Brake Update [was Re: Hydraulic Clutch Bleeding Made Simple]

[Scott Fisher <sefisher@cisco.com>]

Todd Young wrote:
> 
> If you look around at a parts store you can find said piece of tubing with
> a handy-dandy one way valve at one end and a piece of plastic with holes
> in it at the other end. The piece of plastic with holes serves to lock the
> hose onto the bleeder and the one-way valve helps prevent pulling air
> back into the system under ANY circumstances (as long as the hose
> doesn't come off the bleeder). I've had this thing for years, best $5
> I ever spent, turns a two man job into a one man job.

Funny this should come up now.... I spent the weekend doing the brakes
on my '83 Coupe, including flushing out the old stuff and replacing with
new Castrol LMA fluid.  Some recent updates on the procedure:

* For 2WD/LHD Audis of my vintage, the sequence for bleeding is RR, LR,
RF, LF.  This is just the breakdown of "farthest from the master
cylinder first," a pretty much universal rule -- though not always
obvious (some solid-axle cars, for example, have the tee on the
right-hand side of the axle, making the LR wheel the farthest from the
master cylinder).

* If you've got one of the cars with the brake-proportioning valve in
the rear that's hooked up to the rear axle, make sure you press the
lever rearwards before bleeding.  So saith the Haynes manual, at any
rate.

* Brett Dikeman mentioned an important difference for bleeding the
brakes on bomb-equipped cars, a piece of hardware unknown to me but from
his description it sounds like some kind of pressure accumulator. 
Consult the Book of Armaments for details, no doubt...

* Even better than the one-way valve hose setup that Todd mentioned is a
device made by Lisle that my wife picked up when she went to get the
LMA.  It's a short, clear tube that fits into a little translucent
plastic bucket.  A second, even shorter tube goes into the bucket, and
there's a vent on the cap.  When you've pumped about two squirts into
the bucket, it becomes an air trap, and air will not go back into the
tubing.  The system comes with three little L-shaped caps that connect
the vinyl hose to the bleed nipple.  Use the tightest one that will fit.

* My RF caliper took a fair amount of convincing to get the piston to
retract, even after opening the bleed nipple to give the fluid a place
to go.  Not coincidentally, the fluid that I bled from that caliper was
pretty nasty.  On cars I like and/or drive hard, I try to replace the
fluid every two years "whether it needs it or not."  This will help
prevent the corrosion and deterioration of seals inside the calipers (or
elsewhere in the system).  Note that later-model Audis may have
different requirements for brake fluid; my use of Castrol's LMA product
may or may not be appropriate for a newer Audi, so check your
documentation if you have a newer car than my '83.  And LMA *will*
remove paint -- in fact, on a race car several years ago, I used drained
Castrol LMA on a rag to take overspray off some of the poorly-masked
trim pieces (headlamp rings, mirrors, what little brightwork remained on
the car) after an in-the-garage repaint.  Works great...

* The fluid that came out actually had *chunks* of goo in it.  Eurgh.  

Now, how do the brakes feel today?

Pedal feel is *incredible*, like standing on a brick.  There's a short
amount of travel and then *wham*, you're stopping.  I took the time this
morning to bed in the pads (Axxis MetalMasters up front), a step that
always pays off in improved stopping down the line.  That consists of a
series of low-pedal-pressure stops from low speed, progressively
increasing both the speed and the pedal pressure.  

What's all this for, you may ask?  There's a club track day coming up at
Laguna Seca in September, and I want everything to be just right...

--Scott Fisher