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MG MGA - Another Master Cylinder Question

I did not want to hijack the other MC Question thread with this new

I know that there is a rubber disc that gets inserted into the rear of the bore on the brake side of the cylinder. What is the function of this spacer? Simply a bumper/snubber?

rpb bunch

Rick, I think it's a valve that keeps a small amount of pressure in the brake lines when at rest to stop the rubbers in the wheel cylinders from colapsing.
Lindsay Sampford

There is a small rubber 'button' that inserts into the metal 'hat' on the back end of the brake-side return spring. My interpretation is that this is the non-return valve. Perhaps the rubber disc is a seat against which this metal 'hat' rests in the back of the bore? Y/N?
rpb bunch

Rick, I'm sure there must be something on Barney's site about this, but on my drawing in the manual, it shows a rubber washer in the extreme back of the cylinder, followed by a little rubber valve cup with a "mushroom cap" facing toward the open end of the cylinder, followed by the metal valve body with its widest end towards the rubber valve, followed by the spring etc.
Lindsay Sampford

Rick, found the workshop manual on Dominic's site you need page M7
Whoops link doesn't work, needs one of those magic link shortening devices, someone?
Lindsay Sampford

Right Rick, try this Page M7
Lindsay Sampford

Ahhh...this is the view that I have been looking for...Thks!

I'm theorizing that the valve washer is there to provide a seat for the valve body.

The picture depicts exactly how I assembled the MC, I'm just trying to better understand the role of each piece/part.

'Bob's your uncle'...

rpb bunch

The rubber washer at the rear of the bore is for sealing. Without a seal between the check valve body and the rear of the bore, fluid would be able to go right around the valve. The flat area (brim of the hat) is pressed against the rubber washer by the return spring, making a seal and keeping a few pounds of pressure in the brake circuits.
Steve S

This thread was discussed between 11/09/2010 and 15/09/2010

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