Rear brake locked

[monkeyboy]

R1150GSA with ABS

The rear brake pistons only want to come out - and not go back in. When I got back from my last trip the calliper had seized solid due to the floating rods corroding and seizing movement. I replaced the rods and all was well initially. I cleaned the pistons and they went in and out no problem. Brake was fine but then started binding and now I can pump the pistons out but they don't want to go back in - they look clean as you like and as I say, they were fine until recently.

When I wind the pistons in with a GClamp, the level in the reservoir goes up ok...but... I think there is some weeping at the top of the brake hose where it fixes to the solid line. I seem to remember that these braded hoses can collapse inside and lock the flow but I've not heard of a rear doing this. Is there an easy way to test it? I guess the rear hose gets quite twisted as you remove the calliper and twist it about to change the pads etc.. I don't know how that would fit with the top joint leaking though when winding the piston back.

Also - the GSA brakes are linked I think through the ABS. Pulling the front brakes doesn't move the rear callipers at all though.

Any ideas please? I guess I'll try twisting the brake line to see if there is any effect - just to see if it makes a difference to any collapsed section. Flippin ABS lights won't clear now either

 

[monkeyboy]

I should add that I can put my thumbs on the pistons and pump them too and fro without resistance - it's just if I clamp one and try to push the other in then it's locked solid. The problem is definitely up from the calliper

 

[Grizzly]

Check that the master cylinder is returning fully to it's rest position - which should allow fluid to return freely to reservoir.
Maybe push rod from pedal to master cylinder piston has slackened and unscrewed? - or incorrectly set - ie no free-play?

I suppose it could be your ABS unit at fault also? - but I don't have experience of ABS problems.

You shouldn't need to use a g-clamp to push pistons back, that's likely to cause even more problems.


Cheers....................Grizzly

 

[monkeyboy]

Check that the master cylinder is returning fully to it's rest position - which should allow fluid to return freely to reservoir.
Maybe push rod from pedal to master cylinder piston has slackened and unscrewed? - or incorrectly set - ie no free-play?

I suppose it could be your ABS unit at fault also? - but I don't have experience of ABS problems.

You shouldn't need to use a g-clamp to push pistons back, that's likely to cause even more problems.


Cheers....................Grizzly

Cheers Grizzly - I hadn't thought of that. I undid the top connection to the rear master cylinder and the pressure was released immediately proving it's not a collapse in the line. So I exchanged the master cylinder with an old one from an 1100S and bled it best I can (I HATE bleeding brakes) and it seems to have done the trick. I still can't push the pistons back with my fingers... but... you can see a tiny bit of piston retraction when you release the brake. Fitted it all back together and the brake is no longer locked on - not sure how effective it is but it is certainly working to some degree at least. I'll see at the MOT. Fingers crossed!

Thanks again. Judging on where the reverse flow hole is in the master cylinder, it only takes a tiny bit of sticking at it will lock.

 

[cbrgaz]

Sounds like a delaminated rear brake hose to me. My front brakes did the same (Piston comes out but wont return). Do you have an original rubber hose on the rear ?

 

[monkeyboy]

It's the original hose yep. Changing the master cylinder seems to have done the trick though... hopefully

 

[cbrgaz]

It's the original hose yep. Changing the master cylinder seems to have done the trick though... hopefully

I would change the hose, they have a terrible habit of breaking up inside and locking the brakes on as the delaminated internal rubber acts like a one way valve.....................it happened to me and aint remotely funny.

 

[Delboy777]

Hose i would think.

 

[Old Codger]

I would change the hose, they have a terrible habit of breaking up inside and locking the brakes on as the delaminated internal rubber acts like a one way valve.....................it happened to me and aint remotely funny.

Had the same myself .Change the hose ASAP

 

[Baggers1]

Had the same myself .Change the hose ASAP

Sounds like a ruptured rubber hose to me as well. Mine went on the front, definitely not funny

 

[monkeyboy]

Now this is still happening... f'kin thing....

OK - assume it's the hose... then how come if I put some clamps on the pistons to pressurise the system, I remove the fluid return pipe from the bottom of the master cylinder and no fluid comes out.... but there is obviously pressure in the cylinder because the piston can't be pushed up (ie brake applied) and if I undo the union at the top of the cylinder then fluid spurts out and the pressure in the system is released? That would seem to me to mean the master cylinder is not allowing the fluid to return through the little vent hole as it should? Thing is I've swapped the master cylinder I think (maybe I didn't and put the same one back on!) I've subsequently destroyed the 2nd cylinder trying to remove the circlip at the bottom which has rusted in and the tabs have just snapped off

How would there be enough pressure in the cylinder to spurt when the union is opened, but to not push the fluid back up to the reservoir?

I think I'm just going to have to get a replacement hose and cylinder to be sure