[DeTomaso] Wilwood Brakes WTF????

Asa Jay Laughton asajay at asajay.com
Sun Apr 14 17:23:26 EDT 2013


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
******************************
http://www.racingagainstautism.com
http://www.teampanteraracing.com
http://facebook.com/racingagainstautism


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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