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Brake Master Cylinder Rebuild/disassembly 1987 Gmc227

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#1 Harwoods

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Posted 30 August 2020 - 03:29 PM

Once again we have been stumped at rebuilding part of our 1987 Mini Mayfair while repairing the master brake cylinder GMC227 shown below as the rear circuit was completely dry:

OsmGJ3H.png

As you can see we have removed the cir-clip and pulled the piston rod that connects to the pedals out. But we were expecting the spring loaded pistons to push their way out of the cylinder. This has not happened and there is clearly something catching/knocking into that is not allowing the pistons out.

There is a spot on the top of the cylinder that may just be casting but our's is rather dirty so hard to tell if there's something that needs undoing in the top. There is definitely nothing catching the bottom.

We have researched online and found nothing relating to this particular brake master cylinder and have only been able to cross reference to older/newer similar versions with no luck on how this comes apart.

Any help/advice or documents for disassembly we would be very grateful of. 

Further pictures:

EtABFdb.png

A smaller issue we are having is removing the pin that holds to reservoir on as it is rather stubborn and clearly the tank fowls one side of the bolt making is rather a hassle to navigate hammering it through. Advice here is welcome.

tkrGlwR.jpg

As usual thanks again all, very much appreciated.

 



#2 nicklouse

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Posted 30 August 2020 - 03:48 PM

Rust will be holding it in place. Push in and clean.

 

IIRC that is a roll pin that needs pushing out.



#3 JXC Mini GT

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Posted 30 August 2020 - 04:30 PM

I have just removed a master cylinder form my 1980 Mini GT which I believed was faulty, however it turns out that the problem i had was the brake limiter valve.

If you would like the master cylinder drop me a PM, I am based in Tunbridge Wells, Kent



#4 Harwoods

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Posted 30 August 2020 - 04:32 PM

Rust will be holding it in place. Push in and clean.

 

IIRC that is a roll pin that needs pushing out.

Just to confirm then, you're talking about the piston inside is being held in place with Rust? Are you confident there's nothing else that needs undoing/releasing? Otherwise it'll need a lot of elbow grease by the feel of things, seems to be knocking hard into something when releasing the spring pressure after compressing and releasing.

Cheers



#5 nicklouse

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Posted 30 August 2020 - 04:37 PM

 

Rust will be holding it in place. Push in and clean.

 

IIRC that is a roll pin that needs pushing out.

Just to confirm then, you're talking about the piston inside is being held in place with Rust? Are you confident there's nothing else that needs undoing/releasing? Otherwise it'll need a lot of elbow grease by the feel of things, seems to be knocking hard into something when releasing the spring pressure after compressing and releasing.

Cheers

 

yes

b8yshdX.jpg

 



#6 Harwoods

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Posted 30 August 2020 - 04:51 PM

.


Edited by Harwoods, 30 August 2020 - 10:28 PM.


#7 Harwoods

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Posted 30 August 2020 - 04:51 PM

 

 

Rust will be holding it in place. Push in and clean.

 

IIRC that is a roll pin that needs pushing out.

Just to confirm then, you're talking about the piston inside is being held in place with Rust? Are you confident there's nothing else that needs undoing/releasing? Otherwise it'll need a lot of elbow grease by the feel of things, seems to be knocking hard into something when releasing the spring pressure after compressing and releasing.

Cheers

 

yes

b8yshdX.jpg

 

 That is a different brake master cylinder though, do you have any experience with GMC227?



#8 nicklouse

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Posted 30 August 2020 - 05:00 PM

they are all basically the same. see your Haynes manual.



#9 GraemeC

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Posted 30 August 2020 - 05:02 PM

It is, but yours will come apart in the same way and have the same rusty, mucky detritus stopping the piston coming out.
Push it back in, clean the bore as much as possible, add plenty of lubricant and then keep working it against the spring and letting it pop back - they (usually) gradually come a little further every time and eventually pop out.



#10 Harwoods

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Posted 30 August 2020 - 05:07 PM

It is, but yours will come apart in the same way and have the same rusty, mucky detritus stopping the piston coming out.
Push it back in, clean the bore as much as possible, add plenty of lubricant and then keep working it against the spring and letting it pop back - they (usually) gradually come a little further every time and eventually pop out.

Thanks for the confirmation, never want to break anything with these original parts. Will give that a go, does certainly seem like it's knocking into something rather solid and not scraping on rust but will see how we get on, Thanks again.



#11 GraemeC

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Posted 30 August 2020 - 06:02 PM

At the bottom of its stroke it does build up a lot of crap - years of use and always wiping the bore to the same place does create quite a wall of muck

#12 absx2

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Posted 30 August 2020 - 06:02 PM

http://www.minispare...|Back to search

 

£67.71 with the 7.5% discount.

This is without doubt the most important part of the car, i`m a total tight arse and it amazes me that people still think they are worth buggering around with for the price.

The part has failed due to corrosion wearing the seals, the bore will be filled with tiny pits and not so tiny score marks, yes you can replace the seals and it might go on for a bit but you have to ask is it worth it ?



#13 nicklouse

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Posted 30 August 2020 - 06:03 PM

 

It is, but yours will come apart in the same way and have the same rusty, mucky detritus stopping the piston coming out.
Push it back in, clean the bore as much as possible, add plenty of lubricant and then keep working it against the spring and letting it pop back - they (usually) gradually come a little further every time and eventually pop out.

Thanks for the confirmation, never want to break anything with these original parts. Will give that a go, does certainly seem like it's knocking into something rather solid and not scraping on rust but will see how we get on, Thanks again.

 

they do. as we have said push up and clean and then work it out with the spring.



#14 Spider

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Posted 30 August 2020 - 06:47 PM

It is, but yours will come apart in the same way and have the same rusty, mucky detritus stopping the piston coming out.
Push it back in, clean the bore as much as possible, add plenty of lubricant and then keep working it against the spring and letting it pop back - they (usually) gradually come a little further every time and eventually pop out.

 

Then I usually bang them down on a block of timber and they come out pretty easy.

 

That will get the lower piston set out. There's usually a Pin behind the Upper Reservoir Seal that retains the Upper Piston.



#15 Spider

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Posted 30 August 2020 - 06:57 PM

This might also help;-

 

XRywSUA.jpg

 

The Pin I referred to above is item no. 3

 

To remove the Reservoir, it should just pull away, hinging on the Roll Pin, then slide it off to the side. It's only the Seals that hold it in.







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