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Single master cylinder diagnosis
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jmmj
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PostPosted: Tue Nov 30, 2021 8:23 pm    Post subject: Single master cylinder diagnosis Reply with quote

Hey guys, hows it going?

My MC is having an issue. The plunger/piston wasn't coming out after being pressed in. So i took it all apart, it was really dirty and i was surprised that the seals are in good condition and that theres no scoring on the walls. Under the reservoir are two holes, one is pretty tiny, that appeared clogged up so i was hopeful that was the issue. I cleaned it all up, gave it a very light hone, cleaned it again, dried it all off with compressed air and put it back together with fluid.

Its much better but its not right. The plunger/piston doesn't always come back out all the way and then, when i went to bench test/bleed it, the first stroke is solid with pressure through out the stroke, then the next will only build pressure at the very bottom of the stroke, regardless if the piston comes all the way out or not. But if i wait 20 seconds, it'll give another full stroke with full pressure.

Anyone got any ideas?? I'd like to understand whats happening before i make a decision about rebuild/replacement.

Cheers.
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western auto
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PostPosted: Wed Dec 01, 2021 8:09 am    Post subject: Re: Single master cylinder diagnosis Reply with quote

adjust your brakes, bleed out the air
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BarryL Premium Member
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PostPosted: Wed Dec 01, 2021 7:12 pm    Post subject: Re: Single master cylinder diagnosis Reply with quote

jmmj wrote:
Anyone got any ideas??


Part 7, 13, or 10 might be not doing what they are supposed to do.
Image may have been reduced in size. Click image to view fullscreen.


Before the 20 seconds is the pushrod against the piston or is the piston still in?
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jmmj
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PostPosted: Thu Dec 02, 2021 10:57 am    Post subject: Re: Single master cylinder diagnosis Reply with quote

western auto wrote:
adjust your brakes, bleed out the air


Yeah its still in the vise so thats not related thanks...

Cheers!
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jmmj
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PostPosted: Thu Dec 02, 2021 11:10 am    Post subject: Re: Single master cylinder diagnosis Reply with quote

BarryL wrote:
jmmj wrote:
Anyone got any ideas??


Part 7, 13, or 10 might be not doing what they are supposed to do.
Image may have been reduced in size. Click image to view fullscreen.


Before the 20 seconds is the pushrod against the piston or is the piston still in?


Ahh thats a better diagram than the one i found. Cheers Barry. I was suspecting the check valve even though its so simple and seemed ok. But then i remembered that i lent the kombi out to a friend a couple weeks ago, turns out that he may have helped out by topping off the fluid.... with ya know... ATF oil!! So i'm guessing the primary cap swelled up.

Anyways, i went all round town looking for a rebuild kit but to no avail. Ended up buying a replacement MC. Annoying because i didn't want to spend money on this because i'm saving to go the way of disc brakes, new lines with double circuit MC. Oh well. Such is life.

The new MC is in the bus and its breaking better than ever.

Cheers!
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BarryL Premium Member
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PostPosted: Thu Dec 02, 2021 6:40 pm    Post subject: Re: Single master cylinder diagnosis Reply with quote

jmmj wrote:
Ahh thats a better diagram than the one i found.Cheers!

Borrowed it without permission from The Bentley Manual 1963-1967.
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