Rear brake pads

[Mark_h]

I noticed the other day that the outboard pad on the rear of my K3 SV1000 was a bit on the thin side. Up until now I've always shied away from messing about with brakes but thought the rear would be a good place to start.

So.....

After reading the manual I got the calliper pivoted and the pads came out. So far so good. It all came apart pretty easy. I assume that to put in new pads I need to push the piston in a bit. How much force should this take and what is the recommended method? Ideally I guess I should strip the piston down and give it a good clean up but I'm not feeling all that brave so for now it's DIY pad replacement or just take it to someone else to do a calliper rebuild.

The inboard pad had loads left compared to the outboard pad but given that has a more passive role I assume that is OK.

Any advice gratefully received.

Ta,
Mark

[Sid Squid]

The piston should ideally move back smoothly under finger pressure, this however assumes everything is shiny and perfect so it's not unusual to find it takes a good shove to move it, before doing so however, pump the piston out a a few mm more* so there is a ring of shiny clean piston apparent, then clean the piston thoroughly using a toothbrush and hot water and any bike cleaning solution you may have, steer away from harsh solvents. When it's clean it should be possible to push it back without too much force, as stated you shouldn't need tools just a firm press of your fingers. If it's resistant to being moved, then something is amiss, probably this will just be that the piston and seals are gummed with corrosion, which is not as serious as it sounds, but the caliper will need to be dismantled - and this being a single piston caliper it's the simplest kind so if you've never done it before this a great place to start!
Pad wear: One pad being worn more than the other tells us the assembly is sticking, perhaps not enough to be noticeable but enough to raise the rate of wear and cause one pad to be on the limit when the other is still usable**. This may well be the piston not moving and thus retracting correctly which causes the brake to drag a bit. Also as this is a sliding caliper the pins upon which the caliper moves are suspect, remove them both and see if they move easily in their respective holes - I suspect they don't - also check the rubber gaiters around the pins are intact, correctly fitted and not causing more drag.

A note on this: Sliding calipers are prone to wearing one pad a bit more than the other, even when all is well with the assembly. It's hard to give a precise degree to which uneven wear is no cause for alarm, but if one is on the limit, (1mm at the thinnest point), and the other still has 3mm it's worthwhile giving everything a thorough check to ensure it's all working correctly.

* Don't overdo it - if the piston comes out you'll use the sort of language your mother would disapprove of.
**Don't be tempted to replace only one pad.

If I could add my 2p worth.
use a large flat headed screwdriver (or equivalent) to push the pistons back before you take out pad.
This way you do not damage piston.
a quick squirt of brake cleaner in caliper to remove dirt etc.
I would expect pads to wear differently on piston and slave side.
do one pair of pads at a time - most bikes have 'handed pads' i.e. the left pad on one side may be against pistons but on other caliper, the left pad will be slave.
there may be thin shims on one pad only per side - if you only take out 2 (1 caliper) at a time, you will not mix them up.
finally, when done, remember to pump brakes to bring new pads into close contact with disk before going for a run.
This is especially true if your bike has linked brakes.
you may change front only but you still have to pump rear.
I talk from 'brown trouser' experience.

Stephen McG in very warm Glasgow.

I recently got the new Gladius 650.

[Sid Squid]

Brake cleaner is for friction surfaces only - not general cleaning.
There's a good reason for the first go being with the fingers - it tells you much about the condition of the brake. Forcing the piston back against the crud on the piston is not a good move.
As stated above sliding, (or not, depending ), calipers often wear one pad slightly more than the other - but if it's by much, something is wrong. A sliding caliper puts equal pressure on both pads when the system is functioning correctly - minus any drag in the sliding pad, but the caliper slider mechanism needs to be very stuck before this changes significantly. The problem is if the piston or sliders stick the pad is held in increased contact with the disc when the brake is released, this is what causes increased wear, not uneven brake pressure.

[Mark_h]

Thanks gents.

Pads ordered. Will play as soon as they get here. I'm pretty confident now the pads have been out. Gave a gentle push with a screwdriver between old pad and disk and the piston moved in a little so guess that's going to be good too.

Should I get some brake cleaner or would paraffin and a toothbrush do the job for cleaning the pistons?

[Sid Squid]

Brake cleaner is only for friction surfaces - use a bike cleaner, a toothbrush and hot water, rinse everything with clean water. Even some cream cleaner will be fine, in fact just about any non solvent cleaner will be fine - just rinse everything thoroughly. I wouldn't use Paraffin, it's not a harsh solvent, but all the same I'd keep it away from rubber parts.
Don't push the piston back without cleaning it first, I get work freeing stuck brakes caused by this exact reason.

'thats me told' then (wanted to insert smiley face here but could not see them)

my only defence m'lord is that I only ever keep a bike for 2 years and then trade it in.
in that time I usually wear out front and rear pads and the pistons still slide very easily.

I did not know that brake/clutch cleaner was for the friction surface
I had better read the label next time.

SMcG in (very) sunny Glasgow

I just cleaned my front calipers and rebuilt with new seals. I used a tub of brake/clutch cleaner to full immerse them in - cleaned with toothbrush.

I hope this wont cause any problems

[Stu]

Originally Posted by breakz187

I just cleaned my front calipers and rebuilt with new seals. I used a tub of brake/clutch cleaner to full immerse them in - cleaned with toothbrush.

I hope this wont cause any problems

Just so that those that know have more info when they next stick their head in the door...I've never heard of brake/clutch cleaner, but have heard of brake/clutch fluid. Is that what you mean? If so I doubt very much you'll have done any damage so long as you cleaned them well enough (I doubt it's very good at cleaning).
The brake cleaner referred to above is usually an aerosol (IME) rather than a tub.

[jambo]

Originally Posted by Stu

Just so that those that know have more info when they next stick their head in the door...I've never heard of brake/clutch cleaner, but have heard of brake/clutch fluid. Is that what you mean? If so I doubt very much you'll have done any damage so long as you cleaned them well enough (I doubt it's very good at cleaning).
The brake cleaner referred to above is usually an aerosol (IME) rather than a tub.

Clutch/brake fluid is a high boiling point hydraulic fluid.

Brake cleaner is a low flash point solvant, used to spray onto brake pads & discs to remove grime & deposits without leaving a greasy/slippery residue.

Quite different products.

Jambo
Edit: Breakz: This said I'm sure it'll be fine, it's just not the best thing to use for the longevity of the seals. Red rubber grease & hot water are good fro cleaning and prepping rubber seals.