist"

You may review your use of the back brake a touch

D-Rider · #11 Post by **D-Rider** » Sun Jun 09, 2013 8:21 pm

ReggieGasket wrote:Sorry, I need to go take a look, but the bike is back together at present (I hardly ever use the back brake )

If the piston is solid at the end where it pushes the pad, then it's knackered. If it pushes the pad with a circle imprint then it may be OK.

The flat end of the piston is the end furthest into the cylinder - it's just an annulus that presses on the pads (probably to minimise heat transfer)

randomsquid · #12 Post by **randomsquid** » Tue Jun 11, 2013 7:50 pm

D-Rider wrote:it's just an anus that presses on the pads

Or Alad to his friends.

Dalemac · #13 Post by **Dalemac** » Wed Jun 12, 2013 10:11 am

I have locked up the rear on my falco when braking heavily a couple of times. It's quite annoying because it is so easy to do! The difference in pressure for maximum braking and locking up is really small!

BTW, usually only have to apply maximum braking pressure when someone decides to pull out of side roads without looking. Happened to me twice so far this year, locked up the rear both times.

Firestarter · #14 Post by **Firestarter** » Wed Jun 12, 2013 2:09 pm

Dalemac wrote:I have locked up the rear on my falco when braking heavily a couple of times. It's quite annoying because it is so easy to do! The difference in pressure for maximum braking and locking up is really small!

BTW, usually only have to apply maximum braking pressure when someone decides to pull out of side roads without looking. Happened to me twice so far this year, locked up the rear both times.

Easier than you might consider - when you're hard on the brakes, you're transferring the weight of the bike to the front - effectively reducing grip at the rear. As there's less grip on the back, the rear starts to slide, as the rotational force applied between road and wheel is removed - so it's just wheel vs engine, which is not difficult to overcome into a lock (no force to keep the wheel spinning, as you're off the gas as well). I use the rear a lot for small speed mods, and the pressure used to scrub a bit of speed when used in a fast stop would cause the rear to lock for this reason

Plus, if you are at maximum braking, then an infinitessimally small increase would lead to locking up

Dalemac · #15 Post by **Dalemac** » Wed Jun 12, 2013 2:45 pm

Firestarter wrote:
Dalemac wrote:I have locked up the rear on my falco when braking heavily a couple of times. It's quite annoying because it is so easy to do! The difference in pressure for maximum braking and locking up is really small!

BTW, usually only have to apply maximum braking pressure when someone decides to pull out of side roads without looking. Happened to me twice so far this year, locked up the rear both times.
Easier than you might consider - when you're hard on the brakes, you're transferring the weight of the bike to the front - effectively reducing grip at the rear. As there's less grip on the back, the rear starts to slide, as the rotational force applied between road and wheel is removed - so it's just wheel vs engine, which is not difficult to overcome into a lock (no force to keep the wheel spinning, as you're off the gas as well). I use the rear a lot for small speed mods, and the pressure used to scrub a bit of speed when used in a fast stop would cause the rear to lock for this reason

Plus, if you are at maximum braking, then an infinitessimally small increase would lead to locking up

Ahh science :D

I'll have to make a conscious effort to be more weary of the rear brake when people decide to pull out of sidestreets!