Technical Brakes feel like there fading

[dtimmins1985]

Morning guys,

Got a problem with my brakes, think i know what is causing it but wanted a second opinion.

Two weeks ago - the brakes felt like there where fading, overheating, had to dab the peddal a little more than usual to get the same effect of braking.

I checked the fluid level and it was a little low, topped this up and it made no difference, however - i noticed that my brake fluid resovoir cap is damaged, inside the cap is a white bit of plastic, i think this part creates an air tight seal when you screw the cap on, well its broke, its no longer stuck to the inside of the cap and i fear its not creating an air tight seal.

Can the broken part inside the cap cause pressure to drop when braking meaning i have to press the pedal more?

Also, the fluid level has dropped again a little bit - its sort of mid way between min and max after topping up nearly two weeks ago.

I have checked for leaks, cant see any anywhere, the fluid is clean, the resovoir is clean and from what i can see - nothing has leaked out.

Can someone advise?

Thanks,
Daniel.

 

[Ralf S.]

The cap only keeps an "airtight seal" so that the fluid doesn't absorb moisture from the atmosphere. Brake fluid is hydrophilic .. and moisture in the fluid can boil out when it gets hot which produces vapour ... which manifests itself as brake fade.

Obviously too, you want it sealed so that the fluid doesn't leak out and to keep small animals and dirt from finding their way into the fluid.

I would replace the cap anyway... the white doodah is part of the fluid level sensor/float arrangement so it may as well be there like Fiat intended.

Do you have a hydraulic clutch? The "brake fluid" also powers the clutch.

If the slave cylinder is leaking then the fluid level will be falling. If the level was low, you may have introduced air into the master cylinder and hence the brake circuit.

In this case.. you need to a) bleed the brakes and then b) replace the clutch cylinder.

The clutch cylinder is usually on top of the gearbox so get your head in there when the engine isn't running. It's about the same size/shape as a cigar tube... but you can trace the pipe from the master cylinder until you find it. If it's the sausage cylinder it'll cost about £40 and is DIY-able.

If your beast is a diesel, then the cylinder is a concentric one (looks like a big wheel bearing) and lives inside the clutch housing - And you just entered a world of pain.. To change the CSC you have to take the gearbox off, so fit a new clutch at the same time. You don't want to do this again for a very long time. The parts are about £80-£100. It is DIY-able if you dismantle half the car and can dead-lift 40kg of gearbox...

Failing that (if you have a cable clutch) then the problem might be a servo fault or it could be the master cylinder (above the brake pedal but on the bulkhead inside the engine bay).. causing an internal leak (fluid by-passing the seals). The master cylinder is quite a cheap/easy one... Servo is ... you don't want to go there.

Bleed the brakes first and then check the clutch slave.. That's the most likely scenario.


Ralf S.

 

[Ralf S.]

I saw on another thread you have a 1.2. That has a hydraulic clutch with the slave cylinder on top of the gearbox. It looks like a little handbrake. Easy one.

Peel back the rubber bellows and see if it shows any fluid. It should be bone dry.

When you go to change it, put a hose clamp on the rubber tube from the master cylinder (though Tape it with PVC tape so that the clamp doesn't bite in to the rubber). That will prevent air being drawn into the system and all the fluid leaking out.

You'll need to bleed the new one but it'll be simple with just a little air in the system.

Ralf S.

 

[Ralf S.]

Something a little like this:

http://www.ebay.co.uk/itm/Fiat-Stil...:Stilo&hash=item5430107344:g:XisAAOSwmtJXU4sN


Ralf S.

 

[Artermis]

How the hell were you getting brake fade on a 1.2, you weren't driving like a plonker were you? Serious question...

I've only ever cooked one set of brakes, once, schooling some BMW. That was on an Alfa 156 GTA (3.2 V6) from about 120mph braking as hard as it'll give into a 20ish mph 90 degree left. That was running 305mm brembo 4 pots on the front and turned both front discs to cheese immediately and ended running for that day.

That cost me four corners of drilled and grooved discs and all new pads for the pleasure. Praise the lord for proper mechanical limited slip differentials and bridgestone tyres or I'd probably have been wearing a wall of pirellis.

If you're on a track day like I was or driving like your bottom is on fire then you have to expect some issues. We took my mates Ford Focus diesel estate as a support vehicle to the nurburgring a few year back now (rest of crew on bikes). We took it round for an enthusiastic run for a laugh and the rear brakes caught fire. Didnt stop smoking for a good 20 minutes in the car park. The locals in the 911 GT3 RSs thought it was bloody hilarious.

If you were driving more sensibly and still had an issue then you probably need to be more concerned.

As Ralf says the obvious thing to do is check for leaks and solve your cap issue. Brake fluid is hydroscopic, so will naturally take on board water, which will boil at a much lower temperature than the fluid. This causes gas in the system, gas can be compressed and you get spongy peddle.

Brake fluid is a service item which gets often overlooked. It should be replaced about every five years ish I think. If its not been replaced then you should think about bleeding some fresh fluid through, that will help. Bleed in opposite corners. As Ralf says you will need to include the clutch.

Check the wheel arches that the pipes haven't been rubbing and could spring a leak (although it's not that common). The pipes can perish too which is more likely. This can let fluid out as well as moisture in.

Check the metal lines that run front to back for rust. They may well be covered so remove and inspect.

Clutch is probably the most likely suspect as the cylinders take quite a bit of use and abuse.

Last thing to do is to check the discs, pads and calipers. If the calipers seize up (rears are really good at this) then they'll generate excess heat. They're single piston sliders so if they stick on the slider pins the outside pad can look full of meat whilst the inside one is wearing close to the bone.

If you are doing track days or something and this is an issue possibly consider bigger brakes. I dont know if the larger engines (abarth, jtd) have larger brakes which might help you if you can find a compatible setup.

 

[dtimmins1985]

Thanks for advice guys.

I will check clutch cylinder tomorrow.

Checked everywhere else and no leaks.

Brake fade, lol... my old Nissan micra used to brake fade and overheat the brakes until I converted to Nissan sunny calipers and discs... which were vented and larger and forced me to put bigger wheels on lol... after upgrade was done there was no brake fade... I did drive like an idiot in the Nissan but that was 10yrs ago and I've sort of changed into an old grandpa driver...

So the stilo is not cooking the brakes, it feels like a pressure issue in the system.

Clutch is fine, will check cylinder tomorrow

Can someone get me the part number for the cap? Couldn't find it on eper.

Thanks guy, knew I could count on a reply from you two

 

[Mytheroo]

i thought reservoir caps weren't airtight as they have to let air in to replace the fluid that gets pushed through? Which is why some clingfilm in the cap helps to avoid fluid loss when the system is open somewhere.

 

[Artermis]

They have to hold a decent degree of seal as you don't want brake fluid sloshing out. Brake fluid is evil, evil stuff and will burn through all sorts, least of all your paintwork.


The volume of fluid you're pushing isn't enough to cause any significant issue for a vacuum to form anyway. The ABS pump will more than cope with that.


If it's feeling spongy then sounds like time for a brake fluid change. Depends how you're feeling it is easy enough to do as a DIY single handed. Halfords sell a nice cheap and easy to use easy-bleed bottle. It does make it easier with a willing second pair of hands or bribed wife / girlfriend.


As for replacement cap, just go on eBay and find someone breaking a stilo you'll pick one up for pocket change I'm sure.

 

[Mytheroo]

is there a 1-way valve in the cap do you think? This would explain the clingfilm working across the opening, whereas I (wrongly?) thought it was sealing the threads.

 

[dtimmins1985]

Artermis, I get wat your saying...

Tried to find a cap of a breaker but no joy at present.

Mytheroo, I also get what your saying... the cap has a white sleeve inside it, to seal the yellow lid securely and air tight.

In older cars, there is a yellow cap with a tube / cylindricle type fitting going into resovoir, on the stilo you don't have this, it's a type of filter or **** grabber... also seals the system once yellow cap is on, on the stilo that tube is in the resovoir already and the cap is sealed with a white thing flush to the cap rim when you screw it on, mines loose and came away...

Still need to check clutch feed, got to change passenger side headlamp bulb this weekend so it's bumper off for a short time, will check clutch feed and cylinder then.

 

[Mytheroo]

hmm, sounds like I need a proper look at mine

 

[dtimmins1985]

Ok so amidst another issue I have with the stilo... I'm ready to check my clutch cylinder.

Replaced the bulbs, didn't take bumper off, just took battery out to try fix my central locking issue with fob and I prised up the battery tray with my son, gained access to rear of headlight and swapped out the bulbs.

Anyhow central locking still not solved by taking battery off but I have new bulbs (working ones) yey... oh and I also have fog lamps now, idiot who owned it before took out the H1s and never replaced them.