Not that I ever use the rear brake in normal circumstances, but I had cause to last weekend when I did an IAM observed ride.............anyway the bloody back brake is about as much use as men's tits. The brake lever itself is badly designed so you need to be a ballet dancer to get your foot into the position required to be able to press it, plus it's soft as hell and needs bleeding. A friend of mine has said that whenever he's had to bleed the rear brake on his bike he loosens the lid on the brake fluid reservoir then hangs a weight for a couple of days on the brake pedal to force the air back up through the system, then tightens the lid and hey presto. Job jobbed. Has anyone else done this? Or should I just get it to the dealers to sort out?
If it doesn't work properly there is air in there - tried for ages with my 1098R with no luck. Took the calliper off and held it high with a tie wrap, a minute later and it pocks up as soon as you touch it! It will have air in there if it's not leaking and I doubt it will trickle out over a few days....
Sometimes you just have to take the whole thing off and hang in air. All of it. Detached from bike. Completely. Also the master cylinder is shockingly poor quality on rear. Altho tbf the 1299 one has held out, but my 1198 went thru 3.
To develop what's been said above. I take the caliper off fasten it with brake lines vertical ish, with bleed nipple uppermost. Apply pressure to brake pedal, I ratchet it down. More pressure the better. Leave overnight/ 24 hours. Crack bleed nipple and your done. To improve on all this change fluid for Motul 660 before hand. TB
I read an article relating to poor rear brakes. I think it was specifically Ducati but I’ll see if I can find it. In summary it said change your rear brake fluid to a high temperature brake fluid. The rear fluid takes a lot of heat from the engine and exhaust. Different fluids have different tolerance to heat. There are fluids that can deal with heat better than the fluid that the factory puts in or recommends. As we know some Ducati rear brakes are non existent. Once the fluid has been heated up...it’s fkd. My guess is that’s the problem not just air.
That was it, Castrol Srf racing fluid. It has a much higher boiling point. 520 degrees wet to 590 dry. Expensive at £50/litre but if you share it with several other guys it will bring the price down. There’s no point storing brake fluid, it will just absorb moisture and become useless. Hence the lower boiling point of the wet stuff. How many rear brakes could 1 litre do? If it’s 5 that’s 10 Quid for a rear brake. Worth it in my book.
I usually detach the caliper and hang it up I use a MityVac I've had for yonks and that helps as it can pull fluid thru pronto so most of the time air in the line also gets pulled along. I can only speak for 1098 but not only is the whole rear brake system woefully undersized they install "pads for life" I got 2 advisory notices at MOT until I changed to a more aggresive pad compund. Still not wonderful but at least now it does "something, sort of"
These are the data sheets for the Castrol and Motul 660. https://msdspds.castrol.com/bpglis/.../$File/React_ SRF_ Racing_3371486_2013-11.pdf, https://d23zpyj32c5wn3.cloudfront.n.../169/RBF_660_Factory_Line_(GB).pdf?1506679940. I leave you to make your own mine up. Andy
It does seem the thing that works most often is taking the rear caliper off, suspending it as high as you can allowing for the fact it's still attached, and then bleed it through
Mine was bled the other day at my local as it failed it's M.O.T,Caliper removed & held high in a cloth and i pressed down on the level with the technician operating the spanner for about ten odd times,pedal nice and firm again. #No more than ten minutes work! P.S a plastic spacer is required in between the pads!
i always bleed using a loaded syringe and reverse bleed through the caliper up to the master cylinder, no need to remove anything just the excess fluid from the reservoir.
Tried that, only had a 500ml syringe - didn't work - calliper had to be raised - maybe a bigger syringe would be fine...
My Triumph T140 has an underslung calliper and when the bike was released the techs had problems getting them to work properly - not great when working but could be improved. Anyway they eventually released a tech document to dealers informing them to remove calliper - turn upside down, slide a piece of metal between pads and bleed. Big improvement and I apply the same technique to my 1098 with its underslung calliper. Basically I remove , turn the other way up and insert an old rear disk from my monster and bleed. I do use the rear brake on all my bikes - probably due to years of Meriden Triumphs with questionable brakes. In the end I have a great rear brake with feel and can easily lock the rear wheel if required. During mot the testers always comments on my working rear brake.
Pushing the brake pistons back and holding them there with a suitable wedge....I use a small aluminium block. Enables you to remove the air trapped behind the piston that's almost impossible to remove....works for me?
Bit of an update............I thought I’d try the method my friend mentioned (see above ref loosening the reservoir cap and hanging a weight on the brake). I did it for 24 hours and it worked a treat. Before doing it it had about 2” of play in the brake pedal. I would say now it about 0.5”-0.75” of play. He tells me that after a days hard riding it’ll probably go soft again but all you then need do is just hang the weight on the pedal again, and no need to loosed the reservoir cap.
