OT; Service intervals

[bert]

In article , Tim Lamb writes

Many years ago there were two systems Lockheed and Girling which used incompatible fluids mineral and veg based.

[bert]

In article , Mr Pounder Esquire writes

Fluid Fade Cars and trucks from Class 1 to Class 6 commonly use a hydraulic brake systems. A hydraulic brake system works by using a non compressible fluid (brake fluid) to transmit the force of a driver pushing on the brake pedal to the brake linings. Air and vaporized fluid are compressible and, if allowed into a hydraulic brake system, the brake pedal will feel spongy and the force transmitted to the lining will be reduced. Just like water, brake fluid can boil and change to a vapour if it gets hot enough. Fluid Fade is the overheating of brake fluid causing it to vaporize. The vaporized fluid will have to be compressed before the system can transmit pedal force to the lining. In most cases, there will be insufficient pedal travel to do both.

The brake fluid used in cars and trucks typically has a boiling point of around 401degrees at sea level. Brake fluid is also hygroscopic, a characteristic which allows it to absorb moisture. Over time, brake fluid will become contaminated with moisture. As this happens, the boiling point of the brake fluid will be lowered, since the boiling point of water at sea level is only 212 degrees. Wet brake fluid has only a 3.5% water content and the wet boiling point of brake fluid drops to 284 degrees. I have tested the boiling point of brake fluid many times and have tested samples that boiled at temperatures as low as 260 degrees. For this reason, brake fluid maintenance recommendations are that it should be flushed about every 4 years.

The boiling point of a fluid is also reduced as altitude is increased. For example, the boiling point of water is reduced by approximately 1% for every 1,000 feet above sea level. So driving mountain passes, which often exceed 11,000 feet, driving Pikes Peak highway that tops out at

14,110 feet, or Mount Evans Road, that tops out at 14,130 feet can easily cause brake fade, by producing a significant drop in the brake fluid boiling point. These locations also put extreme demands on a brake system that cause brakes to get hot and are the most common places brake fade is experienced.

[Mr Pounder Esquire]

Snipped politely.

I would say that 19 years of owning taxis and never changing the fluid

[Adrian]

The problem is that seals - no matter how good - don't like moving across bores that're roughened by rust because of the moisture in the fluid.

[Scott M]

Yes and it just reinforces why I tend to skip straight over them. I've seen brighter glow-worms.

[kshy]

But its perfectly possible to have bores that don?t rust.

[Tim Lamb]

In message , kshy writes

I think the Girling cylinders I struggled with on early minis were some sort of alloy. White corrosion rather than rust.

For such a vital component, improvements seem sadly lacking.

[kshy]

Yeah, bet that's the reason.

Dunno, whoever it was that said that they had had to replace heaps at one time and none in the last few decades shows that dramatic improvements have been made.

[The Natural Philosopher]

really materials have just got better: old hydraulic fluid absorbed water and it collected in wheel cylinders and corroded them, seals went and that was that..

Its unusual today to get that sort of failure.

[Vir Campestris]

I think I replaced every single cylinder on my Mini, which was only 4 years old. Nearly one a year. I haven't had to do one since.

Andy

[reply]

I see you said "used". Don't Citroen use this system any more? What a shame. I used to own a Xantia and remember it fondly.

[newshound]

Agreed. And, thinking about it, most of my failures in the past were on drum brakes with cast iron cylinders. And on cars which were typically ten years old or more.

Disks seem to cope better, perhaps the cylinder is no longer the lowest part of the system, also I guess calipers tend to be aluminium alloy rather than cast iron these days. I did have to replace one front brake caliper on a Daihatsu Fourtrak three or four years ago.