Technical Brakes help

[Most Easterly Pandas]

Just a little queery, the 1000CL has been sitting of a while and the brakes have gone funny.

Seems to have lost fluid as pedal goes to the floor, and only a little braking is applied when moving the car in the drive. What is likly to have caused this? Is there anywhere that there is likly to be a leak? Wasn't any fluid visable on the ground, and don't know to much about brakes so don't know where to start

The car has fairly new front end brake components (front flexi pipes and calipers) so not sure if these could be the problem or if it's likly to be back brakes

Many thanks.

Jon.

 

[JimMagill]

Has it actually lost fluid or do you think it has lost fluid just because of the pedal sinking to the floor?

 

[default_user]

Have you tried pumping the pedal to see if pressure builds up?

Have the brakes been used since the new replacement parts were fitted?

Could be several things:

Seal gone in the cylinder so the piston just moves fluid around in the cylinder.

Caliper pistons moving out to take up new position if they haven't been used since being worked on.

Air in the system. This compresses and takes effort out of fluid when the pedal is depressed.

A bit more info is needed for helpful troubleshooting.

 

[Most Easterly Pandas]

It would appear to have lost fluid. The resivour was low and when I pumped the pedal it didn't make the braking any worse or better, nor did the pedal get stiffer. The brake warning/handbrake light did start to flickef though. So dad dug out some brake fluid and topped it up. Made no difference to the pedal except light going off. The car has done a few thousand miles since new brake parts being fitted and this. The car had been sitting a while no problem, and then this suddenly happens. Didn't gradually happen, was fine one start up and move on the drive and then compleatly like this the next time.

Jon.

 

[cartledge_uk]

How long has it been sat since the last move?

Unfortunately, brake fluid is soluble in water, so any "tell tale" fluid marks would be washed away.

I would top up the system, rebleed it (very important), check the brakes work and there are no leaks. Park it somewhere dry if possible, leave it a few days and see if there are any puddles or drops form, if not, pump the living frak out the pedal and see if it leaks. If theres still no leaks put it down to the car fairys.

Has it definitely lost fluid though? if not, and the cap wasn't secure, or damaged the brake fluid may have absorbed water (its hygroscopic), this means that when you compress the pedal, all you are doing is compressing the water in the fluid and the energy applied at the pedal isn't reciprocated in the movement at the brakes (the same happens with air in the system).

 

[Most Easterly Pandas]

Not sure on exact time between the two uses and noticing the difference, but no longer than 5-6 weeks. Try and keep starting up and moving about fairly regular.

 

[default_user]

If there are definitely no leaks in the system and the pedal sinks all the way to the floor with no apparent braking effort then it sounds very like there is a seal gone in the master cylinder. Water in the system wouldn't affect it as it is not compressible (at least for our purposes here on planet Earth. I'm not taking black holes or quantum physics into account).

 

[Most Easterly Pandas]

Buggar.

Err, so how easy is it to change the cylinders then? I assume the whole thing needs to be changed? Is using the one out of the donor 750L A plausable idea?

I really should learn more about brake systems. lol.

Thanks again.

Jon.

 

[cartledge_uk]

Water in the system wouldn't affect it as it is not compressible (at least for our purposes here on planet Earth. I'm not taking black holes or quantum physics into account).

Errr, yes it is, anything can be compressed with enough force.

Not to the extent of air, but more compressable than the brake fluid itself, thats why brake fluid is changed at a service and comes in a sealed tub with the label "dispose after opening" (normally)

But agree a seal somewher

 

[Chas Uno]

Water in the system wouldn't affect it as it is not compressible (at least for our purposes here on planet Earth. I'm not taking black holes or quantum physics into account).

Water will affect the braking system. Brake fluid is hygroscopic, which means it will absorb water. Under heavy braking the water contaminated brake fluid will heat up and the water content will boil, which in turn converts the water into vapour (gaseous state). This leads to a soft pedal and spongey brakes as gas is most definitely compressible, or in a worst case scenario almost non existent brakes will result! On top of that water in the system is likely to promote corrosion.

Definitely don't want water in the braking system!

 

[default_user]

..anything can be compressed with enough force..

Of course. But for all practical purposes water is considered incompressible which is why I mentioned black holes etc. Brake fluid and water have pretty much the same specific gravity so it would not affect the amount of force transmitted from the pedal to the pads. In a system such as we are talking about the losses in pressure due to compression of the fluid would be so minute as to be almost completely ummeasurable, whether it be water or brake fluid.


To get back to the point of the thread:

Assuming the brake master cylinder needs to be changed, it's a fairly straighforward task with competence and the right tools. I wouldn't advise trying it if you're at all unsure of yourself though. If you know anyone who could do it for you, great, enlist their help. If not, you'll need to employ the services of a garage. Parts won't be expensive; in fact the members here will probably have what you need. There are several different variations in the port configuration depending on the model/year though so make sure you get the right one before taking everything apart. (I found this out working on my own car which also needed a new master cylinder).

Before we completely condemn the master cylinder though, make absolutely sure you have no leaks. Take the wheels off one at a time and inspect all the braking components for any signs of liquid. Try to follow each the brake lines from the master cylinder to the relevant wheel to make sure there are no leaks in the lines. If you find anything you suspect might be a leak, clean and dry the area thoroughly and check it again later. If it appears wet again, you have probably found a leak (unless it's raining of course, this assumes a nice dry environment).

 

[default_user]

Water will affect the braking system. Brake fluid is hygroscopic, which means it will absorb water. Under heavy braking the water contaminated brake fluid will heat up and the water content will boil, which in turn converts the water into vapour (gaseous state). This leads to a soft pedal and spongey brakes as gas is most definitely compressible, or in a worst case scenario almost non existent brakes will result! On top of that water in the system is likely to promote corrosion.

Definitely don't want water in the braking system!

Good points, all of which I'm aware of. But MEP says in his original post that he's just moving the car around in his driveway.I don't think we need to consider boiling water in his braking system under these conditions to diagnose the problem.

 

[Most Easterly Pandas]

Good points, all of which I'm aware of. But MEP says in his original post that he's just moving the car around in his driveway.I don't think we need to consider boiling water in his braking system under these conditions to diagnose the problem.

Lol. Yes, correct

 

[Chas Uno]

Good points, all of which I'm aware of. But MEP says in his original post that he's just moving the car around in his driveway.I don't think we need to consider boiling water in his braking system under these conditions to diagnose the problem.

Ah, I should've examined MEP's first post more closely - my mistake

In which case your posts dismissing water in the system is valid as you are correct in stating that boiling in those conditions is unlikely to occur. It sounds to me as if MEP has a failing master cylinder or seals somewhere in the system that's allowing air leaks. One other possibility is that when left standing the sliding calipers have a habit of seizing up. This can cause all sorts of strange braking symptoms, such as brake pistons not retracting properly or the calipers not sliding on the 'wedges' correctly. I had this on one of my Unos (same calipers as many Pandas) and the symptoms were a brake pedal that often needed to be pumped before a firm pedal was felt. Removing and cleaning the brake piston along with the sliding wedges had it all working as it should again

 

[carlt]

The brakes on mine have done the exact same thing , but with no fluid loss .
I am completely baffled as to how this happened .
Perfect brakes when parked up .
The car was stood for a couple of weeks , when trying the brakes the pedal went nearly to the floor before solid pressure .
No amount of pumping the pedal changed the position the brakes came on [ about 1" from the floor]
Brakes work fine , even tried them on mates mot brake machine , its just a little disconcerting and not nice to drive
Anyone any ideas ?
Carl

 

[BenW]

I had a problem with mine, went to uni and came back a few months later to find the brakes weren't as good. They were still perfectly good for normal driving but if i'd needed to do an emergency stop they wouldn't have been as upto the task as you'd expect. I replaced the brake fluid which seemed to solve the problem

 

[Uno Momento]

can i suggest a leaky rear brake wheel cylinder, have a look on the back plate to the rear brakes. The may appear to be wet, if so you'll need to replace the wheel cylinder.

 

[Most Easterly Pandas]

can i suggest a leaky rear brake wheel cylinder, have a look on the back plate to the rear brakes. The may appear to be wet, if so you'll need to replace the wheel cylinder.

Many thanks. Will give it a look at the weekend when home.