Technical bleeding the brakes

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Technical bleeding the brakes

gianmarko

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hello all

my B has a very spongy brake pedal and travel is really excessive. it has been like this since i bought it

i have replaced all the brake hoses and done a thorough circuit bleed using a professional equipment. however, even if slightly better, the pedal is still spongy and sinky
pressurizing the circuit (at 2 bars using the pro equipment or an eazy-bleed kit) the pedal travel and sponginess goes away

short of putting the B on its roof, which she doest have, is there any trick to remove all air from the circuit???

rear calipers have a funny arrangements, the hose is higher than the bleeding nipple!! i have checked other barche and the ePer and it looks like it is normal, however bleeding the rear circuit is a PITA, air tends to stay trapped in the top part of the hose
 
do you really know any method by which i can change the brake hoses and bleed the whole system recycling the old fluid? :p

I suppose you could drain off the old fluid first first, collect it and then re-cycle? :chin:
 
hello all
done a thorough circuit bleed using a professional equipment. however, even if slightly better, the pedal is still spongy and sinky
pressurizing the circuit (at 2 bars using the pro equipment or an eazy-bleed kit) the pedal travel and sponginess goes away
I've just changed our 'B' with ABS (05 plate) fluid a while ago with no problems. However I DID NOT use any pressurised techniques and did it the old fashioned way with pure pedal pumping only.

On early ABS systems (10 years or more ago) I believe that you had to use a pressurised system to change/replace fluid.

I also seem to recall reading somewhere that modern ABS system either do not like pressure bleeding and/or repspond better to traditional pedal puming method.

Try using just the brake pedal and an assistant.
 
Are we losing something in translation? Why would anyone want to 'recycle' brake fluid? Do you mean 'replace'? Although brake fluid isn't cheap, it has to be worth trying. If your using a pressurised bleed kit, just keep topping up the master cylinder and eventually you will blow all the old fluid out and replace it with new. Hope this helps.

Steve
 
recycling was just a joke, because someone asked if i had old fluid, which is quite unlikely after changing brake hoses and doing a full bleed

i think master cylinder is ok, i am pretty sure there is some air trapped somewhere.
while bleeding, i noticed the rear brakes bleed very slowly, and i couldnt locate any rear brake bias valve.


as for the "pumping pedal" technique, that is not good at all
the master cylinder usually only use a little portion of the travel, the unused part of the cylinder tends to corrode, and using the pumping system usually knackers the piston seals against the cylinder corrosion. pressurizing the circuit is a much better system.

Are we losing something in translation? Why would anyone want to 'recycle' brake fluid? Do you mean 'replace'? Although brake fluid isn't cheap, it has to be worth trying. If your using a pressurised bleed kit, just keep topping up the master cylinder and eventually you will blow all the old fluid out and replace it with new. Hope this helps.

Steve
 
as for the "pumping pedal" technique, that is not good at all
the master cylinder usually only use a little portion of the travel, the unused part of the cylinder tends to corrode, and using the pumping system usually knackers the piston seals against the cylinder corrosion. pressurizing the circuit is a much better system.

Sorry DO NOT AGREE . Full Stop. Your master and all slave cylinders should always be in the best condition they can be. I'd rather find/expose an internally (at depth) rusted/damaged cylinder sooner than later. If pumping a pedal damages the seals then the device was not fit for purpose. Full Stop.

Besides this minor point, are you absolutely certain about how modern ABS pumping and accumalator circuits work? let alone the traction control, ESP, emergency braking etc. functions built in work?

Most garages I know use two technicians (or one way bleed valves) and pedal pumping to change the fluid on modern cars. As I pointed out some of the older/earlier ABS units (go back to middle 80s) had to be pressure bled. That is not the case for modern systems.

You may have a problem but do not write off old pedal power. Like I originally said I recall (but cannot quote or provide reference at this time) to information that suggested that modern ABS/ESR/Traction Control/Emergency Braking units do not like being force fed with no associated pedal action.
 
I have to agree with Nick here. I apologise for taking the 'recycling' comment too seriously but, if you have a spongy pedal, then there's a good chance that the piston in the master cylinder is already working towards the extent of its possible travel and working against any possibly corroded surfaces. Just a further point, although uncommon, older rubber brake hoses can soften and balloon under pressure giving the 'spongy pedal' syndrome. Hope you get it sorted soon.

Steve
 
Out of interest, has anyone ever seen a corroded master cylinder? They're permanently flooded with fluid unless left off the car for years in the open so on the car the fluid should stop any corrosion.

I ask as I've changed several and never seen internal corrosion. I have seen it on wheel cylinders, but this has usually been where the dust seal isn't in the best of conditions.
 
i am not a professional mechanic, but all the cylinders i have seen, being them masters or slaves or calipers, were corroded internally and the reason is very simple. glycole based fluids are hygroscopic and will absorb a lot of water, which corrodes the pistons. and who ever changes the brake fluid?

the advice of NOT using pedal pumping for bleeding the circuit came from a professional mechanic. besides, pressurizing the system is common practice, lots of specific equipment exist and i cannot see how the max 2 bars used can possibly damage a system designed to routinely withstand 50 or more.

as for old rubber brake hoses getting soft DUH :p do you read my posts?

and this is not rare at all. expecially old fiats suffer from this chronic disease.



I have to agree with Nick here. I apologise for taking the 'recycling' comment too seriously but, if you have a spongy pedal, then there's a good chance that the piston in the master cylinder is already working towards the extent of its possible travel and working against any possibly corroded surfaces. Just a further point, although uncommon, older rubber brake hoses can soften and balloon under pressure giving the 'spongy pedal' syndrome. Hope you get it sorted soon.

Steve
 
I assumed that by posting your story on here that you were inviting a response? Having responded with a genuine suggestion, I'm disappointed to see the

"as for old rubber brake hoses getting soft DUH do you read my posts?"

In answer to this question, 'No, I haven't read this in any of your posts' friend. I still, however, hope that you can resolve your brake issue, especially if you plan on coming up behind me at the lights.

Steve
 
i am not a professional mechanic, but all the cylinders i have seen, being them masters or slaves or calipers, were corroded internally and the reason is very simple. glycole based fluids are hygroscopic and will absorb a lot of water, which corrodes the pistons. and who ever changes the brake fluid?

the advice of NOT using pedal pumping for bleeding the circuit came from a professional mechanic. besides, pressurizing the system is common practice, lots of specific equipment exist and i cannot see how the max 2 bars used can possibly damage a system designed to routinely withstand 50 or more.

as for old rubber brake hoses getting soft DUH :p do you read my posts?

and this is not rare at all. expecially old fiats suffer from this chronic disease.

29 psi is a lot to pressurise the master cylinder, you have probably inverted the cups inside the master cylinder because you have used too much pressure.
I wouldn't feel comfortable using any more than 14psi of pressure.

The brake system can handle a lot more than 2 bar of pressure, but that is after the master cylinder, not through it.

Yes brake fluid is hygroscopic, however what is the key ingredient missing to begin corrosion?

If you have air inside your system then corrosion is the last thing you should be worrying about!
 
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my dear friend, i really thank you for taking the time to answer me, however, in my first post i stated:

"i have replaced all the brake hoses and done a thorough circuit bleed using a professional equipment"

so suggesting to replace the brake hoses or replacing the fluid means you folks either dont read my posts or are just taking the ****. which is perfectly ok. :p :p
feel free to think im an idiot. many think the same just looking at the car i drive. :D:D:D

at any rate, looks like nobody has a clue on what is happening in my brakes. which is perfectly ok too. is probably some air bubble trapped somewhere.

however, to those who claim that pressure bleeding the brakes will damage them, please go and look how a brake pump works. if applying 2 bars (it was probably less, the equipment gauge said max 2 bars and i was not looking at that gauge while working with spanners) will invert the cups, same will do a small amount of pressure on the pedal.

" Yes brake fluid is hygroscopic, however what is the key ingredient missing to begin corrosion?"

water is a very powerful solvent and will contain oxygen and other gases, else all fishes would be dead :eek:
on top of that galvanic corrosion just needs water as electrolyte. otherwise the titanic (or the cooling sleeves of your engine) would be in pristine condition.


I assumed that by posting your story on here that you were inviting a response? Having responded with a genuine suggestion, I'm disappointed to see the

"as for old rubber brake hoses getting soft DUH do you read my posts?"

In answer to this question, 'No, I haven't read this in any of your posts' friend. I still, however, hope that you can resolve your brake issue, especially if you plan on coming up behind me at the lights.

Steve
 
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