The mystery of my brakes!

[liamthedude]

Car is Audi A6 C5 Avant 1.9 TDI manual on 173,000 miles (driven 150-200 miles a week)

Bought the car in June 2018, all was well.
December 2018, light comes on, I check the fluids, top up brake fluid, about 50ml and light goes off.

6 months later, light comes on, top up another 50ml of brake fluid and light goes off.

THEN early October 2019, I get a raised idle, the car normally revs at 800-900 rpm on cold but it now revs at 1,000 or just over. One day I get in the car and the brakes are GONE! No stopping at all until the pedal is down to the floor and I can feel the discs. I asked my friend if he could help. I bought a second hand brake servo/master cylinder, he fitted it and it was all back to normal, but I still had a raised idle.

Early December 2019, about 6 weeks after the brake servo was fitted, the brakes had gone AGAIN! But now I'm losing brake fluid again, I topped up the brake fluid a full 500ml and after 24 hours the brakes were back to full power.

January 2019, the light on dash comes on again, and one day the brakes had gone! This is the 3rd time since October the brakes failed. However the difference is that when I push the brakes hard, nothing happens but when I press the pedal slowly, it actually does a good job of slowing the car down. Also im now losing random amounts of brake fluid, maybe 500ml in a week, and and then lose nothing after 3 days.

So can someone shine some light on what is going on? And please consider

The raised idle has been constant since October, even after the replacement servo, yet the revs drop to normal after a few mins.

Why am I losing random amounts of brake fluid?

Why do the brakes work on a slow press but not when I push them hard?

Is there a link between a raised idle and poor brakes?

What do you think my problem is?

Thanks for any help or advice!
Liam

Edited by liamthedude on Friday 24th January 10:11

Edited by liamthedude on Friday 24th January 10:19

[Olas]

You want to get the car in the air with a helper inside the car revving engine and operating brake pedal.
You visually inspect for damp patches - unlikely corroded lines on a car of that age id guess either M/C failed internally and allowing occasional leakage into servo, OR, a slow drip from a caliper/seal.

Marginal seals & o rings can seal under low pressure but start to fail at higher pressures.

Was your replacement MC new or used? Does your car have a proportioning valve to adjust brake bias to compensate for carrying passengers/luggage?

Check your vacuum pump for signs of brake fluid

[liamthedude]

Thanks for your reply, I am getting the car looked at on Sunday.

The M/C I bought was used.

I've looked under the car. On the O/S/R there is a spring like thing behind the caliper? Well it's dry but on the N/S/R that spring is wet/damp.

I'm trying to upload the pictures but the pics are 4mb and I don't know how to shrink them to 2mb so I can post on this thread.

[the cueball]

My first guess would be a caliper piston seal / bleeder screw.

[liamthedude]

liamthedude]iamthedude said:

Thanks for your reply, I am getting the car looked at on Sunday.

The M/C I bought was used.

I've looked under the car. On the O/S/R there is a spring like thing behind the caliper? Well it's dry but on the N/S/R that spring is wet/damp.

[Matt_E_Mulsion]

First and foremost you need to find the source of the leak and start by repairing that.

[Olas]

There is no mystery, you have identified the leak but failed to inspect further. Get the wheel off and identify what is leaking, then replace it.
Bleed that corner.

[SAS Tom]

If it needs fluid then you know there is a leak, you need to find and repair the leak. From the pictures it looks like the leak is from that caliper.

[paintman]

What 'mystery'?
You have a fluid leak or leaks.

[liamthedude]

Thank you everybody for your input, it has also been suggested that I just buy a new caliper for this corner?

As we have not seen rain for a week, the road is dry but there is a small wet patch of road next to this tyre

Also, I apologize for the title, I didn't mean to make it sound like click bait, but I can't change it now.

[paintman]

liamthedude said:

Thank you everybody for your input, it has also been suggested that I just buy a new caliper for this corner?

As we have not seen rain for a week, the road is dry but there is a small wet patch of road next to this tyre

Also, I apologize for the title, I didn't mean to make it sound like click bait, but I can't change it now.

The wet on the inner rim of your wheel is also fluid & as it's on the road that's a pretty major leak.
Get the whole system looked over to make sure there are other apparent leaks & deal with anything arising.
Hopefully it's just this caliper.

[liamthedude]

[E-bmw]

As has been said by others above, if you need to put fluid in to maintain a level it is getting out somewhere & this NEEDS to be sorted or you potentially have NO BRAKES!!!!

[Matt_E_Mulsion]

It could be the caliper or it could be the pipe. Have a look where the fluid is actually coming from before you buy parts, or get someone else to have a look if you are unsure your self.

[Chris32345]

Matt_E_Mulsion said:

It could be the caliper or it could be the pipe. Have a look where the fluid is actually coming from before you buy parts, or get someone else to have a look if you are unsure your self.

This
Take the wheel off and inspect the caliper brake Flexi hose and the hard brake lines beyond that it could be coming from any one of the three areas

[Elliot2000]

Topping it up more than once should have been a clear sign it’s leaking somewhere, for you to keep driving, keep having failing brakesand keep leaking is idiotic.
The only mystery is why u didn’t realise this