[DeTomaso] Wilwood Brakes WTF????

[Tomas Gunnarsson]

Side note: What are the residual pressure valves doing in your system?
They don't seem to belong there at all.
 
Tomas

<-----Ursprungligt Meddelande----->
From: MikeLDrew at aol.com [MikeLDrew at aol.com]
Sent: 15/4/2013 1:09:26 AM
To: asajay at asajay.com; detomaso at POCA.com
Subject: Re: [DeTomaso] Wilwood Brakes WTF????

In a message dated 4/14/13 14 23 47, asajay at asajay.com writes:


> Could it be there is a restriction to the
> top set of pistons that would allow more pressure against the bottom
two
> than the top?  
> 
>>>Tapered pad wear is common in four-piston calipers with equal-sized 
pistons, because of the spinning rotor causing drag on the pads and
trying to 
lift them upwards (in the case of a rear-mounted caliper) as well as
heating 
the pads unevenly.

> >Could it be that's a design of the caliper?  Could it be
> the calipers are actually mounted upside down?
> 
>>>No. The calipers are actually identical top-to-bottom; the only 
difference is the location of the brake bleeders (at the top) versus the
crossover 
tube (at the bottom).
> 
> >What brake fluid are you running?
> 
>>>ATE Typ 200, really good German DOT 4.

> >When was it last changed?
> 
>>>Just a few days before the track event.

> >When you bled it to take the caliper off, what color was it?
> How dirty did it look?
> 
>>>It looked brand new--because it is. No color to it at all, other than
normal brake fluid color.
> 
> >I think I'd look into the idea that the calipers were mounted upside 
> down?
> 
>>>That would be a very basic problem, but you can see from the photos
that 
they aren't upside down. Crossover tubes are at the bottom, bleeders 
(barely visible) are at the top.

> >Where did you get them?  Dennis Quella?  Send him the pictures and
give
> him a call, I bet he'll know the root cause right off the bat.
> 
> >>>Yes, he'll be hearing about this first thing in the morning and 
hopefully he has some words of wisdom.

>When the system heated up, the piston and ring would
get stuck and the car eventually would cease to move.  Cool it down, and
it
would release and you could keep going.  THis happened at all four
wheels.
But I was able to ge them to move again after popping the bleeder.  This
may be happening (probably is after what you described) with your
calliper
pistons.

>>>The problem you describe is a hydraulic problem--the master would get
stuck and apply brake pressure to all four calipers. When you popped the
bleeder, the pressure would be released and you could move once again.
That 
was my first thought as well--brake pressure remaining in the front
circuit 
and activating the brakes. But I popped the bleeders and there was no 
pressure in the system, but the brakes were all still dragging. The
pistons 
subsequently proved quite difficult to remove from the calipers, even
when 
visibly straight, not cocked.

>Are these calipers equal size bore and if
not, are the smaller pistons at the bottom?

>>>They are equal-size pistons.

>Couple things, if the rears had little wear then the system is not 
balanced. Of course, that has nothing to do with the front issue.

>>>The brakes are *perfectly* balanced. The fronts malfunctioned and got
stuck on, which resulted in massive amounts of pad wear. The rears
didn't 
malfunction.

>Are the front pistons the same size or are they staggered piston
calipers. 
If they are the same size, the problem you experienced is
common. This is why they have staggered piston calipers and 6 and 8
piston 
units.

>>>Same-size four-piston calipers.

>I believe you are driving past the capabilities of the current system.
4 
piston non-staggered calipers are fine for the street but
for the track, they are entry level at best (in my opinion). Sure, there
could be some mechanical issues such as a stuck piston or
air in the system, etc... but since the issue is consistent across both 
sides of the car and across both pads in each caliper, I
believe you have exceeded the capabilities of the current system.

>>>You may well be right. The thing is, real racers have been using
these 
calipers for years, pushing them WAY harder than I do, without these
sorts 
of issues. And in fact, I ran these calipers at other tracks
(admittedly, 
with street tires with much less grip) with no issues. Wilwood makes 
'light-duty' four-piston calipers (the Dynalite series), but mine were,
until 
relatively recently when six-piston became more common, the mainstay of 
Wilwood's business, used by racers of every discipline for years with no
such 
issues.

>I would strongly consider upgrading to 6 piston calipers 

>>>I have given that some thought; however, lots of other people who run
harder than I do with these same calipers don't have these kinds of
issues...

>and also evaluate why the rears are not matching the fronts from a
wear/performance perspective.

>>>Because the rears didn't malfunction. :>)

> I have Wilwood Super Lites and noticed that when I was changing pads,
the 
wear pattern was very similar to Mike's. It took a bit of work to get
the 
pistons out as some were cocked in the bores.  when used with 1.25"
rotors, 
well worn pads will cause the piston to extend so far out in their bores
that 
they will cock. This can happen with as much as 0.250" of pad material 
remaining.

>>>An interesting theory--the front pads started to wear, unevenly,
which 
caused the pistons to cock and become stuck, which caused the brakes to
stick 
on, which caused further wear, etc. etc.

FWIW my '66 Mustang has stock Ford four-piston calipers with equal-sized
pistons, and after hard running on the track, the pads would wear with a
slight taper--but nothing like I have experienced here.

Thanks for the help so far--keep those ideas coming! :>)

Mike
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