VW say I have already damaged my engine?

KiNeL

The characterisation of mega mile company cars being thrashed to death wrecks is as facile as the suggestion that all MSE'rs are skint and can only afford to buy bangers.

Those of us who have not been brainwashed and do not need the latest registration number on our drives all the time to impress the neighbours know what is a good buy and what isn't.

Not so long ago I purchased a 4 year old 140,000 mile VW Golf estate which had belonged to a major UK company, it came with a complete service history and was like a new car.

In three years I drove it up to 241,000, and without spending a penny on it for anything other than scheduled routine maintenance, then sold it on to a friend who took it up to 310,000 before the turbo finally gave up the ghost. It was still on it's original clutch BTW despite being regularly used to tow an 8m3 box trailer.

Low mileage cars being worth a premium is a firmly ingrained myth in the minds of uninformed buyers perpetuated by the motor trade for obvious reasons.

Put the OP's car beside an identical one with 100,000 more miles on it and I'll tell you which I'd buy !

Rover_Driver

usefulmale wrote: »

At no time is the brake system open to the atmosphere.

It is vented to the atmosphere.


Air is admitted to the master cylinder via the master cylinder cap, if it was not, you could have vacuum problems holding back the fluid as the level drops.
As brake pads wear, the pistons in the brakes stay further out, and so the fluid level in the master cylinder drops, replaced by the air (and why you periodically have to top up the fluid).
When you renew the pads, you have to push the pistons back, pushing that extra fluid back up into the master cylinder.

facade

Rover_Driver wrote: »

It is vented to the atmosphere.


Air is admitted to the master cylinder via the master cylinder cap, if it was not, you could have vacuum problems holding back the fluid as the level drops.
As brake pads wear, the pistons in the brakes stay further out, and so the fluid level in the master cylinder drops, replaced by the air (and why you periodically have to top up the fluid).
When you renew the pads, you have to push the pistons back, pushing that extra fluid back up into the master cylinder.

There is a rubber diaphragm under the cap that seals the system.
The diaphragm is concertina folded and expands downwards as the fluid level falls.
(Or there is on both the Japanese cars I have....)

However, pretty much everything is slightly porous so it is best to change the fluid every few years, I change mine whenever a brake component gets replaced , but it only costs a few pounds for the fluid and a few minutes with a spanner with an assistant to press the pedal on command, rather than the £50 a dealer charges for even less work, and cheaper priced fluid :eek:

Stooby2

Rover_Driver wrote: »

It is vented to the atmosphere.


Air is admitted to the master cylinder via the master cylinder cap, if it was not, you could have vacuum problems holding back the fluid as the level drops.
As brake pads wear, the pistons in the brakes stay further out, and so the fluid level in the master cylinder drops, replaced by the air (and why you periodically have to top up the fluid).
When you renew the pads, you have to push the pistons back, pushing that extra fluid back up into the master cylinder.

It depends on the car / vehicle. Most have a rubber diaphragm that seals the fluid from the atmosphere and expands to prevent the vacuum problem above. The area above the diaphragm is vented to the air. This prevents moisture entering the fluid. It's a common mistake to put new brake pads in and not collapse the diaphragm as some don't snap back.

Stooby2

Lol...duo post.

usefulmale

Rover_Driver wrote: »

It is vented to the atmosphere.


Air is admitted to the master cylinder via the master cylinder cap, if it was not, you could have vacuum problems holding back the fluid as the level drops.
As brake pads wear, the pistons in the brakes stay further out, and so the fluid level in the master cylinder drops, replaced by the air (and why you periodically have to top up the fluid).
When you renew the pads, you have to push the pistons back, pushing that extra fluid back up into the master cylinder.

Sorry, no, it's not. If there is a link between a high pressure system and a low pressure one, fluid or gas will leak from the high pressure to the low. It's basic physics.

It's a bit like saying you can change a tap without turning the water off, or opening the airlock on a spacecraft.

If air could be admitted via the master cylinder cap, fluid would certainly be expelled through the same cap as soon as the brake pedal was applied.

Rover_Driver

usefulmale wrote: »

If air could be admitted via the master cylinder cap, fluid would certainly be expelled through the same cap as soon as the brake pedal was applied.

The fluid in the master cylinder is not under pressure at any time, it is just a reservoir for the system. Air is admitted to allow the the fluid level to drop and prevent a vacuum.


Is only the fluid in the system between the pedal slave cylinder and the wheel brake cylinders that is under pressure when the pedal is pressed.

usefulmale

Rover_Driver wrote: »

The fluid in the master cylinder is not under pressure at any time, it is just a reservoir for the system.


It is only the fluid in the system between the pedal slave cylinder and the wheel brake cylinders that is under pressure when the pedal is pressed.

How does the fluid move from the master cylinder to the slave cylinder?

Rover_Driver

By entering the slave cylinder, just in front of the piston.


When the pedal is pressed, the slave cylinder piston moves past that point and then pressurises the fluid in front of it.

usefulmale

Rover_Driver wrote: »

By entering the slave cylinder, just in front of the piston.


When the pedal is pressed, the slave cylinder piston moves past that point and then pressurises the fluid in front of it.

OK. I have read about people bleeding brakes with the brake fluid reservoir cap off and having brake fluid shoot up like a geyser.

Surely that shouldn't happen with the arrangement you describe?