Brake fluid leak from centre of car at front.
 

Hi guys,

Fitted new discs and pads on a 2000 S8. Did one side at a time, pressing brake pedal to set the pistons on one side before starting the other. Then brake pedal felt fine.

Today I moved the car out of the garage since doing the brakes and parked on the driveway. I noticed on the floor, in the middle, around where the bulkhead would've been, was a pool of fluid. I thought I this was hydraulic fluid to start with. But it's actually brake fluid.

I went to start the car and pressed the brake pedal and it slowly sinks to the floor. And other pool of fluid under the car.

The brakes are very weak on the car. Only just stop the car when it's moved on idle in D.

Calipers are fine, flexi pipes are fine.

I need to get the front in the air again and check but has anyone experienced a brake fluid leak like this?

Cheers.

Dan

The likely candidate for rogue brake fluid in the centre after a pad change is simply fluid displacement from pushing the pistons back in to the calipers as it will over flow from the reservoir then run down the scuttle drains on to the gearbox and drip off in the middle, but that wouldn't cause a soft pedal.

How far did you have to push the pedal to seat the pads? Its not uncommon to find corrosion inside the master cylinder on older cars which haven't had a fluid change in a long time. Moisture builds up in the fluid and eats the inside of the cylinder, then when you push the pedal past its normal position the rubber seals are torn up by the corrosion and no longer hold pressure.

Concievably it could be a combination of displaced fluid and a failed master cylinder.

It may also be a split hard line. The two outputs from the master cylinder to the ABS unit and the line from the ABS to the driver's front caliper all run underneath the bulkhead. I'd say the most likely culprit is one of the two front caliper hard lines where they attach to the flexi hoses in the wheel arches as they suffer from corrosion at the union. A leak from those would be obviously on one side though rather in the centre.

Hmm, just re-read and a press of the pedal giving a new puddle does still suggest a hard line.

I'm hoping it really isn't the master cylinder.

There wasn't any over flow of brake fluid. I did have the cap undone and a.cloth wrapped around the fluid reservoir to catch any stray fluid, but it never leaked any.

I'll get the car in the air tomorrow and have a look. If its a hard line that spilt, or whatever it is, I'm glad it's happened now and not en-route to the test centre!

Cheers.

Found a leak. It's on the f/n/s caliper. The lower link pipe which links left pistons with the right pistons, there is a rubber sleeve along the bottom which the brake pipes goes through. It's right at the sleeve it's leaking from.

We never did get a rebuild done as the calipers weren't as bad as we initially thought. Guess that proves us wrong.

Does anyone know if that link pipe can be ordered separately? I've attached a pic of the offending pipe.

Cheers.

Dan

Its not available from Audi but it can be made from standard brake pipe if you have a flaring tool. The big challenge tbh will be getting it out of the caliper without stripping something. They are usually seized in place by corrosion.

When I do those I will hold the caliper in the vice with the pipe upwards and clean as much crud out from the base of the union as possible using a sharp pick, then soak it for a day or so in WD40. Then cut the pipe off flush so I can get a 6-sided socket over the union and gently try and work it free - tighten, loosen, repeat until it comes free. Sometimes it works, sometimes it doesn't. If you strip it, it'll have to go off for a professional refurb.

Due to another project rearing its head before it was due to be completed by a so called 'professional', I have finally managed to get round to removing the calipers. The link pipe came out with ease. Obviously I went steady and gave it plenty of penetrating fluid, but no issues.

I have a brake pipe flaring kit. I think the pipe is 3/16 in size.

Do you happen to know what size the male screws are?
10 x 1 for the link pipe I believe, but the pipe which goes from the rubber flexi to the caliper has a larger hex head. 11mm iirc. May as well replace those while I'm in there as one broke whilst undoing it and while the other is OK, but I may as well replace it as it is a good few years old.

The link pipe on the drivers side caliper has been replaced at some point. They are 11mm hex and the pipe isn't as neatly made as the original one on the passenger side caliper.

Cheers.

Dan

Standard brake flare nuts are M10x1 with 11mm head. Aftermarket nuts vary between 10 & 11mm head.