[s-cars] Brake Fluid Equalizer

[Max Hoepli]

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
> >
> >
>
>