Brake servo assistance - or lack of it

[norwichphoto]

Just found out that the brake servo vacuum does a hell of a lot of assistance on an RS6... Fortunately no particular dramas.

From the little research I've done its probably a vacuum leak from the 'suction jet pump' doofer on the underside of the inlet manifold. A pig of a job by all accounts.

More research this evening...

[Shoppinit]

Yeah, but could be also the vac to the master cylinder or the master cylinder itself.

[norwichphoto]

If it helps diagnose remotely the idle is bouncing up and down between 1209 and 2500 rpm

[norwichphoto]

I'm also wondering if its an opportune moment to change the cam chains and guides whilst taking lots of things apart.

[Shoppinit]

Yeah, the car will be struggling to get the mixture right with a massive vac leak. You’ll probably get a MIL soon.

[steve2003rs6]

When I had a lack of servo brake assist. I was literally stood on my brakes and eventually the car very slowly came to a stop.
Scared the hell out of me.

Unit 20 diagnosed and installed a new brake booster valve.
Problem solved.

[Shoppinit]

Did you have symptoms of a vac leak, too?

I boiled my brake fluid in the Pyrenees once. Brake pedal went straight to the floor when I tried to brake with no slowing of the car at all. New underpants required.

[steve2003rs6]

Hi Ben. Yes mate it scares the hell out of you when you get a massive brake failure.
And yes my revs were up and down but not massively.

The second time I had brake failure was when out on long runs.
After about two hours of driving the brakes would fail. On short distances the brakes were fine.
Turned out to be a seized rear caliper cooking the brake fluid.
With the power of the engine I didn’t really notice that the brakes were binding / overheating.
Again unit 20 to the rescue. New calipers / pads / brake fluid installed.

[norwichphoto]

I have fairly new brake calipers on the back, and the fronts have recently had new discs and pads. Wheels aren't getting hot so I think its a vacuum issue. There is no smell of cooked brakes.

[Felix2566]

Hi Ben. Yes mate it scares the hell out of you when you get a massive brake failure.
And yes my revs were up and down but not massively.

The second time I had brake failure was when out on long runs.
After about two hours of driving the brakes would fail. On short distances the brakes were fine.
Turned out to be a seized rear caliper cooking the brake fluid.
With the power of the engine I didn’t really notice that the brakes were binding / overheating.
Again unit 20 to the rescue. New calipers / pads / brake fluid installed.

Might have just resolved what the issue was for me, I did find that the fluid was high and a few weeks later found that the rear caliper was binding too....but why would it cause the system to not give you braking assistance?

[steve2003rs6]

Felix.
As far as I know your ok til the brake fluid cooks.
Severe overheating of the fluid loses it’s ability to act as it should because the fluid can turn into steam.

Overheating also causes fading. The discs and pads become smooth due to the heat generated. Reducing the brakes effectiveness.

Ps I am not a expert or mechanic.
The above is what I have read up on.

[RS6Rottweiler]

Yeh, I've recently had the same problem, and it was the suction jet pump. it's a big job, lots to stir down and Audi don't have all the required spares you need. I replaced everything while I had it stripped down, better safe than sorry later on.

[Felix2566]

Sounds like something else to look at and check is working properly!
Dont want the assistance to fail again

[norwichphoto]

Audi can still supply the suction pump jet, but they couldnt' supply the inlet manifold gaskets. Fortunately some on Ebay.

[norwichphoto]

Bits starting to trickle in. I'll make a start on Saturday.
Not doing cam chains at moment.
but will tie in with oil and filter change and some new spark plugs.