Master Brake Cylinder Replacement

[bmcecosse]

Shiny car! Yes - I bleed by gravity - tube on nipple and into jam jar with a little fluid in the base to cover the end. Open the nipple 1/4 turn - press down the pedal HARD and then v slowly let it back up. Then generally sit back and drink coffee while the fluid syphons out with bubbles.......

[Trickydicky]

Happy New Year Everyone,

Brakes have now been bled and I now have a Brake pedal second to none, totally firm first press, no sinking.

For information (if it helps others) I bled them the conventional 2 man method, bleeding the following way as I struggled to get the air out bleeding the wheels in the order in the manual or by the gravity method, it must have had an airlock in the line. Once fluid started flowing it was straightforward.

first was the drivers side front, then the passenger side front, then the rear passengers side and lastly the drivers side rear. I then went around an bled them the way the manual states untill I had removed all the air and had clean fluid at all wheels. I used about 1/2 of a litre of brake fluid.

I did mention previously that I would check the seals and bore of my old cylinder and offer it to anyone who wanted it, but the bore is pitted at the front, so replacing the seals would not be a suitable fix. To the scrap bin it goes.

Thanks to everyone for there advice

[micstersmoggy]

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
New developments

Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.

[MarkyB]

This sounds very authoritative, where does it come from and what cars does it refer to?
I think that knackered seals, corroded cylinders and pipes are the most common causes of brake failures on Minors.

[Neil MG]

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.)

I agree with Marky, corrosion and cack in the fluid (due to lack of use and maintenance) is the main cause for Minors. Suspect there are few "system failure(s) caused by a contaminant".

For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

How does this work? The bleed screw is at the top, I didn't check but I suspect water is heavier.

[rayofleamington]

For information (if it helps others) I bled them the conventional 2 man method, bleeding the following way as I struggled to get the air out bleeding the wheels in the order in the manual or by the gravity method, it must have had an airlock in the line. Once fluid started flowing it was straightforward.

Sorry to hear you wasted your time trying to gravity bleed a Minor - that advice is very uncommon as it generally DOESN'T work on a car such as the Minor where the master cylinder is so low - gravity does not work up hill!

[bmcecosse]

Ray - it's a syphon - never failed for me......

[rayofleamington]

it's only a syphon if/when the external tube is full. Due to the lack of gravity bleed capability it's not likely to get full unless you press the pedal... so those new to Minor ownershi[p would be better off pressing the pedal to bleed.

[bmcecosse]

Oh yes - you have to press the pedal one full slow stroke to start it.............

[dukeminor1971]

For what it's worth - I used one of those 'one man/woman' brake bleeding kits (a bit of tube and a non-return valve); very simple and worked a treat. As was metioned earlier... replacing the brake return spring was another matter