ABS unit blocked on front brake circuit.............

During my extended winter maintenance I decided to service the brake callipers (front & rear) including replacing all the seals. No big deal, all went well.

Then the fun started - while bleeding the front brakes I was getting lots of air bubbles in the returns. I had pumped about 500 ml (new fluid from a sealed container) when it began to pressure up and fluid stopped coming out of the bleed nipple. Went through the lines and confirmed the ‘blockage’ was in the ABS unit!

Rearranged the lines to pump through the ABS block in reverse, no blockage. Checked the block diagram and confirmed that the ‘inlet’ control valve had a check valve in parallel, hence the returns in the reverse direction. This confirmed that the 'blockage' was at the inlet valve.

Checked through the online parts retailers in the UK and the best price I could find was £1020 plus P&P, however the bad news there were no ABS units in the UK and delivery would be between 4-6 weeks!

Checked in the USA and came up with $694 inc P&P, with import duty, VAT etc this would come out at £627.

Then checked online breakers in the UK and negotiated one for £259 inc P&P. Made the deal and it arrived next day. It was off a 2009 bike but looked immaculate almost as if the bike had never been outside.

Installed the new unit, bled everything, ran the onboard diagnostics and bingo, back in business. Another bullet dodged!

I still have no idea what happened to cause the blockage. I will hang on to the old ABS unit for now and try to re-assess manyana……..

I have changed the fluid annually just to be on the safe side but................

Glad that you resolve your issue Don,you bought it in a really cheap price!

I have heard for many ABS problems in Gen1 bikes,but first time i hear for a Gen2 ABS problem.

Very strange that this problem started from when you did the service in the brake callipers!

Are you sure that nothing dropped in brake fluid reservoir between the procedure,and through the brake lines to the ABS block?

Or perhaps the old brake fluid was very dirty with some rust and with some very small pieces of the seals or something like that,could cause the blockage in the valve..

Τry with some compressed air in the old unit,or do a surgery inside if you have the time to see where is the problem and what caused the blockage,i am really curious!

Α thought...

Really odd...

Mihalis fjr said:

Glad that you resolve your issue Don,you bought it in a really cheap price!I have heard for many ABS problems in Gen1 bikes,but first time i hear for a Gen2 ABS problem.

Very strange that this problem started from when you did the service in the brake callipers!

Are you sure that nothing dropped in brake fluid reservoir between the procedure,and through the brake lines to the ABS block?

Or perhaps the old brake fluid was very dirty with some rust and with some very small pieces of the seals or something like that,could cause the blockage in the valve..

Τry with some compressed air in the old unit,or do a surgery inside if you have the time to see where is the problem and what caused the blockage,i am really curious!

Α thought...

Really odd...

Click to expand...

Hi Michalis,

I am reasonably confident that nothing dropped in the fluid while topping up the master reservoir. I was pouring from a clean bottle and looking as I poured.......

I change the fluid every year mainly because I do it myself and it only costs a few pounds for 250 ml of fluid (enough for both brake systems and the clutch).

The only thing that 'could' have caused a problem is the master cylinder/seals if they had failed for some reason. As far as I am aware it is working normally....

Still a mystery to me..........

Donal said:

Mihalis fjr said:

Glad that you resolve your issue Don,you bought it in a really cheap price!I have heard for many ABS problems in Gen1 bikes,but first time i hear for a Gen2 ABS problem.

Very strange that this problem started from when you did the service in the brake callipers!

Are you sure that nothing dropped in brake fluid reservoir between the procedure,and through the brake lines to the ABS block?

Or perhaps the old brake fluid was very dirty with some rust and with some very small pieces of the seals or something like that,could cause the blockage in the valve..

Τry with some compressed air in the old unit,or do a surgery inside if you have the time to see where is the problem and what caused the blockage,i am really curious!

Α thought...

Really odd...

Click to expand...

Hi Michalis,

I am reasonably confident that nothing dropped in the fluid while topping up the master reservoir. I was pouring from a clean bottle and looking as I poured.......

I change the fluid every year mainly because I do it myself and it only costs a few pounds for 250 ml of fluid (enough for both brake systems and the clutch).

The only thing that 'could' have caused a problem is the master cylinder/seals if they had failed for some reason. As far as I am aware it is working normally....

Still a mystery to me..........

Click to expand...

Hi Don,

''The only thing that 'could' have caused a problem is the master cylinder/seals if they had failed for some reason''

This was my thought..Even a very small piece of aluminium from the master cylinder or and a small piece of a seal from the master cylinder,i think that could cause the blockage in the valve in the unit.I believe that the clearances inside there are near to zero.

Whatever happened inside there,happened between the procedure.BUT, perhaps the problem was there before the procedure and you didn't knew it because there wasn't air in the system.Perhaps the valve was stuck for a long time.

Did you try last to check if the abs was working before the procedure,i mean if you felt the pulse of the brake lever on a slippery road?

Are you sure that the problem started now,or was there?

The stuck valve sounds like the common Gen's1 ABS problem...

I have stripped the master cylinder and checked everything. The rubber seals are completely normal and no signs of damage in the bore. In fact it all looks brand new. I have ordered a 'rebuild kit' to put it back together.

It may be there was some debris in the system which became dislodged with all the bleeding I had to do. I was using a vacuum pump to 'pull' the fluid through and occasionally used the brake lever when the flow reduced due to air locking.

It was cold while I was doing it but that shouldn't be a problem.

The blockage did occur while I was bleeding. I had bled 500 ml of fluid through the ABS block to the calipers before the blockage occurred.

The mystery continues...............

Couple of pics of the 'old' ABS unit (they didn't plan on making this a user serviceable item)!











Haven't figured out a way to get into the actual flow paths yet......................

Cool. We finally get a look inside the mysterious ABS hydraulic block.

Are those plunger looking things (from the solenoids) all movable?

Do you know anyone working at a place with an industrial X-Ray unit? I would give that a try to see if that would reveal anything...

Clamp the metering block in a surface grinder or milling machine and start subtracting metal until the internal passages start to surface. 08FJR' has the machines, I have a metering block. Maybe we could work something out, Dave making chips fly while a grope, err, group of NERDS stands behind him and photographs the emerging events.

Fred W said:

Cool. We finally get a look inside the mysterious ABS hydraulic block.
Are those plunger looking things (from the solenoids) all movable?

Click to expand...

No, the 'things' you can see are outer casings. The domed ones are the inlet valves. I have butchered the block and got parts of an inlet valve out. There is a port through the valve that is less than 1 mm (that's the smallest drill bit I have and it won't go through). As you can imagine it would not take much to block one of these (as I found out the hard way)!

petey said:

Do you know anyone working at a place with an industrial X-Ray unit? I would give that a try to see if that would reveal anything...

Click to expand...

Nice idea but............. we are lucky to have an X-ray in the local hospital......

Couldn't find a surface grinder or a milling machine so resorted to a hacksaw and chisel!...........

From the left: Outer casing, poppet, spring, valve seat (outlet valve shown above)



Close up of Inlet Valve outer casing, poppet, spring & valve seat (with an Outlet Valve spring & poppet above)



Valve seat showing inlet port (from the bottom)



Block showing internal port.



Valve seat showing outlet port.

Donal said:

Couple of pics of the 'old' ABS unit (they didn't plan on making this a user serviceable item)...Haven't figured out a way to get into the actual flow paths yet......................

Click to expand...

Donal said:

Couldn't find a surface grinder or a milling machine so resorted to a hacksaw and chisel!...........

Click to expand...

So, even if we figure out what is killing the ABS metering block it sure doesn't look like we will be repairing and reinstalling them any time soon

JB Weld will fix her right up..

ionbeam said:

Donal said:

Couple of pics of the 'old' ABS unit (they didn't plan on making this a user serviceable item)...Haven't figured out a way to get into the actual flow paths yet......................

Click to expand...

Donal said:

Couldn't find a surface grinder or a milling machine so resorted to a hacksaw and chisel!...........

Click to expand...

So, even if we figure out what is killing the ABS metering block it sure doesn't look like we will be repairing and reinstalling them any time soon

Click to expand...

Amen to that.................

dcarver said:

JB Weld will fix her right up..

Click to expand...

Don,

Thanks for the pictures!First time we see how the unit looks inside.

Can you see where is the problem?Or what caused the problem?A burnt solenoid valve perhaps?

Or ''the mystery continues''...?!

Mihalis fjr said:

Don,Thanks for the pictures!First time we see how the unit looks inside.

Can you see where is the problem?Or what caused the problem?A burnt solenoid valve perhaps?

Or ''the mystery continues''...?!

Click to expand...

Michalis,

I haven't taken the time to get to the inlet valve seat that was causing the problem. I did 'probe' it using a single wire from a wire brush. It went in part way and stopped. I 'worked' the wire and cleared the obstruction. Sadly I have no idea what it actually was....

A burnt solenoid valve would not cause this problem. The inlet valve (actually all the valves) are de-energised normally and only energise in a 'lock-up' condition.

Having seen the size of the hole through the valve seat I am just amazed that this problem has not occurred before. I guess if there is a very small amount of 'debris' then it can be forced through the valve seat - don't really know? I had a look on the web to see if anyone did an in-line strainer for an ABS system but found nothing. I have ordered a small sheet of 90 micron (0.0035") mesh and will attempt to fabricate something that will fit in a banjo union.

So,we waiting...

I am very curious as many others here i believe,what the @#$&%*@ caused this problem..

I think that something,i don't know what,blocked the passage there..

Mihalis fjr said:

So,we waiting...

I am very curious as many others here i believe,what the @#$&%*@ caused this problem..

I think that something,i don't know what,blocked the passage there..

Click to expand...

Absolutely agree with that . But I am not going to waste any more time or effort to try and find out what it was. We are talking about a very tiny piece of something which is very likely to get lost in all the 'filings' if I try to hacksaw into the valve that was blocked....................