Rear brake saga!

Pale Rider · Aug 29, 2022

Hi guys, Ok, been suffering with a bit of a problem with my back brake on my twin cam GSA. Everything was hunky dorry and working as it should up until a few months ago when i took the bike for an mot and the guy advised that the rear pads were getting a bit low so ok not a problem so I ordered a set and fitted them and right from the get-go I noticed the brake didn’t seem as powerful as it was before, quite a lot less powerfull in fact!

So anyway I carried on riding it and soon got used to the less than powerful back brake then went abroad and started experiencing a lot of screeching from it when braking, when I got home i took the pads out and they were cracked and looked like they had overheated so I checked that the sliding pins were sliding freely, which they were and I fitted another set of pads (different brand this time) re-bled the brake just to be sure and again it seemed very low on braking power, this time however it occurred to me that the brake may be binding slightly so went for a ride and trying not to use the back brake, stopped and put my hand on the calliper and sure enough it was quite hot but on spinning the wheel by hand I couldn’t detect any binding at all.

Stripped the whole calliper down this time, pins running freely, seals not leaking and no crap in the caliper preventing the pistons going back although the pistons did seem quite stiff to push back in once i put it all back together? Put it all back together bled it again and went for a ride today and the brake barely works at all now, checked the calliper for heat and yes yet again it’s running quite hot so must be binding I guess?

Anyone seen anything like this before?

Thanks and sorry for the long post!

squibb34 · Aug 29, 2022

Rear master cylinder maybe? Does the ABS work correctly when you pull the front hard?

Some say they get a dragging rear brake after they have adjusted the pushrod clearance in an attempt to raise the biting point of the pedal. All seems OK on the stand, but drags slightly on the road, heats up nicely & hey, rapid pad wear &, in a short space of time, no brake.

botus · Aug 29, 2022

why are you touching the rear brake lever? total waste of time - they have linked brakes and the front applies the correct amount at the back without ever bothering to move your foot - its a main reason for foot massage when you do try - as topping up with a bit of rear just activates the ABS

couple of exceptions
off-roading
ragging to death in built up areas a bit of rear can calm the bike as you throw it around in ways you shouldn't on a public road

the rear disc can easily get hot enough to burn your fingers from a 5 mile ride only using only the front lever
cheap pads will give nasty results and a nasty feel
heavily worn disc can mean bedding takes ages and will give localised overheating
I'd start with a full brake bled, after fitting quality pads, and likely rebuilding the calipers with a seal kit (so removing the filth that clogs the o ring channel making brake pistons stick)
ACF50 on brake discs stop them doing anything for 18 months - even after wiping 10 times with brush cleaning thinners
BMW say NEVER push the pads back forcing fluid back to the mast cyl - always open the bleed valve and drain off - last told me this is a main driver of ABS module dying - they die so might be worth trying

Pale Rider · Aug 31, 2022

Thanks for the replies, new pistons and seals ordered see if this sorts it.

Kenny Rodkiss · Aug 31, 2022

OP has never said if it has abs or not.
Mine doesn't and the brakes are not linked.
Still on the original rear pads after 60kmiles.
Can only think that maybe the seals have been contaminated with some petroleum based lube or anti corrosion spray, making them swell and difficult for the pistons to return.?

Pale Rider · Sep 1, 2022

Kenny Rodkiss said:
OP has never said if it has abs or not.
Mine doesn't and the brakes are not linked.
Still on the original rear pads after 60kmiles.
Can only think that maybe the seals have been contaminated with some petroleum based lube or anti corrosion spray, making them swell and difficult for the pistons to return.?

Yes mine has linked brakes and abs, cant think how I contaminated anything just doing what was after all a supposedly simple pad change.

botus · Sep 1, 2022

what brand of pads and how scored / ridged is the disc?

there's a huge list of why bikes come with the pads they do - brake feel, performance across lost of different conditions, noise levels and what they do to the disc are huge players - dirt and grim on the rear wheel is never a reason... I'd never fit EBC rot in any vehicle - maybe they improved but they gained a great reputation at a time they were some of the worst products out there - few people have any idea what they are saying

Pale Rider · Sep 1, 2022

botus said:
what brand of pads and how scored / ridged is the disc?

there's a huge list of why bikes come with the pads they do - brake feel, performance across lost of different conditions, noise levels and what they do to the disc are huge players - dirt and grim on the rear wheel is never a reason... I'd never fit EBC rot in any vehicle - maybe they improved but they gained a great reputation at a time they were some of the worst products out there - few people have any idea what they are saying

. Disk is fine and looks newish. Tried EBC HH and Ferodo organic, nothing wrong with either and both manufacturers been going for donkeys years

botus · Sep 2, 2022

lots of fakes out there - most stuff people buy is not what they paid for - ferrodo I'd use - but organic ?

as for ACF50 that stuff gets everywhere when your back's turned, brilliant but near brakes its a nightmare - just about everything else will burn off under one moderate stop

er-minio · Sep 2, 2022

Expand the rear caliper grab the bike from the rear frame/pannier frame and push it with your foot every once in a while.
They tend to bind.

Pale Rider · Sep 10, 2022

So after all that faffing about i replaced the rear master cylinder and all is working fine and as it should.

GSADavidZH2 · Sep 10, 2022

Good, you got it sorted in the end :thumby:

Headtester · Sep 18, 2022

Pale Rider said:
So after all that faffing about i replaced the rear master cylinder and all is working fine and as it should.

Glad you got yours sorted - mine seems to be heading down the same road - the pedal goes soft every now and again, no sign of a leak. Where did you get he replacement rear master cylinder from please?

Pale Rider · Sep 19, 2022

Headtester said:
Glad you got yours sorted - mine seems to be heading down the same road - the pedal goes soft every now and again, no sign of a leak. Where did you get he replacement rear master cylinder from please?

From Motorworks about £45 second hand with a guaranteed which is good as 600 odd miles later it’s gone again

botus · Sep 19, 2022

Headtester said:
Glad you got yours sorted - mine seems to be heading down the same road - the pedal goes soft every now and again, no sign of a leak. Where did you get he replacement rear master cylinder from please?

if you have ABS the rear goes soft a lot - when the front lever already did all the back can cope with, the rear lever goes strange when you add enough the ABS decides to help at the back - unless in traffic or using as TC coming off big cornering, touching the back is mostly a waste

MacJ · Sep 19, 2022

I don't completely agree with Botus that the rear brake is a total waste of time but it should be used appropriately. It's great for bleeding a bit of speed of into a bend, loose surfaces and of course hill starts. Are you relying just on the rear brake? Your front brake should provide the majority of your braking and as Botus says a linked braking system provides rear braking effect when the front brake lever is pulled. You may think that the rear brake is not doing much but try disabling your ABS, find a straight piece of road then stamp on it. You'll probably end up with a flat spot on your rear tyre and a mess in your underpants.

Headtester · Sep 19, 2022

Pale Rider said:
From Motorworks about £45 second hand with a guaranteed which is good as 600 odd miles later it’s gone again ��

Thanks Pale Rider, that's helpful to know.

RallyeGS · Sep 29, 2022

botus said:
why are you touching the rear brake lever?

Hill starts!

Pukmeister · Oct 3, 2022

My old hexhead was a similar story with the rear caliper.

Eventually the rear master cylinder started dripping brake fluid from the spindle due to a worn piston seal, these are crimped/swaged into the cylinder housing on assembly by Brembo so not rebuildable.

Replaced it with a motorworks used item and the rear brake was back to 100% (bike now sold).

Rear brake saga!

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