Classic Performance Products 378 E Orangethorpe Ave., Placentia CA 92870

Classic Performance Products

Replacing the rear suspension in an F-1

By Ryan Manson
When it comes to rear suspension designs, the sky is the limit. Anything from stock replacement parts to Jaguar or Corvette independent suspension designs have found their way under many an old pickup. From mild to wild, anything's possible, so when the time comes to start replacing and upgrading those old components, one's faced with the decision of what to use. Out little hauler is going to be just that a parts truck that's gonna be rode hard and put away wet. Since the F-1 is going to become the primary hauler in our fleet, it needs to be able to not only cope with the Southern California stop and go traffic we're so blessed with, but also needs to be capable of hauling any load we need to throwinto the back of it. The first choice we made was ot ditch the old 9-inch rear and replace it with a brand new Currie 9-inch. While this may seem logical to a few of you, some may be wondering why we tossed aside a seemingly good rearend just to put a new one in it's place. The answer is simple: economics. For starters the old rearend had a 4.11 : 1 gear ratio, which is way too low for our plans to use the truck as a daily driver doing at least 40 highway miles round trip every day. It also had some pretty severe signs of wear on the ring-and-pinion as well as having a bit of metal shavings in the filthy gear oil. A quick call to Currie Enterprises also revealed that the early Ford 9-inch rears had a fairly weak hous- ing, which tended to fatigue with time and a gear case good for only about 200 hp. We crunched a few numbers and realized that for only a few more dollars, a brand-spankin' new rearend assembly could be put together, with an upgrade in the brake department, too! Next we opted to stick with the stock-style parallel leaf spring design and utilize a Total Cost Involved kit. The Total Cost Involved kit consists of a pair of leaf springs, spring pads, U-bolts, shackles, shocks, a shock crossmember, and all the necessary hardware to plug it in. What's even better is that it's a total bolt-in deal with the exception of the spring pads, which we had Currie weld onto our new rear using Total Cost Involved's specs. This kit completely replaces ail that old, worn-out junk and also moves the rearend above the springs, effectively lowering the back of our truck as well. Between the Total Cost Involved kit and the new Currie rearend, the rear suspension went in so quickly and smoothly, it took longer to remove the old stuff than it did to install the new bits. Check out the story and see for yourself.

1. Once all the original suspension junk was removed, it was time to remove the stock Ford spring perches. which are attached via four rivets to the framerail.

2. To remove the spring perches, first the heads of the rivets are ground flush. Each rivet is then center-punched and drilled out with a 5/16-inch drill bit. We're going to be using the holes to locate the new perches, so care is taken not to drill the existing holes larger or off center.

3. We ran into a problem with the two small rear crossmembers that will need to be rectified before the suspension components are installed. They're both a bit tweaked and need to be replaced. For now, they are simply removed and cast aside.

4. The front leaf spring brackets mount using the same four bolt holes as the original and face forward on the outside of the framerail. There is also an additional hole on the bottom of the bracket that requires the framerails to be drilled using a 3/8-inch bit. A total of six 3/8-24x1 1/4-inch bolts, Nylok nuts, and washers attach the two front brackets to the framerails.

5. The rear shackle brackets also bolt up using the original rivet holes. Notice that the orientation of the bracket is opposite of the front, this time facing the rear.

6. Here's our brand new Currie 9-inch rear. We went with their Hot Rod-style housing and had them weld on the spring pads as well at 39 3/4 inch center with a pinion angle of 5 degrees up.

7. The guys down at Currie also put together the third member with a 3.50:1 ratio T.S.D. (Torque Sensing Differential) limited slip unit. Currie performance 31-spline axles were also installed to get the power fro m the rear end to the wheels.

8. Currie also has their own hypoid gear oil specifically formulated for their high-performance rearends. This rearend will take about 2 3/4-quarts of the racing
gear oil along with the 4 fl oz bottle of Torco limited Slip Friction Modifier.

9. Currie offers their rearends with many different brake options, from a simple 11-inch drum brake to a Wilwood disc brake setup with cross-drilled rotors and polished calipers. We opted for the 11-inch Explorer disc brake kit with a 5 x 4 1/2-inch bolt pattern.

10. The rearend is slid into place and the non-shackle side (front) is bolted to the bracket. Before the suspension can be assembled any further, we need to address the ends of our framerails where we removed those offending pieces

11. We picked up some 1/8-inch plate and made a quick crossmember to square up the back of the frame. We'll comeback and make it pretty later, but for now, it allows us to finish in stalling the suspension and get the truck down on the wheels and tires.

12. With the frame all squared up and repaired, the rear shackle assembly could be installed, bolting the springs to the chassis. Note that the front spring mount is bolted directly to the frame bracket, and the rear bolts to a shackle assembly that attaches the spring to the frame.

13. The next step is to place the spring plates under the springs and to install the U-bolts. There are also shock studs that need to be installed on the plates, too. When the plates are installed on the springs, the shock studs should be under the plate and pointed rearward.

14. The last step is to install the shock crossmember. This bolts between the frame rails. slightly behind the rearend and will add a bit of rigidity to the chassis.

15. To locate the shock crossmember, scribe a line 28 1/8-inch in front of the rear bed bolt hole on top of each rail. Center the crossmember in relation to the chassis and mark your hole centers.

16. The final hole is going to be 5/8-inch, but it's a good idea to start out with something smaller and work your way up from there. The top framerail was drilled first and the crossmember put in place. Once it was determined that the crossmember was level, the lower frame rail was marked and drilled as well.

17. Here's the new setup, ready to be blown apart and painted. Note how the mounting tubes on the shock cross member point forward to locate the upper shock mount. The original crossmember in front of the rearend will remain to stiffen up the chassis between the rearend and the transmission mount.