brake conversion-wilwood

[Bernie Benz]

Hi Scott,

I'm in general through with this thread, inasmuch as I don't have Wilwoods,
just opinions (suprise!) hopefully based on sound principles, but I must go
through your response below to challange some of your apparent
misconceptions, Scott.

> From: QSHIPQ at aol.com
> Date: Sat, 11 May 2002 23:24:32 EDT
> To: b.m.benz at prodigy.net
> Cc: 200q20v at audifans.com, DasWolfen at aol.com
> Subject: Re: brake conversion-wilwood
>
> Bernie:
> I'm not at ALL with you, I doubt wilwood is too.  Shims, quite frankly are a
> great idea for a couple reasons.  First, as a pad wears, more of the piston
> is exposed to the elements in a non sealed caliper.  This means (SS or not)
> that surface rust forms on the piston,
If rust forms on a ss piston, it's not stainless.  That's Wilwood's problem.
> the further the pad wears, the more
> rust area will form.  As this crud gets scraped off,
What is scraping it off?  Happens in service or during inept overhaul?
What you absolutely don't want is for the piston seal to scrape it off when
the pistons are forced back into the caliper to make room for shims or new
pads.
>wear of the piston bore occurs, more crud = more potential wear =increased
service interval.
By the piston bore I assume that you are referring to the caliper bore in
which the piston seals.  What wear?  In service the piston never touches the
caliper bore.
>
> WRT dust sealed calipers, as the pad wears, the piston is pushed further from
> rest position.  The further a piston travels to make pad/rotor contact, the
> less stable the piston becomes, and from a strict leverage standpoint, the
> further a piston is extended, the more the caliper tendency to twist.  This
> is especially true of floating calipers, but it certainly applies to fixed
> calipers as well.  As a caliper twists or a piston kinks, the more heat is
> generated.  As heat increases, bye bye dust seal,. btst many times especially
> on G60's
Scott, I just don't know where to start on your apparent misconceptions
above, but I'll try.

First, the pads are rigidly restrained from moving tangentally with the
rotor by the carrier, not the caliper.  There is no force resulting from
braking torque exerted on the caliper!  If braking force is sufficient to
deflect the carrier and inasmuch as it is mounted to the bearing housing off
center of the rotor, this deflection would cause an inperceptively slight
twist at the business end of the carrier which is holding both the pads and
the caliper.  But the caliper is just going along for the ride with the pads
and sees no change, twist, relative to the pad or its slides.  There is no
twist of the caliper relative to the pads or relative to its mounting points
on the carrier!

Therefore, the piston instability problem to which you allude does not
exist.  The piston axis is always perpindicular to its mating backing plate,
therefore is always on axis with the caliper bore (unless the pad has worn
tapered).  This latter unusual condition may cause the piston axis to not be
congruent with the caliper bore axis, but never enough such that the piston
surface contacts the bore.  The piston seal keeps the piston centered in the
caliper bore, such that there is never contact between the piston and
caliper bore and therefore no associated wear.

The only heat generated in the braking system is generated by friction
between the pads and the rotor.  There is no other source of heat!  Twists
and kinks, real or unreal, do not generate heat.  You have kinky pistons?
Kinky pistons must be bad!
>
> I'm not really sure which corner you are presenting your opinions from.  It
> would appear that keith is speaking of aftermarket fixed caliper arrangements
> with no dust shield.  You are speaking of either aftermarket fixed caliper or
> stock floating calipers with dust shields.  IN either perspective, the less
> total piston travel you have, results in ALL good things in terms of service
> life, btdt.
My comments are general, applicable to any braking system excepting where
stated as Wilwood related.  Piston travel relative to its seal interface is
related only to pad wear, therefore with pad wear the seal is moving onto
the clean internal piston surface, never the other way, excepting when one
forces the piston back into the caliper bore (without overhaul) for shim
addition or pad replacement, thus forcing the dirty external surface through
the seal interface.
>
> When you speak of ANY aftermarket brake combination, shims are a key factor
> in them.  For more on this ck the archives, I went a round with MGW on this
> exact point.  Bottom line:  The less piston travel (*however* you achieve it,
> shims are the easiest way) over the life of a given pad, the less service the
> caliper will require.
As I demonstrated above, there is absolutelly nothing negative about outward
piston movement compensating for pad wear, nor does it result in any
required caliper service.  Smart caliper service is performed in preperation
for new pads,   Not so smart caliper service must be performed as a result
of caliper seal failure caused because of dirty pistons being forced into
the caliper bore (obviously such seal failure is much less frequent with
booted pistons than open).
> Remember too, that if you gander about WRT pad
> thickness vs backing plate/shims, the measures are all over the map.  Close
> attention should be paid to the piston extension recommendation, especially
> as you clamp "non app" rotors (ie big reds on A8 rotors for example)
Huh?
>
> Bernie, I service a LOT of aftermarket brake setups on quattros, some better
> n others.  But here, bottom line, I'm just not with you.  With many of the
> wilwood applications, or anyone going after 4x4 pot calipers, you really
> *have* to do the shim routine, or you will find yourself out of master
> cylinder quickly.
Scott, I have never questioned, and have high respect for your service
experience.  But IMO, the use of shims is an old wive's tale (tail),
excepting possibly in the use of unbooted pistons on dirt track, aka
Wilwood.

How does one run "out of master cylinder"?   Are you talking about running
out of pedal stroke?  No, the pad to rotor clearance established by the
flexing of the piston seal remains constant through out the full thickness
life of the pad.  No, not the brake fluid resorvoir volume, as it is
sufficient to allow backing plate to rotor contact on extreemly undersized
rotors without sucking air.

I hope that we are still having fun.

Bernie
>
> my .02 arbitraged thru the peso
> '87 t44tqw mit big reds (dust booted)  and shims

> In a message dated 5/11/02 8:49:30 AM Central Daylight Time,
> b.m.benz at prodigy.net writes:
>
>
> Scott and Keith,
>
> My point is based on the fact that reliable 0-ring and Quad ring seals must
> be protected from the ingestion of even small particles and quanities of
> dirt.
> That's why shocks and all industural hydraulic cylinders use rod scrapers as
> the outside protection from such intrusions.  Inasmuch as this road grime
> cannot be cleaned from the piston surface, short of disassembly, within the
> small piston to bore clearance and the sharp accute angle formed at seal to
> piston interface, it will be ingested if the piston is forced back into the
> bore.
>
> Mark's response from "Todd Howerton" <ToddH at outlawdiscbrakes.com>
> Subject: DUST SEALS indicated that Wilwood pistons are stainless steel and
> he did indicate that some use Keith's "trick" in servicing pads, but hardly
> a recomendation, IMO.  Therefore, from a seal reliability standpoint, in the
> absence of dust boots the piston should never be forced back into the
> caliper without disassembly and cleaning.  And there is absolutely no good
> reason for doing so.  A little ss hanging out in the breeze incours no harm,
> but don't abuse your seals!
>
> Bernie
>