Back brake binding and overheating

[marktheaxeman]

11 hours ago, gstallons said:

# 1 name everything you have done to this bike involving anything rear of the fuel tank filler . ANYTHING

 # 2 how long has this problem existed ?

 # 3 are you telling us everything / have you forgotten anything ?

1. All I have done to the bike since I’ve had it is fit some Mistral pipes and fit a new led rear light and indicators. 

2. It’s happened twice now in the last few weeks. 

3. I’m pretty sure I’ve mentioned everything. 

Cheers. 

[gstallons]

On a rear stand , pump the brakes about 4 Xs . The wheel will not turn . Break the bleeder screw and see if the wheel spins easier . 

 If it spins easier , the problem is ahead of the caliper . Brake hose , master cylinder or adjustments . 

If there is no difference , the problem is in the caliper . 

[sp838]

1 hour ago, gstallons said:

 

On a rear stand , pump the brakes about 4 Xs . The wheel will not turn 

 

Actually, this raises a good question: were you able to reproduce the problem off the road? If you put the bike on a rear stand, pump the rear brake a few times and release, does it bind, or can you spin the wheel? If it only happens while riding, it could very well be something else. Sounds like you are on the right track though, replacing seals etc., and you found some corrosion which certainly wasn't helping...  

[marktheaxeman]

The plot thickens..

I fitted the service kit in the caliper earlier and everything went together really well. The old seals actually looked pretty good. 

On refilling the system with fluid I could not get any to flow down into the master cylinder - tried pumping the pedal - no joy. 

So I took the master cylinder back off took it apart again to make sure everything was spotless and clean (it has a new service kit fitted - I did it last week). 

What I can’t understand is when I blow through the plastic inlet which is attached to the tube going to the reservoir- there is no air flow no matter what position the piston is in. Surely when the piston is right back against the circlip there should be flow through to allow the fluid into the high pressure part (to the caliper). ??

Its as if the black piston needs to come out beyond the circlip. 

I’ll add some pics of the master cylinder. 

cheers

mark. 

[marktheaxeman]

Heres the master cylinder

[marktheaxeman]

[GuzziMoto]

If I understand you right, you should not be able to blow through the hose that connects the reservoir to the master cylinder with the brake line connected to the master. That is basically a dead end system when the brake line and caliper are connected. If you have fluid in the caliper and no fluid in the master it can be hard to get the master filled with fluid. My favorite way is to have enough fluid in the caliper where I can push the pistons in the caliper in to the caliper which forces fluid from the caliper back up into the master. Otherwise, another good way is to use a bleeder, either a vacuum bleeder or a pressure bleeder.

[marktheaxeman]

4 minutes ago, GuzziMoto said:

If I understand you right, you should not be able to blow through the hose that connects the reservoir to the master cylinder with the brake line connected to the master. That is basically a dead end system when the brake line and caliper are connected. If you have fluid in the caliper and no fluid in the master it can be hard to get the master filled with fluid. My favorite way is to have enough fluid in the caliper where I can push the pistons in the caliper in to the caliper which forces fluid from the caliper back up into the master. Otherwise, another good way is to use a bleeder, either a vacuum bleeder or a pressure bleeder.

I have the master cylinder off the bike and i still cant blow through it... nothing connected.

[gstallons]

Fudge , it"s midnight or later where you are . disassemble and make absolutely sure you are putting this together correctly . I've never had one of these apart .
Are you sure the spring goes in with the "shiny thing" outward ?

[Lucky Phil]

16 hours ago, marktheaxeman said:

I have the master cylinder off the bike and i still cant blow through it... nothing connected.

Disassemble the master again and check you dont have a blockage at the master cylinder inlet. Also compare the rebuild kit parts in detail with the original parts.

Apparently your not alone......https://www.dino.co.uk/2011/08/07/bmw-f650gs-rear-brake-keep-seizing-try-this/

Ciao

[GuzziMoto]

On 5/22/2019 at 2:57 PM, marktheaxeman said:

I have the master cylinder off the bike and i still cant blow through it... nothing connected.

Then that may explain your problem, unless this is a result of the re-build.

It sounds like something is preventing the piston in the master cylinder from returning fully to where the chamber where the piston is is open to the reservoir.

I wonder if this was like that all along or if this is an issue with reassembly.

I gotta say, I have never had to re-build a master cylinder. I have replaced a couple, as they are usually cheap enough to replace vs re-build.

[Lucky Phil]

3 hours ago, GuzziMoto said:

Then that may explain your problem, unless this is a result of the re-build.

It sounds like something is preventing the piston in the master cylinder from returning fully to where the chamber where the piston is is open to the reservoir.

I wonder if this was like that all along or if this is an issue with reassembly.

I gotta say, I have never had to re-build a master cylinder. I have replaced a couple, as they are usually cheap enough to replace vs re-build.

Yes, on the surface of it I dont know why you'd bother really for a Brembo rear master. I mean they are only $55US to buy new, or 80 Australian Peso's

Ciao

[marktheaxeman]

I am pretty sure I’ve sorted the problem now!! 

I removed the plastic inlet pipe on the master cylinder and discovered that one of the two small holes was blocked up with crud. 

The hole is tiny and tapered so easy to block up over time. 

So I probably didn’t need the new seals etc fitted  - but at least I know they’re all good for a few more years of riding ! 

 

[Lucky Phil]

59 minutes ago, marktheaxeman said:

I am pretty sure I’ve sorted the problem now!! 

I removed the plastic inlet pipe on the master cylinder and discovered that one of the two small holes was blocked up with crud. 

The hole is tiny and tapered so easy to block up over time. 

So I probably didn’t need the new seals etc fitted  - but at least I know they’re all good for a few more years of riding ! 

 

Good to know, glad you got it sorted.

 

Ciao

[gstallons]

When you get this together and bled , pump the brakes a few ( 10) times and see if the brakes release and the wheel rotates freely and effortlessly . If not , see why .