Rear brake circuit bleeding (with abs)

C

Chris CSTM

Joined
May 7, 2019
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Hello confined bikers
I guess most of us are staying at home. Cleaning and polishing our beauties. on my side I had to move the ABS unit in the tail to repair the bracket. It was cracked.

Then bleed front brake was ok, the rear appears really spongy and I wonder if air wasn’t trapped on the abs as it is really high compare to master cylinder and calliper.... I tried to supply brake liquid under pressure on master cylinder side to circulate. But did improve really much
Any clue on how to bleed the line properly ? thanks
Keep safe.
 
I have had the same issue constantly. I spoke to Rob Jameson when he was at Norton and it appears to be a known problem with ABS bikes, especially if infrequently used. There is a very quick fix without having to touch the caliper. The high point of the system is the ABS unit under the seat, where the air gets trapped. There are four connections on top of the unit. Looking forward, the rear brake is the first connection on the left. As with usual bleeding, depress the brake pedal and release the rear brake connection on the ABS unit just enough to release the air and a drop of fluid. Tighten it back up, wipe the area and check reservoir. It worked me for numerous times and can be done in minutes.
 
Glenn Harman said:
I have had the same issue constantly. I spoke to Rob Jameson when he was at Norton and it appears to be a known problem with ABS bikes, especially if infrequently used. There is a very quick fix without having to touch the caliper. The high point of the system is the ABS unit under the seat, where the air gets trapped. There are four connections on top of the unit. Looking forward, the rear brake is the first connection on the left. As with usual bleeding, depress the brake pedal and release the rear brake connection on the ABS unit just enough to release the air and a drop of fluid. Tighten it back up, wipe the area and check reservoir. It worked me for numerous times and can be done in minutes.
Click to expand...
It didn't work for me, it won't work if the trapped air bubble is in the caliper :cool:
 
Just to clarify. Because of my disability I have to re-work the rear brakes on all my bikes, relocating pipework etc. In recent times I have converted 4 ABS fitted bikes and none of the ABS units needed touching, they are sealed units and the chambers are only exposed to fluid when ABS is actuated so under normal bleeding routines they are effectively closed clam tight. This CAN be a problem on very old bikes where you want to do a 100% brake fluid flush, there are electronic 'tools' available to get the ABS cells to open up to release the held fluid but for most of us this isn't necessary.

When it came time to convert my 961 all went as planned except I could not get rid of the sponginess. I gravity fed fluid, I syringe fed, I tried it in both directions, still spongy. I figured that with the ABS up in the tail unit that this was the likely spot for trapped air, especially when I saw the 'Made in China' label, but no, they are well made units and there is no place where air can trap, I just ended up with a messy clean up of that under seat tray. What Norton have done, in their infinite wisdom, is to fit a rear caliper that they probably bought cheap in bulk and inverted it, so the bleed is in the wrong place..... I removed my caliper, turned it 180deg, gave it a shake and tap with hide mallet, and one very small bubble emerged from the bleed pipe.... all sponginess gone.
 
MxMartin said:
Just to clarify. Because of my disability I have to re-work the rear brakes on all my bikes, relocating pipework etc. In recent times I have converted 4 ABS fitted bikes and none of the ABS units needed touching, they are sealed units and the chambers are only exposed to fluid when ABS is actuated so under normal bleeding routines they are effectively closed clam tight. This CAN be a problem on very old bikes where you want to do a 100% brake fluid flush, there are electronic 'tools' available to get the ABS cells to open up to release the held fluid but for most of us this isn't necessary.

When it came time to convert my 961 all went as planned except I could not get rid of the sponginess. I gravity fed fluid, I syringe fed, I tried it in both directions, still spongy. I figured that with the ABS up in the tail unit that this was the likely spot for trapped air, especially when I saw the 'Made in China' label, but no, they are well made units and there is no place where air can trap, I just ended up with a messy clean up of that under seat tray. What Norton have done, in their infinite wisdom, is to fit a rear caliper that they probably bought cheap in bulk and inverted it, so the bleed is in the wrong place..... I removed my caliper, turned it 180deg, gave it a shake and tap with hide mallet, and one very small bubble emerged from the bleed pipe.... all sponginess gone.
Click to expand...

Logic resigned, bleed nipple should always be at the top , I too have been caught out by that one.
 
Last edited:
MxMartin said:
Just to clarify. Because of my disability I have to re-work the rear brakes on all my bikes, relocating pipework etc. In recent times I have converted 4 ABS fitted bikes and none of the ABS units needed touching, they are sealed units and the chambers are only exposed to fluid when ABS is actuated so under normal bleeding routines they are effectively closed clam tight. This CAN be a problem on very old bikes where you want to do a 100% brake fluid flush, there are electronic 'tools' available to get the ABS cells to open up to release the held fluid but for most of us this isn't necessary.

When it came time to convert my 961 all went as planned except I could not get rid of the sponginess. I gravity fed fluid, I syringe fed, I tried it in both directions, still spongy. I figured that with the ABS up in the tail unit that this was the likely spot for trapped air, especially when I saw the 'Made in China' label, but no, they are well made units and there is no place where air can trap, I just ended up with a messy clean up of that under seat tray. What Norton have done, in their infinite wisdom, is to fit a rear caliper that they probably bought cheap in bulk and inverted it, so the bleed is in the wrong place..... I removed my caliper, turned it 180deg, gave it a shake and tap with hide mallet, and one very small bubble emerged from the bleed pipe.... all sponginess gone.
Click to expand...

Tanks MxMartin !
I didn’t pay attention but indeed it’s upside down... they should have put a screw with bleed valve...
i tried to bleed untightening the ABS banjo, improved but still a little spongy. I will fit screw with bleed incorporated also. should get it this week. Will keep you posted.
 
I removed caliper with lines intact, pushed pads back, gave it a shake, opened bleed while it was upright and out popped the darn bubble that I spent hours earlier trying to locate and dislodge :)
 
MxMartin said:
I removed caliper with lines intact, pushed pads back, gave it a shake, opened bleed while it was upright and out popped the darn bubble that I spent hours earlier trying to locate and dislodge :)
Click to expand...
that worked for me too today! I used an old tyre lever, almost same thickness as disc, taped into position on loose caliper before bleeding. Lying on left side of bike, you can operate the brake lever by reaching under bike !
HOWEVER, the caliper screws were just more than finger tight!!. Some evidence of red loctite, but maybe previous owner/mechanic had undone them. Replaced with PTFE tape as non- loosening aid, and did rear axle adjuster screws at same time. ( Front calipers plenty tight though)
 
A piece of clear tubing with a nr valve fitted, picked up from a motor factors years ago. Used 1st time on the 961 yesterday, works a treat!
 
Duke Multistrada rear brake upside as well , must remove caliper and turn right side up to bleed properly ….
 
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