[Help] Need advice on brake master cylinder replacement.

[Simca]

Hey guys, I'm replacing my brake master cylinder, and booster, along with front lines and hoses, as my brakes have been going almost to the floor lately.

I know it was leaking somewhere but not exactly sure as to where. Anyway, I bought a spare brake booster off a facelift 318i to replace mine (pre-facelift 1987 320i), but upon taking my booster and cylinder out I realised that my entire setup was actually different to the one out of the 318i.

You see my car has a second piece underneath the the master cylinder, like this one:

Assembly (internet example as my phone camera is horrendous):


Piece (also from internet):


The new setup I've bought doesn't come with the extra piece. I've looked the part up and there's not much information on it, some call it a "Pressure Regulator". A Link I found after googling Pressure Regulator, calls it an ABS pressure regulator, but I'm 99% sure my car has no ABS. I'm 99% sure that the car I bought the setup from also doesn't have ABS.

My thought was obviously to just replace my cylinder and booster only but not the pressure regulator. But my cylinder is actually different to the one I bought, and so the lines don't fit and I'm still not sure what the extra piece does, meaning I'm not sure whether I can just run the new setup, or if I need to make up new brake lines to fit the regulator to the new cylinder.

My cylinder (which Ireland Engineering sells as an e21 Cylinder):


New cylinder I've bought (which doesn't have the brake line to passenger side front in the same spot):


Anyway, I'm unsure how to proceed. Do I just whack the new brake cylinder on and ignore the pressure regulator, or do I make new lines up and fit the old pressure regulator (which could still be the part that leaks, I'm not sure), and go from there?

Also I'm broke, that's why I'm buying used parts rather than new, I gotta get to work.

Anyway, any help would be much appreciated, thanks a lot.

PS. My car is Right hand drive if that makes a difference.

[R3VM3UP]

I'm not exactly sure what that second piece under the master cylinder is, do you have a part number? It may be a proportioning valve, which isn't absolutely necessary, but you should probably at least understand what it is before removing it.

You need to be more specific on the exact parts you bought, there are tons of master cylinders that look identical externally but have different diameters internally. What really matters is that your ratio of master cylinder to brake piston area stays relatively unchanged if you want the pedal to feel the same as before. If your calipers are the same as other E30 calipers then you should be able to swap the master from pretty much any other E30. Look up brake bias to understand how these calculations work.

Also, try to figure out what the diameter of the bores on your two master cylinders (old and new) are and post them here, then people can help you better.

[NotJesus]

Bumping this post, has anyone seen that extra piece under the master? It is plumbed in between OEM master and the ABS unit.

My E30 is 91 325i, currently with a Porsche 944 booster, however my master cylinder and this extra piece under it is what came with the car.

Getting ready to switch to a 25mm master, prop valve for the rear brakes in place of the stock one, all in prep to install Lee’s 300x32mm kit.

Curious to know what this piece is, and weather I should leave it and just swap out the master, or eliminate it with the new master and modify the lines to just plumb the 25mm master straight to the ABS.

[mikey.antonakakis]

Bump, what is this thing? Starting an ABS delete and my car also has this.