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Mopar Leaf Spring Relocation

Jim writes:

Below is a conversation I had with Earl Helm about relocating the leaf springs on my 1964 Plymouth.

Q) Any general thoughts before I start?

A) Here are a couple of hints. I know you might not understand this until you have finished your project, but try. Little known fact, it does not matter where the box goes in the frame, as long as it is the same on both sides - side to side - and it is far enough back and up for the spring to fit without binding.

What does matter is where the hole is in the box. Believe it or not, this is the easy part. If one box is a bit higher in the frame or a bit further back it is no be deal as long as you drill the hole for the spring in the right place. Since the stock hangers can be mounted up while your trial fitting the box before welding (the only thing that is important with the trial fit is that it is square and parallel to the frame), you can mark the hole location with the stock frame hangers and a 9/16 bolt through the hole in the stock hangers. Once you have them marked, drill the hole, drill it square thru both sides, then get some 9/16 threaded stock, cut it off about 14 inches long, put it thru the hole in the box, then thru the stock hanger, and bingo, you box is in the right place front to back. Then make sure the box is right side to side, and tack weld it. Then finish welding you box into place and hang your springs. This is way easier to do than to explain. Making a card board pattern the same size as your box, and marking the frame before cutting makes it easy. Cut it smaller than your pattern, and grind to fit.

Q) So if I am reading this right, I leave the stock hangers in position, hold the new hanger next to it (after I cut an opening in the frame rail), and mark the bolt hole. I pull the new hanger down and drill it, then place it back up there and hold in in place with the threaded stock while I tack it in place? (In the BigBlockPart page they just cut away one side of the frame rail did that work for you?)

A) Basically that is right. One thing to do before putting your box pattern on the frame to mark it is to take the front spring eye and insert it into your box so you get an idea of how far from the back of the box you want it. Measure that distance from the back of your box to the center of the eye hole, and mark that line on your pattern. When your marking your frame with the pattern, make sure the line is even with or behind (toward the front of the car) the center line of the hole in the stock frame hanger.

I don’t hold the hanger next to it, I actually bolt the hanger up to the so I absolutely know the hole is in the right place. Then with a bolt that I have cut off that is long enough to get thru the hanger, and short enough to come in from the outside of the hanger, mark it. The same with the threaded stock, except this time your coming in from the middle of the car because there is not room from the outside.

Q) [take the front spring eye and insert it into your box] Not following you on this one ... why am I putting a spring eye in the box before I cut the pattern?

A) With a spring “Off the Car” and the loose box, just fit the box to the front of the spring, so you get an idea of how the spring is going to fit into the box. Make sure you have clearance at the front of the box, and how high you want the spring in the box. Then measure from the front of the box (the closed end) back to where the bolt is going to go through the box. If you mount the box to far to the back of the car, your screwed, and you don’t want to go to far forward either. By making this distance on your pattern, you make sure you locate the box front to back with plenty of room for the spring.

Q) [I actually bolt the hanger up to the so I absolutely know the hole is in the right place] What are you bolting it to?

A) I am bolting it to the stock mount that comes out from the frame. Remember, your cutting the frame in the middle and the stock mount bolts on to a 90 degree mount beside the frame.

Q) I’ve been thinking about this and I’ve got another question ... after the springs are moved in, won’t the shock absorber lower mounts be moved in, thereby changing the angle of the shocks? Did you use different shocks, or does is not matter?

A) Yes, you effectively move the spring shock mount in about 3.5 inches, since the shocks are at about a 30 degree angle, you do shorten the effective length between both mounts. Which by it self would call for a bit shorter throw shock. But - if you use springs with higher arch, you might wind up at the same distance. This is very common, and most mopar shops like Mancini have shocks for this type of application.

Q) A friend of mine and I were poking around under the car last night, getting ready to start the spring relocation project. We’ve chatted a bit about the front mount of the rear spring, but not about the rear ... Do we just drill a hole in the frame section to install the new rear hanger?

A) There are a bunch of ways to go about it. With the spring relocation kit, you get a couple of tube sections. Some people just use a hole saw and drill thru the frame. On the ones I have done, every time there is another hole in the frame that does not make this a clean operation in my mind. So, I make four plates that fit the frame out of 1/8 inch mild steel, drill a hole the size of the insert tube in the plates. The plates are to weld to the side of the frame rails for extra support. I then use the original rear spring mounts to mark the right spot on the frame rails to use a bit larger hole saw to cut thru the frame.

One of my concerns the first time I did it was getting both sides the same. So by going a bit larger in the frame and using the plates on the side, I was able to use a “Hardwood Dowel” (they are pretty straight) as an alignment tool. I insert it into the tubes that come with the spring kit, use clamps to hold the plates on both sides, and align the tubes so they are square and both the same on each side, then tack weld the plates to the frame. It comes out very straight if you do something like that. You then weld the plates to the frame, then the tubes to the plates, grind it off and your there. I have seen guys use just a washer, but I wanted more strength.

Mopar Leaf Spring Relocation
Dressed Cut Left Spring Mount
Mopar Leaf Spring Relocation
Cut Right Spring Mount


Mopar Leaf Spring Relocation
Left Inner Spring Mount, Front
Mopar Leaf Spring Relocation
Left Outer Spring Mount

Mopar Leaf Spring Relocation
Right Inner Spring Mount, Front
Mopar Leaf Spring Relocation
Left Inner Spring Mount, Rear

Mopar Leaf Spring Relocation
Driver Rear Spring Mount
Mopar Leaf Spring Relocation
Passenger Rear Spring Mount


Also see Moparts Rear Suspension Page

Thanks, Jim and Earl!

Good info!   smile!

Gary H.


May 17, 2006

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