bleeding rear brakes - the wrong way around!

[A_morti]

A quick google (don't take this as gospel) suggests your bike has an 11mm diameter piston in the rear master cylinder, and this is the smallest Brembo offer. So, if you want to improve the master cylinder vs caliper hydraulic advantage, you'll need a bigger caliper. Yours (again, not gospel) has 32mm pistons in it. There are plenty of options with 34mm pistons, but I think that's the biggest option. For example a brand new caliper with known good seals and brand new pads:
https://www.ebay.co.uk/itm/266337697155
32v34 gives a 12% increase in surface area which might or might not be enough to feel at the pedal. But in combination with a really good scrub of the disc, it might also sort multiple old-age issues in one fell swoop.
Again, bike-specific groups will probably be more useful for this stuff.

[DefTrap]

I would agree that the consequences of getting it wrong could be awful. However - it's really not that hard! - this is ancient technology that has barely changed for decades and is basic enough that it now features on pushbikes ffs. 'Problems' are typically very clearly displayed by non-working brakes (easy to test at low/no speed without throwing yourself under a lorry) and often accompanied by brake fluid squirting you in the eyeball. There's plenty of YouTube how-tos around these days and they're not all fronted by sarcastic beardy-weirdies. I wouldn't want to discourage anyone because of blind fear of terrible consequences.

I even managed to teach my -really- mechanically inept brother how to do it.

[Noggin]

Advice on brakes. Sorry none as I've the mechanical ability of a mentally challenged hamster

Advice for Noggin. Call an ambulance for standby as you're bound to end up with the bike on your head or something

Good advice, which should be printed on a placard, because I need one too! Take it to a professional.

For engine stuff, yes :!

Brake stuff there's really no reason why I can't do it with some thought and planning! I've helped with front brakes on other bikes - changed disks, wheels n basic stuff like that.

I've never helped bleed the rear brake tho - and now with a spazzy arm (and limited options for helpers!), I'm a lot more cautious about starting things until I have a lot more info!!!

A quick google (don't take this as gospel) suggests your bike has an 11mm diameter piston in the rear master cylinder, and this is the smallest Brembo offer. So, if you want to improve the master cylinder vs caliper hydraulic advantage, you'll need a bigger caliper. Yours (again, not gospel) has 32mm pistons in it. There are plenty of options with 34mm pistons, but I think that's the biggest option. For example a brand new caliper with known good seals and brand new pads:
https://www.ebay.co.uk/itm/266337697155
32v34 gives a 12% increase in surface area which might or might not be enough to feel at the pedal. But in combination with a really good scrub of the disc, it might also sort multiple old-age issues in one fell swoop.
Again, bike-specific groups will probably be more useful for this stuff.

I think the DD racing guys basically said change the caliper - I've resisted until I get the Certificate of Conformity in case everything needs to be physically checked as 'standard'. But that is now very high on the list for February!! (That month cos I won't go skiing cos, well, February!! So with some luck I'll be able to do some stuff to the bike )

I would agree that the consequences of getting it wrong could be awful. However - it's really not that hard! - this is ancient technology that has barely changed for decades and is basic enough that it now features on pushbikes ffs. 'Problems' are typically very clearly displayed by non-working brakes (easy to test at low/no speed without throwing yourself under a lorry) and often accompanied by brake fluid squirting you in the eyeball. There's plenty of YouTube how-tos around these days and they're not all fronted by sarcastic beardy-weirdies. I wouldn't want to discourage anyone because of blind fear of terrible consequences.

I even managed to teach my -really- mechanically inept brother how to do it.

I'm more afraid of my inability to physically do stuff at the mo. I'm a bit daft, but not totally mechanically inept (have made some small errors over the years, but often with 'help' - alone I generally work things out!! )

Having ridden the bike to the valley for a language course in the first November that I had it here, I am very tempted to just continue as it is for the next couple of months (if I can sort insurance and CoC) and just get on with it!!

You have to consider what you're going to be doing - you're going to replace the current fluid with new fluid - so if you pump fluid in from the caliper then where will the fluid in the reservoir go? Unless you suck it out at the same time as you pump the new stuff in then it will go all over the bike and floor as it overflows.

Pumping fluid in from the caliper is good for when the system is empty, because it forces air upwards and into the reservoir, then you stop when the reservoir is full.

Whenever I do just a fluid change then I get someone to pour fluid into the reservoir as I'm drawing it out from the caliper with my big syringe.
As long as your syringe is properly connected to the caliper nipple then air can't get in and you'll draw the old stuff out and the new stuff in - you'll notice new stuff being drawn into the syringe because it's clean, compared to the old stuff you're pulling out.
Tighten up the nipple before you remove the syringe, et voila.

Hope that makes sense.

Actually makes more sense than most things so far, I hadn't quite got as far as asking where the fluid goes, but I'd been churning it over in my head!!

I think I'll have to get a helper at some point and pull the fluid out while they top it up! Although as they've always been the same, maybe I should just leave it!!



Thanx everyone. I appreciate I ask some daft questions! I will learn at some point!! LOL

As I said to DefTrap, I think I'll ride it as it has been for the next couple of months (I survived when I rode it before!! LOL) and just avoid wet weather, like I did before!! Then plan some proper changes in the spring

[DefTrap]

I have to say I rarely use the rear brake on my bike, only really for some emergency style stopping (or if it were wet, and who does that!) and I'm way too cautious these days to fall foul of that sorta shenanigans.

[Ian]

Since its not long since it was rebuilt, if the fluid isn't grim try leaving something resting on the pedal for a couple of days to let air travel up from the caliper to the reservoir (It used to help a little on old front brakes, might work on the rear).

I like a soft rear, its all to easy to lock up in a panic.

[Yorick]

I would agree that the consequences of getting it wrong could be awful. However - it's really not that hard! - .

This is Noggers

[Yorick]

I have to say I rarely use the rear brake on my bike, only really for some emergency style stopping (or if it were wet, and who does that!) and I'm way too cautious these days to fall foul of that sorta shenanigans.

Same here. 99% front on road and track.

But about 50/50 on the enduro bike.

[Yorick]

Since its not long since it was rebuilt, if the fluid isn't grim try leaving something resting on the pedal for a couple of days to let air travel up from the caliper to the reservoir (It used to help a little on old front brakes, might work on the rear).

Yeah, I'd been thinking that

[Noggin]

I have to say I rarely use the rear brake on my bike, only really for some emergency style stopping (or if it were wet, and who does that!) and I'm way too cautious these days to fall foul of that sorta shenanigans.

Oh I'd normally agree. But doing 21 hairpins and 3 roundabouts down a mountain (approx 1500m descent) on damp or wet roads and I'd MUCH prefer a working rear brake!!

I can honestly say that before being here, I very very rarely used the rear brake and generally only in emergencies/wet riding.

But living at 2000m and needing to get to the valley makes things a smidge different And none of the hairpins are flat to go into, they are all sloped entry and exit!! LOL 100% fine on dry roads, not quite so 'happy' on wet Normally I'd just avoid riding in the wet, but,, no car and there's a good chance I'll have to go to 'school' (more French classes) for a couple of weeks and won't have a choice on the weather!!

(No worries if it rains whilst I'm down there - riding up in the wet, no problem!! LOL)

Since its not long since it was rebuilt, if the fluid isn't grim try leaving something resting on the pedal for a couple of days to let air travel up from the caliper to the reservoir (It used to help a little on old front brakes, might work on the rear).

I like a soft rear, its all to easy to lock up in a panic.

Soft is fine. No noticeable braking when standing on the pedal, not so good!

But that's a good call - I'll try that first (this evening ). TBF, I could do that each night if I need to when I have to go to school/language course!

I have to say I rarely use the rear brake on my bike, only really for some emergency style stopping (or if it were wet, and who does that!) and I'm way too cautious these days to fall foul of that sorta shenanigans.

Same here. 99% front on road and track.

But about 50/50 on the enduro bike.

See above - wet mountain roads = different to normal situations! Other than where I live, I'd agree with you!!

[Ian]

Soft is fine. No noticeable braking when standing on the pedal, not so good!

When you are stood on it is there resistance, if there is maybe the pads are be glazed or worse contaminated ? Is the surface of the disk clean and shiny across a wide area or is it rusty in places?

Bodge solution to break glaze is a good few emergency stops (or take them out and rub them on some sandpaper) but the better solution is new pads.

If they are contaminated you need to strip the rear caliper, replace the seals and put new pads in

If the disk isnt shiny all the way across the pads have worn unevenly, they may bed in with wear but its better to bin them

[Noggin]

Soft is fine. No noticeable braking when standing on the pedal, not so good!

When you are stood on it is there resistance, if there is maybe the pads are be glazed or worse contaminated ? Is the surface of the disk clean and shiny across a wide area or is it rusty in places?

Bodge solution to break glaze is a good few emergency stops (or take them out and rub them on some sandpaper) but the better solution is new pads.

If they are contaminated you need to strip the rear caliper, replace the seals and put new pads in

If the disk isnt shiny all the way across the pads have worn unevenly, they may bed in with wear but its better to bin them

From what I remember, the first few times of pressing hard (not quite standing) there was nothing but that would change over about 1-2kms, so there would be 'some' braking. But it was never good!!

Like those above have said, it wouldn't normally be a massive issue. Except for where I live!!

[Ian]

Nothing but getting better does sound like it needs bleeding

[Demannu]

I bled it up last time.
I took the caliper off, span it around so the bleed nipple was the highest point in the system, put 1/2 litre of dot4 through it using a mityvac, it was better but still poor.
Didn't change the pads though, so possibly getting shot of 10yo pads may make a difference.
But IMHO, they are known to be piss poor brakes!

[Noggin]

I bled it up last time.
I took the caliper off, span it around so the bleed nipple was the highest point in the system, put 1/2 litre of dot4 through it using a mityvac, it was better but still poor.
Didn't change the pads though, so possibly getting shot of 10yo pads may make a difference.
But IMHO, they are known to be piss poor brakes!

I knew you'd done all that, but I've not ridden it a lot, so wondered if it was worth doing again given how much it's been sitting (for various reasons!).

I'll look at getting some pads xxx

[Noggin]

Ok, pads ordered. Haven't (can't!) ordered expensive ones but if I'm likely to change the caliper then there's no point. Interesting that some of the sellers say it will take 2 weeks to get here - from Italy FFS!!!

Anyway, in theory they'll be here next week, so I'll hold off on messing with the system until they arrive

[A_morti]

You'll want to give the disc a scrub. Ideally, take the wheel out, the disc off, and get after it with lots of dish soap and a stiff brush, so you also remove any contamination from the holes/slots on the disc.
Trying to clean it fully while still in the bike is one of those short cuts that's actually the long way around.

[The Spin Doctor]

Oh I'd normally agree. But doing 21 hairpins and 3 roundabouts down a mountain (approx 1500m descent) on damp or wet roads and I'd MUCH prefer a working rear brake!!

Perhaps it's an obvious question, but what pads do you have in it?

Manufacturers OE equipment is generally designed to work reasonably well in just about any situation you can throw at it. I

Aftermarket stuff varies.

I've ridden a bike with 'fast road / track' pads that never felt like they were going to work in ordinary riding until the brake had been on a couple of seconds, and another with Armstrong pads which took me back to the dark days of 70s wet weather lag.

I had a lot of quality issues with EBCs back through the early 2000s (one set would be great, the next barely stopped the bike) but have them in the rear of the XJ at the moment since I couldn't get the OE pads in time for the MOT when I realised they were a bit short of material.

[Noggin]

You'll want to give the disc a scrub. Ideally, take the wheel out, the disc off, and get after it with lots of dish soap and a stiff brush, so you also remove any contamination from the holes/slots on the disc.
Trying to clean it fully while still in the bike is one of those short cuts that's actually the long way around.

Good call. I'm hopefully going to give it a short early run up here tomorrow, then I'll look at taking the wheel out - not sure I have the right stand for that, so may have to 'think' about it a bit But as you say - it almost certainly needs doing!

Oh I'd normally agree. But doing 21 hairpins and 3 roundabouts down a mountain (approx 1500m descent) on damp or wet roads and I'd MUCH prefer a working rear brake!!

Perhaps it's an obvious question, but what pads do you have in it?

Manufacturers OE equipment is generally designed to work reasonably well in just about any situation you can throw at it. I

Aftermarket stuff varies.

I've ridden a bike with 'fast road / track' pads that never felt like they were going to work in ordinary riding until the brake had been on a couple of seconds, and another with Armstrong pads which took me back to the dark days of 70s wet weather lag.

I had a lot of quality issues with EBCs back through the early 2000s (one set would be great, the next barely stopped the bike) but have them in the rear of the XJ at the moment since I couldn't get the OE pads in time for the MOT when I realised they were a bit short of material.

Absolutely no idea what pads are in, but they are pretty much guaranteed to be VERY old!! And given the condition of the bike when I rolled it into the Transit on pick up, I probably should have chucked them at the same time as I bought the front ones!!

But as so many have said, I didn't use the rear brake that often before being here - and TBF, with two proper arms I would probably feel more confident as it is!! LOL

[The Spin Doctor]

You'll want to give the disc a scrub. Ideally, take the wheel out, the disc off, and get after it with lots of dish soap and a stiff brush, so you also remove any contamination from the holes/slots on the disc.
Trying to clean it fully while still in the bike is one of those short cuts that's actually the long way around.

Good call. I'm hopefully going to give it a short early run up here tomorrow, then I'll look at taking the wheel out - not sure I have the right stand for that, so may have to 'think' about it a bit But as you say - it almost certainly needs doing!

Absolutely no idea what pads are in, but they are pretty much guaranteed to be VERY old!! And given the condition of the bike when I rolled it into the Transit on pick up, I probably should have chucked them at the same time as I bought the front ones!!

But as so many have said, I didn't use the rear brake that often before being here - and TBF, with two proper arms I would probably feel more confident as it is!! LOL

A baby bottle brush helps with getting grot out of the holes... amazing how much gets stuck in them.

In that case before going the bleeding route, I'd change the pads for something sensible on a road bike and make sure the pistons move freely (and clean the disc FIRST as suggested). Then you'll have a benchmark to figure out if it's the hydraulic system that needs sorting or whether it was simply grotty pads.

[A_morti]

A baby bottle brush helps with getting grot out of the holes... amazing how much gets stuck in them.

I found a bottle brush was too big on my fz.
A nozzle brush was perfect.