mobjak

Hello all,
First post, so please be gentle!

1997 A8 130k 4.2 quatro

Braking issue, while driving and applying the brakes for the first time, they work normal. If I let up on the brakes, but do not accellorate (SP) it is like pressing on a rock with very little braking power. I have determined if I rev the engine the brakes are much better, but to try and say pump the brakes, good the first time and then very weak like no power brake assit.
My first thoughts were...
Power Brake Booster?
Vacum lines to the Power Brake Booster?

Is there any way to test each of these items prior to replacement?
Any other suggestions of things to check.

I have tried many searches on this forum, but have not hit paydirt.

Thanks in advance,
Mobjak

JimR

I'm thinking the vacuum lines should be a) cheap and b) relatively easy to locate, and would be the first thing to try.

mobjak

<center><img src="http://pictureposter.audiworld.com/133525/vacuum_hose.jpg"></center><p>Well, after digging into the vacuum line and following the twisty lines, I actually believe I found the culprit. Historically, it seems that I don't usually find something this obvious. Pic below is the hose that has quite a hole in lower left side branch.

I wonder what else this was affecting?

icsamerica

my guess this that the A8 booster doest have enough vacuum storage and the general efficiency of the motor doesn't let it build sufficient vacuum during rapid deceleration. My 2000 does the same thing. Try a vacuum accumulator. I'm going to do it as soon as I find a place for it.

http://www.jegs.com/i/JEGS/555/63010/10002/-1

This is another issue that make me think the A8 was designed on paper by academics who didn't drive the car enough.<ul><li><a href="http://www.jegs.com/i/JEGS/555/63010/10002/-1">http://www.jegs.com/i/JEGS/555/63010/10002/-1</a></li></ul>

gondar

A little plastic flapper job, its purpose is to keep atmospheric pressure from leaking back in to the lowered pressure area in the booster. The pressure differential provides the boost.

Its another thing to "check" out. They are, or should be, cheap. For all I know the A8 has some sort of nutty integrated assembly, I would not put it past them....my brakes are OK.

Cj7

Did that fix your issue?