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Master cylinder problem
nludkin - 10/4/06 at 10:08 PM

I have just plumbed in the master cylinder and started bleeding the brakes. On pumping the pedal I can get fluid coming out of the rear port but barely any fluid is coming out of the front 2 ports.

Do I have a master cylinder with a screwy primary piston? Or am I missing something? It's a standard sierra one btw.

k33ts - 10/4/06 at 10:43 PM

have you fitted compensater thingy bob maybe round the wrong way

nitram38 - 11/4/06 at 05:22 AM

Are you putting fluid through without the pipes connected?
If you are then the cylinder has a compensation device which will close the fluid off to a leaking circuit. So it you have a leak in the front or rear it will block that circuit off. Also make sure that the circuits are split into 3. (check your manual for the car it came from). There is normally one circuit for the rears plus a split circuit for the fronts.

britishtrident - 11/4/06 at 06:33 AM

Cylinders don't have any fancy devices inside, they are just two pistons with a spring in between.

My procedure with dual circuit master cylinders was to prime the cylinder on the bench before fitting --- screw bleed nipples into each outlet fill the resevoir push the iston in with screw drive and close the nipples, seal the resevoir cap withcling film then fit each connection in turn.

nitram38 - 11/4/06 at 11:15 AM

quote:
Originally posted by britishtrident
Cylinders don't have any fancy devices inside, they are just two pistons with a spring in between.

My procedure with dual circuit master cylinders was to prime the cylinder on the bench before fitting --- screw bleed nipples into each outlet fill the resevoir push the iston in with screw drive and close the nipples, seal the resevoir cap withcling film then fit each connection in turn.


Dual master cylinders with split tandem circuits, do not have any fancy devices, but the pistons will close a circuit with low pressure, so you at least have one circuit working. Normally the front circuit is split. If you get a leak in the rears, then the master bias is towards the front two circuits. If one of the front circuits breaks, then you will have a rear circuit and one of the front circuits still working.
I suggest fitting the master cylinder and trying it. If it is faulty, just change it.
Testing it on a bench can only be done if all circuits are closed.

nludkin - 11/4/06 at 12:36 PM

I have just screwed nipples into the front 2 outlets and kept the rear one plumbed into the proportioning valve / rear brakes.

After pumping the pedal lots, it goes hard. However, on loosening the front nipples there appears to be little to no fluid getting through. The pedal also goes soft again within seconds.

Have I got a dud master cylinder? Did I fit the proportioning valve the wrong way around (Pointing upwards at the inlet?)
I hope it's not a dud master cylinder, I bought it reconditioned only a week or two ago.

ditchlewis - 11/4/06 at 03:26 PM

Just an idea

I could not get my brakes to bleed at all, and it would take a lot of pumping to get any pressure. I even bought a new master cylinder

eventually traced the problem to having the front brake calipers on the wrong wheel and thus they were upside down

felt a right fool but problem solved.

just a thought but it tends to be the bl***y obvious that is over looked.

good luck and keep going it will be worth it in the end.

ditch

nludkin - 11/4/06 at 09:11 PM

Thanks for all your replies guys. I finally got it cracked! Looks like the master cylinder wasn't properly primed and it unexpectedly shut off the front circuit.

Anyway, at least the brake fluid is coming out of the right places now!

Cheers.

nitram38 - 15/4/06 at 08:55 PM

quote:
Originally posted by nludkin
Thanks for all your replies guys. I finally got it cracked! Looks like the master cylinder wasn't properly primed and it unexpectedly shut off the front circuit.

Anyway, at least the brake fluid is coming out of the right places now!

Cheers.


Looks like my theory was right?