Author Topic: rear brake cylinder strip down  (Read 736 times)

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Offline mts

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rear brake cylinder strip down
« on: June 14, 2018, 05:20:37 PM »

having struggled with a sticking rear brake and after stripping and cleaning the rear caliper to no avail my thoughts turned to the master cylinder itself

It was as i expected full of rust and general crud  as youd expect after 40 + years service.   to remove the actuator rod you have to remove the small gator then the internal circlip under which is a c shaped metal plate that sits on the top
of the hydraulic fluid chamber. once past that   in the chamber itself you can then get to the inner main seal  and the return spring.

all pretty easy really and all cleaned up nicely and now moves as it should

the problem is theres a  outer chamber sized  diameter o ring   and i forgot to note  were  it goes   in the reassembly order,    its  not in the chamber itself its in the c plate circlip gator section 

can anyone remember whos had one apart   ,,i think it sits in the groove  above the circlip just as a dust seal  but its not easy to see   and the exploded diagram in the manual is too vague

any help appreciated   if all else fails i will reassemble and just try it for leaks and adjust if required

Offline chrisg.007

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Re: rear brake cylinder strip down
« Reply #1 on: June 14, 2018, 06:48:23 PM »
Hi, I posted a photo of the components, but unfortunately I cant find it. Check the little hole (approx. 1mm) on the side. I had to drill mine out as it full of crud. If you do, ensure that there is no burring in the chamber. I cleaned and polished mine with a dremel and solvol autosol.
That cured my rear brake sticking (works on front brake too)
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Offline twostrokelooney

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Re: rear brake cylinder strip down
« Reply #2 on: June 14, 2018, 07:24:36 PM »
Hi, I posted a photo of the components, but unfortunately I cant find it. Check the little hole (approx. 1mm) on the side. I had to drill mine out as it full of crud. If you do, ensure that there is no burring in the chamber. I cleaned and polished mine with a dremel and solvol autosol.
That cured my rear brake sticking (works on front brake too)

Good advice, I think all RD owners have suffered from the dreaded "blue disc" syndrome at some point. The rear brake in particular for some reason........... ??? ??? ??? ???
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Offline nsrnick

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Re: rear brake cylinder strip down
« Reply #3 on: June 14, 2018, 08:29:45 PM »
From top to bottom (top being banjo bolt)

Spring
Seal
Disc
Piston with seal approx halfway along its length
C shape retainer
Circlip
Rubber dust boot

There isnt an o ring

Out side=
Hose union
Copper sealing washer

On a D/ C cylinder=
As above plus brake light switch and copper sealing washer.

Offline joolsuk

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Re: rear brake cylinder strip down
« Reply #4 on: June 14, 2018, 08:51:26 PM »
Here a schematic for my rd250d 1977.
Another pic i might have grabbed off here to he,p me when i did it.
And my one
1977 RD250D (mechanical restore)
1980 GS550E
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Online iranana

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Re: rear brake cylinder strip down
« Reply #5 on: June 14, 2018, 09:06:15 PM »
Hi, I posted a photo of the components, but unfortunately I cant find it. Check the little hole (approx. 1mm) on the side. I had to drill mine out as it full of crud. If you do, ensure that there is no burring in the chamber. I cleaned and polished mine with a dremel and solvol autosol.
That cured my rear brake sticking (works on front brake too)

Quick question about the polishing - it seems to me that the cylinder should be smooth and polished since the rubber seal is doing all the work. How come some people hone their brake cylinders? I had some varnishy kind of gunk in mine and managed to scrape most of it out with a wooden dowell, but I had wondered if polishing the cylinder was a bad idea. I didn’t hone because that seemed like a worse idea. I haven’t finished putting the rear caliper on so no idea if my rebuild was successful yet...

Offline chrisg.007

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Re: rear brake cylinder strip down
« Reply #6 on: June 14, 2018, 09:06:56 PM »
Thats the pic I posted some years ago. The red one.
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Offline davecumbria

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Re: rear brake cylinder strip down
« Reply #7 on: June 14, 2018, 09:08:19 PM »
Are you sure the o ring isn't the remains of the inner ring of the boot which has split away?
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Offline chrisg.007

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Re: rear brake cylinder strip down
« Reply #8 on: June 14, 2018, 09:09:09 PM »
Hi, I posted a photo of the components, but unfortunately I cant find it. Check the little hole (approx. 1mm) on the side. I had to drill mine out as it full of crud. If you do, ensure that there is no burring in the chamber. I cleaned and polished mine with a dremel and solvol autosol.
That cured my rear brake sticking (works on front brake too)

Quick question about the polishing - it seems to me that the cylinder should be smooth and polished since the rubber seal is doing all the work. How come some people hone their brake cylinders? I had some varnishy kind of gunk in mine and managed to scrape most of it out with a wooden dowell, but I had wondered if polishing the cylinder was a bad idea. I didn’t hone because that seemed like a worse idea. I haven’t finished putting the rear caliper on so no idea if my rebuild was successful yet...

My concern was that after drilling out the compressed crud in the small return hole, was that there would be a small burr on the inside of the chamber and cut my expensive seal. >:(
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Offline mervin

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Re: rear brake cylinder strip down
« Reply #9 on: June 14, 2018, 09:48:05 PM »
Are you sure the o ring isn't the remains of the inner ring of the boot which has split away?

just what i was gonna say Dave
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Offline WillieRD

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Re: rear brake cylinder strip down
« Reply #10 on: June 14, 2018, 10:24:15 PM »
found this picture of mine when i done the rear brake

 

        hope this helps cheers willie
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Offline mts

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Re: rear brake cylinder strip down
« Reply #11 on: June 15, 2018, 08:28:38 AM »
thanks for all the replies guys   seems ive got an extra bit   will post up a pic when home

i will check its not come off the gator but seems too perfect for that 
 
thanks for all the info  good to know its not a key bit 

Offline chrisg.007

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Re: rear brake cylinder strip down
« Reply #12 on: June 15, 2018, 06:31:59 PM »
Maybe someone's been tinkering  :(
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Offline mts

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Re: rear brake cylinder strip down
« Reply #13 on: June 18, 2018, 11:19:20 AM »

all back together  and i just put it in before the gator so dust sealing only but all good now

Offline chrisg.007

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Re: rear brake cylinder strip down
« Reply #14 on: June 18, 2018, 02:24:22 PM »
I found the best way to bleed the system, was to use a syringe and force the fluid in from the calliper. When it starts to fill the reservoir, I stop and pump the pedal a couple of times, top up to correct level, lock nipple up. Clean fluid from around the nipple.Done. Easy peasy.
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