Help Needed Bleeding M750 Rear Brake Caliper

motomartin11 · 20-03-2021, 04:11 PM

The rear brake on my bike has always been spongy so I'm just trying to bleed it now. I know it can be a common problem but I can't get any pressure in the system having released the bleed nipple and expelled some of the fluid. I've removed the caliper from its mount and raised it up higher than the rest of the system but still no luck.Just can't get the system to pump at all and there's no movement of the pads. Any ideas please?

adie851 · 20-03-2021, 04:30 PM

Crack the banjo bolt on top of the master cylinder....and the one on the caliper itself( one at a time),make sure you've got the pedal pressed b4 you crack them otherwise you'll just draw more air in....they can take a while to bleed up...be patient ....good luck

Darren69 · 20-03-2021, 04:38 PM

What he said, but wrap something around the banjo bolt so you don't get brake fluid spitting everywhere, what's that you did? You should be able to hear the air hissing out of the system.

I had the same issue with my front ones until I did just that, they get airlocked inside the master cylinder esp if you fitted new lines that pumping them will not shift. On some of the later master cylinders they put a bleed valve for that same reason. The volume of air/fluid pumped is just not enough to push the air out but if you crack the banjo it should be.

rollo22 · 20-03-2021, 04:38 PM

It may help if you push the piston all the way back in to make sure you have a system full of new fluid.
It will also help to tell if you have sticking piston.

motomartin11 · 20-03-2021, 05:43 PM

Right -thanks. Update : piston seems to be pushed as far back as it can go. Tried bleeding from the master banjo as well separately .have got the fluid moved through the system now so that's all new but still no brake pressure.

Mr Gazza · 20-03-2021, 06:30 PM

I find the back brake so awkward to bleed on the bike, or even trying to hold the caliper above the master, that I just take the whole lot off the bike. Caliper, master, line and reservoir.. The whole lot complete. Removes the risk of getting fluid on the bike too.
I can take it all off mine complete by just removing the hugger and it all threads out from the frame and swinging arm. You'll have to look at yours to see if it's possible.
I then rig it up in a vice with bits of wood to hold everything in the right plane and relative height for bleeding, not really as hard as it sounds.

Luddite gave a tip some while ago of winding a couple of turns of PTFE tape around the thread of the bleed nipple to stop air leaking back past when you crack it off, I now do this and I think it helps.
I always have a clear tube pushed tight onto the nipple which runs down into a jar with some fluid already in it. You can buy kits with the tube and a non return valve at the end which dangles in the fluid.. Sometimes they work and sometimes they're not worth the faff.
With the master in the vice, I operate the piston using an Allen key or screwdriver to push it. Open nipple, push piston, close nipple, release piston, ad nauseum whilst keeping an eye on the fluid level. Best to have a block of something between the pistons so you don't blast them out when you finally get pressure.

adie851 · 20-03-2021, 06:34 PM

Has it got the original rubber brake line or is it a braided brake line.....if it's the original one it could be well past its best...and needs replacing with a new brake line....the other thing to check is the caliper itself..the seals on the piston(s) could be U/S...and will need the caliper stripping down and refurbishing...they don't last forever..the other thing to check is if the seals are U/S in the master cylinder...its a process of elimination....you can get seals off ebay if you know what u r looking for...I did all my brakes refurb on a m900 many years ago...

Mr Gazza · 20-03-2021, 06:45 PM

Well the only original parts on mine are the caliper, pistons and reservoir. I've changed everything to get it to work properly over the years. Well the hose was a bit of vanity as it happens, because the original was a bit brown. Changing the master made the most difference.

motomartin11 · 20-03-2021, 06:53 PM

Thanks. Yes it's the old OE rubber hose.I've been using a brake bleeding kit I got a few years ago from Halfauds with a one way valve.
I know from past experience sometimes perserverance with bleeding can pay off eventually if you're lucky.... I remember doing this years ago on an old Kawa triple I was restoring.Master cyl top off and bugee around the front brake lever over night!

The whole system-front and rear probably needs going though TBH although the front single disc with the OE rubber hose works well enough for me.
Don't know how easy it would be to remove the whole system from the bike although I've heard it can be done.Could be a plan over the winter maybe.

Do you mean ptf tape around the bleed nipple threads Mr. Gazza?

Mr Gazza · 20-03-2021, 07:21 PM

Yes I did mean PTFE tape. I've edited the post to actually include the words PTFE tape!! (helpful!)
I am sure it will help your bleed kit work more effectively as the nipple could well be letting in air past the threads as fast as you are bleeding it out!

I would definitely have a look to see if you can take the whole system off complete. I find it well worth the effort for how often you have to bleed the rear brake.

jerry · 21-03-2021, 11:39 AM

A 100ml syringe acting as a pump / reservoir is so useful for all brake bleeds

motomartin11 · 21-03-2021, 02:52 PM

Update. Thanks for all posts. I crimped the brake line by the master and was eventually able to get some pressure back in the master by bleeding from the banjo and then the caliper end. However the rear brake pistons are definitely not moving as they should and although the lever now feels good the pads are definitely binding.I've just done a quick test and even without using the rear brake the disc is much hotter than the front. I also noticed from the date that the bike is on its original rubber hose.

Nickj · 21-03-2021, 03:24 PM

Upside down is a real pain to bleed, it was on the 750's and my S2R. I have a bit of ply a little thicker than the disc itself, take the caliper off, stick it on the wood, rotate to the 'wrong' way up.
Bleeds a real treat ... assuming the pistons are moving and the master working.

motomartin11 · 28-03-2021, 09:36 AM

Further update:well I removed the back wheel to effect a puncture repair.Have now taken bike for a test ride following re-assemby and all seems well.No binding and travel at the pedal feels better-so hopefully a result.

Darren69 · 28-03-2021, 11:17 AM

Good news! What did the trick?

20-03-2021, 04:11 PM	#1
motomartin11 Registered User Join Date: Sep 2010 Location: stourbridge Bike: M750 Posts: 352	Help Needed Bleeding M750 Rear Brake Caliper The rear brake on my bike has always been spongy so I'm just trying to bleed it now. I know it can be a common problem but I can't get any pressure in the system having released the bleed nipple and expelled some of the fluid. I've removed the caliper from its mount and raised it up higher than the rest of the system but still no luck.Just can't get the system to pump at all and there's no movement of the pads. Any ideas please?

20-03-2021, 04:38 PM	#3
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,023	What he said, but wrap something around the banjo bolt so you don't get brake fluid spitting everywhere, what's that you did? You should be able to hear the air hissing out of the system. I had the same issue with my front ones until I did just that, they get airlocked inside the master cylinder esp if you fitted new lines that pumping them will not shift. On some of the later master cylinders they put a bleed valve for that same reason. The volume of air/fluid pumped is just not enough to push the air out but if you crack the banjo it should be. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

20-03-2021, 04:38 PM	#4
rollo22 Moderator Join Date: Apr 2008 Location: Moreton-in-Marsh Bike: M1100evo Posts: 1,082	It may help if you push the piston all the way back in to make sure you have a system full of new fluid. It will also help to tell if you have sticking piston. __________________ IF ALL ELSE FAILS READ THE INSTRUCTIONS

20-03-2021, 06:30 PM	#6
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,810	I find the back brake so awkward to bleed on the bike, or even trying to hold the caliper above the master, that I just take the whole lot off the bike. Caliper, master, line and reservoir.. The whole lot complete. Removes the risk of getting fluid on the bike too. I can take it all off mine complete by just removing the hugger and it all threads out from the frame and swinging arm. You'll have to look at yours to see if it's possible. I then rig it up in a vice with bits of wood to hold everything in the right plane and relative height for bleeding, not really as hard as it sounds. Luddite gave a tip some while ago of winding a couple of turns of PTFE tape around the thread of the bleed nipple to stop air leaking back past when you crack it off, I now do this and I think it helps. I always have a clear tube pushed tight onto the nipple which runs down into a jar with some fluid already in it. You can buy kits with the tube and a non return valve at the end which dangles in the fluid.. Sometimes they work and sometimes they're not worth the faff. With the master in the vice, I operate the piston using an Allen key or screwdriver to push it. Open nipple, push piston, close nipple, release piston, ad nauseum whilst keeping an eye on the fluid level. Best to have a block of something between the pistons so you don't blast them out when you finally get pressure. __________________ Last edited by Mr Gazza; 20-03-2021 at 07:16 PM..

20-03-2021, 06:45 PM	#8
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,810	Well the only original parts on mine are the caliper, pistons and reservoir. I've changed everything to get it to work properly over the years. Well the hose was a bit of vanity as it happens, because the original was a bit brown. Changing the master made the most difference. __________________

20-03-2021, 04:30 PM	#2
adie851 Member Join Date: Jan 2015 Bike: S4r Posts: 104	Crack the banjo bolt on top of the master cylinder....and the one on the caliper itself( one at a time),make sure you've got the pedal pressed b4 you crack them otherwise you'll just draw more air in....they can take a while to bleed up...be patient ....good luck

20-03-2021, 05:43 PM	#5
motomartin11 Registered User Join Date: Sep 2010 Location: stourbridge Bike: M750 Posts: 352	Right -thanks. Update : piston seems to be pushed as far back as it can go. Tried bleeding from the master banjo as well separately .have got the fluid moved through the system now so that's all new but still no brake pressure.

20-03-2021, 06:34 PM	#7
adie851 Member Join Date: Jan 2015 Bike: S4r Posts: 104	Has it got the original rubber brake line or is it a braided brake line.....if it's the original one it could be well past its best...and needs replacing with a new brake line....the other thing to check is the caliper itself..the seals on the piston(s) could be U/S...and will need the caliper stripping down and refurbishing...they don't last forever..the other thing to check is if the seals are U/S in the master cylinder...its a process of elimination....you can get seals off ebay if you know what u r looking for...I did all my brakes refurb on a m900 many years ago...

20-03-2021, 06:53 PM	#9
motomartin11 Registered User Join Date: Sep 2010 Location: stourbridge Bike: M750 Posts: 352	Thanks. Yes it's the old OE rubber hose.I've been using a brake bleeding kit I got a few years ago from Halfauds with a one way valve. I know from past experience sometimes perserverance with bleeding can pay off eventually if you're lucky.... I remember doing this years ago on an old Kawa triple I was restoring.Master cyl top off and bugee around the front brake lever over night! The whole system-front and rear probably needs going though TBH although the front single disc with the OE rubber hose works well enough for me. Don't know how easy it would be to remove the whole system from the bike although I've heard it can be done.Could be a plan over the winter maybe. Do you mean ptf tape around the bleed nipple threads Mr. Gazza?

20-03-2021, 07:21 PM	#10
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,810	Yes I did mean PTFE tape. I've edited the post to actually include the words PTFE tape!! (helpful!) I am sure it will help your bleed kit work more effectively as the nipple could well be letting in air past the threads as fast as you are bleeding it out! I would definitely have a look to see if you can take the whole system off complete. I find it well worth the effort for how often you have to bleed the rear brake. __________________

21-03-2021, 11:39 AM	#11
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,822	A 100ml syringe acting as a pump / reservoir is so useful for all brake bleeds __________________ MONSTERMAN

21-03-2021, 02:52 PM	#12
motomartin11 Registered User Join Date: Sep 2010 Location: stourbridge Bike: M750 Posts: 352	Update. Thanks for all posts. I crimped the brake line by the master and was eventually able to get some pressure back in the master by bleeding from the banjo and then the caliper end. However the rear brake pistons are definitely not moving as they should and although the lever now feels good the pads are definitely binding.I've just done a quick test and even without using the rear brake the disc is much hotter than the front. I also noticed from the date that the bike is on its original rubber hose.

21-03-2021, 03:24 PM	#13
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,192	Upside down is a real pain to bleed, it was on the 750's and my S2R. I have a bit of ply a little thicker than the disc itself, take the caliper off, stick it on the wood, rotate to the 'wrong' way up. Bleeds a real treat ... assuming the pistons are moving and the master working. __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

28-03-2021, 09:36 AM	#14
motomartin11 Registered User Join Date: Sep 2010 Location: stourbridge Bike: M750 Posts: 352	Further update:well I removed the back wheel to effect a puncture repair.Have now taken bike for a test ride following re-assemby and all seems well.No binding and travel at the pedal feels better-so hopefully a result.

28-03-2021, 11:17 AM	#15
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,023	Good news! What did the trick? __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage