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Rear brake lock-up/overheat
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Rich Simpson View Drop Down
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    Posted: 11 Jun 2022 at 22:34
Always seems to happen on the first ride of the year...I'm wise to it now and stop when I feel the pedal travel disappear.

No harm done.

Opened the bleed nipple, and a puff of steam came out.

I can only think that the fluid absorbs water when the bike is laid up over winter, then it boils and pressurises the brake.

It always happens in traffic...engine heat on the master cylinder must be doing it.

Ordered some Motul Dot 5.1 in hope of a cure.

Anyone else had this?
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badapple View Drop Down
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Points: 5776 		Post Options Post Options   Thanks (0) Thanks(0)   Quote badapple Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jun 2022 at 00:16
Yep exactly the same! Nearly had me off first time it happened. Second time I qas on the ring road and some meat head Pr**k pulled up in front of me,  I thought he was going to help move my bike but no he went metal telling me to move it out of his and everyone else's way. Yeah sure I'll push a 200kg bike with siezed brake no problem at all Angry
I started out with nothing and I've still got most of it left
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jun 2022 at 09:28
Sorry to hear that.

Luckily, I was only in Bodmin, and a small crowd of helpers soon gathered, blokes arrived with toolboxes etc.

The Cornish are 

a) Very kind

b) Love fixing things.


See this story
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Mikey View Drop Down
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Points: 56 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Mikey Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jun 2022 at 14:29
I had that issues once - because I had tried to 'fix' the missing brake by adjusting the push-rod.
RSV1000R, m.y. 2007
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jun 2022 at 14:55
The rear brake seems to be the most troublesome part on the Mille.
Needs to be bled 'just right' and set up 'just right'...I've now got mine set up with a good bit of slack in the pedal, so you can tell straight away if it's on the point of locking itself up.
I'll report back on what difference, if any, Motul DoT5.1 fluid makes.

I've also seen a sudden fall in the fluid in my clutch MC, so there's an Oberon slave cylinder coming too. Hopefully the new fluid will help here too, and that has to work in a very hot environment.

Ironically, the front brakes have the easiest time...cold air all over them.
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2022 at 17:22
Thanks to AP Workshops the slave cylinder arrived today.
Now waiting for the fluid
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Points: 1481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Stevex Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jun 2022 at 15:58
I've had the lack of rear braking problem with a Mille and T Racing previously, but since the mc has been fitted vertically on the bikes AP rear sets of my current Tuono, I've never had the problem in about 8 years.
Most who get rear lock ups have put it down to incorrectly adjusted input rods. 
People say I don't know Jack Sh1t; but I do, he lives next door.
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Points: 6699 		Post Options Post Options   Thanks (0) Thanks(0)   Quote legend88 Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jun 2022 at 16:50
Originally posted by Stevex Stevex wrote:

I've had the lack of rear braking problem with a Mille and T Racing previously, but since the mc has been fitted vertically on the bikes AP rear sets of my current Tuono, I've never had the problem in about 8 years.
Most who get rear lock ups have put it down to incorrectly adjusted input rods. 
 
I have an RSV4 rear master fitted to AP rearsets and the brake works really well. Certainly capable of locking up the rear wheel.
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jun 2022 at 17:02
Fluid is here now...I'll let you know how it goes...
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug 2022 at 21:03
In a word...badly.

New fluid in, brake bled, all well.

Then today riding slowly up a steep hill in traffic with a hot engine, it locked up.

Undid the bleed nipple half a turn, and a spectacular ejaculation of boiling brake fluid resulted

The caliper is now leaking when the brake is applied...am going to order a £16 heat shield, strip the caliper and rebuild with new seals.

Good job I've got some brake fluid left over.

On a brighter note, the Oberon clutch slave works really well!
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Points: 16331 		Post Options Post Options   Thanks (1) Thanks(1)   Quote redratbike Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug 2022 at 22:35
sounds like you set the feee play wrongly on the lever common mistake 


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Rich Simpson View Drop Down
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It started off with loads of free play...but I'll take a look again
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Rich Simpson View Drop Down
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Gen 2 heat shield ordered from Fowlers and arrived next day. £20 inc post

I had to cut it down to get it to fit, and lined it with heat-reflective insulation on the engine side.

Brake freeplay checked and all OK (I run slack back brakes on all my bikes anyway). Fluid topped up (but not over-filled) to replace what was lost. Linkage moving freely.

Will let you know how it goes. If it still gets hot, I will try insulating the line, which runs horribly close to the engine. If that doesn't work, then it's time to get some aftermarket footrests that relocate the master cylinder away from the engine and into the airstream...there is a duct in the bellypan which is obviously designed to cool the MC, but it's not going to do anything at 10 mph!
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2025 at 18:29
Three years later.

None of the above was any help.

In the end...purchased another new master-cylinder and fitted to the AP rearsets.

Ditched the Brembo caliper and replaced it with on from Hel (which is just up the road in Devon).

Sat and thought about things for ages while bleeding the new caliper in.

Does the reservoir get hot?
Well less so than when it was under the fairing, but there's still a lot of heat around that area.
Does that create pressure in the reservoir?
Yes because it's not vented.
Looked carefully at the cap, and there's two little dimples on the inside.

Hmmm, drilled them through with a very small Dremel drill.

Have stressed-tested bike by riding slowly in high temperatures, and all was ok. Went for a longer ride, and the brake works perfectly and no longer gets hot.

Was it either of the expensive components that I replaced, or just the two little holes I drilled.

I've no idea, but anyone experiencing this problem would do well to drill the holes first!
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Spoonz View Drop Down
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Points: 10957 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Spoonz Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2025 at 23:02
Originally posted by Rich Simpson Rich Simpson wrote:

Three years later.

None of the above was any help.

In the end...purchased another new master-cylinder and fitted to the AP rearsets.

Ditched the Brembo caliper and replaced it with on from Hel (which is just up the road in Devon).

Sat and thought about things for ages while bleeding the new caliper in.

Does the reservoir get hot?
Well less so than when it was under the fairing, but there's still a lot of heat around that area.
Does that create pressure in the reservoir?
Yes because it's not vented.
Looked carefully at the cap, and there's two little dimples on the inside.

Hmmm, drilled them through with a very small Dremel drill.

Have stressed-tested bike by riding slowly in high temperatures, and all was ok. Went for a longer ride, and the brake works perfectly and no longer gets hot.

Was it either of the expensive components that I replaced, or just the two little holes I drilled.

I've no idea, but anyone experiencing this problem would do well to drill the holes first!





The reason that brake systems aren’t generally vented is that the fluid is hydroscopic. Not an immediate problem but your fluid life will be reduced and you may introduce some corrosion if you don’t keep on top of fluid changes. 
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2025 at 10:01
there's a rubber bellows and a sealing ring protecting the fluid, so it should be OK.

I checked the condition of both carefully.
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Rich Simpson View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rich Simpson Quote  Post ReplyReply Direct Link To This Post Posted: 22 Aug 2025 at 11:38
Just had MoT test, and the rear brake recorded its best-ever figure!
Heartily recommend switching to the HEL caliper.
It's not at all grabby in normal use...came with EBC organic resin pads, not sintered metal.
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