[s-cars] Brake Fluid Equalizer

Wed Jun 27 16:15:23 EDT 2007

Mechanic advised me that it is the left cable that is the problem, if there
is something to change out. Calibers are OK.

Max

----- Original Message ----- 
From: "motogo1" <motogo1 at cox.net>
To: "Max Hoepli" <mhoepli at vif.com>
Sent: 27, June 2007 14:04
Subject: Re: [s-cars] Brake Fluid Equalizer

> You may need the replace the parking brake cable/cables. They break near
the
> rear of the car, where they make a 90 degree bend and let in dirt and
> corrosion. Not a fun job. Did it on both my 91 200 and 94 s4.
>
> Gary
> ----- Original Message ----- 
> From: "Max Hoepli" <mhoepli at vif.com>
> To: "DeWitt Harrison" <six-rs at comcast.net>
> Cc: <s-car-list at audifans.com>; "Quattro List" <quattro at audifans.com>;
> <w-t_audifans at yahoogroups.com>
> Sent: Monday, June 25, 2007 8:33 PM
> Subject: Re: [s-cars] Brake Fluid Equalizer
>
>
> > In  response to this informative email from Harrison.....Why not have a
> > brake line for both the rear left and rear right caliber from the brake
> > master cylinder with the rear left and rear right having its own
> > proportioning valve?
> >
> >
> > Having parked the car over the weekend without parking brake applied,
> > drove
> > 180 km, then parked with parking brake applied. Drove off 2 hours later
> > and
> > realized car was dragging, parking brake had an empty feeling, don't
think
> > brakes in back were released. stopped, rear left wheel smoking and
> > smelling
> > burnt. Tapped on rear left caliber with a small hammer. Drove off, the
> > parking brake had the good full feeling again as it normally does. Car
no
> > longer was dragging. would greasing parking brake cable help?
> >
> >
> >
> > Max
> > 1986 type 44 turbo quattro
> >
> > ----- Original Message ----- 
> > From: "DeWitt Harrison" <six-rs at comcast.net>
> > To: <mhoepli at vif.com>
> > Cc: "Quattro List" <quattro at audifans.com>; <s-car-list at audifans.com>
> > Sent: 18, June 2007 22:01
> > Subject: Re: Brake Fluid Equalizer, a.k.a. the Thingy
> >
> >
> >> On Mon, 18 Jun 2007 17:04:00 -0400
> >>      "Max Hoepli" <mhoepli at vif.com> wrote:
> >>
> >> > Just had the original brake fluid equalizer/proportioner [C$355]
> > changed.
> >> Found in front of the left rear wheel.
> >> > Anyone know what the equalizer has inside? Mechanic says equalizer
was
> >> seized, practically only the front
> >> > brakes were working. Anyone can give some knowledge of the function
of
> > the
> >> equalizer? The car with the
> >> > old equalizer was making boing-boing spring noises at the back, most
> >> noticeable in an underground garage.
> >> > With the new equalizer very smooth, quiet boingless braking.
> >> > The rotors in the back were rough, rusty on the inner surfaces. only
> >> > the
> >> outer surfaces were touched by
> >> > disc pads.
> >> >
> >> > Should the mechanic 3 weeks earlier who changed the front brake shoes
> >> C$135 and both front rotors,
> >> > each C$140 have noticed that the equalizer was defective? The car was
> >> making rubbling noises when
> >> > the brakes were applied after this service, with time I was aware
that
> >> this noise was coming from the
> >> > back, which prompted me to see my other mechanic.
> >> >
> >> > There has never been discussion of the brake fluid equalizer as far
as
> >> > I
> >> know in this group.
> >> > It seems to me it might be a good idea to grease the shoulder joint
of
> > an
> >> equalizer to prolong its life.
> >> >
> >> > Max
> >> > 1986 Quattro type 44
> >>
> >> You're right. This is an overlooked item on the list. The following is
a
> >> discussion on
> >> the topic which, I think, pretty well sorts out what's going on. Tell
me
> >> what you think.
> >>
>
>> -------------------------------------------------------------------------
-
> > --
> >> ---
> >>
> >> By George, I think we've got it! I would explain it this way,
> >> short story made long:
> >>
> >> The first priority of the engineers was to adjust fore/aft
> >> brake bias by sensing rear cargo loading. It is always the case
> >> that fore/aft bias means reducing the pressure to the rear wheels
> >> since the rear tires become unloaded during normal braking
> >> maneuvers. As the rear trunk is loaded up with cargo, it is
> >> desirable to have less pressure reduction to the rear brakes
> >> since there will then be less forward weight transfer during a
> >> stop and the rear brakes become more effective.
> >>
> >> How to adjust for rear cargo loading? Put in a brake pressure
> >> proportioning valve that senses rear suspension displacement.
> >> Where? On the left trailing arm. Oh, but wait. The right
> >> and left rear suspension deflections also respond oppositely
> >> to cornering forces. Now what? Put in a second pressure
> >> reducer that can distinguish between left and right turns.
> >> (Let's call this valve the Thingy.) Apparently, with the load
> >> sensing reducer looking only at the left rear corner, we need
> >> to put this second reducer to work at regulating the other corner.
> >> (Maybe this problem could have been solved with independent
> >> rear brake line pressure sensing reducers. Or -oh I know! -
> >> independent ABS circuits for the rear wheels a la ur-S4.)
> >>
> >> In a right hand turn, there will be weight transfer onto the left
> >> suspension members both front and rear. From the perspective
> >> of the left side mounted load sensitive proportioning valve, the
> >> rear will appear to have become more heavily loaded, and it
> >> will increase the pressure in the rear brake circuit. But at this
> >> moment, the right tire has become unloaded and it will
> >> lose traction and lock up, especially with the surge in rear
> >> brake line pressure. What to do? What to do? Well,
> >> why not just but a pressure reducer Thingy in front of the right
> >> rear caliper that is sensitive to that right turn? Now, if it is a
> >> right turn, reduce pressure to the right caliper. Clever.
> >> Meanwhile, in a left turn, the fore/aft sensitive pressure reducer
> >> thinks a sky hook is lifting the back of the car off the ground and
> >> reduces the overall rear pressure accordingly, trying avoid
> >> rear lockup on both sides. However, this action will fail to
> >> take advantage of the braking forces that would be available
> >> at the now heavily loaded right rear wheel.
> >>
> >> In an asymmetrical system like this, barring the intervention of
> >> some pretty darn smart software and electronic brake actuators,
> >> it will never be possible to tweak it enough to realize optimum
> >> performance. If I was willing to give up the rear cargo loading
> >> input to the rear brake bias, I would install either a fixed
> >> proportioning valve to regulate the rear or a cockpit
> >> adjustable rear proportioning valve and remove the Thingy.
> >>
> >> DeWitt
> >>
> >>  ----- Original Message ----- 
> >> From: "Scruggs, Gross Jr." <gscruggs at nmic.navy.mil>
> >> To: "'DeWitt Harrison'" <six-rs at comcast.net>
> >> Sent: Wednesday, November 16, 2005 9:05 AM
> >> Subject: RE: rear brake circuit on a 5ktq
> >>
> >>
> >> > >
> >> > >
> >> > > I have a Thingy Theory. It came to me in the dead of night.
> >> > >
> >> > > The rear, load sensitive proportioning valve senses rear ride
> >> > > height. But WHERE? ON THE LEFT REAR TRAILING ARM!
> >> > >
> >> > > Is that a large enough clue? Would you care to take a stab
> >> > > at completing the description of my theory?
> >> >
> >> > Well... lessee now...
> >> >
> >> > If load valve sees increase in ride height then it must conclude that
> > car
> >> is
> >> > braking in either straight line or left turn... and ABS keeps left
rear
> >> from
> >> > locking.  Right rear not an issue because: if straight line braking
> >> > then
> >> ABS
> >> > reduces pressure (actually pulses) and if in left turn then increased
> >> normal
> >> > force keeps RR from locking.
> >> >
> >> > If valve sees decrease in ride height and incipient loss of traction
> >> > (through ABS) then car is braking in right turn and Thingie comes
into
> >> play
> >> > by reducing pressure to right rear brake.  Left side not an issue as
> >> > increased normal force keeps from locking.
> >> >
> >> > Agree with yours?
> >> >
> >> > Gross
> >> >
> >> >
> >>
> >>
> >
> >
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