Bit late to say it, but I'd put problem down to air in system. Years ago I got  an easy bleed system which consisted of a sprung valve on the nipple.Back off thge nipple and pump brake. Fluid + air came out and once pressure was released, the valve  closed off the system . Tighten the nipple and no fluid came out.

It's known that pedal feel and response may be an issue with the 312s. Caliper piston area is larger but you're using the same master cylinder. Therefore you have a longer, more gradual pedal than with the 288s.

 

A number of topics around the Fabia1 section over the years.

I'm pretty certain there's no fluid now within the lines as the pedal is nice and firm again. Surely the pedal would still be mushy if there was?

 

I did read up on the servo/vacuum issues, and did find a thread on how to test if its working.

Am I right in saying that you; 

1. pump brake pedal with the engine off 
2. brake pedal goes hard 
3. maintain pressure on brake pedal and start engine
4. pedal should drop a couple of inches
5. whilst maintaining brake pressure, pedal should drop a little further, but not completely hit the floor?

 

Got to book the car in for its service at Unit 18 in a couple of weeks anyway, so I may just get Ali to give things a once over aswell for peace of mind

 

It's known that pedal feel and response may be an issue with the 312s. Caliper piston area is larger but you're using the same master cylinder. Therefore you have a longer, more gradual pedal than with the 288s.

 

A number of topics around the Fabia1 section over the years.

 

That certainly makes sense! Takes me back to those physics lessons on Pascals law haha 

I'm pretty certain there's no fluid now within the lines as the pedal is nice and firm again. Surely the pedal would still be mushy if there was?

 

That certainly makes sense! Takes me back to those physics lessons on Pascals law haha 

 

Ah, I've just spotted your problem - though I'm sure that you meant "no air" and not "no fluid"!!!

 

One issue can be, if you are being a bit restrained when using an Easibleeder, if that you will only be cracking the bleed valve open very slightly, that combined with using very low pressure can mean that if there is air pockets at high points, most of the air will stay there while fluid passes through below, increasing the bleed pressure and volume will sort that, like pumping the pedal did.

 

I'd love to be able to get off my bottom and replace the seals on all the callipers as I'm sure that when they age they will cause the pistons to stay out further when the brakes are off, I'd guess this seal replacement should be done every 6 years or so as that would stop drag.

Edited 19 November, 201411 yr by rum4mo

Ah, I've just spotted your problem - though I'm sure that you meant "no air" and not "no fluid"!!!

 

One issue can be, if you are being a bit restrained when using an Easibleeder, if that you will only be cracking the bleed valve open very slightly, that combined with using very low pressure can mean that if there is air pockets at high points, most of the air will stay there while fluid passes through below, increasing the bleed pressure and volume will sort that, like pumping the pedal did

I'd love to be able to get off my bottom and replace the seals on all the callipers as I'm sure that when they age they will cause the pistons to stay out further when the brakes are off, I'd guess this seal replacement should be done every 6 years or so as that would stop drag.

 

Ooops, yep my mistake!

 

I'm pretty sure that's what was happening when I was using the Eezibleed the first time round, there was simply air getting trapped of which the pressure of the Eezibleed could just not budge. That's why second time round I resorted to removing the calipers and rotating / giving them a good shake whilst the Eezibleed was pushing fluid through. Result was more air was removed and my brake pedal felt like it used to again!

Ok, just to recap:

 

 

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:

 

 

Then you said:

 

 

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.

 

 

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.

tl;dr.

 

Or, more helpfully - Your absence of personal experience of a specific problem with a specific set of hardware does not mean that someone who works with that hardware daily will not have encountered it. Neither does your cite of a different set of hardware which does the same job not having that problem.

tl;dr.

 

Or, more helpfully - Your absence of personal experience of a specific problem with a specific set of hardware does not mean that someone who works with that hardware daily will not have encountered it. Neither does your cite of a different set of hardware which does the same job not having that problem.

 

Whatever Ken, just, whatever.

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'm currently experiencing my own brake troubles at the moment, and so went back to the workshop manual...just for a bit of reference.

 

Here's a quote that may help?

 

"WARNING

On vehicles with ABS/EDL/TCS or ABS/EDL/TCS/ESP BOSCH 5.7 or ABS/TCS/ESP BOSCH 8.0 a filling pressure of at least 0.2 MPa (2 bar) must be maintained when filling with brake fluid using brake filling and bleeding device. If the filling pressure of 0.2 MPa (2 bar) is not reached, proper bleeding of the hydraulic unit is no longer assured. Distinction between ABS, ABS/EDL/TCS and ABS/EDL/TCS/ESP BOSCH 5.7 as well as ABS, ABS/TCS and ABS/TCS/ESP BOSCH 8.0"

 

That's 29 psi...ish