We've built plenty of Jeeps up over time, constantly busting, changing and upgrading components because of an ever-increasing tire size. This time, we wanted to get straight to the big Jeep without throwing money and resources away on a smaller Jeep we weren't really happy with in the first place. Few other Jeeps accept monster tires as well as the FSJs. All of the short Jeeps require wheelbase-lengthening custom link suspensions to the tune of 105 to 125 inches. Starting with our 1973 Hot Dog J-truck, we already had a 120-inch wheelbase that made it a perfect candidate for monster meats. The plan is to keep it affordable, at least as affordable as big Jeeps are. Originally, we had intended to use some 44s, but we were told that something bigger was just around the corner. After taking some initial measurements, we upped the ante to the biggest tires available in the Interco Super Swamper line: the Irok 49s. They're 21 inches wide and are available for 16.5-, 17- and 20-inch wheels. We opted for the 17s. If you want big tires, prepare to pay big bucks for them. The tires alone cost twice the amount of the initial purchase price our J-Truck.
To handle the large tire size, we passed on the typical Dana 60 or 14-bolt option and went straight for 2 1/2-ton Rockwells for three reasons: They're cheap, and they're easy and inexpensive to modify. We'll tell you more about our axles in the next issue.There are a few different leaf suspensions found throughout the FSJs' model years. The three major groups are the '63-'73 Wagoneers and Cherokees, the '63-'73 trucks, and all '74-'91 FSJs. The '74-and-later FSJs have the most desirable design. They enjoy the greatest number of aftermarket lift and spring options. As it turns out, our '73 is the least desirable of all the FSJs, especially for bigger lifts. Following is our planning, the roadblocks we hit and the first installment of our Hot Dog's budget big Jeep buildup.
At first, we figured the suspension our '73 J-2000 had was somewhat similar to the '67-'69 M-715 Kaiser military truck. Boy, were we wrong, at least partly. Of course, we knew our '73 J-2000 had a factory spring-over at the front and rear, and we knew that M-715s are spring-under. We thought that M-715s came with more arched leaf springs, along with huge fender openings to fit the factory 9.00-16 tires. We ordered some stock front and rear M-715 leaf springs from Eaton Spring. The first plan was to simply bolt the M-715 leaf springs onto our J-truck with the spring-over to gain a huge amount of lift.
What we found out is that M-715s have dropped spring mounts that provide the additional lift. The leaf springs are nearly identical to those on our truck. With this combination of parts, we would have simply ended up with a stock-height truck. There were other problems, too. Since the spring mounts on our truck ('63-'73 trucks and M-715s as well) were outboard of the frame, they could interfere with the 21-inch wide tires, especially when steering. The factory front springs are narrow (2 inches wide) and looked as though they would fold under 49-inch tire use. Also, the frame mounts on our '73 are pin-style, which is kinda weak. We prefer the double-shear under-the-frame mounts found on the '74-and-later FSJs. The factory front mounts and springs had to go. Out back, the plan is to still use the new thick Eaton M-715 spring pack.
We burned off the old springs and mounts with our Matco torch set, then smoothed the frame with a grinder and took some measurements for new under-the-frame springs. We decided to stick with Jeep stuff, so we scoured the Rancho suspension catalog for dimensions on the company's '74-and-later FSJ front lift springs. We found a 2 1/2-ton lift spring for the big Jeeps (PN 44044). Combining these with a spring-over on our 2 1/2-inch front axle and trimmed fenders seemed like it would give us the lift we needed to clear the 49s. Mountain Off Road Enterprises (M.O.R.E.) offers shackle reversal brackets designed for CJs but that are easily modified for use on almost any Jeep, so we ordered a setup for our J-truck. In the light-truck market, finding U-bolts that fit around Rockwells is impossible. If you need 'em, then you may need to hit up a spring shop that deals with heavy trucks. We had a high-clearance idea using some off-the-shelf Rancho U-bolts that you can read about when we finish up the suspension in the next couple issues.
When swapping front axles on FSJs, the spring perch width of the front axle can really put a damper on your options. Here are some FSJ dimensions and other potentially imprortant measurements.
'63-'73 Wagoneer and Cherokee spring perch width: 32 inches.
'63-'73 J-truck and M-715 spring perch width: 39 inches.
'74 and later FSJ spring perch width: 32 inches
Typical full-size spring perch width: (GM & Ford): 31 1/4 inches
Factory 2 1/2-ton Rockwell spring perch width: 31 1/4 inches.