Front brake

[bobv7]

I'm sure this is not a new problem but not one I've encountered before as my bikes are normally used regularly, but having a few problems this year the CB500 Four is not getting ridden and the front brake keeps sticking on. I've just taken it apart, cleaned up and copper slipped inside the calliper. I will change the brake fluid but is there any way I can stop this happening again?

[Erny]

Make sure that tiny hole connecting MC and fuild reservior is not clogged. It is very tiny but it is there

It should be one on red circle on attached photo - tine hole in the bigger one

[Bryanj]

Also crud build up behind the caliper piston seal and makes the piston too tight to slide, plus the pivot pin in the swinging bracket the caliper bolts to

[Johnwebley]

The caliper seal may have hardened. So it will not retract the piston

Sent from my SM-A750FN using Tapatalk

[K2-K6]

You can easily test for the above two posted comments.

By unbolting the active side of caliper,  then holding your hand round the pad and caliper, very gently squeeze the brake level such that you can feel the pad start to move,  now when you let it go it should be felt retracting.

You are, in effect,  feeling the elasticity of the seal moving in it's clear groove.  If there's no retraction it indicates what the others have said above.

[bobv7]

Thanks all. Yep there was a bit of crud behind the piston and the 2 holes were free. What was more surprising was that the bleed nipple needed quite a bit of persuading to move even though I had cleaned and copper sliped it last time. Now brake fluid, DOT4 or 5? Good point about the seal, I'll check that too.

[Bryanj]

Dont be tempted to reuse the seal as the sides deform to the crud in the groove which needs to be super clean, use a dental pick or similar not a dremel brush as the crud is so hard all the brush does is polish it.
Any pitting on the piston is bad, new stainless piston and seal about £30 on ebay.

Unless you can guarantee to get every last tiny bit of old fluid out dont use dot5.

I always warm the caliper before attempting to undo the bleed nipple and use a long 8mm socket with a tee bar so as not to stress it sideways as they snap off very easily

[philward]

Dont be tempted to reuse the seal as the sides deform to the crud in the groove which needs to be super clean, use a dental pick or similar not a dremel brush as the crud is so hard all the brush does is polish it.
Any pitting on the piston is bad, new stainless piston and seal about £30 on ebay.

Unless you can guarantee to get every last tiny bit of old fluid out dont use dot5.

I always warm the caliper before attempting to undo the bleed nipple and use a long 8mm socket with a tee bar so as not to stress it sideways as they snap off very easily

If you are buying the SS piston and seal as Bryan suggests ebay seller), just check the edge of the piston isn't square as opposed to having a chamfer (compare it with the original piston) - I've had 3 or 4 of them over the years and the last 2 have been square - which wrecks the seal as you push it in to the caliper. I emailed the seller on the previous purchase and he checked his stock and said they where ok but the one I've bought (and not yet fitted) looks to have the same problem. It's not a big deal as you can chamfer the edge but if you don't you'll end up with a leaking seal.

[bobv7]

Changing the seal but fortunately the piston looks OK. Lot of difference in prices being charged for 1L of brake fluid.

[Bryanj]

Go to a local motor factors after Dec 2nd

[smoothoperator]

I got this recently from Amazon at £9.48; febi bilstein 23930 Brake Fluid DOT4 Plus. Free delivery on Prime.

[K2-K6]

Changing the seal but fortunately the piston looks OK. Lot of difference in prices being charged for 1L of brake fluid.

I use silicone grease in the seal area and to push the piston into it's bore. Available from plumbing supplies in small pot for reasonable price.

It's specified from the original 750 workshop manual and works really well. All but impervious to heat,  it also has near perfect rejection of water so will best prevent corrosion re-establishing in that area from any moisture around.

These caliper have no weather sealing at all,  it's really just down to that grease in provision of some measure of protection.

[deltarider]

I always warm the caliper before attempting to undo the bleed nipple and use a long 8mm socket with a tee bar so as not to stress it sideways as they snap off very easily

Most models have the 7mm bleed nipple actually, which means even more caution.

[bobv7]

Just finished fitting new seal and bleeding the front brake. New seal £7.00, 1 litre of DOT 4 £5.00 and the level in the bottle has hardly dropped. The rest is destined for recycling as I'm informed it can't be kept 'cos it absorbs water. Anyone need their brakes topped up?

[Brian.]

Just finished fitting new seal and bleeding the front brake. New seal £7.00, 1 litre of DOT 4 £6.00 and the level in the bottle has hardly dropped. The rest is destined for recycling as I'm informed it can't be kept 'cos it absorbs water. Anyone need their brakes topped up?

Well...... maybe I've been doing something wrong, but I've used it when it's been in my garage for (probably) two or three years, maybe more, and I have never had a problem with it.  I always keep the top on, but yes - never a problem.

It is hygroscopic (if that is the right word) and if you were keeping it in an open bowl then yes, the exposed surface area could absorb a lot of moisture I suppose.  But in a capped bottle, I really can't see it being a big deal.  Any more than it is in a car or bike master cylinder reservoir.

But that's just me!

I woiuld say that there will be far more knowledgeable opinons than mine that will follow, do be guided by them!

Hope this helps,

Brian.