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Offline DanceswithTiger

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Sticking rear caliper
« on: January 06, 2019, 02:14:51 PM »
My 2012's rear brake releases slowly after I step on the pedal hard. Acts almost like a parking brake until I've rolled a few feet, and then it releases enough that I no longer feel any drag. Could it be as simple as polishing the pad carrier pins? Anyone added a helper spring to force the pads apart?

Thanks for the assist,
Dave
Dave
Rochester, NY

'12 Tiger 12

Offline Stillwobbling

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Re: Sticking rear caliper
« Reply #1 on: January 06, 2019, 03:52:43 PM »
What pulls them off is effectively the negative pressure in the brake line. When you let go of the lever, that slight negative pressure should be enough to back the pads off. So, it doesn't take much for them to stick on. Yes it could be the pins, they get into a terrible state but more likely it's the piston. This particular set up doesn't have a bellows that extends with the piston so most of its life is spent in dirt and filth. As the pads wear and the piston extends even more of it gets exposed. It's easy enough to get the caliper off without disconnecting the brake hose so you can have a good look at it. My 2017 only has 5k miles on the clock and I serviced my rear caliper last week and was shocked at the state it was in. Fortunately I was able to buff the marks out of the piston and once I'd worked it back and forth a few times it was working well. I used the Vac bleeder to pull off a little dirty fluid whilst I was at it. For the cost, perhaps order some pads and a pair of new pins ready to go in.

Offline DanceswithTiger

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Re: Sticking rear caliper
« Reply #2 on: January 06, 2019, 04:25:49 PM »
Did you do a complete tear-down and rebuild, removing the pistons from the calipers? I was hoping to avoid that mess, but can do it if I need to. I replaced the pads and rotor about 3000 miles ago, at 49,000 miles, so maybe the problem is that the previously exposed parts of the pistons are now deeper in the calipers and not moving smoothly.

*Originally Posted by Stillwobbling [+]
What pulls them off is effectively the negative pressure in the brake line. When you let go of the lever, that slight negative pressure should be enough to back the pads off. So, it doesn't take much for them to stick on. Yes it could be the pins, they get into a terrible state but more likely it's the piston. This particular set up doesn't have a bellows that extends with the piston so most of its life is spent in dirt and filth. As the pads wear and the piston extends even more of it gets exposed. It's easy enough to get the caliper off without disconnecting the brake hose so you can have a good look at it. My 2017 only has 5k miles on the clock and I serviced my rear caliper last week and was shocked at the state it was in. Fortunately I was able to buff the marks out of the piston and once I'd worked it back and forth a few times it was working well. I used the Vac bleeder to pull off a little dirty fluid whilst I was at it. For the cost, perhaps order some pads and a pair of new pins ready to go in.
Dave
Rochester, NY

'12 Tiger 12

Offline CaptainTrips

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Re: Sticking rear caliper
« Reply #3 on: January 06, 2019, 04:43:49 PM »
*Originally Posted by DanceswithTiger [+]
Did you do a complete tear-down and rebuild, removing the pistons from the calipers? I was hoping to avoid that mess, but can do it if I need to. I replaced the pads and rotor about 3000 miles ago, at 49,000 miles, so maybe the problem is that the previously exposed parts of the pistons are now deeper in the calipers and not moving smoothly.
Every time I replace pads, I take the opportunity to clean the piston with brake cleaner and a toothbrush. Very carefully extend the piston about a 1/4" using the brake lever, then clean it and push it back in and repeat until it moves easily in and out.

In the beginning, you may need to use a thin piece of wood and a c-clamp to retract the piston. Also, watch out for overfilling the reservoir when you do this. You may need to suck a bit of brake fluid out first.

I also use a cheap Mitivac to pull fresh brake fluid in from the reservoir, being careful not to introduce air into the brake lines.
"The test of the machine is the satisfaction it gives you. There isn't any other test."   --   Robert M. Pirsig

Offline DanceswithTiger

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Re: Sticking rear caliper
« Reply #4 on: January 06, 2019, 04:48:37 PM »
I'll take a closer look at the condition of the pistons. It'd be way easier if I can avoid the tear-down, but colder, because the garage is unheated.

*Originally Posted by CaptainTrips [+]
Every time I replace pads, I take the opportunity to clean the piston with brake cleaner and a toothbrush. Very carefully extend the piston about a 1/4" using the brake lever, then clean it and push it back in and repeat until it moves easily in and out.

In the beginning, you may need to use a thin piece of wood and a c-clamp to retract the piston. Also, watch out for overfilling the reservoir when you do this. You may need to suck a bit of brake fluid out first.

I also use a cheap Mitivac to pull fresh brake fluid in from the reservoir, being careful not to introduce air into the brake lines.
Dave
Rochester, NY

'12 Tiger 12

Offline Stillwobbling

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Re: Sticking rear caliper
« Reply #5 on: January 06, 2019, 05:36:40 PM »
No, I didn't need to do that though it wouldn't have been an issue. As this was the first set of pads, the piston wasn't too bad and a light polish with some mildly abrasive compound cleaned them up. I put a G clamp in the piston and used the lever to push it out as far as I needed to go. That way I wouldn't accidentally pop the sucker out. As it's still quite new, I was able to clean and rotate the piston a section at a time then I gave it a good smear of red rubber grease and work it in and out several times. If the chrome has really gone then it will damage the seal and most likely lead to failure.

Offline DanceswithTiger

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Re: Sticking rear caliper
« Reply #6 on: January 06, 2019, 08:02:01 PM »
Getting this far wasn't so bad.


The pins are a little rusty but didn't seem to drag much on removal. I'm guessing that the imperfections (crud or small gouges) are what's causing my problems. So, new pistons and pins? Or try to ease these out as far as I can and try to clean them up?
Dave
Rochester, NY

'12 Tiger 12

Offline eps

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Re: Sticking rear caliper
« Reply #7 on: January 06, 2019, 08:09:17 PM »
All good sensible advice - the Triumph calipers can be a little suspecible to sticking especially the rear - but most bikes do the same if you ride them all year round.  I used to keep a spare caliper on the bench for my 1050 it used to get so bad !! Clean everything , I've removed pistons before and reused existing seals several times- I'm not remcommending that but it works for me. Little bit of rubber gease on reassembly.
I use a syringe when bleeding the brakes - works fine and costs little !! :002:

Offline CaptainTrips

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Re: Sticking rear caliper
« Reply #8 on: January 06, 2019, 08:39:26 PM »
*Originally Posted by DanceswithTiger [+]
Getting this far wasn't so bad.

The pins are a little rusty but didn't seem to drag much on removal. I'm guessing that the imperfections (crud or small gouges) are what's causing my problems. So, new pistons and pins? Or try to ease these out as far as I can and try to clean them up?
Seeing the rust, I would pop the pistons out and see if they will polish up. Afterward, if you can feel any grooves when you run your fingernail around the piston, then I would replace them.

If the cylinders in the caliper are scored, I have had good luck with wrapping extra fine steel wool around a wooden chopstick, and then sticking the chopstick in an electric drill and using that to gently polish the cylinder prior to rebuild. This works on master cylinders too. Of course, as with anything to do with brakes, use caution when applying home-made remedies!
"The test of the machine is the satisfaction it gives you. There isn't any other test."   --   Robert M. Pirsig

Offline DanceswithTiger

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Re: Sticking rear caliper
« Reply #9 on: January 06, 2019, 09:00:36 PM »
The pins cleaned up nicely chucked into a drill and spun with emery cloth. I sprayed a bit of brake cleaner on the pistons, hit them with a toothbrush and then a clean rag. Only way to get them retracted into the caliper was to use the c-clamps to drive them in. I'm thinking a rebuild is in my future and will order pistons and seals.

Thanks for all your help and advice. I'll be back when it's time to bleed 'em... :002:
Dave
Rochester, NY

'12 Tiger 12

 


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