13-01-2019, 11:23 AM
If the OP will indulge one further comment on this detour -
Modern hydraulic brake systems are extremely reliable and should last the expected life of a modern vehicle (let's say 20 years) without trouble. The most common cause of incident is accidental contamination with either solid matter or incompatible fluids (especially mineral oil, which will rapidly kill the EPDM rubber seals in quite small concentrations).
Older systems, with cast iron or steel master cylinders perhaps, were somewhat less durable. Glycol based brake fluids are hygroscopic and absorb water from the atmosphere (principally through the hoses, which are micro-porous). The uptake of water is typically 1.5%/ year until saturation is reached at about 3 or 4%. The principal difference between the grades of DOT brake fluid is boiling point, the higher the grade the higher the BP. However add 3% water and the BP of your DOT4 will plummet below that of a DOT3. This is why your brake fluid should be changed every 2 years. The fluid contains a corrosion inhibitor pack but this of course is not inexhaustible. A system which has been sitting for extended periods with 'vintage' fluid in it will almost certainly be corroded inside leading to seizure or at best rapid wear of seals, which themselves are likely to have aged, hardened and set. This is why fluid soaks your linings.
At one time Castrol fluid was reckoned to have higher lubricity than most, which tends to enhance durability. Not sure if this is still the case.
For the purposes of an A7 system, any modern fluid will do, the mere fact of having fresh fluid and a good air bleed is likely to improve things. Higher DOT grades need only be considered if heavy brake applications in rapid succession are contemplated. From a practical perspective DOT4 is easier to come by (in the UK) than DOT3 these days so it's a no-brainer. I would not advocate DOT 5 or silicone fluid. This is incompatible with glycol-based fluids and most of the arguments in its favour are weak (it is mostly used by the US military, due to its lower viscosity in arctic conditions, scarcely relevant to most 'classic' use).
The great merit of hydraulic systems of course is that they balance the force applied to the shoes evenly at each brake. One brake suddenly becomes four! They have little advantage over a perfectly adjusted cable system (I know, easier said than done). I for one turned my back on 'upgrades' of this kind many years back, if it's a Spridget you want why not just buy a Spridget... I've even taken off the Bowdenex conversion recently and reverted to the standard A7 system, which initially works better! Though yes Steve you are right about steering lock! I haven't quite mastered front cable adjustment yet, the arc compensator doesn't seem to do a lot.
Apologies if I've bored everyone, I'm in post-op and need something to occupy me! Perhaps somebody learned something!
Modern hydraulic brake systems are extremely reliable and should last the expected life of a modern vehicle (let's say 20 years) without trouble. The most common cause of incident is accidental contamination with either solid matter or incompatible fluids (especially mineral oil, which will rapidly kill the EPDM rubber seals in quite small concentrations).
Older systems, with cast iron or steel master cylinders perhaps, were somewhat less durable. Glycol based brake fluids are hygroscopic and absorb water from the atmosphere (principally through the hoses, which are micro-porous). The uptake of water is typically 1.5%/ year until saturation is reached at about 3 or 4%. The principal difference between the grades of DOT brake fluid is boiling point, the higher the grade the higher the BP. However add 3% water and the BP of your DOT4 will plummet below that of a DOT3. This is why your brake fluid should be changed every 2 years. The fluid contains a corrosion inhibitor pack but this of course is not inexhaustible. A system which has been sitting for extended periods with 'vintage' fluid in it will almost certainly be corroded inside leading to seizure or at best rapid wear of seals, which themselves are likely to have aged, hardened and set. This is why fluid soaks your linings.
At one time Castrol fluid was reckoned to have higher lubricity than most, which tends to enhance durability. Not sure if this is still the case.
For the purposes of an A7 system, any modern fluid will do, the mere fact of having fresh fluid and a good air bleed is likely to improve things. Higher DOT grades need only be considered if heavy brake applications in rapid succession are contemplated. From a practical perspective DOT4 is easier to come by (in the UK) than DOT3 these days so it's a no-brainer. I would not advocate DOT 5 or silicone fluid. This is incompatible with glycol-based fluids and most of the arguments in its favour are weak (it is mostly used by the US military, due to its lower viscosity in arctic conditions, scarcely relevant to most 'classic' use).
The great merit of hydraulic systems of course is that they balance the force applied to the shoes evenly at each brake. One brake suddenly becomes four! They have little advantage over a perfectly adjusted cable system (I know, easier said than done). I for one turned my back on 'upgrades' of this kind many years back, if it's a Spridget you want why not just buy a Spridget... I've even taken off the Bowdenex conversion recently and reverted to the standard A7 system, which initially works better! Though yes Steve you are right about steering lock! I haven't quite mastered front cable adjustment yet, the arc compensator doesn't seem to do a lot.
Apologies if I've bored everyone, I'm in post-op and need something to occupy me! Perhaps somebody learned something!