Rear brake binding and master cylinder Brembo PS11

[Scud]

I'll post pics when I get home but in the meantime Scud is my witness!

 

I saw it. It happened. So did this: 

 

SP - it would be cool if you could write up the master cylinder replacement for our burgeoning encyclopedia. I bet people (self included) would be interested in your gas cap too.

[pasotibbs]

I have just toasted the snit out of my rear disc, which melted the lovely gold anodising and left it crisp-shaped. Hashtag sadface.

The cylinder looked clean enough on disassembly.... got a replacement disc coming tomo but concerned it'll happen again...

Why are these rear brakes so crap? Always thought brembo were highly thought of...

Master Cylinder corrodes so piston doesn't fully return blocking hole to reservoir , owner adjusts clearance on pedal because it now appears to have loads of travel,goes for a ride and when the brake warms up the fluid expands but can't get to the reservoir so applies brake instead creating more heat and more pressure and so on....

Don't ask how I know this

[sp838]

SP - it would be cool if you could write up the master cylinder replacement for our burgeoning encyclopedia. I bet people (self included) would be interested in your gas cap too.

Will do. I'm traveling overseas this week, will post more specific part numbers etc. here and in the encyclopedia when I get back.

[bbolesaz]

While were on the subject of rear brakes, I spotted fluid under the Scura last night. It looked to be leaking from the left side of the battery tray.  Thought I had a cracked battery at first, but the fluid was a light oil.  Hmm.  Removed the battery and the tray had a couple tablespoons of brake fluid in it.  Looked at the reservoir and the cap was on and there wasn't any sign of brake fluid running down the side or down the hose.  Odd.  Took off the cap and the reservoir was empty and the diaphragm was sucked down to the bottom.

Last ride was back from AZ Gathering of Eagles in Cottonwood. Rear brake seemed normal for the entirety of the ride, but I'm not a big rear brake user. Mostly just holding a stop and sometimes to scrub a little speed in a corner or the occasional total panic stop.

Almost seems as if the fluid would have to have been pumped out from under the cap under pressure to end up where it did. 

Going to start by replacing the reservoir.

[stewgnu]

Heh! Sometimes i forget that i'm a plasterer and not a mechanic! Of course it's my error, just cos i thought i'd bled it well, doesn't mean i did so. (Sorry Brembo!) This time I'll take all the good advice here and try to do the job reet. Hashtag Contrition, hashtag Justcosyouownaguzzidoesntmakeyouwellversedinmechanicals.

[stewgnu]

 

I have just toasted the snit out of my rear disc, which melted the lovely gold anodising and left it crisp-shaped. Hashtag sadface.

The cylinder looked clean enough on disassembly.... got a replacement disc coming tomo but concerned it'll happen again...

Why are these rear brakes so crap? Always thought brembo were highly thought of...

 

Master Cylinder corrodes so piston doesn't fully return blocking hole to reservoir , owner adjusts clearance on pedal because it now appears to have loads of travel,goes for a ride and when the brake warms up the fluid expands but can't get to the reservoir so applies brake instead creating more heat and more pressure and so on....

Don't ask how I know this

Well I stripped&cleaned it and it looked very good inside, thankfully. Couple of teeny nicks on the sleeve... but took them back with a bit of wet+dry.

Chuck- I found a old post mentioning cone-shaped, warped discs (mine also is very badly coned) and poss shimming the caliper across to counter this somehow? I'd have though the caliper would be 'self-adjusting' for lateral grippage? However, I'm on the verge of fitting a couple of washers between the hanger and caliper... Do we have any thoughts about this here and now in the really real times?

[Scud]

Stew - if the rear rotor is warped, I think the best solution is a new rotor. But if a new rotor is not in this month's budget, and you can see that a couple washers will bring things into closer alignment, I can't see the harm in that - especially if you don't use the rear brake much.

[stewgnu]

Stew - if the rear rotor is warped, I think the best solution is a new rotor. But if a new rotor is not in this month's budget, and you can see that a couple washers will bring things into closer alignment, I can't see the harm in that - especially if you don't use the rear brake much.

New disc already on old bean! Seriously, the old one was distorted quite alarmingly- i'd say about 3-4mm out of flat. Which lead me to the notion of shimming the caliper.

[Scud]

Oops... so I see from re-reading the last page.

 

So now I am wondering if the pistons are working evenly. If one piston comes out faster than the other then one pad will push the rotor into the other pad - which will bend the disc over time. Maybe a deep clean, rebuild, or replacement of the caliper is in order. Single piston calipers are laterally self-adjusting (they ride on greased pins), but two (and four) piston calipers are fixed in place - they rely on equal operation of the pistons.

[docc]

Plus, the pads slide on a single pin that rides in the road spray, especially if the plastic protective cap has gone missing.

 

The pin gets awfully nasty, corroded, and can even develop grooves that can cause the pad to drag even if the piston retracts. Make sure the pin is clean, polished with something like 600 grit wet-dry paper, and lightly coated with silicone brake grease.

 

 

The careful (nipple up) bleeding, overnight brake application, and thoroughly restoring the even piston motion are also all necessary, as well as fettling the activation at the master cylinder as have already been mentioned.

[stewgnu]

Right o, i'll re-fit and see how i go i suppose.

The pistons wouldn't retract independently when it was looked at, so poss just a bit of crud in the system.

[stewgnu]

Yeah that pin does get awful don't it? Good advice on givin it a good fettle.

[docc]

It's one of those systems that if each of the five or six things mentioned is a bit marginal, it all adds up to a significant problem.

[Baldini]

I think brake pedal benefits from a return spring. I used a bit of old inner tube, but as I recall, others have done job more elegantly.