[DeTomaso] Wilwood Brakes WTF????

Sun Apr 14 22:16:20 EDT 2013

Marks reply makes the most sense. You probably just wore the pads down far enough that the pistons were out far enough that they cocked in the bore. As far as the uneven wear that's just the 4 piston calipers but I don't think related to the stuck pistons. At any other track your set up (assuming pads that have plenty of material left) is probably more than up to the task, but Laguna is just exceptionally hard on brakes!

Gray

-----Original Message-----
From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com] On Behalf Of Asa Jay Laughton
Sent: Sunday, April 14, 2013 5:17 PM
To: detomaso at poca.com
Subject: Re: [DeTomaso] Wilwood Brakes WTF????

This makes a lot of sense.  Please see this photo of the stock calipers from my 1973 Pantera:
http://www.teampanteraracing.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=1535&g2_serialNumber=1

Notice the caliper on the lower right.  That is the caliper for the
-right- front wheel (not left).  Note the brake line input is on the left, meaning that side of the caliper is mounted high.  Now note the size of the bores in the caliper.  If that caliper were oriented on the car (as taken off) the smaller piston would be applying braking force first (picture the rotation of the wheel is clockwise) and the larger piston immediately after that.

Now recall Mike's picture:
http://www.poca.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=39264&g2_serialNumber=2

it would appear all four pistons are the same size.

In all the hard track use I've put my Pantera through (not as hard as Mike by any means) I have not noticed any kind of odd wear patterns on the front pads.  I have noticed a nice even wear and plenty of pad left.  I've yet to experience brake fade either.  This is with the stock Girling calipers and Porterfield R4S pads.

The presumption may be correct; that his calipers are not suited to the kind of hard braking needed in a track event.

for what it's worth,
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 3:02 PM, Ken Green wrote:
> I don't know if this has anything to do with your wear, but just about all the high end calipers are differential bore, at least partly to even out wear.  The  996 turbo front calipers have 36 and 44 mm dia pistons (the trailing pistons have 50% greater area.  If the leading edge of the pad wore more, this might explain it, but I have no real experience.  One of the serious racers would know a lot more.
>   
> from the Internet:
>   	* Differential bore calipers -- As the surface of the rotor heats up, the clamping force of the pistons has to be increased to avoid brake fade. If the caliper has multiple pistons (or multiple pairs of pistons), the brake rotor surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the rotor surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger. Differential-bore calipers use smaller pistons up front, larger pistons toward the back.
>
> From: "MikeLDrew at aol.com"<MikeLDrew at aol.com>
> To: detomaso at POCA.com
> Sent: Sunday, April 14, 2013 2:07 PM
> Subject: [DeTomaso] Wilwood Brakes WTF????
>
>
> 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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