Annoying dragging brake problem

[Willie]

Oh dear, since not all of the cylinders are sticking it obviously rules
out a Master Cylinder problem. Perhaps your pattern cylinders
are the problem? I mean that I assume they came complete with
the rubbers fitted which may be suspect? I have had no further
problems with mine which were 'genuine' type and which were fitted
a long time before yours. !!!!!!!!Having just reread your post it
appears that when you remove the piston the cylinder is full of fluid
ABOVE the rubber?? That is obviously wrong as there should be no fluid
allowed to by pass the rubber under normal circumstances? If this is
correct then the rubber is definitely faulty and the piston would not have
enough power under the brake shoe springs pressure to force the fluid
back past the rubber??

[Chris Morley]

the piston would not have enough power under the brake shoe springs pressure to force the fluid back past the rubber??

Willie, the brake fluid is leaking past the rubber and its collecting in the bore between the rubber and the end of the piston. As you say that isn't right. It also seems that the fluid isn't able to get to the slave cylinder.

I got the pattern types as the originals I fitted in 2001 didn't last very long anyway. There's a new one in the post so I'll replace it and see what happens.

[Chris Morley]

I've replaced the dodgy cylinder and that wheel isn't dragging anymore - which is nice... No idea why the faulty cylinder was blocked as it seem to be OK now it's been disconnected from the plumbing.

In the process I've learnt something - the pattern cylinders are a bit different to the originals. The brake fluid enters the piston chamber and pushes against the metal end of the piston. It's prevented from leaking out by a rubber sealing ring on the piston. In this case the fluid remained in the bottom of the chamber and didn't drain off as it should. From memory the original cylinders work on the same principle but they have a large rubber seal which pushes against the end of the piston.

[Matt]

Yeah, and its really annoying when you have a pattern one leaking, but only have "genuine" seals

[bmcecosse]

I think it is more the standing about not being used that gums up the cylinders. If used daily then that shouldn't happen. If you hook the return springs in to the second set of holes - the ones further away from each other it makes the brakes a bit heavier - but it sure as h*** pulls the cylinders back to base each time ! Also brake fluid absorbs water - and should be pumped through once a year - for me it's the annual pre MOT bleeding !! Just be aware that now your brake shoes have had a really good roasting the characteristics will have changed - they may now 'snatch' and they may not have as good a coef of friction as before. On the same overall subject - anyone using Silicone brake fluid ? Does it help to preserve cylinder life ?

[Matt]

Chris, this might be one of my crazy ideas but.....

did the cylinder have any gritty stuff in it? in one of the staff car sagas a little while ago someone said how the flexi pipes had disintergrarted (sp) and filled the cylinder with grit. If someof the grit got between the cylinder and the seal surely it would cause some grooves and let fluid past?

[57traveller]

On the same overall subject - anyone using Silicone brake fluid ? Does it help to preserve cylinder life ?

Silicone fluid pros and cons have been discussed before but I have Automec in both my cars, one for 6 years and the other for 4, without problem (but see below). The concensus seems to be that there could be seal rot if they are not ALL renewed prior to using the silicone fluid. That was done on both my cars anyway.
What I have found is that because the system is not being flushed out with a change of fluid any "rubbish" seems to migrate to the bleed nipples and blocks them. So the systems have an annual part flush to remove any nasties lurking around. Just a teaspoonful from each cylinder.

[bmcecosse]

Thanks 57 - wonder why it would rot the seals. Hmmm.

[rayofleamington]

Thanks 57 - wonder why it would rot the seals.

30 year old seals that have been used with prehistoric brake fluid, new brake fluid (Dot 4 etc..) and temperature (all brakes get hot) and then used with silicon have a well known tendency to fail - often this is due to swelling but could be due to many other seal failure mechanisms.
I'd guess that the combination of different fluids, temperature and lifetime effects are just too much.
On modern stuff, seals are usually only tested with one specific fluid for any given application, so changing fluids is delving into the unknown (not a great idea with brakes)

[bmcecosse]

I think I will just stick to the standard fluid - and bleed it through once a year. The silicone business sounds like a terrible kerfuffle ! Shame really - because I have a bottle of it on the shelf!

[Chris Morley]

the (brakes) may now 'snatch' and they may not have as good a coef of friction as before

As they were nearly new I'm glad that weren't badly glazed. There were some small patches of glazing so I used a fine file to roughen them up. There doesn't appear to be any difference in performance.

Chris, this might be one of my crazy ideas but.....

did the cylinder have any gritty stuff in it?

Not that I could see - in fact the brake fluid wasn't leaking out of the piston. As soon as the brake pipes were disconnected the piston returned to it's normal position. I'm wondering if there was grit in the pipes as the cylinder seems ok....

[doobry]

have you replaced the flexi? It is unlikely (but not impossible) that it is a fluid restriction somewhere in the pipes or in the hose.

[Chris Morley]

The Flexi pipe on both sides were replaced about five months ago - I know that perished flexi hoses are the most likely cause of brake fluid being unable to return.

[catsoup]

Glad you solved it.

Incase anyone else reads this looking for a solution, here is another option.

A few years ago I was too lazy to fit a new master cylinder myself. When I collected the car the mechanic had a big smile on his face, saying that he had got a fantastic brake pedal. He had adjusted it rock hard - with no play.

Apparently the play the manual recomends allows the system to depressurise. The result was that each time I put my foot on the brake, the brakes dragged worse and worse. Eventualy the engine would stall!

Never used that mechanic again....

[Willie]

Yes that is a well known problem on the Minors.....indentified by
the fact that all four brakes will drag! There is a small hole which
allows the fluid to flow back into the reservoir, but only when things
are correctly adjusted!.