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Spring Over Conversion for CJs, Using YJ Springs
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By: John Nutter - 12/2000

From the Archives: CJ Spring Over using YJ Springs, for 1976 to 1986 CJs

The Jeeping guru Jefe once said "Eventually, every serious rock crawler will go spring over." Jefe was trying to express that this is the best way to increase the ground clearance under the axle tubes and smooth the underside of the Jeep for easier passage over rocks. The virtues and faults of SOA have been debated many times, but eventually all discussions come to the conclusion that going SOA is the only way to free up the very significant space under the axle tubes where the spring packs normally reside on a Jeep CJ or YJ. SOA has been used by many manufacturers on both front and rear ends, and these OEM setups prove that it works well.



Photo by: Janet Nutter
A Spring Over Axle conversion is the only way to totally free up the space below the axle tubes.
Photo by: John Nutter
The red arrow points to the rivet to be removed and the blue line shows where to weld the cross member to the frame rail.
Photo by: John Nutter
The arrow points to the spacer made from the old front spring hanger.
Photo by: Janet Nutter


YJ Wrangler springs can often be found for free from a friend who has installed lift springs or purchased cheaply used from a 4wd shop. YJ Wrangler springs work well for CJ spring over axle (SOA) conversions because their length and their arc. The YJ springs are slightly longer than CJ springs and a longer spring has more travel than a shorter spring. The stock YJ springs are almost flat under load which makes them good for a spring over because they do not provide any more lift than is necessary. A spring over alone normally provides more than sufficient lift, however it is easy to add more leafs into the pack to get more lift or a higher spring rate. Another advantage of the flat springs is flat springs articulate better than arced springs during compression.

Flat arch front springs such as YJ springs make an expensive shackle reversal unnecessary and even counter productive. With flat arch front springs that are anchored at the rear the tire will move towards the rear on either compression or extension. The reason is the flat arch places the tire at it's farthest forward point when the suspension is at rest, and when the spring arches either positively or negatively the arch will cause the tire to be moved slightly rearwards. The goal of a shackle reversal is to improve ride by making the tire move towards the rear on compression, however a shackle reversal has the opposite effect when used with flat arched springs. Shackle reversals do work properly with springs with a greater arch such as 4" lift springs for a spring under application.

With the flat arch springs on a SOA you can also angle your front shackles further forwards than most people normally would. The reason you can do this is similar to the reason a shackle reversal becomes unnecessary, the shackle end spring eye will move towards the rear on either compression or extension. This has 2 benefits. First it gives the shackles more room to move rearwards and frees up more droop. Secondly having the shackles raked forwards makes it less likely that you will pop one over center to the rear and bend a spring.

Springs and Spring Hangers

The rear springs used in CJs and YJs are the same width, so the rear springs bolt right in. The YJ front springs are a little longer and wider than CJ front springs. The fixed spring hanger for the CJs front spring is the correct width because the CJ front spring uses a wide bushing in the back. It is the shackle side of the CJ that is not compatible with the YJ front springs.

For the shackle end of the front springs, stock CJ rear spring hangers are the right width and are inexpensive to purchase. They need to be moved forward so that the rear hole in the spring hanger goes where the old front hole used to be. There is a rivet in the frame at the location where the new front hole needs to be. The rivet holds the cross member in place. I welded the cross member to the frame, ground the heads off the rivets and punched them out. The bolt holes lined up perfectly.

Moving the hanger forward leaves a space between the steering box bracket and frame where the back part of the spring hanger used to be. I cut off a piece of the old spring hanger and used it as a shim. The red arrow in the photo to the right points to the spacer for the steering box made from the old front spring hanger.

The rear hangers do not have an extra hole to clear the rivet that you knocked out, so they are much stronger than the stock front spring hangers. This swap makes expensive after market spring hangers unnecessary.

Bushings

I used polyurethane bushings meant for the rear of a CJ in the frame part of the shackles and the fixed spring eyes on both the front and rear. I left the factory rubber bushings in the shackle ends of the springs to increase flexibilty.

Polyurethane bushings for the main spring eyes often need a little work to get them to really work right. When they work right there is little friction and the metal sleeve inside the bushing is locked in place by the clamping action of the bolt through the spring hanger. The polyurethane should rotate around the sleeve like a hinge. The sleeve shouldn't rotate with the polyurethane because this will cause wear on the bolt and become a possible failure point down the road. To accomplish this you'll want to install the main eye bushings and sleeves into the springs and see how far the polyurethane sticks out past the sleeve on each side. Use an angle grinder with a coarse disc to remove material from the sides of the polyurethane bushings until they are just flush with the metal sleeve.

Tighten the main spring eye bolts well, they are supposed to lock the metal sleeve inside the bushing to the spring hanger. Don't tighten shackle bolts too tight, shackle bushings are designed to rotate around the bolt and the bolts only need to be snug for this. Overtightening shackle bolts will only cause binding at the bushings. Use good quality self locking nuts on all suspenion parts, and don't ever re-use self locking nuts becuase they probably won't stay locked the second time they go on.

Shackles

For shackles I used 2" x 3/8" bar stock all the way around and I made the bolt holes 4" between centers. The shackles have a good rake forwards on the front and rearwards on the rear. Because the YJ springs are flat the shackles move inward on both compression and extension and the rake is actually an advantage since it gives them more room to move and less chance of getting stuck over center.

U-Bolts, U-Bolt Plates and Shock Mounts

If you have kept the stock Dana 30 you will probably need to fabricate some spring plates to accommodate the wider YJ springs, but your stock U-bolts should still work. If you have gone to a Dana 44, FSJ spring plates work well and U-bolts can be purchased locally at a good auto parts store. Lower swaybar mounts from a late '70s full sized Jeep fit between the springs and spring plates and have worked out very well for me.

You will need to weld new shock mounts to the axle tubes on the rear, and possibly on the front depending on the year of your Jeep. Make the bottom of the mount roughly parallel with the bottom of the axle tube. Early CJ7 owners will want to change to the later CJ7 shock towers to allow a longer shock, but beware of the shocks rubbing on the tires if you have narrow axles. Full sized Jeeps also use the same towers and are good donor vehicles. Don't try to use the shock mount stud on the U-bolt plate once you are spring over, they are too high and severley limit shock length.

Brake Hoses

You'll need to give some attention to brake hoses due to the added lift and flexibilty that your new SOA will provide. If you use stock hose in their stock locations, it is very likely your hoses will limit travel. Consider buying longer hoses from an aftermaket source if you have kept your Dana 30. If you've swapped in a Dana 44, full sized Jeep (FSJ) or Chevy Blazer brake lines relocated to mount off the bottom bolt of the shock tower work well.

Spring Rates and Sagging

A common complaint of CJ owners who have used YJ springs SOA is that they are too soft or sag easily. I've found that a good quality, full length adda-leaf from Rubicon Express or Rancho helps cure sagging and makes handling much more acceptable without compromising articulation or ride quality. For Project DIY I made my own adda leafs from another set of YJ springs. I cut the eyes off of the main leafs and placed them just below the existing main leaf in the pack. I also added in another shorter leaf from a stock YJ pack further down. Plan on adding or subtracting leafs until you are satisfied with the ride, handling and articulation of your spring over conversion.

Pinion Angle, Steering and Axle Wrap

Pinion angle must be addressed while the spring perches are being installed. Steering and axle wrap will be major concerns once you have the springs and axles in place. These topics are important enough that I've addressed them in sepparate articles, the links are below.


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