New BMC fitting/bleeding......

[simonbuk]

Bought one of those new BMC's (Metelli 05-0190) but am having trouble trying to bleed it. Put the reservoir on top and then fitted a brake master cylinder bleed kit to it. Put some brake fluid in the top and it just p*ssed out the front of the BMC ??
What am i doing wrong ??!!

Somebody suggested on one of the Facebook groups that when the BMC is on the car it is slightly pre-loaded with pressure so the rod and rubber sleeve are in a different position, but then how would you bleed it when its off the car ? Which I believe its something you can/should (?) do ??

[dapinky]

Simon,

Although I have heard people talking about it, bleeding a new MC is not something I have ever done. I believe that the thought process goes back to a much earlier time when there was maybe a necessity for it, but on "modern" stuff (ie, anything I have worked on made in or after the 60's) I have just fitted the cylinder and added the pipework.

That said, if you are doing it, I don't see how fluid would (or, at least, should) come out from anywhere other than the 4 pipe ports.

A 'slight pre-load' may make sense, but I can't see that the resting pressure of the activation rod would make a lot of difference from when it comes out of the box.

All I can think of is that you manually push the piston into the cylinder using a screwdriver or other rod - actually, a wooden spoon handle may be better - and allow it to come back under spring pressure to a resting position, and then see if fluid still escapes - if it does, then it sounds like the seal is either misplaced or missing, and you may need to return the cylinder for an exchange.

[simonbuk]

I wouldn't have thought that I needed to do it either but what with the problems I had when I put my previous BMC back on (bled the brakes for many, many hours without success) I kind of gave up and thought there must be air in the BMC which I simple couldn't remove. I tried an easybleed, a one way valve bottle, friend sitting in the car, etc, but I just couldn't bleed the brakes. Apparently if you have got air trapped in there no amount of normal bleeding will get it out ?

I would have thought that it's unlikely that they have made a mistake when assembling it from the factory but could be a possibility ?

[simonbuk]

Bleed complete.

I decided just to fit the BMC to the car and see what happened. Well it worked and I bled each corner easily. No idea why the original one wouldn't work when it went back on the car but there we go.

It needs to be on the car as the rod/shaft that comes out of the servo needs to be inside the BMC, this completes the seal as it goes into/through a rubber seal. Don't know how you could ever bleed it off the car therefore ??

Anyway, job done (so far), only completed one quick bleed of each corner last night, so off to check everything is ok and maybe bleed it some more to make sure everything is air free.

[chrism]

That's really good news
Let's know when you get the final bleed done and the brakes applied in anger. The Metelli 05-0190 seems to be good v-f-m if it ticks all the boxes.
Does it have a different pedal travel? etc...I wonder why your old BMC was such a pain? And were there any particular symptoms causing you to replace in the first place?

[simonbuk]

No symptoms on the old one, I was just trying to refit it after I had things dismantled. Just wouldn't bleed properly again no matter what I tried. Then when examining it and putting it back together *someone* buggered it so had to buy a new one.

Haven't driven it around yet .