STOP­PING ON A DIME

ADDING WIL­WOOD REAR DISC BRAKES TO A 1969 DODGE DART

Mopar Muscle - - Contents - TEXT AND PHO­TOS: CHRISTO­PHER HOL­LEY

Adding Wil­wood rear disc brakes to a 1969 Dodge Dart

With the ad­di­tion of re­cent per­for­mance up­grades, our 1969 Dodge Dart has the po­ten­tial for speed (in mph) close to twice the speed of many U.S. high­ways. Re­fer to any physics text­book, and you’ll find the term ki­netic en­ergy, the en­ergy of an ob­ject in mo­tion. While trav­el­ing at the same speed, heav­ier ob­jects pos­sess more ki­netic en­ergy than lighter ob­jects. Fur­ther­more, faster-mov­ing ob­jects have more ki­netic en­ergy than slower-mov­ing ob­jects of the same weight. Ki­netic en­ergy dou­bles as the weight of an ob­ject dou­bles, but as the speed in­creases, the ki­netic en­ergy will in­crease by the square of the speed of the ob­ject. This means as the speed dou­bles, the ki­netic en­ergy quadru­ples. With speed, there’s a greater amount of ki­netic en­ergy the brak­ing sys­tem must con­vert to an­other form of en­ergy (usu­ally heat) to stop the ve­hi­cle. To keep up with the in­creas­ing speeds, the Dart’s pow­eras­sisted four-wheel drum brakes gave way to 1973 man­ual fac­tory front discs, and even­tu­ally, a com­plete Wil­wood front disc brake kit was in­stalled in 2002. With

the lat­est in­crease in speed and want­ing to take ad­van­tage of the ben­e­fits of disc brakes (self-ad­just­ing, ease of in­spec­tion, bet­ter cool­ing, fade re­sis­tance, free­dom from pull, and self-clean­ing), we con­tacted Wil­wood Engi­neer­ing about a pair of rear disc brakes to com­ple­ment the front disc brakes. The reps at Wil­wood sug­gested a pair of fixed calipers and match­ing ro­tors with a univer­sal park brake kit.

Be­fore we could or­der the brake com­po­nents, Wil­wood re­quired sev­eral mea­sure­ments to con­firm a proper fit of a Wil­wood kit for our ap­pli­ca­tion. It was pro­posed that we use a 12.19-inch ro­tor with our 15x7 Weld wheels. Sev­eral il­lus­tra­tions (eas­ily found on Wil­wood’s web­site) pro­vided the ex­act mea­sure­ments that Wil­wood re­quired to pro­vide an in­ter­fer­ence­free assem­bly for our Dart. We made mea­sure­ments of the axle flange to axle­hous­ing flange along with ro­tor and caliper fit­ment checks in­side the hoop of the Weld wheel. We made the mea­sure­ments with ma­chin­ist rules, depth mi­crom­e­ters, and even mocked-up card­board cutouts as ad­di­tional clear­ance checks to guar­an­tee the proper fit of the disc brakes. The mea­sur­ing took some time, but the ef­fort would be worth it if we or­dered parts that fit prop­erly. When­ever there’s any doubt about the fit­ment of the parts, Wil­wood has plenty of help­ful rep­re­sen­ta­tives to pro­vide as­sis­tance.

The mea­sure­ments con­firmed that a pair 12.19-inch ro­tors (PN 160-7508) would fit on our Dart with a 2.36-inch axle off­set. We se­lected a com­plete kit (PN 1407144), in­clud­ing two four-pis­ton calipers (PN 120-13839-BK), pads (PN 150-8850K), and bracket kit (PN 2497116/17) — back­ing plate and drum park brake assem­bly. Ad­di­tional parts in the kit were the caliper bolts, shims, and cot­ter pins. We se­lected 2.33-inch ro­tor regis­tra­tion ring adapters for the axle hub and tube adapters to fit the fac­tory (hard) brake lines to the new calipers. Lastly, we elected to keep the park brake op­er­a­tional, so we se­lected the Wil­wood univer­sal park brake ca­ble kit (PN 330-9371).

Be­fore our brake kit ar­rived, we per­formed some pre­lim­i­nary work. We had been run­ning the fa­mous “Green” bear­ings for years, but th­ese bear­ings had the pressed flange (aka the Mopar Per­for­mance Green bear­ing, PN RP400), which wouldn’t work with the Wil­wood kit. Rather, the snap ring style, loose flange (aka the Strange/moser Green bear­ing, PN MO400) was re­quired. To swap the bear­ings, we pulled each axle from the 8¾-inch, used a hy­draulic press to push the Mopar Per­for­mance bear­ings off the axles, and pressed on the Moser Green bear­ings. We omit­ted the in­stal­la­tion of the loose flange that came with the Moser

Green bear­ing, be­cause Wil­wood pro­vides their re­quired flange with the kit.

The disc brake in­stal­la­tion got un­der­way by dis­con­nect­ing the driver-side drum park brake ca­ble from the front park brake ca­ble adjuster, un­thread­ing and cap­ping the brake line from the wheel cylin­der, and re­mov­ing the en­tire drum brake assem­bly from the axle­hous­ing. We slid the back­ing plate onto the axle after re­mov­ing the snap ring from the new Moser bear­ing, and with the plate lo­cated, the snap ring was re­in­stalled. The axle assem­bly was slipped into the axle­hous­ing, and the back­ing plate was lined up with the five axle­hous­ing flange studs. Fi­nally, we at­tempted to slip the bear­ing re­tainer into place when we no­ticed the axle flange was mak­ing con­tact with the out­er­most re­turn spring on the drum park brake. After many at­tempts, there was no ad­just­ment that didn’t re­sult in con­tact be­tween the spring and axle flange. It turned out that the af­ter­mar­ket Moser axles we had in­stalled in 1990 had ex­tremely beefy flanges and the screwin wheel studs in­ter­fered with the re­turn spring. A call to Wil­wood pro­vided us with the fix. The spring could be re­moved with­out any re­duced park brake per­for­mance.

With the spring re­moved, we in­stalled the back­ing plate and axle. A sec­ond chal­lenge re­sult­ing from the Moser axle was the in­stal­la­tion of the bear­ing re­tainer (loose flange). A fac­tory axle has an ac­cess hole in the axle flange to al­low the bear­ing re­tainer nuts to be torqued into place. Our Moser axles didn’t have this ac­cess hole, so we had to use a thin-line ope­nend wrench to tighten all five of the nuts. Nei­ther this con­cern nor the park brake spring were the fault of Wil­wood or Moser, but rather the domino ef­fect of one mod in­flu­enc­ing an­other mod. The Moser axles worked for 28 years with the drums, and the Wil­wood brakes would’ve in­stalled with­out any dif­fi­culty on fac­tory axles (or af­ter­mar­ket axles with an ac­cess hole), but in our case, it took more ef­fort and time to make them work to­gether.

The hub reg­is­ter ring was in­stalled on the axle flange hub to cen­ter the ro­tor onto the axle. We slipped the ro­tor onto the wheel studs and over the reg­is­ter ring, and the calipers were in­stalled onto the back­ing

plate. We fol­lowed Wil­wood’s rec­om­men­da­tion of in­stalling two shims be­tween the caliper mount­ing ear and the back­ing plate clinch nut. The two shims were a start­ing point in an at­tempt to cen­ter the fixed caliper over the ro­tor; how­ever, we ended up re­quir­ing an ad­di­tional shim on each bolt. We re­moved the caliper and the ro­tor and re­in­stalled the caliper with­out the ro­tor. With the num­ber of shims de­ter­mined to cen­ter the caliper, we needed to es­tab­lish the cor­rect depth of the caliper bolts in the back­ing plate’s clinch nuts. The end of each caliper bolt needed to be flush with the end of the clinch nut. Shims were in­stalled be­tween the head of the bolt and the caliper-mount­ing ear to es­tab­lish the flush fit that was de­sired. Each caliper bolt (on the driver rear) re­quired one shim be­tween the caliper bolt head and the caliper mount­ing ear to es­tab­lish the cor­rect bolt depth, and each bolt re­quired three shims be­tween the caliper mount­ing ear and the back­ing plate’s clinch nuts to cen­ter the caliper over the ro­tor. It’s im­per­a­tive to use an equal sum of shims on each bolt on an in­di­vid­ual caliper. After de­ter­min­ing the nec­es­sary shims, the caliper was re­moved.

One last time, we fit­ted the ro­tor fol­lowed by the in­stal­la­tion of the caliper. We ap­plied a dab of red thread locker to each prop­erly shimmed caliper bolt, and then torqued each bolt to 40 ft-lb. Both brake pads were slipped into the caliper, and a large cot­ter pin was pushed through the caliper body and each pad’s back­ing plate to hold the pads in place. With the caliper in­stalled, a tube adapter was threaded into the caliper fol­lowed by the fac­tory hy­draulic brake line be­ing threaded into the adapter. While Wil­wood of­fers var­i­ous flex­i­ble brake lines, we elected to use rigid brake lines to the caliper, so the fac­tory brake line had to be ma­nip­u­lated (care­fully bent) to move the end of the brake line to the tube adapter in­let housed in the caliper. If the brake lines were sus­pect, new brake lines should’ve been run, and those lines could be bent as needed.

With the brake assem­bly on the left rear com­pleted, we re­peated the same pro­ce­dures on the right rear. Wil­wood of­fers Hitemp brake fluid, but we used a new bot­tle of DOT 4 brake fluid (DOT 3 or DOT 5.1 are also ac­cept­able). Wil­wood doesn’t rec­om­mend us­ing DOT 5 Sil­i­cone brake fluid for per­for­mance driv­ing. Re­gard­less of how the brakes are bled (grav­ity, pres­sure, or vac­uum), the goal is to bleed each

caliper of any trapped air. Four bleeder screws are on each caliper, but only the top two (one on each side of the ro­tor) are used to bleed air from the brake caliper. We found a gen­tle tap on the caliper body with a soft mal­let aided in free­ing any air bub­bles that may have stuck to the ma­chined sur­faces in the caliper body. After bleed­ing the sys­tem, the brake pedal felt firm and very sim­i­lar to the pre­vi­ous disc/drum setup.

The last step in our up­grade was to in­stall the univer­sal park brake kit on the Dart. We trimmed the ca­bles and sheath­ing to the re­quired length, and we used the supplied hard­ware to at­tach the sheath­ing to the back­ing plate and the ca­ble to the park brake lever at the top of the back­ing plate. The fac­tory-in­stalled clips on the axle­hous­ing and mount­ing points on the chas­sis routed the ca­bles in a sim­i­lar man­ner as the fac­tory. We ended up mod­i­fy­ing the ca­ble clamp from the kit and slip­ping it over the threaded end of the fac­tory park brake ca­ble that ex­tended from the front of the car. The ca­ble lay­out is clearly cov­ered in the pho­tos.

Wil­wood has a very spe­cific pro­ce­dure for bed­ding the pads to the ro­tor, and after ob­serv­ing the bed­ding meth­ods, the rear discs have pro­vided ex­cel­lent brak­ing per­for­mance. We don’t have ac­cess to a skid­pad, but at Beaver Springs Drag­way, the brakes hus­tle down the Dart to make the first turn off after a quar­ter-mile run, which was never a con­sid­er­a­tion with the drum brakes.

The drum-to-disc con­ver­sion re­quired a full week­end to com­plete, but the re­sults have been ex­cel­lent. A hy­draulic press may be nec­es­sary, but the rest of the in­stal­la­tion can be per­formed with hand­tools. A ve­hi­cle lift would be nice to use, but jack­stands will suf­fice. The keys to the disc in­stal­la­tion are ac­cu­rately mea­sur­ing ev­ery pa­ram­e­ter Wil­wood re­quires, fol­low­ing the in­stal­la­tion in­struc­tions, and if a prob­lem arises con­tact­ing a Wil­wood rep­re­sen­ta­tive for ad­vice and di­rec­tion. Re­spect­ing th­ese three keys will pro­vide a straight­for­ward Wil­wood disc brake in­stal­la­tion, fol­lowed by years of re­peat­able, trou­ble-free stop­ping power for your Mopar.

The rear drum brakes have served with­out any prob­lems for the last 28 years. The duo-servo drum brakes of­fer great stop­ping power and pro­vide out­stand­ing park brake per­for­mance. As the Dart’s mph out­put has in­creased, it was time to up­grade our trusty drum brakes with rear disc brakes to take ad­van­tage of the ben­e­fits that discs can pro­vide.

The 10-inch drums were orig­i­nally drilled for the 5 on 4-inch small bolt pat­tern. The au­thor re-drilled (with an elec­tric hand drill) the drums for the 5 on 4.5-inch big-bolt pat­tern when the Moser axles were pur­chased in 1990. The big bolt pat­tern was de­sired be­cause of the brawnier axle flange and greater wheel se­lec­tion op­tions.

Wil­wood sug­gested a 12.19-inch ro­tor to fit in­side our 15x7 Weld wheel. Mea­sure­ments were made based upon Wil­wood’s il­lus­tra­tions found on their web­site. Ma­chin­ist rules, depth mi­crom­e­ters, and even card­board mock­ups were made to guar­an­tee the ro­tor and caliper would fit with­out in­ter­fer­ence. When the ro­tors and calipers ar­rived, the mea­sure­ments proved ac­cu­rate, and the ro­tor and caliper fit in the wheel with­out any im­ped­i­ment.

The axle flange hub had to be mea­sured for the cor­rect reg­is­ter ring. The mea­sure­ment was just un­der 2.30 inches. Wil­wood of­fers many dif­fer­ent-sized rings, and the 2.33-inch reg­is­ter ring was the clos­est to our hub, so one for each axle was se­lected.

With all five axle flange nuts re­moved, the axle was slipped from the 8¾-inch axle­hous­ing. When re­mov­ing the axle from the hous­ing, sup­port the axle flange with one hand and pull the axle gen­tly, while ex­tend­ing the other hand down the axle. Be ready for the axle weight, as the axle is fairly heavy. Once the axle is free from the axle seal in the hous­ing, the axle can be set aside. The bear­ings are af­ter­mar­ket Mopar Per­for­mance “Green” bear­ings.

The top left bear­ing is the Mopar Per­for­mance-style bear­ing that was pressed off the axle. It has a fixed flange. The top right bear­ing is a Moser-style bear­ing that was the re­quired re­place­ment bear­ing. The bot­tom right was the loose flange that was omit­ted dur­ing the in­stal­la­tion. Wil­wood pro­vides their re­quired flange with the kit.

The “Green” bear­ings used on the Dart have the pressed flange (aka the Mopar Per­for­mance Green bear­ing, PN RP400) that wouldn’t work with the Wil­wood kit. The snap ring style, loose flange (aka the Strange/moser Green bear­ing, PN MO400) was re­quired.

When the Moser axles were in­stalled in 1990, the axle flange didn’t have an ac­cess hole as a fac­tory axle would have. While in­con­ve­nient, for all th­ese years, an open 9/16-inch wrench has been used to re­move the five bear­ing re­tainer nuts. The lack of the ac­cess hole be­came a big con­cern dur­ing the in­stal­la­tion of the Wil­wood disc brake kit.

The use of a hy­draulic press is nec­es­sary for all of the bear­ing press­ing. When press­ing the bear­ing on to the axle, all the hy­draulic pres­sure must be pro­vided through the col­lar and the hub of the axle. Press slowly and de­lib­er­ately, and if any­thing hangs up forc­ing the hy­draulic pres­sure to rise greatly, stop press­ing and re­solve the con­cern be­fore con­tin­u­ing.

With the brake line re­moved and capped and the rear park brake ca­ble loos­ened from the front park brake ca­ble, the fully as­sem­bled drum brake assem­bly was re­moved from the rear end hous­ing. The assem­bly will still op­er­ate if needed (on an­other ve­hi­cle), so it was wrapped and stored for fu­ture use.

The axle with the disc brake back­ing plate slid into the rear axle­hous­ing. The back­ing plate had to en­gage with the five bear­ing sup­port studs on the rear end hous­ing. The small shoes on the back­ing plate act as a drum brake for the park brake ap­pli­ca­tion for the Wil­wood kit.

The loose bear­ing flange snap ring was re­moved. This al­lowed the back­ing plate, with the one park brake spring re­moved, to slide onto the axle and bear­ing. Once the back­ing plate was in­stalled, the snap ring was re­in­stalled in its groove on the bear­ing.

When the back­ing plate was in­stalled onto the Moser axle, the front side park brake drum re­turn spring made con­tact with the much beefier, when com­pared to the fac­tory’s axle, flange and the af­ter­mar­ket screw-in studs. The fix was to re­move the sin­gle spring, which left only one spring on the park brake. The per­for­mance of the park brake wasn’t af­fected by the re­moval of the spring.

The en­tire Wil­wood kit in­cluded a pair of back­ing plates, ro­tors, four-pis­ton calipers, two bear­ing re­tain­ers, reg­is­ter rings, a univer­sal park brake ca­ble, and all the hard­ware to mount the com­po­nents to the Dart. Plenty of in­struc­tion ma­te­rial was in­cluded with the kit. Take the time to read all the in­struc­tions be­fore jump­ing into the disc brake in­stal­la­tion. This will al­low the in­stal­la­tion to progress smoothly.

The supplied bear­ing re­tainer flange had to be slipped onto the five bear­ing sup­port studs on the rear end hous­ing, so the nuts could be in­stalled. The fit was tight due to the sub­stan­tial heft of the axle and the screw-in studs. The re­tainer was wig­gled into place fol­lowed by some wrestling to get the nuts threaded into place. This took some time, and when it came to tight­en­ing the nuts, a slim-line open end wrench was the only op­tion. If the axle flange had in­cluded the ac­cess hole, the en­tire ordeal with the flange nuts would’ve been negated.

The reg­is­ter ring was slipped onto the axle hub with the step on the outer cir­cum­fer­ence fac­ing out­ward. The ro­tor was pushed onto the axle studs, and the ref­er­ence ring’s step en­gaged with a match­ing step on the ro­tor’s hat. The reg­is­ter ring cen­ters the ro­tor with­out re­ly­ing upon the axle studs.

A pad was slipped be­tween the caliper pis­tons and each side of the ro­tor. A large cot­ter pin was pushed through an ac­cess hole on the caliper, a hole in each pad’s back­ing plate, and then through an­other ac­cess hole on the in­board side of the caliper. The cot­ter pin was bent and trimmed so it wouldn’t con­tact the wheel.

The sin­gle shim be­tween the caliper bolt head and the caliper ear en­sured the caliper bolt didn’t ex­tend be­yond the end of the clinch nut in the back­ing plate. Wil­wood re­quires the bolt end to be flush. If the bolt ex­tends out too far, the bolt may con­tact the ro­tor, so shims are re­quired. If the bolt doesn’t reach the end of the clinch nut, shims must be re­moved to en­sure full bolt thread en­gage­ment to se­cure the caliper.

A fi­nal check of the caliper lo­ca­tion con­firmed that it was prop­erly cen­tered over the ro­tor. With the caliper prop­erly cen­tered, the caliper bolts were dabbed with red thread locker, threaded into the back­ing plate, and each bolt was torqued to 40 ft-lb.

To cen­ter the caliper over the ro­tor, three shims were re­quired on the caliper bolt be­tween the caliper ear and the back­ing plate. An­other shim was nec­es­sary be­tween the caliper bolt head and the caliper ear to prop­erly lo­cate the caliper bolt’s depth in the back­ing plate.

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