Have got great help here in the past with my Mark 1 Fabia. I am now looking for help with a mark 2 Octavia.

The problem is the brake pedal feels very spongy and has too much travel. So far I have changed the brake fluid and thoroughly bled the

system and am satisfied there is no air trapped. I have also checked the calipers, pads and have good movement in the sliders.

I now think it has to be either the master cylinder or the ABS unit. Should I try changing the master cylinder or is it more likely to be the abs unit?

Is it a very difficult job to change the master cylinder?

Thanks in advance!

Is the car new to you or has this spongy pedal developed in your ownership?

I'm thinking Master Cylinder seal on its way out. 

 

Not tricky but time consuming and the system will need draining to the point the Master Cylinder is empty and the whole system will need bleeding properly again.

 

Kirkynut 

The master cylinder is easy enough to remove bar the stupid torx screw down the outboard side securing the reservoir.

 

It features a solid piston into a sealed bore so I would not suspect wear unless the fluid was contaminated.

 

The master cylinder should also self bleed over time with slight and slow pedal application to help any air rise back up and out.

 

If all else checks out, I'd get the ABS purged.  Buy a tool or take it to a garage.

 

One other thing to check is the vacuum pipework from the tandem pump.  The nipple on the pump is a well known weak spot, becoming loose, and the rigid pipe can split.

 

The tandem pump can be fixed by applying thread lock/silicone RTV etc and any splits in the pipe can be sleeved and clipped or a new item fitted.

Edited 3 February, 20197 yr by MicMac

8 hours ago, SuperbTWM said:

Is the car new to you or has this spongy pedal developed in your ownership?

The car belongs to my neighbour and he says he noticed first well over a year ago.

It still passed the NCT /MOT last year but failed this year so it is off the road at the moment.

 

8 hours ago, MicMac said:

The master cylinder is easy enough to remove bar the stupid torx screw down the outboard side securing the reservoir.

 

It features a solid piston into a sealed bore so I would not suspect wear unless the fluid was contaminated.

 

The master cylinder should also self bleed over time with slight and slow pedal application to help any air rise back up and out.

 

If all else checks out, I'd get the ABS purged.  Buy a tool or take it to a garage.

 

One other thing to check is the vacuum pipework from the tandem pump.  The nipple on the pump is a well known weak spot, becoming loose, and the rigid pipe can split.

 

The tandem pump can be fixed by applying thread lock/silicone RTV etc and any splits in the pipe can be sleeved and clipped or a new item fitted.

Thanks for that, Micmac.

I presume the tandem pump is easy enough locate by following the pipework from  the servo?

How expensive would a pump be to purge the ABS?

The tandem pump is on the right side of cylinder head as you look at engine:

 

 

The cheapest electronic gizmo I've had confirmed has the ABS purge facility is this type:

 

https://www.ebay.co.uk/itm/R3-VCI-OBD2-Diagnostic-Tool-Scanning-Apparatus-For-Delophi-Software-For-Car-MB/183516040203?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20180213162448%26meid%3D1067428f551d4182af0c5ed1e5f830ab%26pid%3D100930%26rk%3D3%26rkt%3D8%26mehot%3Dpp%26sd%3D382753528753%26itm%3D183516040203&_trksid=p2349624.c100930.m5375&amp

Edited 4 February, 20197 yr by MicMac

2 hours ago, MicMac said:

The tandem pump is on the right side of cylinder head as you look at engine:

 

 

The cheapest electronic gizmo I've had confirmed has the ABS purge facility is this type:

 

https://www.ebay.co.uk/itm/R3-VCI-OBD2-Diagnostic-Tool-Scanning-Apparatus-For-Delophi-Software-For-Car-MB/183516040203?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20180213162448%26meid%3D1067428f551d4182af0c5ed1e5f830ab%26pid%3D100930%26rk%3D3%26rkt%3D8%26mehot%3Dpp%26sd%3D382753528753%26itm%3D183516040203&_trksid=p2349624.c100930.m5375&amp

Bit of movement on the nipple on the tandem pump but does not appear to be leaking vacuum. Put a vacuum gauge on one of the smaller rubber hoses and reading good + feel strong vacuum by putting thumb on it. 

 

For the the life of me, I can’t find a torx screw holding reservoir to master cylinder? 

Appreciate the help

I don't know what the picture is...

 

The torx screw is tucked away on the outboard side of the Ate MC at the lower of the reservoir and simply secures the reservoir from escaping, even though it is held captive by two chunky rubber grommets.

 

Use an inspection mirror if you can't find the screw.

 

I still don't think it needs disturbing.

When changing a brake line I once made a mistake and let all the brake fluid drain out. I must have bled all the lines half a dozen time but the thing that sorted the spongy pedal in the end was bleeding the rears in tandem and then bleeding the fronts in tandem, before going round individually.

 

This seemed to get some trapped air out of the ABS pump so its worth a go if you have not got the means of running the pump electrically. 

Not sure about the MK2 but the MK1 had 2 bleed nipples on the master cylinder itself, I had changed the fluid and no amount of bleeding could get back a good pedal feel until I bled both of these.

 

Worth a look.

4 hours ago, J.R. said:

Not sure about the MK2 but the MK1 had 2 bleed nipples on the master cylinder itself, I had changed the fluid and no amount of bleeding could get back a good pedal feel until I bled both of these.

 

Worth a look.

 

 

Just a quick update - decided not to throw a master cylinder at it as it does seem to be more like air in the system.

I decide to go around all 4 wheels and bleed the system again after taking it out for a fast spin on loose gravel to activate the ABS.

I also bled both nipples at the master cylinder as suggested by J.R. I appeared to have a very solid pedal until I start up the engine and

then the pedal goes spongy again. Don't think there is much more I can do without access to a tool to control the ABS pump?

Once again really do appreciate all the help have got here .

On 04/02/2019 at 17:09, transfreeze said:

Don't think there is much more I can do without access to a tool to control the ABS pump?

 

 

Did you bleed the front and rear axles in tandem? (as in both rears at the same time, and then the two fronts.)

Edited 11 February, 20197 yr by SuperbTWM

On ‎04‎/‎02‎/‎2019 at 10:31, MicMac said:

I don't know what the picture is...

 

The torx screw is tucked away on the outboard side of the Ate MC at the lower of the reservoir and simply secures the reservoir from escaping, even though it is held captive by two chunky rubber grommets.

 

Use an inspection mirror if you can't find the screw.

 

I still don't think it needs disturbing.

 

Micmac, is it definitely a torx screw holding on the reservoir? I have tried all the smaller sizes and cant seem to get one to fit - it is extremely awkward to get to

On ‎11‎/‎02‎/‎2019 at 00:21, SuperbTWM said:

 

Did you bleed the front and rear axles in tandem? (as in both rears at the same time, and then the two fronts.)

I bled the axles in tandem as you suggested and it certainly improved the pedal, though I am still not a hundred percent sure its fully ok.

Its going back for re-test next week and if it fails I will try changing the master cylinder.

Here's what came off my Ate reservoir, completely redundant given the hold the rubber grommets have.

 

Torx 20.

 

IIRC I used a T20 bit secured in a ¼" ring spanner with masking tape to get access.

 

If it makes you feel any better I have just been acquired a Mk4 Golf with the same issue. My Dad changed the rear calipers and let the system run dry. Now the car has exact same symptoms as you. It brakes well, passed MOT fine, but pedal is a bit spongy but firm when engine off.

 

I have bled the ABS pump with VCDS and got a bit of air out of the rear caliper when changing the rear pads but its still not perfect. I've got plenty of brake fluid so I think i'm going to go for a high pressure bleed from master cylinder again and then run the ABS pump a bit more to try and see if I can sort it. 

17 hours ago, SuperbTWM said:

If it makes you feel any better I have just been acquired a Mk4 Golf with the same issue. My Dad changed the rear calipers and let the system run dry. Now the car has exact same symptoms as you. It brakes well, passed MOT fine, but pedal is a bit spongy but firm when engine off.

 

I have bled the ABS pump with VCDS and got a bit of air out of the rear caliper when changing the rear pads but its still not perfect. I've got plenty of brake fluid so I think i'm going to go for a high pressure bleed from master cylinder again and then run the ABS pump a bit more to try and see if I can sort it. 

 

 

It it actually does make me feel better!!!!

I was actually starting to think I was imagining the spongy pedal or was it as bad as I thought it was. 

Let us know how you get on. 

I will update if I get any further with this.

18 hours ago, MicMac said:

Here's what came off my Ate reservoir, completely redundant given the hold the rubber grommets have.

 

Torx 20.

 

IIRC I used a T20 bit secured in a ¼" ring spanner with masking tape to get access.

 

  

 

Thats exactly what I was looking for, MicMac! 

Really appreciate your help.

Have you pressure bled or vacuum bled the system?

 

Sometimes you are better off paying the money and getting the workshop to use their expensive equipment.