Ti Brake Shields

[widebody911]

I was intrigued by the Ti brake shields from Seine Systems, so I bought a set for the front. It's too early to tell how effective they are, but the math and theory sound promising. I was getting my brakes hot enough to burn the paint off of the pads, although not hot enough to cause any significant fade. As my skill and confidence levels improve, I figure I will start getting brake fade.

The shields were a piece of cake to install - remove the pads, push the pistons back, slide the shields and the pad in, bleed the brakes. Bleeding probably wasn't necessary, but that's one of the few things I'm AR about, the others being oil and trans fluid changes. I'll drive a car that's half-sanded and half-primer and 5 different colors, but those fluids better be in damn good shape or it doesn't leave the garage!

[gchappel]

I tried these shields on my 85 carrera, that used to get to the track several days a month. I think they helped. I had already optimized my present brakes, at least to a point. I had installed cooling ducts, was using AP600 fluid, which was bled before each event, and sometimes during events. I was using pagid orange pads and stock rotors. I would get a little soft pedal feel near the end of a hard day, but not until near the end of the last run of the day. After I installed the shields I didn't get the soft pedal- which means they help at least a little, I think.
Gary

[island911]

Originally posted by widebody911
. . .It's too early to tell how effective they are, but the math and theory sound promising.

Do you have numbers for the thermal conductivity of the brake material? . . I would guess, that while Ti is very low, the brake material would be even lower. (Making new, or thicker, pads a better insulator.)
FWIW; The thickness of a the pad is the only difference between the S-caliper and the later SC and Carrera caliper. (the "S" being thicker)

I would also think the design of the Ti shim would have holes stragically placed to further reduce heat transfer . . and the weight.

[911pcars]

Island911,
Here are a few thermal conductivity numbers to compare:

Material Grade Thermal conductivity W/mK
Steel 1330 51.9
Steel Alloy 4118 44.5
Titanium Grade 5 6.7

The thermal conductivity of brake materials is variable since the material content is variable. I don't know if anyone has those figures, but a substantial amount of heat generated by the rotor/brake pad interface gets to the calipers and fluid; in many cases high enough to boil the fluid (that's +450ºF). Brake pads have a steel backing which is probably closer to the low carbon steel material on the above list. Ti brake pad backing plates would be trick except for the expense of changing $500 pads every track session. Some caliper manufacturers opt for titanium caliper pistons and/or ti shields formed to fit the pad-side of the caliper.

"The thickness of a the pad is the only difference between the S-caliper and the later SC and Carrera caliper. (the "S" being thicker) "

You are citing pad thickness rather than rotor thickness. Yes, the S pad is thicker, but
the added thickness of the Carrera rotor (24mm) provides a slightly larger thermal mass. Even if pad material is superior for thermal conductivity, with new pads there is no additional room for more pad thickness.

Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com

[island911]

I went and looked it up, since it was only a hunch on my part. . . .and indeed the thermal conductivity of brake materials is much lower than Titanium.
My handi-dandy Mechanical Design Handbook (Rothbart) gives the thermal conductivity of brake materials as;

Automotive (truck and bus) 3.5 - 4
Automotive (passenger car) 3

Although the units are (Btu*in/hr*ft²*°F) Converting to SI (W/mK) the difference becomes huge:

Automotive (truck and bus) 0.5 - 0.58
Automotive (passenger car) 0.4
( comparing to Titanium at 6.7)

So even if there is 100% variation in thermal conductivity of brake materials they are still much lower than Titanium.

[CamB]

Soooooooooooo (enter clueless Cam)

Does this mean new pads are more fade-resistant (due to heat).

[911pcars]

".......and indeed the thermal conductivity of brake materials is much lower than Titanium. "

I guess the brake pad manufacturers should apply friction material to both sides of the backing plate or use friction material to make backing plates.

Sherwood Lee

[Early_S_Man]

I doubt that the conductivity figues in that handbook have been updated since the '60's ... and certainly do not take into account the higher percentages of carbon and metals such as iron, copper, bronze, and brass in high-performance brake pad materials used in the last 25 years or so. The conductivity could approach that of mild steel! I cite Repco Metal Masters as one example ... a very high percentage of steel, copper, brass and carbon can be found, and they are by no means new or state-of-the-art these days! I also remember Velvetouch brake linings from more than 30 years ago, and they were essentially powdered iron and graphite with a binder compound!

Porsche used Titanium pistons in 917 calipers during their experimentation attempts to get better longevity from pads in '69-'71 at Le Mans, and the Ti pistons were were inverted to put a large air gap rather than brake fluid closest to the pads! I shudder to think what Ti brake pistons would cost to get fabricated these days, but given their corrosion resistance ... the results would be impressive, I suspect!

Chrysler has used bakelite pistons in selected calipers beginning around 1973 ... and the benefits vs cost is outstanding, to say the least! Maybe a low-tech plastic piston in Porsche calipers is the most effective solution!