S3 Brake fluid draining from higher reservour to lower reservour

I have a new problem with my S3 that I hope someone can help me with. My brake fluid is draining from my higher reservour RH to my lower LH reservour. On filling the lower reservour it leaks out through the sensor wires.

I have had he car for about 4 years and this has never happened before. Anyone with any ideas how to fix this?

Bobby

It’s a leak inside your booster.

Thank you so much Andrew. Would that be the brake master, slave or servo? Is there a way to test?

Bobby

After you have replaced the seal on the shuttle inside the booster, consider mounting the slave reservoir at the same height as the master. This means it’ll only ever transfer a couple of drops over and left overnight, no liquid will leak as there is no head of liquid for one to drain into the other.

It’s a glaring design fault on Jaguar’s part to have not done this, as the failure mode is completely contained and you have weeks or months in which to decide whether bother fixing it or not.

kind regards
Marek

Thank you Marek. Much appreciated. I made a $US50 donation to Jag lovers.

Bobby

Intermediate seal in the slave cylinder. You have to disassemble the booster to get to the problem, so you’re in it for the full kit.

Thank you for the information Michael. I would like to make sure I buy the correct kit as I am based in Australia and these parts have to be ordered from the UK. Are you talking about the slave cylinder (front end) to the brake master on the RH of the car or are you talking about the slave (front end) of the dish-like brake servo on the LH side of the car?

If one has failed and they are all the same age, It’s probably best to replace all the brake rubber parts, master, slave (booster) and all wheel caliper seals and rubber brake lines.

That’s true, but the immediate problem is in the slave, and to repair it you have to do the whole servo. And think about doing the master also:

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My Servo was replaced (new) 2 years ogo and my master has been rebuilt about a year ago. Really appreciate your advice. From memory you don’t get kits for the servo slave so that will mean a new servo after replacing the servo only two yeas ago.

Is it possilbe that the problem could be elsewhere?

Bobby

The servo kit includes rebuild parts for the slave.

I’m not sure if the pressure differential warning switch could be a failure point.

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Thank you Michael.

Last question. I ordered the servo kit from SNG Barratt. Can this kit be installed withhout removing the Servo housing (easy job) or not. If not, this may be a big job as I believe it also involves removing the tortion bar to gain access from undeneath the car (hoist)

Kind regards, Bobby

The servo kit arrived, Michael. What is the best way to drain the brake fluid without making a mess? I have sucked as much out of the reservoirs as possible with a syringe but not sure where to disconnect the hose line?

Kind regards
Bobby

I clamp the line with a small vice grip, then remove it from the master. Put the end of the hose in a cup and release the clamp.

Brilliant. Why didn’t I thank of that?

Bobby