Sweating brake fluid!

MikkiJayne · #1 27th January 2016, 10:52 AM

Hi all,

Has anyone seen rubber hoses 'sweating' brake fluid before? The hose running across the firewall from the ESP pump and the fluid reservoir constantly appear to be covered in condensation, but while poking about I've discovered that this 'condensation' has actually dissolved the paint where the hose is in contacts with the body! Its not just abrasion, as the paint has gone soft and bubbled up.

The fluid hasn't been changed for a very long time so I'm wondering if the water content in the fluid could be assisting the fluid in getting through the hose? Osmosis perhaps? I'm inclined to change the hose to be safe, and the reservoir since it's filthy inside, but that then leads to the question of bleeding the system which seems to be a bit of a problem area from other threads on the subject.

Elsawin covers the procedure to activate the pump using basic settings, as described elsewhere. This can be replicated in VCDS, so it sounds entirely safe to me, but others have mentioned it can cause damage. Does anyone have 1st hand experience of this?

Thanks

David's8 · #2 27th January 2016, 12:19 PM

Hi Yes. I looked at the bleeding procedure after replacing rear brake calipers myself. In the end I got the local garage to bleed the brakes as I needed them to do some work on the front calipers. The (very) experienced boss said that he had never heard of the procedure for any ESP fitted car. However, he did presssure bleed the brakes which got them SO much better than my attempts (after fitting the refurbed rears) which did not include the ESP procedure.

paulrstaylor · #3 27th January 2016, 12:29 PM

Sounds like the pipe has started to become porous, I'd definitely want to replace and check all the others ASAP!

The_Laird · #4 27th January 2016, 01:05 PM

Yes, I've had mine pressure bled on numerous occasions (as David) and it works loads better than the manual bleeding. But never tried the pump activation method.

And yes, replace the hose first (and resolve to change your brake fluid regularly!)

MikkiJayne · #5 27th January 2016, 11:35 PM

Thanks guys

More stuff to add to the TPS shopping list! I have a pressure bleeder so all good there. I'll report back on how it behaves once its all back together.

I've never seen the additional pump on ABS/ESP systems before either. It seems particularly out of place considering my 2001 A6 also has ESP but everything is contained in the one ABS unit. It leads me to wonder if the A6 unit could be transplanted in to a D2 to simplify the system. Its just sensors and can-bus right...? Maybe I'll try that if it explodes when I do basic settings

MikkiJayne · #6 4th February 2016, 04:25 PM

I checked the hose again this morning and sure enough, sweating fluid still. Damn thing is like old dynamite sweating nitro! Here are some pics of the paintwork damage:

The hose is £30 from TPS. Vexing, but not the end of the world.

The reservoir however... £240!!!!

For that much I can buy a whole master cylinder and reservoir for a 4 or 6, so sod the '8 tax' unobtanium stuff - retrofit the cheap versions

Initial tinkering suggests a C5 RS5 setup will go in, and the bore is identical and the reservoir for that is about £35...

MikkiJayne · #7 26th February 2016, 07:51 PM

Had a phone call from TPS today - after 2 weeks of being on back order, the hose turns out to be NLA

Not sure what I'm going to do with it now tbh. Hose suppliers look at me like I've got two heads when I ask for brake-fluid resistant hose. Apart from HEL of course, but theirs isn't big enough. The factory rubber hose has such tight bends that OE clutch hose won't bend that tight, nor could I bend metal pipe that tight either.

Possibly I could cut the bends off the hose and use alloy tube for the main run across the bulkhead. Or maybe just encase the original hose in adhesive-lined heatshrink...

Oh, and after tinkering and measuring and pondering, there is no space for any other model's fluid reservoir

The recess in the bonnet is so tight around the reservoir and the m/c is so high in the car there's no option other than the proper one. I'm going to try various ways of cleaning my original reservoir in the hope it won't sweat with new fluid, and if that fails I'll import a new one from ECS. Its £150 to buy in the US with the crap exchange rate, but even with postage that's cheaper than here. I have plenty of friends in the US who can post it for me.

Nick Jones · #8 27th February 2016, 11:03 AM

Guess I'm glad mine doesn't have EPS then.......

For brake fluid you need EPDM or EPDM lined hose
https://www.merlinmotorsport.co.uk/p...100mm-m-sph8-4

Not sure what to suggest re. the bends. I have used the metal insert method before for NLA/stupidly expensive boost sensor pipework on my A6.

Nick

MikkiJayne · #9 27th February 2016, 07:33 PM

Thanks for the link

I'll ask what the minimum bend radius is. Maybe it'll work.

MikkiJayne · #10 5th March 2016, 05:33 PM

I've given up messing about with this as its a battle I can't win.

No off the shelf EPDM hose will match the bend radius of the factory hose so I've covered it in adhesive-lined heatshrink. Polyolefin heatshrink is basically the same as polypropylene which is what the reservoir is made of so it should be resistant to brake fluid on the inside and waterproof on the outside. I think water vapour / condensation was allowing the fluid to get out by osmosis so hopefully isolating it from that will solve the problem.

I've tried cleaning the black streaks out of the reservoir with everything I have in the workshop: ultra-aggressive degreaser, acetone, celly thinners, contact cleaner, wheel cleaner (phosphoric acid) and even hydrochloric acid. Nothing has any effect whatsoever

They come off easily with a cotton bud, but of course you can't get to 99% of the inside of it so it looks like they'll be staying. I'm just going to put it back together and see how it behaves.

Not the most successful part of this restoration