Brakes driving me mad! - Long pedal travel

[Ryanfsr]

Hi all

 

Ive been having an issue with my rear brakes recently in that they were sticking slightly causing the wheels to not rotate as freely as they should.

 

Purchased myself set of new piston seals and went about fitting them yesterday. All went to plan, disconnected calipers; un-wound the pistons out; removed old seals; installed new ones with a bit of red rubber grease to aid in lubrication, and refitted everything.

 

Bleeding wise I've got myself a Gunson Eezibleed which I rigged up as per the instructions; cracked open the bleed port and air/fluid started to trickle out. I let it flow a little until no air bubbles could be seen in the tube and closed the bleed port. Disconnected all the Eezibleed system, and refitted the master cyclinder cap.

Jumped in the car, started the engine and pumped the brake pedal a few times.... pedal went straight to the floor!

Repeated the bleed process again (no air bubbles were visible which I thought was a little odd...) but still the brake pedal went to the floor!

 

Decided to resort back to the two man bleeding method with my dad sat in the car and a block of wood under the brake pedal. First push of the pedal and a load of air shot out of the bleed port!!! (Makes me wonder if the Eezibleed system is all its cracked up to be!?)

Did this a couple of times until no bubbles were present again - keeping an eye on the fluid in the master cylinder of course

 

Jumped back in the car and the brakes certainly felt a lot better, but it did feel as if I had more travel in the brake pedal until the brakes started to engage.

Took the car for a careful spin round the block, performing a couple of hard stops to try and dis-lodge any more trapped air, and then bled the brakes once more using the two man method. (No air came out this time, so I felt pretty sure i'd removed all air from the system), but the brake pedal still has quite a lot of travel before the brakes engage!

I feel as if i've been quite thorough in the bleeding process, so I can't seem to find a reason why it's doing this?

 

Any thoughts?  FU-BAR'ed master cylinder maybe?

 

Cheers

 

 

Edit: Car's a Fabia vRS btw, with 256mm upgraded rear brakes

[Olly87]

Did you bleed the whole brake system or just tears buddy? Starting from NSR as furthest from master cylinder, pressure bleeders are a pain. I fitted clutch at work other day and still needed to be manually bled after using pressure bleeder. I would just persevere mate to get pedal 100%. Only other thing is if you have small leak somewhere under pressure? 

 

Olly

[Ryanfsr]

Did you bleed the whole brake system or just tears buddy? Starting from NSR as furthest from master cylinder, pressure bleeders are a pain. I fitted clutch at work other day and still needed to be manually bled after using pressure bleeder. I would just persevere mate to get pedal 100%. Only other thing is if you have small leak somewhere under pressure? 

 

Olly

 

Just the rears as they were the only ones I removed to replace the seals.

 

Just been searching and managed to find this thread: http://www.briskoda.net/forums/topic/308778-changed-rear-calipers-now-i-have-really-long-brake-pedal-air-in-system/

 

Seems like this guy had exactly the same issues i'm having!

One question though.... If I have the Eezibleed system attached and the bleed port open pushing fluid through, is it ok to press the brake pedal down and then release, or will I need to close off the bleed port before releasing the pedal?

[Olly87]

You need to bleed the whole system mate, best practice is to always bleed whole brake system. You will never achieve a good pedal otherwise mate. So start nsr then work forwards. I usually do 10 manual pumps from the person on the brake pedal per brake etc. 

 

I would try that and see how you get on mate, I've tried just bleeding rears when changing a caliper and had to re bleed again as trying to rush etc. 

[Ryanfsr]

Ok thanks that, job for the weekend!

If I have the Eezibleed connected though pushing fluid through, can I pump the pedal without having to open and close the bleed nipple like you would normally do bleeding the two man method?

[KenONeill]

Er, DO NOT use a pressure bleeder above 15PSI, or you'll pump air into the ABS block, after which you need to bleed the system using VCDS to get that air out again. Actually, that might explain your issue.

[Ryanfsr]

Er, DO NOT use a pressure bleeder above 15PSI, or you'll pump air into the ABS block, after which you need to bleed the system using VCDS to get that air out again. Actually, that might explain your issue.

Don't worry, it states that quite clearly in the Eezibleed instructions so I made sure to deflate the spare tyre to 15 psi before I connected it all up!

[sepulchrave]

Did you clamp off the rear brake hoses before removing the calipers, if not air will have got everywhere and you'll have to re-bleed the entire system from scratch.

[Ryanfsr]

Did you clamp off the rear brake hoses before removing the calipers, if not air will have got everywhere and you'll have to re-bleed the entire system from scratch.

Nope because prior to carrying out the job I read that you shouldn't because you run the risk of damaging the brake line.

I did however submerge the end of the hose in a bag of brake fluid when removed from the caliper to try and prevent air being introduced

[sepulchrave]

Nope because prior to carrying out the job I read that you shouldn't because you run the risk of damaging the brake line.

I did however submerge the end of the hose in a bag of brake fluid when removed from the caliper to try and prevent air being introduced

 

Ok, well you need to start from scratch then and bleed the whole lot.

[KenONeill]

Don't worry, it states that quite clearly in the Eezibleed instructions so I made sure to deflate the spare tyre to 15 psi before I connected it all up!

That's new from the last time I was talking to anyone using an Eezibleed. 

[sepulchrave]

That's new from the last time I was talking to anyone using an Eezibleed. 

 

You're like that character off Harry Enfield "You don't want to do it like this, you want to do it like that"

 

 

In thirty years of using an Eezibleed I have never worried about the air pressure, the only reason that 15 psi guff is there is so that a hose can't pop off the device and shower you or your paintwork with brake fluid leading to a potential lawsuit.

There is NO mechanism whereby air from the spare tyre can migrate through the fluid and into the brake system unless you run out of fluid, how many psi of pressure do you imagine the seals in the ABS system can cope with safely?

[Ryanfsr]

It actually states 20 psi in the manual, but I ran it a little less to be on the safer side.

But what Sepulchrave says sounds right though. The fixings on the Eezibleed kit are not the best in the world, more so on the cap that goes onto the master cylinder.

Thanks for the advice though everyone! More bleeding to be done this weekend I guess!

Can someone let me know though that if I have the Eezibleed system running, am I ok to pump the pedal without having to open/close the bleed nipple?

[TMB]

Can someone let me know though that if I have the Eezibleed system running, am I ok to pump the pedal without having to open/close the bleed nipple?

 

Not sure why you'd want to pump the pedal whilst the Eezibleed is running? The whole point of the Eezibleed is so that you don't have to touch the pedal.

[sepulchrave]

Can someone let me know though that if I have the Eezibleed system running, am I ok to pump the pedal without having to open/close the bleed nipple?

 

You don't need to pedal it, but you may need to bleed the ABS valve block as well now if there's air in it, I didn't need to because I didn't drive the car with air in the brakes, I just changed all the fluid out after replacing the brake master and did the clutch at the same time.

[Ryanfsr]

Not sure why you'd want to pump the pedal whilst the Eezibleed is running? The whole point of the Eezibleed is so that you don't have to touch the pedal.

 

Because as I said in the first post, i bled the brakes twice with the Eezibleed system and the pedal went straight to the floor on both occasions.

 

It wasn't until I resorted back to the old two man method of opening/closing the bleed port whilst having someone press the pedal that a load of air shot out. Almost seemed as if there wasn't enough 'ooomph' from the Eezibleed kit to evacuate the trapped air within the caliper.

[TMB]

Because as I said in the first post, i bled the brakes twice with the Eezibleed system and the pedal went straight to the floor on both occasions.

 

It wasn't until I resorted back to the old two man method of opening/closing the bleed port whilst having someone press the pedal that a load of air shot out. Almost seemed as if there wasn't enough 'ooomph' from the Eezibleed kit to evacuate the trapped air within the caliper.

 

Fair enough mate, not had that issue myself. I use the Eezibleed at 20 psi and it's always worked OK for me.

[KenONeill]

You're like that character off Harry Enfield "You don't want to do it like this, you want to do it like that"

 

 

In thirty years of using an Eezibleed I have never worried about the air pressure, the only reason that 15 psi guff is there is so that a hose can't pop off the device and shower you or your paintwork with brake fluid leading to a potential lawsuit.

There is NO mechanism whereby air from the spare tyre can migrate through the fluid and into the brake system unless you run out of fluid, how many psi of pressure do you imagine the seals in the ABS system can cope with safely?

I tell you what; you try having that argument about not using over 15PSI on a pressure bleeder with Tech1e, or another VAG master tech. After which I will expect your apology. 

[Ryanfsr]

But surely 15psi worth of pressure is easily achieved through everyday braking?

[sepulchrave]

I tell you what; you try having that argument about not using over 15PSI on a pressure bleeder with Tech1e, or another VAG master tech. After which I will expect your apology. 

 

VAG mastertechs use Eezibleeds?

 

I'm an engineer Ken not a technician, if I can't see a good reason not to do something then I'll do it because my training means THINKING about everything rather than just parroting received wisdom.

 

Now are you going to tell me why I can't use more than 15 psi please given that I've been doing it on every car, bicycle and motorcycle I've owned or worked on for so long.

[Olly87]

We use a VAG specific brake bleeding unit which is the same a cross all VAG main dealers. Awesome bit of kit, unsure of the exact psi it's regulated too tbh, it's run off a huge compressor but has regulation valves built inside etc to make sure everything is safe for the vehicle. 

[KenONeill]

1. VAG mastertechs use Eezibleeds? 

I'm an engineer Ken not a technician, if I can't see a good reason not to do something then I'll do it because my training means THINKING about everything rather than just parroting received wisdom. 

Now are you going to tell me why I can't use more than 15 psi please given that I've been doing it on every car, bicycle and motorcycle I've owned or worked on for so long.

1. I did not say that. VAG procedures require the use of vacumn bleeders, which intrinsically means not using >15PSI. Since you say that you're "an engineer" I'll presume you understand why this is the case.

You're not actng like an engineer, but like a hacker with this "I'll do it unless I can see a reason not to" attitude rather than a "use best practice" one.

Are you listening? It is proven that positive pressure above 15PSI can drive air bubbles into the ABS block. If you've never done this, it means you've got away with it, not that it's good, never mind best, practice.

[sepulchrave]

Ok, just to recap:

 

Er, DO NOT use a pressure bleeder above 15PSI, or you'll pump air into the ABS block, after which you need to bleed the system using VCDS to get that air out again. Actually, that might explain your issue.

 

I still have no idea where this notion that forcing fluid into a system under pressure will 'magically' cause air to fill the valve block, where does this air come from?

So I said:

 

There is NO mechanism whereby air from the spare tyre can migrate through the fluid and into the brake system unless you run out of fluid

 

Then you said:

 

I tell you what; you try having that argument about not using over 15PSI on a pressure bleeder with Tech1e, or another VAG master tech. After which I will expect your apology. 

 

Attempted expert invocation because you didn't answer my question, why is it a problem to push clean fluid through a system at >15 psi?

I will however apologise for taking the mickey if you're feeling sensitive, it was good natured humour at the expensive of your slavish procedural pedantry.

However we still don't have an answer do we.

 

 

1. I did not say that. VAG procedures require the use of vacumn bleeders, which intrinsically means not using >15PSI. Since you say that you're "an engineer" I'll presume you understand why this is the case.
2. You're not actng like an engineer, but like a hacker with this "I'll do it unless I can see a reason not to" attitude rather than a "use best practice" one.
3. Are you listening? It is proven that positive pressure above 15PSI can drive air bubbles into the ABS block. If you've never done this, it means you've got away with it, not that it's good, never mind best, practice.

 

 

Ok, fair accompli incoming.

 

1.

 

A vacuum bleeder uses atmospheric pressure to push the fluid out of the system so about 14.3 psi, the pressure of the compressed air feed to the device is irrelevant.

Vacuum bleeders are truly universal and don't require any extra kit, they just connect to the bleed nipple of any vehicle, they can't spray fluid around if they fail and as long as you keep the master cylinder topped up they are easier and safer to use.

They are also very expensive and require a high pressure air supply.

 

2.

 

There is nothing wrong with the pressure bleeding principle, as long as you have a master cylinder cap that fits and seals properly and the device is correctly assembled, filled and doesn't fail during use they are very effective indeed.

 

3.

 

So here we are:

 

Many ABS systems actually require the use of a pressure bleeder rather than a vacuum bleeder, GM Delco units for example require at least 35 psi to clear the valve block of air pockets, many valve blocks require the cycling of the solenoids to release pressure from the accumulator to guarantee that the system is fully purged and every line has been open to allow all the entrained air to escape.

When I replaced my master cylinder I knew this could be a problem but reasoned that under normal circumstances the valves are all wide open allowing full fluid pressure to all the calipers and that the system will only become active once a lockup is detected electronically.

Given that the hydraulic pressure in the brake system can exceed 1000 psi I knew that my little pressure bleeder wasn't about to force open any valves or flip any seals so I went ahead and changed out all the brake fluid starting with the longest pipe run and finishing with the clutch. Bingo, no air and a rock solid pedal as I expected.

 

To summarise:

 

There is no reason why an ABS valve block will get air trapped in it unless it becomes active while there is air in the system or you have disconnected the block to repair or replace it. Not all ABS valve blocks are the same but they all work on the same principle, this is the engineering bit, I understand how pretty much everything works, why it does what it does and how, I don't have the model specific experience of a trained technician but you can blindfold me and stick anything mechanical under my nose and I'll know what I'm looking at and therefore how to go about testing or repairing it.

 

So, I've apologised for taking the mic, I've explained why I'm not a 'hacker', a boring part of my job is to specify method, assess risk and actually define 'best practice' for the applications I've worked on, I've listened to you as patiently as possible, now show me the proof you're referring to please.

 

You can keep your apology, I don't need it.

[Ryanfsr]

Update:

Bled the brakes again over the weekend with the Eezibleed. Tried a different approach this time though. Rigged it up as I had done before, but this time once I'd opened each of the rear bleed ports I removed the calipers and rotated them around whilst fluid was being pushed through. (I had them loosly attached to the carriers for easy and quick removal) Hey presto!! More air bubbles came out!

I can only guess that air is quite prone to getting trapped inside the rear calipers due to all the handbrake mechanism thats built within them.

 

Whilst I was at it I did the fronts aswell so the entire brake system had fresh fluid. Brake pedal feels SO much better!

 

 

One thing I do want to ask though, even though i'm running this 312 and 256 setup I have to say the initial bite to the brakes has always been quite vague ever since I've had them fitted. Not saying they're not powerful by any means; the ABS kicks in no problem at all when I brake heavily, but having driven my mums Golf (1.6 Tdi Bluemotion) and dads Passat (2.0 Tdi) this week I about put myself through both their windscreens on the first couple of brake applications before I got used to them. Do you reckon this suggests somthing is not quite right, or has the Fabia always had vague biting brakes compared to other VAG platforms?

[Breezy_Pete]

Well done for sorting the bleeding bleeding.

 

I wouldn't describe the Fabia's bite as vague at all, I frequently seem to stop dead on the spot in the missus's Fabia by comparison with my Mk2 Golf, both with 239mm VWII/Skoda equiv. systems up front.  Possible servo vacuum issue on yours? (And my Golf?  )