C5 A6 Brakes stuck on

Thompy · 28-04-13, 08:43 PM

Hey guys, first of all apologies about the no classic content, but I'm a bit stuck (literally)
My car is a C5 A6 2.7Tq
Went out this afternoon to take some boxes to the local recycling centre. About a quarter of a mile from the recycling centre I pressed the brakes, found the pedal hard and the brakes seemed to be binding (not releasing when I released brake pedal). The binding got worse and by the time we got to the recycling centre the car was really straining against the brakes. Emptied the car and decided to try to get home, when I tried to set off the brakes seemed to be solidly on and the brake pedal was rock solid. I tried a couple of things - disconnected the vacuum hose to the servo and pulled the plug on the ABS pump. Neither had any immediate effect, but after about half an hour, once the car and brakes had cooled there didn't seem to be the same degree of binding. So we set off for home, only to feel the brakes starting to pull again after about 1/4 mile. Same thing again, after a period of time we could move and get a bit further up the road. I didn't have any tools with me, no breakdown cover and no phone a friend available, so we made it home in this fashion about 2 hours later (luckily we were only about a mile from home). I'm thinking it may be a problem with the master cylinder, since disconnecting the vacuum to the servo had no effect and the chances of both front callipers sticking at the same time is unlikely. I've had the car jacked up and there's nothing obvious wrong.
So what I'm asking is do you reckon it's the master cylinder, if so is it reasonably easy to remove/replace (I'm fairly handy with a set of spanners and generally tackle most things myself) and finally do you guys have any other suggestions before I start into a process of elimination.

Bit of a wordy one here but I've tried to give as much info as possible.
Thanks in advance

Andrew.

John. · 28-04-13, 09:24 PM

Master cylinder was sticking on my CQ but nowhere near as bad as what you're describing. If you get it to do it again what about releasing the M/C from the servo.....if brakes then free off it would suggest linkage(if there is much linkage??).
Strange that the pedal went hard??

Cuppatea · 29-04-13, 06:12 AM

I saw this happen years ago on a 2.7 bi-turbo a6 auto, but it went to audi for diagnosis, same problem - solid pedal!

Check the bulkhead scuttle drains aren't blocked, the servo may have drawn in some rain water?

missfire · 29-04-13, 02:23 PM

Quote:

Originally Posted by Thompy

any other suggestions before I start into a process of...

Vagcom it maybe, any lights on? There is a bit of the servo hose that cracks and people epoxy it back together, causes hard pedal obviously, but jammed on calipers.. who knows, ESP/ABS problem maybe? The brakes on mine are cr*p! Calipers are free, pads are fine, hoses fine, going to check mine over next weekend, have lots of new bits to go on... Will soon find out if it makes any difference.

TeXerv · 30-04-13, 09:05 PM

When this symptoms appear again pour some cold water onto the master cylinder (water must not get in contact with brake fluid reservoir). If the break releases quickly, the master cylinder, especially the Central Valve is blown.

styler · 30-04-13, 09:12 PM

when i worked in a garage in philadelphia, a chrysler lebaron came in with a similar problem, would drive fine for a while then the brakes would jam on leave it sit and cool and it was fine, till it heated up again.. .. when i checked the resevoir it looked as if there had been oil poured into it (instead of brake fluid ) so we changed the master cylinder and flushed the brake system, solved the problem.. maybe not whats wrong with yours but theres a wee story for ya anyway..

Thompy · 08-05-13, 09:42 PM

Thanks for all of the replies. Didn't get a chance to look at the car until the weekend. Following styler's story above I thought I would check the fluid first as that would be an easy and cheap fix. When I compared the fluid in the reservoir to the bottle of Dot4 I have there was a significant difference in both colour and consistency/texture. The fluid in the reservoir was greenish/blue vs brown and it was quite a bit "thicker". So I flushed the system with new Dot4 and have done about 250 miles since with no problems.
Bit of a strange one, I know I've only ever put Dot4 fluid from local motor factors in and that was when I had a flexi hose develop a pinhole and I topped it up enough to get it to a branch of Farmers Autocentre to have the hose replaced as I didn't have time to do it myself. That was about 2 months / 1500 miles ago though.
Can't say I've paid much attention to the brake fluid in the 18 months I've owned the car apart from checking the level every now and again, so don't know if the colour/consistency has changed in that time.
Is it normal for there to be such a difference between "new" and "used" fluid?

Again thanks for the comments and pointers and I'm just glad that the problem is (hopefully) fixed

Andrew

missfire · 08-05-13, 10:14 PM

Bought a wee 80 last year that looked like it still had the original fluid in it! Fekn like black-brown treacle, chunks of rusty-all-kinds-of-stuff coming out. Flushed it.. obviously.

a change every couple of years would be good in an ideal world, with plenty of spare time. Cheap enough to do, if yer nipples hold up!

TeXerv · 09-05-13, 09:29 AM

Not changing the brake fluid every two years saves your moneybag. Not changing the brake fluid regularly also provides a few more advantages, making the owners and drivers life more eventful:
Old brake fluid keeps the environment clean by absorbing fine dust. Following the surface of your brake cylinders and calipers are always pretty nice ground. So you don't need to dismantle your master cylinder regularly for grinding the inside with coarse sand cloth.
And due to a nice collection of all-kind-of-stuff surrounding the master cylinders central valve, your car may perform funny surprising braking manoeuvres on its own, without the need to step on the brake pedal. I love that!
It also keeps the environment cosy and dry because it absorbs water. The older the fluid is, the better it works! This can make a simply ride downhill some highland roads a thrilling adventure! Air bubble kicking until the brake is working makes the difference! Are you quick enough? Good training for Speed Metal drummers, of course.

Let's have a look inside a master cylinder, that has suffered a 10-year-maintenance-intervall.
1. Mind the RED circle at the cylinder housing. Due to old an dusty brake fluid deep scratches are sanded onto the cylinder surface.

2. The area around the central valve (of the same cylinder).
Mind the orange circle again (and ignore the German lyrics

). The valve is clogged by a heap of mud. This cylinder had performed automatic braking action - not really funny, I guess.

So change your brake fluid regularly every two years when you have it on the road.

andy quattro · 10-05-13, 07:53 AM

I would say its the servo, as someone had said water builds up if the bung is not cleaned out often. Just had the same thing with my A4.

30-04-13, 09:12 PM	#6
styler Moderator Classic Audi Club Member Join Date: Jul 2009 Location: Donegal, Ireland Posts: 3,443	when i worked in a garage in philadelphia, a chrysler lebaron came in with a similar problem, would drive fine for a while then the brakes would jam on leave it sit and cool and it was fine, till it heated up again.. .. when i checked the resevoir it looked as if there had been oil poured into it (instead of brake fluid ) so we changed the master cylinder and flushed the brake system, solved the problem.. maybe not whats wrong with yours but theres a wee story for ya anyway.. __________________ CRASH VALLEY CUSTOMS get 'er done...

09-05-13, 09:29 AM	#9
TeXerv Grown up member Join Date: Oct 2011 Location: Northern Krautland Posts: 241	Not changing the brake fluid every two years saves your moneybag. Not changing the brake fluid regularly also provides a few more advantages, making the owners and drivers life more eventful: Old brake fluid keeps the environment clean by absorbing fine dust. Following the surface of your brake cylinders and calipers are always pretty nice ground. So you don't need to dismantle your master cylinder regularly for grinding the inside with coarse sand cloth. And due to a nice collection of all-kind-of-stuff surrounding the master cylinders central valve, your car may perform funny surprising braking manoeuvres on its own, without the need to step on the brake pedal. I love that! It also keeps the environment cosy and dry because it absorbs water. The older the fluid is, the better it works! This can make a simply ride downhill some highland roads a thrilling adventure! Air bubble kicking until the brake is working makes the difference! Are you quick enough? Good training for Speed Metal drummers, of course. Let's have a look inside a master cylinder, that has suffered a 10-year-maintenance-intervall. 1. Mind the RED circle at the cylinder housing. Due to old an dusty brake fluid deep scratches are sanded onto the cylinder surface. 2. The area around the central valve (of the same cylinder). Mind the orange circle again (and ignore the German lyrics ). The valve is clogged by a heap of mud. This cylinder had performed automatic braking action - not really funny, I guess. So change your brake fluid regularly every two years when you have it on the road. Last edited by TeXerv; 09-05-13 at 09:48 AM.

10-05-13, 07:53 AM	#10
andy quattro Grown up member Classic Audi Club Member Join Date: Jan 2008 Location: north wales Posts: 400	I would say its the servo, as someone had said water builds up if the bung is not cleaned out often. Just had the same thing with my A4. __________________ AUDI QUATTRO WR (85) AUDI 80 QUATTRO (84) AUDI 90 20V QUATTRO (89) EX PRESS CAR(sold) AUDI 100 AVANT (88) AUDI A4 2.5 TDI QUATTRO(2001) VW POLO 1.9D(97)

28-04-13, 09:24 PM	#2
John. 4 ring whore! Classic Audi Club Member Join Date: Mar 2011 Location: Scottish Borders. Posts: 7,529	Master cylinder was sticking on my CQ but nowhere near as bad as what you're describing. If you get it to do it again what about releasing the M/C from the servo.....if brakes then free off it would suggest linkage(if there is much linkage??). Strange that the pedal went hard??

29-04-13, 06:12 AM	#3
Cuppatea Grown up member Join Date: Feb 2011 Location: Somerset Posts: 105	I saw this happen years ago on a 2.7 bi-turbo a6 auto, but it went to audi for diagnosis, same problem - solid pedal! Check the bulkhead scuttle drains aren't blocked, the servo may have drawn in some rain water?

30-04-13, 09:05 PM	#5
TeXerv Grown up member Join Date: Oct 2011 Location: Northern Krautland Posts: 241	When this symptoms appear again pour some cold water onto the master cylinder (water must not get in contact with brake fluid reservoir). If the break releases quickly, the master cylinder, especially the Central Valve is blown.

08-05-13, 09:42 PM	#7
Thompy Grown up member Classic Audi Club Member Join Date: Aug 2008 Location: Dromore NI Posts: 61	Thanks for all of the replies. Didn't get a chance to look at the car until the weekend. Following styler's story above I thought I would check the fluid first as that would be an easy and cheap fix. When I compared the fluid in the reservoir to the bottle of Dot4 I have there was a significant difference in both colour and consistency/texture. The fluid in the reservoir was greenish/blue vs brown and it was quite a bit "thicker". So I flushed the system with new Dot4 and have done about 250 miles since with no problems. Bit of a strange one, I know I've only ever put Dot4 fluid from local motor factors in and that was when I had a flexi hose develop a pinhole and I topped it up enough to get it to a branch of Farmers Autocentre to have the hose replaced as I didn't have time to do it myself. That was about 2 months / 1500 miles ago though. Can't say I've paid much attention to the brake fluid in the 18 months I've owned the car apart from checking the level every now and again, so don't know if the colour/consistency has changed in that time. Is it normal for there to be such a difference between "new" and "used" fluid? Again thanks for the comments and pointers and I'm just glad that the problem is (hopefully) fixed Andrew

08-05-13, 10:14 PM	#8
missfire making wooden things Classic Audi Club Member Join Date: Dec 2009 Location: cow land Posts: 8,156	Bought a wee 80 last year that looked like it still had the original fluid in it! Fekn like black-brown treacle, chunks of rusty-all-kinds-of-stuff coming out. Flushed it.. obviously. a change every couple of years would be good in an ideal world, with plenty of spare time. Cheap enough to do, if yer nipples hold up!