Have a very frustrating problem with my Fabia... The rear offside brake cylinder developed a bad leak, braking power very poor, near home so very carefully managed to get it home. Left it outside, pouring rain. Next day I discovered the cylinder had seemingly emptied a lot of brake fluid overnight. I couldn't do anything with it for a week. My driveway is on a slope downhill, I got the car down the drive very carefully without using brakes but just using clutch biting point in 1st gear. Positioned at the bottom of the drive. Removed the drum, wet mess inside throughout. Got new shoes & new cylinder, cleaned it all up, fitted new cylinder & new shoes, replaced drum and began trying to bleed it. Suspected the master cylinder had gone dry. Put 500ml brake fluid into the master cylinder reservoir - brimmed. Initially some tiny amount of air came out through the hose on the bleed valve but then it stopped & now nothing comes out at all despite assistant pressing brake pedal (up, down, up down etc). Fluid level still brimmed at reservoir. Tried sucking the air through the bleed valve with a pump but again, nothing. Figure there's an airlock somewhere? Have read that if a master cylinder is allowed to go dry then it itself needs to be bled of air - how would I do that? Location of the reservoir likely prohibits sitting a container onto it...

Your valuable advice would be most appreciated!

With the. Amount of fluid lost did the reservoir got empty? Because in that case it could be necessary to bleed the abs module I suspect

I agree it may be ABS where the air is. You could try a pressure bleeding kit to see if that works. Also try removing bleed screw in case its blocked. Another point is that if one rear cylinder has failed the chances are the other is on its way out as well. I would replace other one as they arent expensive. Sons mk1 failed in the same way and when I checked the other it was just starting to leak with a fair bit of corosion inside it when I took it apart.

Alasdair

ABS... ok thanks, I'll have a look at that this weekend 👍

Hi, the factory says to bleed the system with 2 bar pressure min to avoid issues. Then use a diagnostic tool to bleed the ABS hydraulics.

I can give you some info to help visualise why you have not completely lost braking even though it feels like it:

The reservoir is divided internally into three chambers, all of which use the same fluid until below the half way mark which will bring on the low fluid level indicator on the dash. As the leaking circuit continues to loose fluid due to blown cylinder seals, it's chamber will empty but fluid is maintained in the good circuit chamber hence you will still have some diagonal braking.

Automatics will have the three chambers too, but the clutch one will be sealed off at the exit tube.

The reason for compartmentalising the reservoir is to provide an emergency backup should a circuit fail as in your case. You will still have normal braking on one diagonal split which provides emergency braking. In your case the NSR and the OSF will still have a sound circuit, but you will have lost your OSR and NSF circuit.

If you have a manual transmission, and the clutch circuit has sprung a leak, the fluid in the whole reservoir will drop to half way, then continue to empty the clutch chamber, but the two brake circuits will be protected from losing fluid from their chambers.

Prob won't help you much as you need a pressure bleed by sound of it once the shoes and cylinder have been replaced.

Did my daughters yesterday.

Once pressure bled and less than 1/3 pedal travel confirmed, you use diagnostic tool to bleed the ABS. Both fronts then both rears at same time following GFF on VAS PC V19 until the end of the test.

Edited 7 hours ago7 hr by 3T51704x4
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