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Old 01-26-2015, 01:36 AM   #1
Xoliul OP
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BMW G650 X (brake) parts madness

I have an Xmoto with a really, really stubborn front brake that refuses to bleed properly and feels spongy after 6 attempts at it (using almost every trick imaginable).
I'm just going to rebuild it a bit, but finding parts is extremely hard.

I know all these parts are probably generic and shared, but it's nigh on impossible to find what is what exactly.

-I have a friend's Monster 620 standing next to it, and noticed the front brake caliper looks almost exactly the same. Seems to be a Brembo 6800 4-pot. The only difference I see online is often that it looks like this instead of this. The brembo text is smaller and has the logo above it. I suspect this is purely a visual update/difference, as the 6800 is used for both.
I want to confirm if buying this kit for Monster 620, would work?
-Is the front brake master cylinder the same as the F650? There seem to be differences. I want to know what kind of maintenance kit for the master cylinder I could buy?

Finally, not brake related, but I have a set of Zeta 'bend' handguards, seen here: http://i.imgur.com/8qbj5Wh.jpg
They never fit that well, they seem to have been made for handlebars with more pullback (not how the end parts are at a slight angle). Result is they drag against the grips and slow the throttle down when it returns...
Anybody can shed some light on if the pullback is standardized between bikes? Like I have no idea what will fit what. Even better if the straight one would fit, as these are way cheaper than barkbusters or SW-motech and look better and have more options
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Old 01-26-2015, 02:16 AM   #2
Pejie
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got a replacement rear mastercylinder for my XC a brembo part for ducati for about 1/3 bmw price plus a brembo microswitch for the hand brake but can't help with the front brake.
My front break was really spongy - made sure the front master cylinder reservoir was dead horizontal then the reprom advises pulling the brake on moderately hard then let it off & repeat until air bubbles stop coming out. Took a while but worked like a charm, brake is the best it has been. Non ABS.
goodluck
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Old 01-26-2015, 02:24 AM   #3
Xoliul OP
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Trust me, I've tried all of that and can still pull the lever into the bars without much effort. Me and 2 others have spent hours on it already, so spending 80 euro on parts isn't a big deal to me. I do want to avoid going to the bmw dealer since they are slow and expensive.

Some more research suggests it's a Brembo P4 30/34, shared with a lot of other bikes that should have seal kits available. Now I just wonder about the pump/master cylinder.
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Old 01-26-2015, 04:36 AM   #4
The Jester
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I had a similar issue on an X-challenge - excessive brake lever travel - which I cured by replacing the brake lever.

On the X-challenge the lever is non-adjustable. The lever is made of alloy and has a socket where the steel pin from the master cylinder locates. Over time this socket wears leading to excessive lever travel as the pin springs out and this slack has to be taken up before the brakes start to work. It doesn't take much wear to transfer into quite a lot of travel at the end of the lever. I replaced the lever with a pattern part for a honda cb500 twin commuter bike which restored the normal brake travel and feel.

Not sure if the X-moto has the same master cylinder, but if the lever is non-adjustable I would try replacing that before going any further.
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Old 01-26-2015, 05:00 AM   #5
coyotedave
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Try putting a strap around the lever and handlebar and pulling the lever into the bar and leaving like that for a couple of days.
This will make any trapped air rise up the brake line into the master cylinder.

An old trick that still works.


Cheers Dave.
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Old 01-26-2015, 05:11 AM   #6
Bli55
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See photo, Xoliul already has adjustable levers...

Xoliul, I see your bike is non-ABS, so bleeding it should especially be non-problematic...
Have you got an inner hex bolt inside the master cylinder? If you do (if they exist on non-ABS) - you need to bleed that circuit too!!

!!!
http://www.advrider.com/forums/showthread.php?t=461275
!!!


Additionally, read this:

http://www.f650gs.crossroadz.com.au/...BrakeParts.pdf

http://www.advrider.com/forums/showthread.php?t=406344

http://www.advrider.com/forums/showthread.php?t=796605


And an extremely interesting topic over on an Aprilia forum:

http://www.apriliaforum.com/forums/s...r-Brake-Issues


Enjoy!
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Old 01-26-2015, 05:32 AM   #7
Xoliul OP
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Jester: I have one, had it for 2 years already. I tried switching between that and the old one (which wasn't worn either), not much difference, if any.
I could set my lever to max to make it impossible to pull into the handlebars, but that doesn't feel like the proper solution. I have 3 other bikes in my garage and they all encounter serious resistance before 1/3rd of the lever travel, this bike only gets that after 2/3s.

Coyotedave: I did that, multiple times: no change.
I even tried crazy stuff like using a big syringe to inject fluid from the bottom up to the top.

Bli55: that's actually the first thing I read I had not encountered yet. That mystery bleed screw might be there, I have no idea, will check tonight.
And yes I agree this bike should not be an issue, i've bled way more complex systems without issues before, hence why I'm a bit stumped.

If it's not that mystery screw, I suspect:
-small leakage at either bleed screw or copper washers
-Small leakage at caliper piston seals
-Master cylinder seals got tired and worn
-Braided hose has gotten a bit tired (unlikely but not expensive to replace)

Hence why I want to find proper replacements for those parts.
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Old 01-26-2015, 06:35 AM   #8
Bli55
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You should find very useful a Brembo yododyne(?) catalogue.
Google should know...
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Old 01-26-2015, 07:49 AM   #9
beerbuzz
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Try re sealing your banjo fittings, heat the copper crush washers with a torch and let cool slowly to anneal them. This softens them up so they are ready to crush again. If your master is too small (moves smaller volume) it will be spongy, opposite is true for oversized master, it will lock up if you look at it Wrong. If all air is out and the system is matched I would suspect the lever. I thought my YZ brakes sucked until I adjusted the lever to provide proper engagement, now it makes me wipe out when it locks up. Guess there's a sweet spot there somewhere.
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Old 01-26-2015, 03:11 PM   #10
motorrat
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Contrary to steel, copper softens when it is shock-cooled.

Find the little Hex, but be carefull, the brakefluid will squirt out.
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Old Yesterday, 03:33 AM   #11
Xoliul OP
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I checked: there is no extra nut/hex inside the reservoir, like that picture.
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Old Yesterday, 05:30 AM   #12
MJS
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I would try the following.

Bleed MC separately (with brake hose disconnected)
Bleed caliper by fully compressing pistons and injecting fluid into the bleed screw and up to the MC banjo.
Connect line to MC and finish bleeding normally.

This will remove most of the air from the system before the final bleed. If you know you have the air out of the system and still have a soft lever then I would look at the MC as a problem. Any external leakage will weep fluid when under pressure and be visible. A caliper with leaking seals will be obvious since it will leak fluid past the seals to the outside as will a crush washer. A bad seal on the MC piston can allow pressure to escape from the high side of the piston back to the low side and return to the resivoir.

Just my $.02
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Old Yesterday, 06:22 AM   #13
The Jester
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My money is still on the brake lever. I replaced mine a number of times in the 46k miles I had the X-challenge. Each time it brought back original lever travel, feel and power.

I checked the pictures and the master cylinder is the same set up as the X-ch. As I said, the pin wears the socket on the lever. Since it is on a spring it then moves out and this slack must be taken up before the brakes start to work. The thing is, you don't notice it as free play like you do on the clutch because you are compressing the spring.
The adjustable lever you have adjusts for span; it does not adjust the point of contact on the pin. Say you have 2 inches of travel on the lever. If you adjust the lever you still have 2 inches of travel; the only difference is the lever starts further away from the bar.

I know the adjustable levers aren't cheap but if it is 2 years old it has probably worn to the point that it is causing the problem. I was able to buy pattern levers for 5 a time so why not try one of those to see if this solves the problem. What have you got to lose?

If it does you can then decide whether you want to replace the adjustable lever. If it was me though, I would try something like a piece of thin stainless sheet, punched to match the shape of the socket and glued in place. It would take up the slack and not wear so much in future.
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Old Yesterday, 08:45 AM   #14
Xoliul OP
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How do I bleed the master cylinder with no hose attached? Just let the fluid trickle out of the hole?

And Jester, I will inspect the hole in the lever, should be easy to see if it is worn or not using the pin. I've only done like 5-6000 miles with it though, I don't ride that much.
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Old Yesterday, 09:00 AM   #15
MJS
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To bleed the MC use a short piece of brake line looped back into the reservoir or into a container with some fluid in it.

Or you can submerge the entire cylinder in brake fluid but that's a bit messy for me :)
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