Watts What?


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Mus­tangs to Fear’s

Watts Link rear sus­pen­sion keeps your rear cen­tered for max­i­mum han­dling ca­pa­bil­ity


When Ford de­signed the Fox chas­sis for 1979 and later, they did away with the pre­vi­ous Mus­tang ’s rear sus­pen­sion de­sign of leaf springs to sus­pend and lo­cate the rearend and con­verted to a four-link with coil spring setup. This made for a marked im­prove­ment in han­dling, but the four-link de­sign wasn’t very ef­fec­tive at keep­ing the rearend cen­tered un­der the car. Dur­ing hard cor­ner­ing, the rearend hous­ing was al­lowed too much side­ways move­ment, which causes the car to point in a dif­fer­ent di­rec­tion than where the driver is steer­ing. This ef­fec­tive “rear steer” makes the car un­pre­dictable.

There are two com­mon fixes to keep the rear cen­tered with ei­ther sus­pen­sion—a Pan­hard bar or a Watts link. You prob­a­bly know what a Pan­hard bar is; it’s a solid bar that con­nects to the chas­sis on one side of the car and runs par­al­lel to the rearend hous­ing, at­tach­ing to the hous­ing on the other side. A Pan­hard bar is ef­fec­tive at cen­ter­ing the rearend, but it still al­lows some side-to­side move­ment due to the ba­sic ge­om­e­try in the de­sign, which puts a small arc in the bar’s move­ment. A bet­ter, but more com­pli­cated so­lu­tion is a Watts link, which at­taches to the rear hous­ing with a pivot point, with arms that bolt to the car’s body. As the body moves up and down, the pivot point will move up and down, trav­el­ing in a line. Since the pivot point is trav­el­ing in a line, it keeps the axle lo­cated di­rectly un­der the car.

Tra­di­tion­ally, Watts link­ages have been bulky, with brack­ets and bars hang­ing off the hous­ing, but Mus­tangs to Fear (MTF) just came out with a de­sign that is un­ob­tru­sive, a bolt-in in­stal­la­tion (if you get the 9-inch rear hous­ing from them), and works just as well as any of the more com­pli­cated de­signs. The kit is avail­able three dif­fer­ent ways: with a full-floater 9-inch rearend; a stan­dard semi-float­ing 9-inch; and a “knock down” kit that re­quires you to weld on the Watts link shock sup­ports, swing arm mounts, and pivot mount to your ex­ist­ing 9-inch hous­ing. If you add MTF’s front sub-frame kit, the Watts link kit es­sen­tially turns the Mus­tang into a full-frame de­sign with­out cut­ting out the en­tire floor­pan of the car.

What are the dif­fer­ences and pros/cons be­tween a full-floater ver­sus a semi-floater rearend? With a semi-float­ing rear (which the vast ma­jor­ity of au­to­mo­tive rearends are, in­clud­ing the 9-inch), the wheel bolts di­rectly to the axle. This is a sim­ple, in­ex­pen­sive, and ef­fec­tive de­sign, but if an axle breaks there’s noth­ing keep­ing the wheel and tire from fly­ing off

the car. Fur­ther­more, hard cor­ner­ing im­parts de­flec­tion and a lot of load on the axle and wheel bear­ing, cre­at­ing all sorts of po­ten­tial prob­lems.

By con­trast, with a full-floater the wheel mounts to a two-bear­ing hub and not the axle; there­fore, there’s no axle de­flec­tion since the hub car­ries the weight of the car, not the axle and bear­ing. If the axle should break, the wheel re­mains on the car and won’t exit the car. The axle only car­ries ro­ta­tional power, no ver­ti­cal load. Which type of rear do you want? If you’re us­ing the car for mostly cruis­ing and not plan­ning on heavy-duty han­dling such as an open track event, the semi-float­ing de­sign is more af­ford­able and sim­ple to deal with.

Here, we show what goes into in­stalling the MTF Watts Link

un­der a 1966 Mus­tang hard­top. Kits are in stock at MTF now and re­tail for $2,495 (knock down kit), $6,300 (with 9-inch semi-float­ing assem­bly), and $7,600 (full-floater).

01 This is Mus­tangs to Fear’s Watts Link setup with their stan­dard semi-float­ing 9-inch rearend hous­ing—us­ing an ex­ist­ing hous­ing re­quires weld­ing on the shock sup­port brack­ets, swing arm mounts, and pivot point, and that can be tricky to avoid hous­ing warpage and get ev­ery­thing lo­cated prop­erly. In­spect and lay out all the parts be­fore start­ing with the in­stal­la­tion. Use red Loc­tite on all the bolts dur­ing fi­nal assem­bly.

11 In­stall one end of the Watts link arm into the pivot and tighten to 35 lb-ft of torque. Raise the axle assem­bly to the lower and up­per swing arms. Us­ing a drift pin, align the holes of the up­per swing arms first and insert 5/8x3-inch bolts with wash­ers. In­stall the lower swing arms into the dif­fer­en­tial bracket’s mount­ing hole and tighten all swing arm bolts to 100 lb-ft. Insert the other end of the Watts link arm to the Watts link mount­ing holes on the frame bracket rail. Once fit­ted, insert 1/2x2-inch bolt and wash­ers and tighten all bolts to 70 lb-ft.

08 In­stall the up­per and lower swing arms next. Align one end of the lower swing arm to the lower swing arm frame bracket mount­ing hole. Again, a drift pin may be re­quired. Once fit­ted, insert a 5/8x3-inch bolt with washer. In­stall 11/4x7/8x5/8-hole spacer to­ward the out­side of the lower swing arm frame bracket mount. In­stall the up­per swing arm to frame bracket mount­ing hole—no washer is used on the up­per bolt head side and the bolt will be in­serted from out­side of the frame in­ward. Use a 5/8x4-inch bolt and tighten to 100 lb-ft. (There are no spac­ers for up­per swing arms.)

07 Next, in­stall the up­per shock sup­port. A drift pin is help­ful at align­ing the sup­port holes. Once fit­ted, insert 1/2x2-inch bolts with wash­ers and tighten them to 70 lb-ft.

10 If us­ing the “knock down” kit with an ex­ist­ing rearend hous­ing, the pivot stud must be welded to the top of the hous­ing along with, of course, the shock brack­ets. In­stall the Watts pivot arm to the up­per rear axle­hous­ing with the 90-de­gree bends fac­ing up. In­stall5/8-18 washer and nut and tighten it un­til the lock­nut washer makes light con­tact with the top of the pivot arm. Insert the grease fit­ting into the up­per rear axle­hous­ing. Ap­ply grease un­til it starts to come out from the sides of the pivot arm. In­stall one end of the Watts arm into the pivot arm and tighten to 35 lb-ft, then in­stall the jam nut and also tighten to 35 lb-ft.

09 Us­ing a vise, press the bush­ing into the Watts link pivot arm.

14 All of Mus­tangs to Fear’s kits come with QA1 ad­justable shocks. Us­ing a vise, press the insert 5/8 inch into the shock. As­sem­ble shocks and springs us­ing the man­u­fac­turer assem­bly in­struc­tions that are with the shocks.

13 Raise and lower the dif­fer­en­tial and ad­just the Watts link arms for smooth op­er­a­tion by us­ing a twist­ing mo­tion on the arms. Through the travel up and down, there should be no bind­ing. Af­ter the ad­just­ment has been made and the jam nuts are snug, raise and lower the dif­fer­en­tial and check for any bind­ing again.

12 At­tach the other end of the Watts link arm to the frame bracket mount­ing holes and ad­just length as needed. Then use 1/2x2-inch bolts to mount and tighten to 70 lb-ft. This is how the Watts links should look.

15 In­stall the shocks to the up­per shock sup­port mount holes us­ing a drift pin. Once fit­ted, insert 5/8x3-inch bolts with wash­ers. Insert a 5/8x6-inch bolt with washer on the shock bush­ing side, then into the shock and add a 13/4-inch spacer be­tween the shock and the mount. We rec­om­mend in­stalling the lower shock to the mid­dle hole on the lower shock mount. Tighten all 5/8-inch bolts to 100 lb-ft of torque.

16 Ad­just the axle to be cen­tered in the wheel­well us­ing a ruler to find cen­ter, then make even ad­just­ment of the swing arms to cen­ter the axle and set the pin­ion an­gle at the de­sired set­ting. It is rec­om­mended a pro­fes­sional four-wheel align­ment be per­formed along with sus­pen­sion tun­ing for even weight dis­tri­bu­tion and cor­rect ride-height set­tings.

17 Voilà, this Mus­tang now has a race-bred Watts link rear sus­pen­sion to se­curely lo­cate the rearend un­der the car and max­i­mize han­dling po­ten­tial.

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