Brake bleeding problems - possibly Master Cylinder

[nthomas1]

I I decided a while back to put new brake fluid in the car as the existing fluid has been sitting there for at least five years.  Unfortunately I walked into a can of worms.

The front bleed nipples wouldn’t budge initially, but with a few days soak in WD40 they came free and I’ve replaced them with new ones.

At the rear I was puzzled to find no bleed nipples, just solid Allen key grub screws.  They were M8 and coarser thread rather than the correct M7.  I managed to find some nipples of the correct specification, but they wouldn’t screw in which led me to believe the ends of the original nipples were probably still seized in place.  Seems a previous owner  had drilled out part of the seized nipples and enlarged the accessible part of the thread to allow a grub screw to be fitted.  So the car had no bleed capability at the rear!  

I took the calipers to Classicar Automotive in Cheshire and they did a lovely job repairing and refurbishing them.  They removed the seized nipple portions and fitted ball bearings to seal the fluid entry, and put a concave surface on M8 bleed nipples to mate with the ball bearings.

I fitted the new calipers and tried today to bleed the system.  I used the old fashioned manual system, with my wife pressing the brake pedal when I shouted,  and releasing it on a subsequent call. I read the dozen or so forum threads on this topic and decided to keep things simple, especially as I was starting with a filled system, rather than one that had been drained.  I started furthest away from the master cylinder, with the back of the car jacked up by the axle.  Both rears seemed to bleed alright.  

Then I started on the front left.  The lower nipple bled as I would have expected, but when I loosened the top nipple I had no fluid flow. I checked that the nipple passageway was clear, and I checked that fluid flowed freely when the nipple was removed.  So I was puzzled as to why I would not get the normal stream of fluid when the brake pedal was depressed with the bleed nipple opened.

I then moved to the  front right, and my experience was exactly the same as with the left.  The bottom nipple seemed to bleed correctly, but no fluid flow from the top nipple.

Does anybody have any suggestions as to what might be happening.  One person has suggested that front top nipple and and rear nipple on one side of the car should be bled simultaneously, but I’ll need a third person to try that.

[SanRemo78]

Hi Norm, I'd say shout if you need another pair of hands (or feet) but at the moment I'm not free due to family issues.

Have you tried bleeding the front circuits without the upper bleed nipples in at all? If you get fluid out it must be blocked nipples? Can you blow through the nipples?

Guy

[SanRemo78]

And not being familiar with Fulvia callipers... Should they have bleed nipples top and bottom on a single piston brake? If not then I'd suggest that you've got the callipers on the wrong sides? Swap them over and the nipples that you can bleed will be at the top?

Guy

[nistri]

According to Lancia instructions, on S2 cars the first nipple to be bled is the top one on the passenger side, then the other top one, then the lower ones etc. You might need a suction pump to get the flow now, Andrea

[nthomas1]

Hi Guy - the nipples are brand new each side and are not blocked.  The Fulvia has twin pot brakes, hence two nipples each side.

Andrea - fluid flows freely when the top nipples are removed so I don't have an air blockage.   I'm trying to figure out why pressing the pedal doesn't result in fluid flow. 

Could it be that the second pump in the master cylinder is not working? Is it that second pump that feeds the top front pistons?

[Neil]

Are the flexible hoses new, could they be collapsed or blocked the inside?

[nthomas1]

The hoses and pipes look fine Neil, and fluid flows when the top nipples are removed so there are no blockages.

I'm still suspecting that the master cylinder second circuit is not pumping but not sure how to confirm it.  I'm hoping someone on the forum has encountered a similar situation and can advise.

[Richard Fridd]

Perhaps check for pressure at the m/c outlet?

[nistri]

Norm, I think there might be a problem with the front piston in the master cylinderb as this is the one feeding the flow system for the top nipple circuit. Slacken (don't remove it) the front tube connection at the master cylinder and try to see if there is fliud coming out when pressing the pedal. Andrea

[nthomas1]

Thank you Richard and Andrea - I'll do as you both suggest and see if I've got fluid flow from the m/c front outlet. I'll track the plumbing to see which pipes feed the front top caliper nipples.   The nuts holding the outlet pipes won't budge at the moment so I'll give them a good soak in WD40 for a few days and then try again.

[Richard Fridd]

Also some people suggest filling a new master cylinder with brake fluid before fitting it to the car, as an extra precaution against air being present. I am hopeful you will have this all solved very soon! As for the rears, the bias valve needs to be in the open position to let fluid passed, although I expect you are aware of this. Richard

[nthomas1]

Richard - thanks for that.  I was aware of the rear brake bias issue, but thanks for the tip about fitting the master cylinder "wet".

[davidwheeler]

I have always used a vacuum device to bleed my Fulvia but I suspect positive pressure from above might do as well.   Perhaps the piston in the master cylinder is so far forward fluid cannot get in?  (hence, fill the cylinder first)   Positive pressure from the caliper upwards, such as I use on a motorcycle would get round that one - reverse bleeding.    Just a thought, have not had this particular problem myself.

[chriswgawne]

I have always fitted S1 & S2 Fulvia brake master cylinders 'primed' and then I have always used the 'positive pressure' method using either a Gunson kit or (now) a home made method of clamping a lightly pressurised fluid reservoir to the Lancia fluid reservoir.
Always worked for me apart from one occasion when I didnt realise there was a 'rolling ball' rear brake bias cylinder with a bleed nipple on my GTE which was hidden between the rear of the gearbox and the rear of the subframe.
Chris

[lancialulu]

Some master cylinders do not have a front fluid feed hole from the reservoir to the front circuit but rely on the one way valve between the pistons to fill the front. These may be gummed up. Additionally I have found if there is a feed hole at the front it is small and sometimes aligned behind the piston. One one master cylinder I opened up the hole 1mm and this cured the feed problem.

Obviously is makes sense Norman to remove the master cylinder and give it a service anyway.