Brake master cylinder question

Post by **Velocemitch** » Fri May 05, 2006 9:26 pm

I'm puzzled, why is there a little squirt of brake fluid coming out of the breather hole on the master cylinder every time the brake pedel is pressed?.

Mirium hasn't had a vast amount of use recently and I jumped in her today to move her off the drive, only to find the brake pedal went straight to the floor with only a very slight braking effect. Could have been a bit frightening, but as it happens I only reversed off the drive so I just stopped and put it straight into the garage to investigate.

The master cylinder was virtually empty, I have thoroughly checked all the cylinders and the unions and can't find a leak. Having bled the system taken up a little bit of adjustment on the shoes and topped up the reservoir I now have a good feel on the pedal, but as I said at the top of the post it's squirting the fluid out, I suspect it's being doing it all the time and just emptied the reservoir. The kids use the car as a sort of 'wendy house' stting in it on the drive and I suspect they have pumped the brake pedal exasperating the problem.

Is this normal?, or is there a non return valve between the reservoir and the cylinder which has failed?.

Post by **bmcecosse** » Fri May 05, 2006 9:35 pm

There is normally a wee 'pulse' of fluid when pressed - but the screw on top keeps it in normally - have you filled the reservoir too full ? Should be about 1/2" from the top.

Post by **rayofleamington** » Fri May 05, 2006 9:43 pm

you get a little 'fountain' if you press the pedal quickly enough - that is normal. When you say 'it comes out of the breather' do you mean that it comes out of the oin hole in the cap?
If so, then the screw cap is faulty as it should have a baffle plate to stop that happening.

Most likely cause of no fluid in the reservoir (if the pipes or wheel cylindrs are not leaking) is the m/c secondary seal is leaking. From here it will leak into the boot (the boot that goes over the rod from the brake pedal) and out of the boot into the chassis leg.

Post by **Velocemitch** » Fri May 05, 2006 9:51 pm

It seems to push fluid out even if it isn't too full

The cap is nicely made brass screw, looks OK, but is there something missing?.

There was no sign of any fluid around the boot, which looks in good order, I will have another look tomorrow, is the Boot easy enough to get off?.

Strange place to put a master cylinder isn't it. It's well protected, which is more than you can say for the one on my Alfa Guilia which hangs under the floor right in the line of fire for all the road sh** flying about. But if it is leaking it will do a good job of dropping corrosive fluid all over the inside of the box section, clever that!

Post by **bmcecosse** » Fri May 05, 2006 9:57 pm

It's not corrosive -but it does melt paint!

Post by **bigginger** » Fri May 05, 2006 9:58 pm

It was put there 'cos there was no room for it in the engine bay with the flat 4 the car was originally designed for. I've long cursed whoever decided to leave it there when they changed their minds about the engine...

Post by **rayofleamington** » Fri May 05, 2006 10:00 pm

It's not corrosive

it sucks in moisture and ensures rapid corrosion. hence the whole purpose of (expensive/difficult) Silicon Fluid to avoid this.

Post by **bmcecosse** » Sat May 06, 2006 5:23 pm

If it was that corrosive - it would rot the pipes out. It is best to renew the fluid from time to time - just push some through the bleeders - but silicone fluid is a bit too far !

Post by **bigginger** » Sat May 06, 2006 5:46 pm

I think Ray agreed about it not being corrosive already.

Post by **Onne** » Sat May 06, 2006 9:14 pm

brake fluid is hygroscopic, so it attracts moisture (water) which in turn makes things rot.

And one doesn't want water in one's brake fluid since it evaporates at a relatively low temperature, causing compressable gasses, the last thing you want in a hydraulic system!

At least that is what I learnt

Post by **d_harris** » Sat May 06, 2006 10:05 pm

I thought I might go down the road of silicon in the trav

Post by **Onne** » Sat May 06, 2006 10:09 pm

That does include replacement of all pipes doesn't it?
What about the 7 cylinders? Do they need to be replaced as well, or just the seals?

Post by **Velocemitch** » Mon May 22, 2006 12:56 pm

Still struggling with this, I borrowwd a spare cap from someone to see if it cured the problem, trouble is it didn't fit

His cap was slightly larger and had a finer thread, presumably they changed the cylinder at some point and I need the later one, mines a 69 Car.
The other worry is, I mentioned the problem to a mechanic who I beleive his quite experianced with British classics and he told me the M/C would be faulty if it pumped fluid back into the reservoir when the pedal was pressed. I can see the logic behind this as I would have thought there would be a one way valve or something, but a couple of posts above seem to confirm the 'fountain' is normal. I don't fancy changing the M/C to find the problem could have been solved by a new cap, equaly I don't much fancy driving around with a faulty M/C.

Post by **rayofleamington** » Mon May 22, 2006 2:17 pm

the 'fountain' is normal.

Many m/c will do this, but some designs do it more than others. The Minor m/c does it to an 'extreme' but that really is how they are meant to work.
At the end of the spool return travel, the bore needs to be connected to the reservoir to refill the bore. As the spools starts to travel it will close off the connection to the reservoir and then push fluid into the brake pipes, but before it has travelled far enough to close the refill hole it pushes fluid back to the reservoir (this is a major factor to help the spool 'self bleed')

If you get a bubble rising into the reservoir at the same time as the little fountain, this means there has been air sucked into the bore as well as fluid

This will be a leaking secondary seal and that nearly always means a corroded m/c bore (terminal).

Post by **Velocemitch** » Mon May 22, 2006 3:46 pm

Ok thanks Ray, so I need to check that there is no bubbles in my fountain. Then if not try to find a new cap, nobody lists them on the parts sites I have found yet. The M/c looks fairly new.

Post by **rayofleamington** » Mon May 22, 2006 4:21 pm

The M/c looks fairly new.

oh

It sounds like it might be a 'pattern part'. Do you know where it came from? Parts have to be 'fit for purpose' if they are sold in this country, despite what a trader may want you to think.

All the lockheed m/c I've had use the same cap.

Post by **Velocemitch** » Mon May 22, 2006 7:31 pm

No idea where it came from, I don't have much history for the car. There are no markings visible.
On the plus side I don't have air in my fountain.
But the fluid still leaks out of the air hole

So did both the smaller and the larger Lockheed type have the same caps then?. It just seems a bit daft having to change a £50.00 cylinder for a £1.00 cap!.

Post by **rayofleamington** » Mon May 22, 2006 7:34 pm

So did both the smaller and the larger Lockheed type have the same caps then?. It just seems a bit daft having to change a £50.00 cylinder for a £1.00 cap

Yes - they have the same cap.
You couldd probably 'fix' yours by altering the breather hole / fitting a baffle in the cap 'somehow'

Post by **Willie** » Mon May 22, 2006 8:14 pm

Forgive me for butting in this but,as RAY says it is perfectly normal to get
a strong spurt in the Master Cylinder reservoir when the pedal is depressed
and surely if your fluid was coming out of the cap it would be coating the whole area. As you say you have restored a good pedal feel have you tried
pressing hard on the brake pedal and seeing if it goes slowly to the floor and
has the' topped up' level dropped since? The only time the Master Cylinder
was changed was when the 8" front brakes came in (1962 onwards) when the
bore was reduced to 13/16" from 7/8".

Post by **Velocemitch** » Mon May 22, 2006 8:28 pm

Willie, the problem is as soon as I give the pedal any real pressure the fluid comes out of the top, so the whole area is covered anyway. The Car is up on stands and has been for a few weeks now as I sort some body issues, but I can see there is no fluid leaking anywhere visible, if there is some coming out under the M/C I would struggle to spot it for the reason mentioned above.

Not sure how I could fit a baffle, what ever I do needs to be perfect or I might end up with no fluid again.

I'm running out of ideas now, what was all that I read about jacking the torsion bar out of the way??