Stuck caliper pistons - retracted

Good intentions and oil smoke heating of caliper and ice on cap and slam bam on factory tool did not work at'all, as expected. So propped side stand and turned wheel to let drain on rags, about 3-4 reservoirs full of DOT3. Just wondering if that actually gets much of the water dense fluid out of the bottom or mainly just absorbs what moisture remains into the new drier fluid? Did not let it get so low in reservoir to need to bleed air but it did burble at the wide open bleeder hole.

Ceramic-based thermal grease has generally good thermal conductivity and is usually composed of a ceramic powder suspended in a liquid or gelatinous silicone compound, which may be described as 'silicone paste' or 'silicone thermal compound'.
http://en.wikipedia.org/wiki/Thermal_grease

hobot said:

Ceramic-based thermal grease has generally good thermal conductivity and is usually composed of a ceramic powder suspended in a liquid or gelatinous silicone compound, which may be described as 'silicone paste' or 'silicone thermal compound'.
http://en.wikipedia.org/wiki/Thermal_grease

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Good Lord - is that a confirmation that this stuff does not damage rubber seals? I can't read all that sh&6t ... thanks for the link, just the same.

I was just checking to see what the ceramic carrier agent was, being sillyone should not bother seals, friction nor electrically short across the pucks to weld in place via the Faraday current eddies : )

contours said:

I went on to install everything and used a tiny bit of sealant on the threads of the lower pipe since that was where I got some leaking last time around. Then on to bleeding the air out. It took quite a while and I'm still not finished, but at last I have a front brake! At this point it just requires some pumping. It is nice and solid when the pressure is up. I hope to get back to bleeding again on Monday. With any luck I can feel confident about rolling it out and down the ramp to start 'er up. It's been several weeks since I rode it into the shed.

Thanks so much for everyone's advice. This forum is such a help!

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Pump it up until the lever feels solid, then tie or bungee the lever in place keeping the pressure on. Come back the next day and see if your lever isn't solid all the time. If not, no damage done, but I find this usually works for that final bit of air that's hard to get out.

Thanks for that tip! I also found a leak in the line after I stopped so fixing that will help, too.

Oh my yes do check fluid about each ride to make sure its holding as there is no hint going from perfect brake to none next instant.

sounds like you may have gotten the pistons cocked in the bore. They shold push in easy with a little fluid of them. never use grease on the install just a little dab of brake fluid. Blow the compressed air in through the bleeder hole after you put a piece of wood or something slim in between the pucks first. you don't want to blow them totally out just enough to free them up. Then maybe pour a little fluid in the caliper before you start the bleeding process again.


Tim_S

These brakes are giving you far more problems than they have a right too. I use to work on Nortons and have rebuilt a number of systems for customers, never encountering the issues you have. At the customers request, because of budget restraints, I've re-used slightly pitted original pistons (above the seal), stainless replacements, and new chrome plated Andover parts. All bled up quickly and hard using a half a pint or so of DOT4. The calipers seals I've encounted are all square section 'O' rings. The caliper seal grooves are machined with a taper at the bottom which effects a twist on the square section rubber seal forming the lip that seals the piston. These grooves must be scrupulessly clean of any kind of build-up or the seals won't seat correctly and may stick out of the groove too far thus binding the piston.There is no backwards or forwards, you can't put them in wrong. With the seals installed, a finger run into the bore over them should slide in smoothly but drag a bit on the way out as your finger print snags the 'lip'. Pistons lubed with only brake fluid should pop in easily once squared up. Seals that have seen a lot of service or softened by petroleum contamination will take a set from the seal groove and look like they came with a taper, they did not. If you are sure at this point all is right with the calipers, I'd take an inside look at the new master cylinder. New doesn't necessarily mean put togrther correctly.

LOL!!! KSGGs [knee slapping giggles] Contour's I got exactly the same looking down advice on my learning curves balls with pre Peel, on 3 older forums that no one else had experience with so you will have to take the implications that you are a screw up mechanic that can't even pour oil out a can and should be ashamed to take on something so over your little bitty head. Yet they are right unless ya did cock em wrong or something else is out of spec like the pucks or bores. In my case or rather Peel's the pucks seemed to clean up ok but they got jam tight on retest fits so had to fight em back out again and give up to get SS. Trixie worked as expected after few decade set up caliper worked out as normal people encounter. So will ya try the plain pucks in again or just give up on the mystery and reputation? I was told by many to just dig right in mate', no worries - its as simple as a lawnmower... what could go wrong..

Biscuit said:

These brakes are giving you far more problems than they have a right too. I use to work on Nortons and have rebuilt a number of systems for customers, never encountering the issues you have.

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I agree totally. Along with my lack of experience, maybe the bike's history has something to with it. It was ridden for 12K miles until about 1980. Then it sat in a barn in New Hampshire under a sheet of plastic for 25 more years. The restoration took place between 2009 and 2010. Then I bought it.

Biscuit said:

Seals that have seen a lot of service or softened by petroleum contamination will take a set from the seal groove and look like they came with a taper, they did not. If you are sure at this point all is right with the calipers, I'd take an inside look at the new master cylinder. New doesn't necessarily mean put togrther correctly.

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Wish I knew that before I reassembled everything. I will replace that seal after I put 'er away for the winter.

I appreciate the vote of confidence, hobot! For now I am content with the new SS pistons and one potentially bad seal. I have a brake now!

An old deformed-denatured seal snagged ya huh, I thot you'd put in new ones - no wonder some get to sneer at your missing that little detail. If ya ain't red hot nail poked out the master cylinder rubber restriction valve hole you still ain't got all the factory brake power of your lever grip available to depend on.

They were actually new! But on that first install (I assume) one became deformed. After the confusing discussion about whether the seals were tapered or the seat was tapered ... ah well, who cares. This was my very first caliper rebuild, let alone that it was on a Norton. I'll live.

Oh, and it's a new Brembo 13mm master cylinder. I replaced the stock component.

Ok I've learned off your distress what i may run into again so thanks for sharing. After having both 12mm m/c and just a poked out factory one I now feel most the improvement is just removing the restriction, more so than the slight increase in ratio. I hate the stresses these Commando put us into yet it sure beats the snot out of life's other varieties. Ride long and prosper.

Got me a nice, solid front brake now after properly tightening down the upper pipe.

Only thing left to do is wire up all the new handlebar controls and pray for some warmer weather.

So true. Disconnect caliper. Bench dis-assembly time . Order in new seal kit. Brake fluid for assembly only. Buffing or polishing only for external appearance, never internal work-ages. Plus -the new seals must be installed as specified. Stainless pistons , never steel for such a rebuild ,but you know.

Wondering if anyone has followed Hobot's advice with the hot nail poking out rubber restrictor valve re: MK 111 rear brake master cylinder ? Does this unit even have that restrictor plug ? If so I'm willing to give it a try , the rear could benefit from more hydraulics for sure.

contours said:

I searched the forum for posts about stuck caliper pistons in the retracted position and nothing came up. So I am asking a fundamental question here: after rebuilding my front brake caliper (cleaned, replaced seals and pads, bled, etc.) the pistons do not move. They are stuck in the retracted position which I put them in so I could get the new pads in place. My specific question is while they are stuck shouldn't my brake lever be hard to pull? After hours of bleeding a new master cylinder and new braided steel lines I still have no pressure. Yet the pistons remain retracted.

Anybody have a guess as to what the problem is? I am about to remove the caliper and start over.

Thanks in advance!

Peter

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Hello Peter,
Try using compressed air to push the pads hard against the disc prior to bleeding.

Ummm..... I guess I need to look at the new format before posting.

contours said:

I searched the forum for posts about stuck caliper pistons in the retracted position and nothing came up. So I am asking a fundamental question here: after rebuilding my front brake caliper (cleaned, replaced seals and pads, bled, etc.) the pistons do not move. They are stuck in the retracted position which I put them in so I could get the new pads in place. My specific question is while they are stuck shouldn't my brake lever be hard to pull? After hours of bleeding a new master cylinder and new braided steel lines I still have no pressure. Yet the pistons remain retracted.

Anybody have a guess as to what the problem is? I am about to remove the caliper and start over.

Thanks in advance!

Peter

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How did you replace the seals without removing the pistons? if you did and just got them stuck shoving them all the way in, hydraulic pressure (when you get it) should push them out. I just got the front brake on the Titanic functional yesterday. The inner piston had to be blown out with compressed air before the caliper could be cleaned and seals replaced. I bled the m/c with a bolt in place of the line (which was in the mail at the time) and then attached the two-piece line to the dry caliper and began pumping fluid down the line to the caliper. After refilling the reservoir, I began bleeding out the air at the caliper. Once all the air was gone, continual pumping at the lever pushed the pistons and pads out against the rotor. I also used synthetic brake grease to lube the pistons and seals as they were assembled.

You all know this thread is from 2013??

I am assuming the "similar threads" section that I have just seen appearing recently is the reason it was clicked on and reappeared?