High-Tech Brak­ing Sys­tems

The Lat­est De­vel­op­ments in What’s Stop­ping You!

Hot Rod - - Contents - Bill Fowler Richard Prince and Cour­tesy of the Man­u­fac­tur­ers

h The disc brake as we know it was first pa­tented in 1902, but it failed to gain ac­cep­tance in the U.S. un­til the early 1960s, when vac­uum-as­sist power brakes made the pedal ef­fort ac­cept­able for the Amer­i­can driv­ing pub­lic. Euro­pean au­tomak­ers had adopted disc brakes in the 1950s, rapidly fol­low­ing Jaguar’s dom­i­nance in the 1953 24 Hours of Le Mans race, thanks in no small part to the car’s four-wheel disc-brake sys­tem.

Disc-brake sys­tems can be di­vided into two key com­po­nents: the fric­tion side, which is the hub/ro­tor and caliper clamp­ing sys­tem, and the ap­ply side, which in­cludes the pedal, pushrod, booster (if any), mas­ter cylin­der, and hy­draulic lines. In more mod­ern ve­hi­cles, a third sys­tem has been in­tro­duced: elec­tro-me­chan­i­cal con­trols like an­tilock brak­ing sys­tems (ABS). Orig­i­nally, ABS was de­vel­oped to rapidly mod­u­late brake pres­sure to pre­vent lock­ing up the brakes or tires, putting an end to un­con­trolled skids. Rel­a­tively sim­ple ABS sys­tems have mor­phed into com­plex car-con­trol and hy­draulic-force ap­pli­ca­tion sys­tems for elec-

tronic brake force dis­tri­bu­tion (EBD), such as anti-skid, sta­bil­ity con­trol, and yaw con­trol. By 2020, all new ve­hi­cles will have some form of au­to­mated emer­gency brak­ing (AEB), along with a sen­sor, ECU, and al­go­rithm-based pre­dic­tive brake as­sist— and, yes, fully au­tonomous ve­hi­cles are com­ing soon.

One of the most in­ter­est­ing tech­nolo­gies on the hori­zon for en­thu­si­asts will be in­te­grated brake con­trols (IBC). An IBC uses a smaller, high-pres­sure pump that re­places vac­uum pumps, vac­uum boost­ers, or hy­dro-boost units. It is a com­pact unit that func­tions sim­i­larly to drive-by-wire throt­tles, weigh­ing about 11 pounds less than the units it re­places. The con­trol sys­tem will come from the OEs, much like GM and Ford crate en­gine/ trans com­bi­na­tions or the af­ter- mar­ket’s adapted elec­tronic-trans­mis­sion con­trols like those from TCI, HP Tuners, FiTech, and Hol­ley. This will al­low en­thu­si­asts to add ABS, sta­bil­ity con­trol, and other sim­i­lar fea­tures to their clas­sic cars and rods with far less fab­ri­ca­tion and has­sle.

On the fric­tion side, two ma­jor el­e­ments are driv­ing the tech­nol­ogy: 1) the need to ab­sorb and dis­si­pate more heat due to heav­ier, higher-horse­power cars and trucks, and 2) the need to re­duce weight to im­prove sus­pen­sion con­trol, steer­ing re­sponse, and fuel econ­omy.

In both cases, tech­nolo­gies de­vel­oped for rac­ing are trick­ling down into the en­thu­si­ast’s bud­get. The first such tech­nol­ogy was alu­minum calipers, made pos­si­ble by im­proved ma­te­ri­als such as 6061 and

7075 alu­minum al­loy and, more re­cently, 2618 forg­ings—the same al­loy used in rac­ing pis­tons. The next tech­nol­ogy wave was the multi-pis­ton caliper, which al­lows for the use of larger, curved pads with more swept area. More pis­tons of grad­u­ated size al­low for fine­tun­ing of brake pres­sure across the pad face. How­ever, more pis­tons add cost and ma­chin­ing com­plex­ity. While 8- and even 12-pis­ton calipers had been de­vel­oped at one time for cost-is-no-ob­ject rac­ing, 6-pis­ton calipers re­main the gold stan­dard for high-end sports cars like Fer­rari, Ford GT, and the ZR-1.

The other ma­jor fric­tion-side de­vel­op­ment was big­ger ro­tors en­abled by big­ger wheels. Much like us­ing a 1/2-inch breaker bar in­stead of a 3/8-inch ratchet, a larger-di­am­e­ter ro­tor pro­vides greater me­chan­i­cal ad­van­tage for the same pres­sure ap­plied at the caliper. How­ever, big­ger ro­tors mean more weight, so two-piece ro­tors with alu­minum hats have be­come the se­ri­ous up­grade for hot rod­ders look­ing to off­set the nec­es­sary in­crease in ro­tor mass. For rel­a­tively lit­tle money, a two-piece ro­tor with op­ti­mum ma­te­ri­als will not only look great but can also re­move as much as 8 pounds per wheel, which helps ac­cel­er­a­tion and brak­ing. As wheels have grown, so have ro­tors—now up to 16 inches on many trucks,

SUVs, and high-end cars.

Large ro­tor di­am­e­ters have brought about the next evo­lu­tion: float­ing ro­tors.

As ro­tor di­am­e­ter and thick­ness have in­creased to keep up with to­day’s faster and heav­ier cars, in­creased ro­tor mass has ex­ac­er­bated the ef­fects of dif­fer­en­tial rates of heat ex­pan­sion. To al­low for that, ro­tors—or more of­ten the ro­tor hats—are now slot­ted to al­low the ma­te­ri­als to grow ra­di­ally while still be­ing safely re­tained to pre­vent or min­i­mize side-to-side mo­tion. For street use with ac­cept­able noise lev­els (the two parts can rat­tle un­der some cir­cum­stances), two ap­proaches have been used: T-shaped bob­bins that lock the hat to the ro­tor and more com­plex CNC-shaped ro­tor stan­chions typ­i­cally com­bined with anti-rat­tle clips.

The T bob­bin is more com­pact and sim­pler to pro­duce, sav­ing some cost and al­low­ing for tighter fit­ments. The stan­chion style, while sub­stan­tially more ex­pen­sive, is bet­ter for elim­i­nat­ing or re­duc­ing noise, and due to its in­creased size and flat ver­sus round sides, it can sup­port 1.125-inch-thick ro­tors in 15- and even 16-inch­di­am­e­ter sizes. The stan­chion style is used al­most ex­clu­sively for car­bon-ce­ramic brakes due to its greater sur­face and clamp­ing area.

01] ZF TRW’s in­te­grated brake con­trol (IBC), in­tro­duced this year, re­places the elec­tronic sta­bil­ity con­trol sys­tem, vac­uum/booster pump, and the as­so­ci­ated ca­bles, sen­sors, switches, elec­tronic con­trollers, and vac­uum pumps with a sin­gle unit. IBCs also pro­vide faster re­sponse, par­tic­u­larly for au­to­mated emer­gency brak­ing trig­gered by on­board prox­im­ity and radar sen­sors. That faster re­sponse can mean a re­duc­tion of 10 to 20 feet in over­all stop­ping dis­tance, of­ten the dif­fer­ence be­tween stop­ping just in time and a crash.02] This pro­to­type 12-pis­ton rac­ing caliper was at­tempted in the late-1990s, but the com­plex­ity of six in­di­vid­ual pads, guide rods, and tiny pis­tons over­whelmed the in­tended ben­e­fits. 03] These calipers il­lus­trate the growth in size of brake calipers over the last 20 years. Caliper size can in­crease as wheel size in­creases, al­low­ing for larger ro­tors, calipers, and greater swept area. These larger calipers also show how rac­ing tech­nol­ogy has im­proved the brakes avail­able to the per­for­mance af­ter­mar­ket, with grad­u­ated pis­ton sizes and castel­lated (slot­ted) pis­tons, or as shown here sec­ond from top, two-piece pis­tons with crenelated (com­plex, FEA-de­signed) milled caps.

04] These OE and af­ter­mar­ket pads il­lus­trate the ef­fect of larger caliper size and in­creased swept area over the past two decades. Pads can be iden­ti­fied and pur­chased by ap­pli­ca­tion and cross-ref­er­enc­ing us­ing the Fric­tion Ma­te­ri­als Stan­dards In­sti­tute (FMSI) num­bers. From bot­tom to top: The pad shape and size used in Baer and Wil­wood com­pact four-pis­ton calipers, FMSI 480, the then-rev­o­lu­tion­ary 1984 C4 Corvette PBR pad, FMSI 412, Gen 4 Ca­maro, FMSI 731, C6 Corvette, FMSI 1247, and an FMSI 1405 pad used in af­ter­mar­ket rac­ing and ul­tra-per­for­mance street calipers.

01] Here is a 2015-and-later Mus­tang GT Per­for­mance Pack ro­tor and a sim­i­larly sized, two-piece re­place­ment ro­tor. The re­place­ment two-piece ro­tor weighs 7.9 pounds less, which helps re­duce stop­ping dis­tance and lap times. It has curved vanes for bet­ter cool­ing and uses NAS S287 fas­ten­ers(see side­bar, above).02] On these 14-, 15-, and 16-inch ro­tors, we see the three types of two-piece ro­tor at­tach­ments: the fixed T-shaped bob­bin and the stan­chion-style bob­bin.03] This two-piece, slot­ted ro­tor shows the T-style bob­bin com­po­nents used to fas­ten the hat to the ro­tor in lat­eral at­tach­ment; they still al­low for dif­fer­en­tial growth due to heat in the ra­dial di­men­sion.04] The Corvette Z06/Z07 pack­age’s car­bon-ce­ramic brakes; note the float­ing ro­tor hard­ware and the small drilled holes. These holes are more for fash­ion than func­tion.05] This stan­chion-style bob­bin shows the pre­cisely ma­chined di­men­sions, the 0.0001-inch tol­er­ances, the anti-rat­tle re­tain­ing clips, and a plain ro­tor for this road-race-only ap­pli­ca­tion.

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