Brake bleed(ing) help!

I have put in new brake lines for the rear brake and am now struggling to remove an air lock. I have been bleeding brakes for 40+ years and feel pretty skilled at it but this one has me beat and refuses to give me any pressure at the lever. The only minor complexity is that my 961 is a EURO4 with ABS which is located under the seat hump. I made exactly the same changes to my other bike which is also ABS and bleeding the brakes was a 5 minute job, but the ABS unit was down under the airbox on that one. I have put bleed nipples on the ABS banjos to help me remove the airlock but no joy, I can get DOT4 fluid freely flowing without bubbles at both the ABS unit and the rear caliper but still no pressure on the lever (I can get the brake light to briefly illuminate, flicker). My new line from thumb brake down the bike adds 150cm to the length of the brake line but rear brake line is still shorter than the front lines which have to go from handlebars to ABS at rear then back to fork trees then down to front calipers. I have even swapped the 13mm Brembo master cylinder of the thumb brake with the 11mm Brembo that is std on the rear footbrake thinking my new master cylinder was faulty but no difference. Tomorrow I will try adding fluid at the rear caliper bleed nipple using a syringe and push fluid back up to the handlebar reservoir, maybe doing it in reverse might shift the air lock but right now I feel about as frustrated as you can get having spent best part of 2 days on this little bleeder

Do you guys have a foolproof method of bleeding brakes? Or is there a particular issue with bleeding the rear Brembo caliper?

Have you tried searching the internet for Brembo instructions?

I fitted a Brembo stuff from cNw to my old Cdo, I struggled like mad with the front brake using all of my ‘traditional’ methodology to bleed it. Later on I fitted a Brembo hydraulic clutch kit... only this time I read and followed the Brembo instructions and it was a piece of cake!

Failing that, how about asking Olivia... ?

I don't know why the ABS would stop the bleeding process ? Can you get a vacuum pump to pull the fluid down into the caliper ? I've seen these as hand operated also . Try pushing back on the pistons and get some of that fluid back into the master and expel some of that air. You will see the air bubbles coming out in the reservoir .

Some ABS systems require the dealer computer system to activate the ABS for bleeding. I do not know if this is the case with the new Norton systems!

Fast Eddie said:

Have you tried searching the internet for Brembo instructions?
Failing that, how about asking Olivia... ?

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These 11mm/13mm M/C's are straightforward to bleed and mine are pumping fluid through to the rear caliper bleed ok but it isn't dislodging the air in the system.

If all else fails I shall get Norton to flush the rear line when I get 1st service done, riding without rear brake for a few hundred miles won't be a problem as I rarely use it, as long as it works by the time it needs it's MoT lol

TonyA said:

I don't know why the ABS would stop the bleeding process ? Can you get a vacuum pump to pull the fluid down into the caliper ? I've seen these as hand operated also . Try pushing back on the pistons and get some of that fluid back into the master and expel some of that air. You will see the air bubbles coming out in the reservoir .

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Yes, the ABS shouldn't prevent a good bleed, it is just the position of it, high up under the seat bump so the brake lines follow a rollercoaster path leaving lots of places where air can get trapped.

I will see if I can drop the caliper tomorrow and push the pistons back in.

BPHORSEGUY said:

Some ABS systems require the dealer computer system to activate the ABS for bleeding. I do not know if this is the case with the new Norton systems!

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I think that is required when you want to completely flush the system of old fluid as the ABS valves will retain some of the old fluid unless they are activated.... which is where the dealer comes in.

Reverse bleeding is the best method.
Air rises, feeding fluid into the bleeder and pushing it up into the master cylinder is the best way to remove any air. I been doing this for years. look into a Phoenix bleeder.

Another frustrating day, I have free flowing fluid no matter which way I try to bleed, but no pressure on the caliper.... this 961 is already beginning to lose favor and I haven't even put it into gear yet

Have you spoken to Norton at all?

Fast Eddie said:

Have you spoken to Norton at all?

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Not yet, I would imagine that they will probably say bring it in. I can't even begin to sum up just how frustrating an exercise this has become, what should have taken me 20 minutes tops and I am still no closer to determining where the pressure is going.... I think it can only be that ABS unit with the lovely 'Made in China' sticker!

1degC out in my shed but I needed to go try one last thing.... I removed all the clamps and zip ties on the rear brake line/ABS line allowing me to remove the caliper clear of the swingarm/paddock stand and also allowing me to twist and turn it through 360deg and low and behold, with bleed nipple open and in one position only, I got a hint of a bubble forming, followed by another, and a few more rather large bubbles!!! I now have brake lever pressure

The bleed nipple in it's natural mounted position facing out from the left side of the caliper and forward of the inlet banjo DOES NOT ALLOW A FULL BLEED, the nipple needs to be oriented pointed upwards and above the inlet banjo in order to get all the air out. I can now have my first peaceful sleep in days and fall in love with my 961 all over again

Does anyone know what the rear caliper mount bolts should be torqued up to?

According to the workshop manual, rear caliper to carrier should be 28 nm.

Well done with the brake bleed, I had a similar situation when I fitted a Brembo master cyl and Pretech caliper to my old Cdo, if I’d had hair, I’d have pulled it out!

All these things are sent to try us tho eh?!

Ah. The old "air floats up" theory. Science. Glad your frustrating ordeal is over. Go thrash the beast.

Britfan60 said:

Go thrash the beast.

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Never mind wasting time with that, go and ride the bike...

Britfan60 said:

Ah. The old "air floats up" theory. Science. Glad your frustrating ordeal is over. Go thrash the beast.

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Do you recall the Fawlty Towers sketch where Basil gives his trusty Austin a good thrashing, I might carry a small Birch just for the 961

Fast Eddie said:

Never mind wasting time with that, go and ride the bike...

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Ha-ha!

Just under a fortnight to go now, must remember to check oil level and make sure it isn't all sitting in the sump before we fire up!

I found this old post as I had same issue on my ABS commando to bleed rear spongy brake ... abs is on high position and impossible to bleed so the easiest option is to replace banjo bolt by bolt with bleed nipple !! And this is done in 10min ! I fitted on both front and rear a bleeder at ABS input port.

I feel almost guilty when I have an issue which I cannot cure and do a search whereupon finding someone else's misery gives me a 5-10 minute fix. I really don't think they're given enough credit for their research as they battle their way through and help tp keep all of us on the road. There should be an award for the individual, doled annually, for the survivor of the largest headache.... Such as an extra large bottle of Excedrin and/or T-shirt to show proper recognition for sacrifice and tenacity..... The true 'Commando Hero' of the year.... Yes...all Norton motorcycles.

Use large stones please because I really don't enjoy teases.