Rear brake seals

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Rear brake seals

Postby 550 Dunc » 15 Oct 2020, 13:33

Hi need to change rear brake seals on a 1991 550. Just trying to work out how to get the pads out in order to get the pistons out. Do the 2 10 mm pins push in to release the rear pad, they seem stuck if that is the case? Any ideas thanks
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Re: Rear brake seals

Postby Freddy » 16 Oct 2020, 01:25

550 Dunc wrote:Hi need to change rear brake seals on a 1991 550. Just trying to work out how to get the pads out in order to get the pistons out. Do the 2 10 mm pins push in to release the rear pad, they seem stuck if that is the case? Any ideas thanks


If its anything like the 750, one pad just falls out, and yes the pad with guide pins running through it can be tricky to get out. The sliding half needs to be pushed right home and then the pad that the fixed guide pins goes through will come out, even though it seems it won't. It just take a bit of twisting and sometimes a mild bit of persuasion by hand. Genuine pads seems a neat but easy enough fit. It's aftermarket pads being ever so small variation that seem to create the fit problem, but they will go in/out. Anyhow that's the story for a 750, and from the description of your problem it sounds like it might be the same.
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Re: Rear brake seals

Postby 550 Dunc » 16 Oct 2020, 06:02

Yes my sliding bit seems to be seized so might not be the seals causing the the brake to bind.
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Re: Rear brake seals

Postby Freddy » 16 Oct 2020, 07:46

As I suspected, the 550 rear caliper is for all purposed exactly the same design as the 750.

The procedure is ..... Remove it completely from the bike if not already, take out the smaller inside pad (43082). Remove the 2 'plugs' out the end of the pistons, and with a G clamp push both pistons (43020) to the bottom. Then push the caliper holder (43044) all the way to the bottom, and then work the larger brake pad out. Then with compressed air, blow the two pistons out. One will pop out first, put a rag in the 'line of fire' as it will come out with quite some force. Then sit it lightly back in place using your small G clamp to hold in to seal up the hole, then blow out the other piston.

Now to your problem, the caliper seized on the guide pins. Lifting the rubber boots get some penetrating fluid like WD40 etc into the guides and allow it to soak in overnight, repeat a coupe time. Then a little 'gentle' persuasion should get it to move.

On reassembly, use new piston seals, polish the old pistons (assuming they are stainless steel they should come up like new), plenty of brake grease on those guide pins, and reassemble pistons using a fully synthetic grease like 'Super Lube'. Do NOT use mineral grease or stuff sold as brake grease (its the right stuff for the guide pins only). Mineral based greases will destroy the rubber piston seals, and using brake fluid for reassembly is old fashioned and inadequate. Being water soluble it'll wash completely away in the first decent bit of rain, leaving the piston ends and outer seal dry, prone to corrosion, and sticking.

Good luck.

Image
Freddy
 
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Re: Rear brake seals

Postby 550 Dunc » 16 Oct 2020, 12:58

Thanks Freddy i will try that over the next week or so and post how I got on. Cheers
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Re: Rear brake seals

Postby 550 Dunc » 20 Oct 2020, 19:09

Took the Caliper off to release the sliding pins. Once the sliders were free everything was ok when refitted so there was no need to disturb the piston seals.
550 Dunc
 
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Location: Nottingham UK

Re: Rear brake seals

Postby Freddy » 20 Oct 2020, 21:14

550 Dunc wrote:Took the Caliper off to release the sliding pins. Once the sliders were free everything was ok when refitted so there was no need to disturb the piston seals.


For future reference, you really should have done the seals. I completely overhaul the calipers EVERY time I change brake pads. A crud free polished well lubricated piston running through lubricated seals not only gives significantly better braking force at the wheel for the effort at the pedal/lever, it also significantly reduces the amount of travel before the pads apply pressure.

When you blow the pistons out the caliper you get to actually see how much force is being 'robbed' by a corroded piston trying to move through a bone dry dust seal. It's actually not uncommon to find a dust seal partly hanging out, such is the amount of drag that has pulled it out of its seat.

Replacing the seals and polishing up the pistons is a quite easy job, so don't be put off tackling the job by thinking it might be difficult.
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