[DeTomaso] Wilwood Brakes WTF????

[MikeLDrew at aol.com]

In a message dated 4/16/13 13 39 46, theemonkey at yahoo.com writes:


> I talked with Bob Benson last night.He is unable to post to the forum at 
> the moment as he just got a new computer and something is not set correctly 
> yet.He is running the same brake pad compound you and i are both 
> using(Wilwood BP20),and his pads are barely worn down at all.
> 
>>>I don't think he was using the brakes very hard. :>) :>) :>)

> >Granted his were installed just before Laguna Seca so they will have 
> less wear than yours as i believe you have had the Bp20's on for awhile 
> including being used at ThunderHill last fall correct?
> 
>>>True--they worked great there, with almost no wear whatsoever.   The 
pads looked like new when I installed my slicks in the pits that morning at 
Laguna.

> >By the way he had the BP10's before and they lasted 7 years and they are 
> nowhere near as good as the BP20's.
> 
> >>>I have been VERY impressed with the BP20s as well.   They worked really 
well on the street, and at every other track I've been to.

> >He does however have 6 piston front calipers which use a longer pad than 
> the 4 piston calipers.
> 
> >>>Some do, some don't.   He has larger rotors and probably larger 
calipers/pads than I do.   Some of the smaller six-piston Wilwoods use the same 7420 
pad as the four-piston Superlite IIs that I have.

> >I do not think the larger front calipers are the reason that his lasted 
> longer than yours.Although they certainly did not hurt.I think either the 
> bias is off(not enough rear bias versus front)or the fronts got really hot 
> versus the rears and thus wore out faster.
> 
>>>Excess front bias would tend to overwork the fronts and thus get them 
really hot and make them wear out faster.   So that is really a single, long 
explanation rather than two different ones.

> >I am leaning towards a bias issue as at first glance as i do not know 
> why the rears would be that much cooler than the fronts.The fronts will work 
> harder as they do more,but not as much as the wear differential between 
> front and rear as you describe.
> 
> Just guessing on my part.
> 
>>>It's an excellent point.   I did note that when the front got hot, the 
front brakes had reduced effectiveness (although the pedal remained 
rock-solid) and I eventually developed excessive rearward bias.
> 
> >PS, do you have an adjustable proportioning valve?If so do you know how 
> it is set at the moment?
> 
> >>>No, I don't have an adjustable valve.   When Dennis Quella marketed this 
as a complete system, he said that he had calculated piston area and 
achieved proper proportioning by using smaller-piston calipers in the rear, and 
that therefore the stock pressure-reduction valve needed to be removed from 
the system.   You may well be right though--I might have insufficient rear 
braking due to the lack of a pressure-reduction system in the front (the same 
problem that Panteras with street brakes when the pressure reduction valve is 
removed).   I could experiment and put an adjustable proportioning valve in 
the front circuit to try to shift the brake bias rearward.   Alternately, I 
could buy six-piston front calipers, and move my existing larger-piston 
front calipers to the rear, which would theoretically improve braking at both 
ends (although at that point, front/rear bias becomes just a guess).

Or I could fit different-compound pads in the front to cope with the higher 
heat.   And I could/should fit floating rotors in the front to eliminate 
the chatter that seems to be common with Wilwood hats.

But, the doorbell just rang, and my package from Summit with new caliper 
seals and new BP20 pads just arrived, so in the short term, I'm going to the g
arage to just put everything back together as it was, so I can go to 
Phoenix!   After I'm done paying for a wedding, I can turn my attention back to 
this issue and see what might be done to improve things.

Thanks again for all the suggestions!

Finally, I should share this, which just arrived from an engineer-type in 
the Nor-Cal Shelby Club with lots of Laguna Seca track experience.   His 
experience tracks with mine, with respect to the improvements to be realized by 
simple brake cooling.   Don wrote:

====
Ahhhh …. Laguna Seca ….  Brakes!
 
For my own history, I used to run my ’88 Corvette at NorCal open tracks. 
The car handled well but was a bit short on braking at Laguna. On one hot day 
I went through a set of just installed brake pads in one day! Let’s say 2 
hours of track time. The brake pedal went to the floor a couple of times going 
into turn 2 (I was braking early kinda expecting this to happen), you pump 
the brakes real fast when this happens! So, I backed off a bit on my pace to 
keep things from going completely to hell. Also, when the friction material 
gets thinner, more heat goes into the caliper pistons, so you are more 
likely to boil brake fluid. At the end of the day, the friction material was 
almost gone. Yes, the seals in the calipers were cooked. Brake material was on 
the inside of the front wheels, not just powder, but bigger pieces almost 
the size of sand particles.
 
It is my opinion that once the brake pad material gets really too hot, it 
ablates. Now, ablation means that the surface of the pad material burns off 
and with the flaming effluent, it keeps the brake pad (and rotor) surfaces 
from getting even hotter. That means the pads won’t last very long.
 
Most people would say, “get bigger brakes” or “you need to get so.and.so’
s brake pads, they’re great.” Now, that may work fixing the symptoms. But 
it does not address the problem.
 
The problem is inadequate brake cooling. Look at it this way: how big is 
your radiator? How much air is forced through the radiator? Now, how much 
cooling is there for your brakes? Keep in mind that as far as “horsepower” is 
concerned, your brakes have at least 4 times the horsepower that your engine 
puts out. (Your case may vary … according to your engine horsepower and your 
brakes).
 
So … I went to the trouble to put cooling inlets in the air dam of the 
Corvette, and plumbed “SCAT” (flexible aircraft ducting) tubing to the brakes … 
wherein I fabricated a backing plate on each front wheel with the air 
ducting into the hat of the rotor. From then on, I did not have any braking 
problems at Laguna, no soft pedal into turn 2, no easing off the pace to keep the 
brakes cool, and little pad wear after 2 days of running. Same stock 
rotors, same stock pads (stock Corvette pads are actually pretty good).
 
For the next example on my ’87 Mustang coupe track car which I bought in 
2001. It started out with stock brakes and aftermarket pads. These brakes were 
“OK” but sometimes going into turn 2 at Laguna, I’d get a really soft 
brake pedal, with resultant ‘more furious brake pedal pumpin.’ In 2002 I had 
the rear drums replaced 12” disk brakes (Corvette), which replaced the totally 
inadequate drums back there; that worked better. In 2003, I had 13” Brembo 
brakes installed in place of the stock brakes. That worked way better, but 
when the front pads would get thin, I would still get a soft brake pedal 
going into turn 2 at Laguna. In 2005 when I was reworking a lot of things on the 
car including decent paint, I installed front ducts (using the running 
light holes in the GT nose) and SCAT tubing forcing air into custom fabricated 
front disk backing plates forcing air into the hat of the rotor. I also did 
underbody air scoops and SCAT tubing into the hat of the rear rotors. Since 
then, these brakes have been awesome; even with Hoosier slicks braking from 
the California Speedway oval from 130 MPH into the abrupt 90 degree left 
hander going into the road course, I always have had more brake than tire. Oh, 
and the front pads last about 40 hours of track time. I have a hobbs meter in 
the car to keep track of running time, so this isn’t a guess.
 
I also did some measurements on the brake temperatures at Laguna after 10 
hard laps, using an IR heat gun for measurements.
With duct air:
Right Front rotor: 102 C Right Front Caliper: 66 C                Left 
Front rotor: 89 C      Left Front Caliper: 117 C
With ducts plugged:
Right Front rotor: >400 C  Right Front Caliper: 132 C          Left Front 
rotor: >400 C Left Front Caliper: 121 C
With duct air:
Right Rear rotor: 84 C     Right Rear Caliper: 105 C               Left 
Rear rotor: 180 C     Left Rear Caliper: 161 C
 
 
My comments about these measurements are:
 that the brakes were cooling rapidly, which probably accounts for some of 
the right/left variances (it takes time to take the temperatures). To do it 
right, it would have to be done very quickly … which it wasn’t.
With the ducting plugged, the front rotor temps were “off scale” on the IR 
temperature gun which means the temperatures were over 400 C. At LEAST 300 
C hotter without air blowing at the rotors. My friend who took the 
measurements said he was “overwhelmed” by the heat coming off the rotors when he 
took the measurements with the ducting plugged.
 
So, Mike, my recommendation is to first remove the calipers and rebuild 
them properly. Clean all parts with solvent, install new seals (using brake 
fluid as a lubricant when installing the pistons). New brake fluid and bleed 
the brakes (obviously, if the calipers were removed). Then go look at what the 
best way to blow air at your front brakes. Then have some fun fabricating 
ducting.
 
Don Wollesen

====

Off to the garage I go!

Mike