Master cylinder

[ajs18s]

So I replaced all seals as well as piston in the callipers, bleed them but could not build up pressure. Maybe I’m doing it wrong as I have never done this on twin nipple callipers before. However I believe maybe the master cylinder is the issue. What is the kit number that I would need for a 1974 3C?
Any advice or help is much appreciated.

 

[martymoose]

What angle is the mc at? Get it off the bar and tilt it up, most common problem is air in the right angle banjo fitting

 

[The Sock]

Were the brakes working properly before you overhauled the calipers?
Does the bike have "Brevetatto" handlebars?
If so, try this method, taught to me by Phil Todd:
Chaeck the fluid level in the master cylinder.
Remove the bar Allen Screw (yellow arrowed).
Hold the bar end vertically, with the lever ball up.
Pump the lever, momentarily holding it pulled.
If more than ten strokes, re check fluid level.

 

[ajs18s]

This maybe a silly question, but do I need to replace the lid every time I fill it up?

 

[ajs18s]

So after last ride nil by issues. Parked up then a few weeks later I noticed brake fluid on the ground and master cylinder was empty. So I made the assumption it was the callipers, to be honest the seals looked ok.

 

[The Sock]

This maybe a silly question, but do I need to replace the lid every time I fill it up?

Yes, and the bellows.

 

[The Sock]

So after last ride nil by issues. Parked up then a few weeks later I noticed brake fluid on the ground and master cylinder was empty. So I made the assumption it was the callipers, to be honest the seals looked ok.

Check all unions and lines, especially the rubber hoses.
New ones can be got from Alfa or Mercedes suppliers.

 

[Schurminater]

This maybe a silly question, but do I need to replace the lid every time I fill it up?

A curious question Yes?.............but I can see your thinking and it can have a couple of answers.
If you are topping up and just bleeding the system you don't have to fit the cap and bellows every time, unless of course you are tipping the master cylinder up as Hamish suggests. (very messy!)
If you are leaving the master cylinder upright on the bars you don't have to replace the cap and bellows every time as with pumping fluid through to bleed the calipers (obvious really) but just have a cover rag suitably placed to protect the paintwork in case of splash back or spillage.

Finally ,if you mean replace as with new? ......no you don't need to as long as the cap and bellows are serviceable.

Ps. You tend to have to bleed the air out of the master cylinder before it will pump fluid through the lines down to the calipers, make sure the little holes in the master cylinder are clear before starting.......can be a long tedious job sometimes!....

Good luck.

 

[ajs18s]

Having 4 nipples, is there a sequence to bleeding?

 

[The Sock]

Having 4 nipples, is there a sequence to bleeding?

I start with the furthest from the master cylinder first, (the outboards).

 

[henrywillms]

In theory its an easy job. In practice there are lots of tips how to make it less frustrating. A search will bring you lots of recommendations.

 

[Andy]

If you don’t put the lid on you can get a squirt of fluid at the first part of the lever action if you’re too quick, no problem if you take your time. Also by gently manipulating that early part of the action you can encourage air to bubble out of the top of the system, which you can see with the lid off, very useful technique once the system has settled for a bit if it’s still a bit spongy. As mentioned though, you need to make sure the master is horizontal at least.
Also, if you’re bleeding the system purely for maintenance reasons it’s important to push the calliper pistons all the way back in once or twice during the process to make sure you get most of the old fluid out

 

[Rob]

Parked up then a few weeks later I noticed brake fluid on the ground and master cylinder was empty. So I made the assumption it was the callipers, to be honest the seals looked ok.

More likely to be the master cylinder in my experience...could even be a leak from the cap!
As others have said, plenty of guidance on bleeding via a search. Twin bleed screws make little difference to the process.
If the system is completely dry I find it can help to prefill the master cylinder piston bore with fluid. Means removing the m/c and brake line to do so. But do first carefully check that the two tiny holes in the base of the m/c reservoir are clear - very thin wire needed. One hole is slightly larger than the other.
If you are in Brisbane then Redax won't be far away

 

[Dellortoman]

Make sure that when you release the lever, the master cylinder piston is returning far enough to uncover the little port from the reservoir so that fluid can enter the cylinder. If it doesn't, you'll never build pressure or be able to bleed the system.
I reckon this is the problem 90% of the time when you rebuild a master cylinder. It's a tiny little port about 0.25mm in diameter so a fraction of a millimeter can make the difference between working properly and not working at all.

You can easily diagnose this problem. With the reservoir about half full, leave the cap off and pull the lever. if you don't get the little spout of fluid as mentioned in previous posts, then the port is more than likely blocked.

It can happen a couple of ways:
1. If you press the retaining ring in a bit too far when you reassemble the cylinder, it could limit piston travel.
2. If the new rubber seal on the M/C piston is a bit wider than the old one it could cover the port. I've had this happen a couple of times with new rubbers.

In either of the above cases, the piston needs to return a wee bit further. If the piston retaining ring is seated properly, you may need to file a wee bit off the outer end of the piston or the heel of the lever.

 

[Vince]

I spent a very frustrating weekend with exactly that issue on the rear brake of my Pantah, I tried every trick in the book but didn't know about that tiny hole. I had an extra washer that stopped the piston too early in the rear sets.

 

[piranha-bro2]

I had an extra washer that stopped the piston too early in the rear sets.

Yep, that'll do it!

 

[ajs18s]

So, I am assuming that the master cylinder needs a new kit or I’m doing something completely wrong. There are no blockages in any of the hoses and as I try to build pressure no luck. Yes as I pump the ms without the lid on I get a little squirt and it builds up a little pressure but it then fades away, plus I don’t get brake fluid from the nipples on the inside.

 

[Andy]

If the pressure keeps fading I’d blame the master, but:

I don’t get brake fluid from the nipples on the inside.

I don’t suppose it’s possible to muddle up the left and right calliper halves during reassembly is it?

 

[martymoose]

If it's squirting fluid out of the compensating port I would say it is pumping. If you have lifted the angle to let the air bubble come out of the banjo, just move the lever a small amount. Are you seeing bubbles?
Options
Vacuum bleed top to bottom
Reverse bleed, push fluid in from the bottom with a syringe.
Good luck

 

[Schurminater]

I know that when I serviced my callipers with new pistons, seals etc I then had trouble as you described.After hours of trying to pump fluid effectively a new master cylinder rebuild kit fixed it.