Re: 5000 brake booster (servo)

[Carl DeSousa <desousa@cisco.com>]

Brake boosters!  Oh I know them *well* because I have to pick up our 
car from the dealer this afternoon to pay the bill for the new one
that they are installing as I type this message.  The bill after
replacing the master cylinder, pressure accumilator, and booster is
coming out to $1300.00!  This does not make my wife happy, let me tell
you.  And thats paying wholesale prices for all the parts.

> From: "New England: July-August & winter  16-Nov-1994 0826" <samaras@wrksys.enet.dec.com>
> 
>      This discussion applies to 5000's etc. with hydraulic power assist.
> 
> I've found that failed hydraulic boosters are a fairly common problem. I bet
> lots of folks are driving around with marginal boosters. I also "think" that
> replacing the pressure accumulator will make a marginal booster look good due
> to the higher hydraulic pressure available.  

I agree with you, failed hydraulic boosters are a fairly common
problem and especially on higher milaege 5000s.  We drove around with
not a perfect feeling brake pedal for more than a year.  First we
replaced the master cylinder.  It was good till about a week ago, then
the new master cylinder failed.  I opted for the OEM master cylinder
this time as apposed to an aftermarket one.  Its just not worth it to
me anymore to put in aftermarket parts.  This is about the 3rd time
I've had to replace an aftermarket part. As an example the aftermarket
master cylinder cost $130 last year.  Now I paid $175 for one from Carlsen.  

The pressure accumilator may not have been bad in our case.  But he
claimed he measured its ability to hold pressure and it failed.  I
wonder if the failing booster threw him off.  The technician at
Carlsen struggled with trying to diagnose the exact problem.
It wasn't till after the master cylinder and pressure accumulator
were replaced that he concluded the booster needed replacing as well.
With 120K miles on the car, and a pregnant wife driving it in through
the winter, I felt it was better peace of mind to have all these
components changed anyway.

> 
> Anyhow, the telltale booster test is to disconnect the return line from the
> booster (the one that goes back to the reservoir). If _any_ hydraulic fluid is
> dribbling out of this line when the brake is not applied, the booster is
> marginal. The higher the leak rate from the return line, the more "bad" the
> booster. Since this is an internal leak, it's easy to understand why folks may
> not know they have a problem.
> 
> Symptoms of a bad booster are: a bit higher pedal effort (but not too bad) and
> lack of pressure reserve. Try pumping the pedal hard 5-10 times while the car
> is idling. Can you make your brake warning light come on? Suspect the booster,
> especially if the pedal effort seems to remain normal.  

Yes we had all of the above symptoms.

> Be careful that a bad
> accumulator can create similar symptoms. If the booster leaks all the time, the
> pressure accumulator may never reach full pressure. Old accumulators that are
> OK, but are holding less pressure are "bothered" more by booster leaks.
> 
> I got my "new" booster from a junkyard (an Audi with 40K on it). As someone
> mentioned, there are 4 nuts that have to be removed from _way under the dash.
> You have to remove all of the tricky trim panels, but the actual unbolting
> isn't all that hard, just tedious. Be real careful to put penetrating oil on
> all of the brake line fittings that connect to the master cylinder (yup, that
> comes out with the booster). Bently says that the rod length between the
> booster and the master cylinder is very critical. I didn't mess with it.  If
> you aren't sure, read the book.

I didn't have the time to do all this myself and I knew when I looked
under the dash that it would be time consuming.  Carlsen charged me 2
hours to diagnose and replace it.  I'll post a breakdown of the parts
and labor costs when I get the final bill in front of me.

> 
> Bently is pretty good in this area,  It explains the drip test I mentioned
> above, and has good pictures.
> 
> The whole hydraulic power assist idea is kinda neat.  The booster is real small
> and light. The hydraulic pump is only marginally bigger than a normal power
> steering pump, so all together, there's a pretty good weight/space savings.
> BUT, these components just aren't good enough for a production environment.
> With the overall attention to durability in an Audi, the hydraulic system is a
> real letdown. Good idea, but it wasn't ready.  What are the "newer" Audi's
> like?

Bill, again I agree with you, the hydraulic system just doesn't cut it for the
long haul.  

All you 5000 owners need to consider all the factors like steering and
brake hydraulics repairs as an expense that you will need to face
sooner or later(if you haven't already).  Fact is 5000's and
100's/200's have a lot more to go wrong than the 4000's/90/80's.  And
it can get expensive.  Buy them cheap and plan for the repairs/costs.
You'll probably really enjoy the car for a long time.  I just lectured
my sister last week about maintening here 89 200 Quattro.  She hadn't
changed the oil for 6 months.  I told her to sell her Audi and buy a
new Toyota or expect some very expensive repairs in the future.  These
cars need to be maintained properly.  She moped a said she loves her
Audi and would get better at servicing her car.  :)

I won't recommend buying 5000's in the future to friends and family
unless its at least 87 or preferably newer.  The 84s adn 85s are the
worst, 86's are better.  The technician at the dealer voiced this
same opinion.  Most of you probably already know this.

Carl DeSousa





; Carl DeSousa