Master Cylinder Plug Vent Hole

[glcaines]

I just finished installing my new master cylinder on my M151A2. When filling the MC with DOT 5 fluid, I noticed that the fill plug on my original MC had a vent hole in the center of the plug. The new MC fill plug has no hole and is not vented. Which is correct? You can see the difference in the attached photo. Also, the new MC has a rubber gasket for the plug. The original MC had a copper washer to seal the plug.

Brake MC Plugs.jpg

[m3a1]

I think you can see by the quality of the plug's casting (vs that of the original) not a lot of care was taken to make these. Make of that what you will.

Cheers,
TJ

[rickf]

Use your original cap. You need the vent.

[glcaines]

I'm going to use the old plug as suggested. The new plug, in addition to the lack of a vent hole, has threads that are difficult to screw into the new MC. The old plug screws into the new MC with ease. Still not sure about using the copper washer or the rubber gasket to seal the plug.

[Horst]

copper.

Hopefully you will not disappointed as it looks like the repro MC is not of the best quality. Given the fact that this is a single circuit brake system, a single failure means total failure of the brake. Hate to say it but I probably would remove it again and have a look at the internals.