2008 GSA Fr Master cylinder locked on after bleeding

[andeebee]

Bike has been unridden for a year. In preparation for its MOT I thought I would go round and sort the usual, including bleeding the brakes as the fluid was started to look discoloured.
I have Stahlbus bleeders fitted to the front (spring loaded preventing back flow of air/fluid) , so bleeding is usually a 15 minute job. But this time I started having problems with the left hand caliper and the lever wouldnt come back to the bar when the bleeder was open.
And then it would and then it wouldnt. I thought the bleeder must be a bit seized as they havent been used for a long time.
Eventually finished bleeding and the brakes felt OK at the lever and I set off on my journey.

About a mile down the road I encountered first roundabout and had no front brake lever travel. It was rock solid, so I slowed with the rear and pulled over to investigate.
The front brake would not activate the front calipers unless squeezed really hard, still with almost no lever travel, rocking the bike back and forth.
Made my way home and thinking I had a seized caliper, I stripped the pads out and sure enough the pistons were stubborn, but a few cycles in and out and a clean with a tooth brush, they freed up so I could push back in with hand pressure.
But still the lever is solid and isnt activating the front calipers in the slightest. I removed the pads again to watch the pistons and they arent moving on (trying) to squeeze the lever.
Now I suspected the front master cylinder, so removed that from the bike. On disconnecting the top brake hose, the lever now operated freely.

So I think the problem is between the m/cyl and the ABS unit.
Does anyone have any experience with this and how to resolve or any ideas on what to investigate next?
I have cycled the ABS pump using the service mode and although I could hear the pump, it made no difference.

 

[chris99]

collapsed Flexi pipe?

 

[Mistacat]

Just for reference it takes about 20 pumps of the front brake lever to bring the pads into contact with the discs after the pistons have been pushed fully back. ( Obviously varies with pad wear)
The fact that the lever is going solid and the master cylinder feels free ( bleeding brake fluid at the banjo`s)
Is it possible that one of the valves is sticking in the ABS module.
These valves can be cycled using the GS911 and can be herd operating.
Photo of GS911 page the first photo includes the option to run the ABS pump, second photo is showing all of the valve options.

 

[andeebee]

Thanks for the suggestions. I dont think the hose has collapsed but it is possible (stainless lines but original ones). I will test whilst off the bike.
The inlet valve activation sounds like a possibility, thanks for the screenshot of the 911 brake section.
I dont have a 911, I have a cheaper and less functional (I think) MotoScan. I dont recall seeing the options to activate the valves like your screenshot does,
I have the option to cycle the ABS for bleeding.
I thought the system would fail 'safe', given that I got a mile down the road with the brakes working before the lever locked up, however if I have bled them incorrectly I guess Im responsible.

The master cylinder is still off the bike. I am going to try and fab a quick circuit to an old caliper I have, to see if I can operate the caliper minus the ABS circuit.

 

[andeebee]

Replaced master cylinder with a used part, bled out the air, same problem. Lever locked out at m/cyl.
Found the valve actuator controls on the Motoscan app. All the valves give an audible whine and click when 'on' except the front inlet - it just whines.
I went round them all several times, same results.
Cycled ABS bleed operation, same.
No error codes.
Time for an ABS investigation...

 

[botus]

can you trace the front brake pipe to each union one by one closer and closer to the ABS module - checking if with each of these cracked open if the master cyl works OK each time ?

Are we sure you haven't accidentally just snagged a pipe or hose and it somehow blocked it ?
How much crud appeared to be in the system ?
Which ABS system has it got ? - ABS2, the one like any normal vehicle has, came in 2007 (I thought), the other earlier ones were very special disaster zones

If the ABS unit did this it would be 1) fail dangerous and thus not likely its allowed, 2) unusual as we've not heard /come across this before

 

[andeebee]

Stripped bike down to look at ABS (see above)
The front hose is the nearest on the photo, so I will undo and see what I can see/do.
Fluid wasnt bad, maybe 3 years old. Was just doing a standard bleed and I had sucked out the contents of the reservoir before refilling with new fluid, so that doesnt go though the system

 

[botus]

nice its the ABS2 easily repairable one - same basic designed (to fail) unit as fitted to 90% of the worlds vehicles
but it should have codes if it where playing up and the warning lights on the dash - sounds more like a blocked pipe way before it gets here....

 

[andeebee]

I bled the right caliper first and that bled fine. Problems started with the bleeding the left caliper and the lever started 'ratcheting' as I bled
Brakes worked at first, enough to get me down the road and a couple of junctions before they locked the lever.
No ABS light. Rear ABS still functioning when I forced it to kick in on the way home.

 

[andeebee]

Found some crud under the first inlet port, thats the line connected to the reservoir. Sucked that out and reassembled but the lever is still solid.
When the line is disconnected the lever pumps fresh, clean fluid through no problem.
Undone the front outlet and that was silvery, murky but the lever wont push the fluid through to this port.
Whatever is in there is well and truly blocked.
Tried the front actuator and still no click from the front port.
I cant see an obvious way into this valve block and nothing on YT other than changing the brushes in the motor side.
Anyone have any experience with the valve block side?

 

[botus]

ummm... so you are saying with that pipe off fluid pumps normally (to here) ? if so still NOT confirming its ONLY stuck at the ABS unit - what happens on other pipework... trace back from the front calipers going back to the module and crack off the outlet of the ABS unit (AKA to the front wheel)

After that conclusion - if seems stuck at the ABS module - the black bit (with the multiplug) is held on by 4 or 6 small screws and comes off - leaving a load of weird dangly bits - forget as not looked in ages - the winding for the electromagnetic valves is on the black bit and the dangly parts the end of the valves / solenoid - I suspect you'd just damage it try anything external to physically manipulate each solenoid - but might be worth a look for corrosion and providing some lubrication - dry film PTFE ?

how about a blunt implement (soft metal drift) and giving the aluminium block a hefty whack quite a few times - and maybe a bit of heat (carefully) from a heat gun ? - not sure if you can try and push backwards

did get a BM tech two years back claim half the ABS failures (of this model unit) are due to people pushing back brake pads and reversing fluid flow through the module - can't see how - but he was adamant this is the killer - recco'ing NEVER to push fluid to the master cyl - but rather always cracking off bleed nipples to replace pads

FYI the brains AKA coding for wheel size / bike fitment / ABS behaviour and Traction control (if enabled - retrofit of TC is a choice if you want to pay 140 for the software licence ) - are inside the black bit - most faults are the pump motor brushes - so you can split and play mix and match without needing full on diagnostic tools to code a unit to a particular bike

 

[andeebee]

Your info about the pistons pushing dirty fluid back up is the likely culprit here and I think it has blocked the tiny passageway within the block. I found a 'frozen lever' thread on a Harley site which was diagnosed as the same symptoms and it seems cars can also loose rear wheel braking due to these blockages, but goes undiagnosed until MOT time as the other brakes work fine.

 

[botus]

there should never be crud in the systems to block anything - they are meant to get a full change every 2 years - and in reality nothing should be going wrong even if its been 10 years since anyone bothered

the idea about forcing pistons back and thus fluid backwards through the ABS module is I believe more the possible damage of the flow doing something it shouldn't - not the non existent crud being an issue

on cars or bikes with rubber hoses that are 20 to 30 years old, these can collapse and or breakdown - but the GS gets plastic tube with a stainless wrap and they don't (shouldn't) add any extras to the party, leaving only the Master Cyl / piston seals that if you get a solid lever (must still be all, or mainly there) or unusual corrosion from horrific maint practices