[DeTomaso] Wilwood Brakes WTF????

Sun Apr 14 18:05:15 EDT 2013

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. 
Mark

________________________________
 From: Tomas Gunnarsson <guson at home.se>
To: detomaso at poca.com 
Sent: Sunday, April 14, 2013 5:51 PM
Subject: Re: [DeTomaso] Wilwood Brakes WTF????

Air in one place in a hydraulic circuit doesn't make the circuit
pressure differ from piston to piston, like you concluded. The tapered
wear is typical for equal piston calipers run hard. The stock calipers
try to combat that by having the leading pistons (where we now see more
wear) be slightly smaller. Are these calipers equal size bore and if
not, are the smaller pistons at the bottom?

Tomas

<-----Ursprungligt Meddelande----->
From: Asa Jay Laughton [asajay at asajay.com]
Sent: 14/4/2013 11:23:53 PM
To: detomaso at poca.com
Subject: Re: [DeTomaso] Wilwood Brakes WTF????

I am not an expert, but here are some theories:

You had air in the system, most specifically at the -top- of each 
caliper. Air compresses, fluid doesn't. Therefore the bottom pistons 
applied with full force, but the tops didn't; compressing the air 
instead until it reached an equilibrium with the fluid and then pressed 
on the piston. The difference in all four pistons application against a 
common solid object (the brake pad) caused the pistons to -tilt- 
sideways in the bores. Note the wedge shape of your pads, tops are 
thick, bottoms are thin, all four pistons are slightly cocked.

With that said, you'd think the pressure against the air at the top 
would distribute to the bottom as well. Yea, I'd think that too, that's 
why this is just a "theory." 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? Could it be that's a design of the caliper? Could it be 
the calipers are actually mounted upside down?

What brake fluid are you running?
When was it last changed?
When you bled it to take the caliper off, what color was it?
How dirty did it look?

I think I'd look into the idea that the calipers were mounted upside
down?
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.

Asa

Asa Jay Laughton, MSgt, USAFR, Retired
& Shelley Marie
Spokane, WA
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On 4/14/2013 2:07 PM, MikeLDrew at aol.com wrote:
> Hi guys,
>
> So, you may recall my description of me beating the snot out of my
Pantera
> at Laguna Seca a couple of weeks ago. I had a super, super time!
>
> Partway through the second session, I started to get some juddering in
the
> steering, from the brakes. I presumed that the cheapo rotors had
warped
> slightly, but I was able to drive through it, and then unwarped when
the car
> cooled off. I noted with some surprise that the front pads had worn
down
> 50% in just two 30-minute sessions while the rears looked perfect. The
wear
> was perfectly even.
>
> I then had an uneventful three-hour drive home. During one of my
stops, I
> took the time to feel the wheels for any excess heat that might be
caused
> by brake issues, and didn't feel anything untoward.
>
> The next time I drove the car, I noted that the brakes were definitely
> sticking (or at least, SOMETHING was sticking). I could drive down a
gentle
> slope, put it in neutral and the car would gently come to a stop.
Obviously
> not right.
>
> Today I jacked up the car and pulled the wheels, and was shocked at
what I
> found:
>
> http://www.poca.com/index.php/gallery/?g2_itemId=39244
>
> http://www.poca.com/index.php/gallery/?g2_itemId=39260
>
> Both brakes were clearly stuck on, with the pads badly tapered and
worn
> within microns of bare metal on the bottom sides.
>
> Since I have 2 psi residual pressure valves in the system, I thought
that
> perhaps the front one had failed and stuck on. If that was true, then
it
> would act almost as if somebody was stepping on the pedal. To test
that
> theory, I cracked a bleeder on each caliper, expecting brake fluid to
jet out.
>
> Nothing.
>
> So the problem is more mechanical in nature, rather than hydraulic. I
bit
> the bullet, pulled the pads and then removed the passenger side
caliper.
> The pistons were very, very difficult to move within the caliper; I
managed
> to compress one almost all the way before wising up to the fact that
it
> would be almost impossible to remove if it was flush. The other three
came out
> with some work, that first one came out after a LOT of work.
>
> The rubber seals inside the calipers look and feel just fine--having
said
> that, I don't exactly know how they are supposed to feel, but they are
soft
> and pliable. The pistons were covered with brake dust, but a few
minutes
> spent with brake cleaner and a rag, and some emory cloth, and
everything
> cleaned up perfectly.
>
> http://www.poca.com/index.php/gallery/?g2_itemId=39251
>
> So, the question is, what caused this? Could excessive heat have
caused
> the pistons to expand and swell and jam in the caliper? Not what I
would
> expect from 'racing brakes', and the pedal never went even slightly
soft, so
> it's not as if the fluid was boiling.
>
> Does anybody have any other theories as to the cause?
>
> And more to the point, what should I do now? I suppose since they are
20
> years old, and apart already, I should probably buy new seals (or new
seals
> and pistons?) and swap them out before reassembling everything. But
this
> still begs the question--why did this happen????
>
> Looking forward to words of wisdom (along with inspired wild-ass
guesses!)
>
> Mike
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