Installing Brake Master Cylinder

[uofom3]

I'm going to bleed my brakes today, and it's the first time i've done it since I put in a new brake master cylinder (25mm for firmer pedal). When I put the new BMC in, I just unbolted the old one, moved the Oring from the old one to the new one, and bolted it back in place. I then wired up the hardlines, and reconnected it to the resevior. Is there anything that I needed to do here that I should have done? Anything else to do before I start bleeding it? TIA.

[Van Westervelt]

Some people say bench bleed them first. I didnt. I just vacuum bled my system a couple times fully, and all was well.

[E30_fiend]

You need to work the air out of the new master. Even though its new, when the brake fluid goes into it, so will air.

A good way to do this is take the master back off and place it in a vise or something that will hold it in place. Install the reservoir on it if it isn't already done. And get two clear tubes and run both of the tubes from the inlet and outlet of the master back into the reservoir. When you have this little recycle system going, take a screwdriver or a punch, something strong with a good handle on it, and from the plunger end, push the plunger in and out. You will see the fluid start to circulate. Keep doing this until no or very minimal bubbles are left. THEN you can install it.

If you were to just put it on, you would have a very soft pedal due to the bubbles inside the master. This also eliminates having to bleed the rest of the brake system. At least it did for me. I thought I might have to bleed the brakes still but the pedal was perfect.

Hope that helps.


E30_Fiend

[uofom3]

So my procedure regarding installation was right? It was very easy... so easy that I was a little worried about it.

[uofom3]

You need to work the air out of the new master. Even though its new, when the brake fluid goes into it, so will air.

A good way to do this is take the master back off and place it in a vise or something that will hold it in place. Install the reservoir on it if it isn't already done. And get two clear tubes and run both of the tubes from the inlet and outlet of the master back into the reservoir. When you have this little recycle system going, take a screwdriver or a punch, something strong with a good handle on it, and from the plunger end, push the plunger in and out. You will see the fluid start to circulate. Keep doing this until no or very minimal bubbles are left. THEN you can install it.

If you were to just put it on, you would have a very soft pedal due to the bubbles inside the master. This also eliminates having to bleed the rest of the brake system. At least it did for me. I thought I might have to bleed the brakes still but the pedal was perfect.

Hope that helps.


E30_Fiend

This I will considder - thanks for the response!

I think I need to flush the system anyway, I haven't dumped it since a track day at PIR and it sat for a long time.

[E30_fiend]

But you probably already know the bench bleed proceedure. Didn't think about that.

You know your shit.


E30_Fiend

[Van Westervelt]

You had your MC off, replaced it, and didnt bleed your system at all? Bad idea.

[uofom3]

You had your MC off, replaced it, and didnt bleed your system at all? Bad idea.

Haven't used the brakes :)

I took it off, replaced it, and have yet to drive the car where I would need the brakes (i.e. first gear no throttle on clutch).

who would have thought to bleed it before driving it!? :)

[Van Westervelt]

Ah, sorry. Should have specified, I was referring to E30 Fiend.

[Stu]

When I installed the 25mm MC, I immediately pressure bled it at 20psi and once again at ~25psi. I had no problems. It's a good idea to replace the 2 grommets while you have the reservoir off though.

[E30_fiend]

Ah, sorry. Should have specified, I was referring to E30 Fiend.

Yes, I did do that. Later on I bleed the brakes but at the time they felt just fine. And I was referring to the install of the MC for getting the air out. You are right that is a bad idea but my procedure made the actual bleeding of the rest of the system quite easy due to the lack of air left in the system.


E30_Fiend