Classic cars forum & vehicle restoration.

RotaryBri · Joined: 20 Dec 2007 Posts: 465 Location: Warwick

It is a dreadful feeling when you put your foot on the brake pedal and it sinks to the floor with no braking whatever. This happened to me as I was approaching a junction on the Fosseway. Rapid pumping on the pedal and the use of the handbrake stopped me in time but it was not a nice moment.

I was only half a mile away from my destination, a motoring festival, so I gingerly drove there and then started to look at the problem. My Ro80 is fitted with dual circuit brakes so theoretically you should always have some brakes. I opened the bonnet expecting to see a total loss of brake fluid but I was surprised to find that both master cylinder reservoirs were full.

I asked friends for advice and the consensus of opinion was a servo fault but there were no obvious faults with the hoses etc.

As I had only about 12 miles to get home I decided to take the slow way home driving very carefully but I found that when I applied the brakes all was well and they were working correctly. So what went wrong?

What happened and what caused it? Any advice welcomed.
_________________
Keep Torqueing,

RotaryBri

1976 NSU Ro80

PAUL BEAUMONT · Joined: 27 Nov 2007 Posts: 1281 Location: Barnsley S. Yorks

A servo problem should not leave you without brakes. You would just need to push hard.
How about a very tight brake or sticking calipoer or some such that had caused a vapour lock? otherwise suspect the main seal in the master cylinder. As you say, a dual circuit system should always give you brakes. The vapour lock is about the only way I can think of that might not and then it will depend on how the system is piped up.

Paul

michael1703 · Joined: 22 Jul 2009 Posts: 349 Location: suffolk

Main seal(s) plural, could be faulty/degraded rubbers or the cylinder is corroded

faulty servo would still give you brakes

RotaryBri · Joined: 20 Dec 2007 Posts: 465 Location: Warwick

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

Brake fluid is hygroscopic. That is, it attracts and absorbs water which lowers the boiling point. Eventually critically.
General reccomendations are that brake fluid should be renewed annually. But how many of us do it?
The water content can also cause internal corrosion of brake pipes and components.
How long since you renewed your brake fluid?
Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

peter scott · Joined: 18 Dec 2007 Posts: 7117 Location: Edinburgh

Whilst there may be some water contamination in brake fluid and it will turn to vapour if sufficiently heated I don't think this ever occurs in normal driving. You have to be tearing down the Stelvio pass for noticeable vapourisation. The odd dab on the brakes for approaching a roundabout or two just won't cook it.

Water in its liquid state is not compressible. If the pedal is going to the floor there must be air in the system. This will probably be because of bad seals or bad master or slave cylinder walls.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

I totally agree with you Peter, but some people use brakes a lot harder and often than others. As I live in the Peak District I have perhaps come across more instances of brakes failing than most.

When I worked at Cambridge Tech. We did some tests on old and new brake fluid. Even under pressure some old test examples vaporised their water content at quite low temperatures. When you remember that a brake disc can exceed 1000 degrees C in operation ................?
Oh, and I don't believe any liquid is compressible.
Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

RotaryBri · Joined: 20 Dec 2007 Posts: 465 Location: Warwick

[quote=
How long since you renewed your brake fluid?
Jim.[/quote]

12 months Jim.
_________________
Keep Torqueing,

RotaryBri

1976 NSU Ro80

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

oldtimer · Guest

I feel that I need to enter this erudite discussion but as a pupil only.On a number of occasions and on different forums recently I have heard that loss of the servo doesn't mean loss of brakes but I have to challenge that,from personal experience.If the assertion is "doesn't always mean loss of brakes"then I can accept that,but failure of the servo on my Volvo resulted in the fluid being sucked through the engine and emitted from the exhaust in a cloud of white smoke and definitely no brakes.
I note the input from gents far more knowledgeable than I and for whom Iha ve the highest regard,so perhaps they can take this factor on board,please.
John

Phil - Nottingham · Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham

Quite correct OldTimer - the vacuum will lquickly draw all the fluid into the vac reservoir and then into the engine where it burn. This can happen with only a few applications of the brakes

Suspected servo faults must be investigated and rectified immediately
_________________
Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2