Brake master cylinder.

[JulianS]

My 2009 Octavia needs a new brake master cylinder. No bother you would think. Well there are seemingly dozens available and none are correct, Euro Car Parts came the closest to listing one, (at £350 which I reduces to £220 with a discount code I found, but even so - yikes!) but when it arrived it was missing an all important provision for a connection to the wiring harness. Physically it was correct though. I'm awaiting a call back from Morcambe Skoda as the parts man seems to have taken off, however I'm expecting a daft price assuming they can source one.

 

Any thoughts on where I may go for a correct master cylinder for my vehicle please? The regular motor factors with a good reputation, and ECP are telling me dealer only which I find astonishing given the tens of thousands of the things in use as taxis up and down the UK.

 

Julian.

[Tech1e]

The only electrical connection on the master cylinder should be the brake switch and that just unclips and swaps over. 

[JulianS]

See this picture. I think it's a hall sensor and doesn't just swap over - well it does but the MC needs to be able to take it.

 

https://www.ebay.co.uk/itm/Skoda-Octavia-1Z-04-13-1-9-Diesel-Brake-Master-Cylinder-Ate-0000233512/293212370385?hash=item4444d1b5d1:g:AagAAOSwhNNdbk2B

[Tech1e]

Yeah, you still need the correct master cylinder for the car.

[JulianS]

2 hours ago, Tech1e said:

Yeah, you still need the correct master cylinder for the car.

Indeed. But I've drawn a complete blank from any number of factors. So I've ordered one from the local Skoda dealer and should be with me tomorrow. It seems they swapped from a regular switch on the pedal to the Hall sensor on the master cylinder at some stage. Why they're not available is a mystery to me as you can find them on Golfs and Seats etc, as it's all the same stuff. Plenty of them from scrappers on ebay but there's no guarantee that it's going to be any good.

[Tech1e]

I've never had to replace one before now on an Octavia 2.

[JulianS]

I'm surprised too, to be honest. I had the clutch slave go, nasty cheap plastic job, so I swapped the clutch slave and master to same a break down miles from home.  But this brake master has definitely got leaking seals as if you keep you foot hard on the pedal it slowly sinks down to about 1/2 way saying to me that one of the seals is going. it's still driveable but these things only get worse. Car has done about 130K, much of it on long trips so I wouldn't have expected it, but mechanical stuff does sometimes do weird things.

[J.R.]

Mine does that and I asked on the forum and the consensus was that they all do it, nobody knows why but its not a fault or failure.

 

I bet it doesnt do it when the engine is not running and the ABS vacuum accumulator emptied, bet you have a rock solid pedal then so no hydraulic seals leaking back.

 

"They all do that sir!" 😀

[JulianS]

From the MOT manual: ''This Inspection applies to all vehicles where pedal creep has been detected when pressurising the brakes with the engine running.'' (method of inspection) 3. With servo assistance fully depress the pedal. (reason for rejection) 3. With servo assistance the pedal creeps down and touches the floor.

 

I'm really not sure that it should be doing it, it's an MOT failure. I have to say that I never noticed it before and it is creeping down at a fair old rate and it's hard to come up with a reason for it other than internal seals although I'm happy to be proven wrong. I've got the new part coming now so it's going to be highly interesting and head scratching if it doesn't fix it.

 

http://www.partinfo.co.uk/files/VOSA Inspection Manual Classes 3 4 5 %26 7.pdf

[J.R.]

Bet you also that it doesnt creep to the floor but stops albeit with a little bit of sponginess some way short.

 

I have been through exactly what you are feeling, do a search on the site and you should find the thread I created.

 

Reading myself to sleep one night with the VAG self study guide on all the ABS & electronic stability systems I think I found the technical explanation for the phenomenon.

 

Try the tests that I mentioned above, you can get a similar pedal travel and stopping short of the bottom if you repeatedly abuse the ABS system trying very feorcefully to deglaze the discs, never happened on my MK1 that had an earlier ABS controller without this hydraulic feedback loop.

[J.R.]

I hope you are proved right because I would be mighty pi55ed if I had bought a new one at main stealer prices, fitted it, gone through all the purging and bleeding rigmarole for it to make no difference.

 

There is a reason why the MOT testers text is so detailed and says "touches the floor".

[JulianS]

Indeed. I think you have to be a bit careful with the ''touches the floor'' thing. As you know it's a dual circuit system so there's effectively two master cylinders built into that one unit. For it to touch the floor would necessitate a failure (or failing) of both brake circuits. Arguably, at the moment I have a brake system that could revert to braking just 2 wheels. (I don't know if it's a diagonal split or a fore/aft slit system)