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MGB mgb master cylinder

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SilentUnicorn

SilentUnicorn

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Replacing a b master today- and i notice a 4th port? on the bottom- the original has a rubber plug in it. The new one has no plug, but the port is there with the shipping cup in place.

What is this port all about? Can i just plug it like the original?
Is it for a different application?
Is this port a pressure port?

The cylinder body and mounting is just like the original.



m
 
Ok - I guess this is a tuff question. Since the original was plugged- i will plug this new one and see what happens. Guess i am the first one to notice/question this. I am just curious as to why this extra port is there?

m
 
nobody knows about this port?....

m
 
Can't imagine, Mark. Plug th' thing, do a driveway test before ya count on it.
 
Thanks Doc,

Kinda what i plan on doing.


m
 
Here is what i am asking about. the photo shows the two master cylinders. the one on the right is the old one and on the left the new one. the port directly on the bottom is my curiosity. That black bump on the bottom, on the right hand cylinder, is a rubber plug that looks like it has been there since before time began. The shipping plug is still in the one on the left. Holes are tapped, and there looks to be some kind of valve up inside there.

DSCN1195.jpg


m
 
My bro called me yesterday. You MG guys might be familiar with some of the post I have made with his stuff.
Well the very end of last year he replaced his MC and all the rubber lines with stainless.
Bleed the system took it for a test drive and pretty much put it away for the season.
When he uncovered it and started driving this season, besides the rack problem, his foot went to the floor.
He has pretty much left it alone and went to check it out and there is silicon fluid all down the body work under the MC and pretty a much empty reservoir.

What could have caused the stuff to leak out of a brand new MC.
Bad MC, or is there something on these I don't know?
 
Bad mc is my guess. I replaced mine 2years ago and had to replace it a year later (under warranty) am now trying to sort out if the replacement is leaking also. This the clutch mc mind you. Mine came from the usual suspect and my parts guy said it had happened before.
 
I'll guess that this was purchased through Moss or one of their suppliers. Moss has contacted BCF and other groups re: their "Classic" master cylinders. There has been some concern about quality and problems, but I believe if you contact them directly (assuming you have one of the suspect units), they may be able to help.
 
I believe that port on the bottom is where the brake pressure failure switch is located.

I plugged the port with a bolt and brass washer for my V8.
 
Nial, discussed that problem with him and he said the recall was NOT on the "B" MC's.
Is there something with the "sili" fluid that would cause it to blow by a seal if it was basically bleed then put to bed for 8 months?
 
Ricks right the port is for the brake pressure failure switch and normally if the master cylinder is good they will not leak however if they go bad they leak and you need to replace the master cylinder. I think moss has a bad batch as there has been more than a few reports of them leaking and I recently got one that also leaked in short order.
 
DOT5 will leak out of MC like no tomorrow....on some.
Had a 1950 Ford Convertible I did a full resto on years and years ago....leaked like a sieve. Eventually it seated and quit.....and he went through 42 brake light switches until he did a body-mount switch for the pedal arm. DOT5 went right through the seals on the brake switch.
Could be a bad MC, but if you add fluid and actually DRIVE it, watching the levels, it will probably seat in.

BTDT.
 
Well... turned out not to be the MC.
Twas the dreaded PDWA, ...
Do they call it that on an MG?
 
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