Rear leaf springs, 4" lift, too short?

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J7M46sn
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Joined: Tue Nov 30, 2021 8:46 am

Rear leaf springs, 4" lift, too short?

Post by J7M46sn »

I recently ordered a 4" all spring lift kit from Skyjacker for my '77 J20 truck. Last night I tried to install one of the rear 4" lift leaf spring assembly. I am re-using the stock shackles with new poly bushings in them. My shackle, hangers and truck frame are in great shape, very little surface rust is all.

On my first try, I tried to install the spring by inserting the front bolt first, and then I tried to install the bolt at the rear of the truck through the shackle. No matter how hard I tried, I couldn't get the shackle close enough to even get the bolt through both pieces, frame and shackle. The holes were always at least about an inch apart.

On my second try, I removed the front bolt, and figured I'd try to install the rear shackle bolt through the frame first. So I did, and then it appeared that at the front of the spring, the holes were mis-aligned by about the same amount, approximately an inch. While I was trying to 'pull' the spring towards the front of the truck to close the one inch mis-alinement, it appeared to me that the rear shackle on the spring, was bottoming out against the shackle mount on the truck frame, preventing me from pulling the spring forward.

I don't think the springs in the kit are actually too short, I believe they are the correct ones for the truck. (I don't think Skyjacker made a mistake). I'm guessing that because of the increased spring arch, the horizontal distance between mounting points is a little shorter than stock springs, and that I'll need to flex or compress the springs a bit to get both mounting points to align.

I'm semi-concerned that because I was seeing the rear shackle contacting the mount on the frame, I might not even be able to compress the spring enough to install the spring, or that once installed, the shackle may always be in contact with the mount on the frame.

My questions are: How do you compress or flex the spring enough to install them? Should I be using a different shackle to install the springs?

Thanks for any hints, tips or tricks to installing these!
Mike
1977 Jeep J20, 360, T18, D20, D44, D60, 4:10s

OldFarmTruck22
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Re: Rear leaf springs, 4" lift, too short?

Post by OldFarmTruck22 »

This is a common issue when installing lifted spring packs. You will need to connect the front end of the rear spring, then use a 4x4 block above the rear end of the rear spring and between the frame of the truck. Jack up the spring pack somewhere around the middle of it from below, this will push the end of the spring pack towards the rear of the truck and you can put your bolt through when you have jacked it high enough. You are effectively straightening out the spring pack by an inch or two.
Be real careful that you use a SAFE JACKING METHOD SO YOU DON''T HAVE THINGS SHIFTING AND squirting that spring into your head at the tail end.
Last edited by OldFarmTruck22 on Mon Feb 06, 2023 1:06 pm, edited 1 time in total.
78 FSJ AMC 360 Quadratrac

OldFarmTruck22
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Re: Rear leaf springs, 4" lift, too short?

Post by OldFarmTruck22 »

What spring packs did you order ... the JP40Rs /JP40FS ?
78 FSJ AMC 360 Quadratrac
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kjandb
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Re: Rear leaf springs, 4" lift, too short?

Post by kjandb »

'71 Wagoneer - 4" BJ's Leaf Lift - early 360 - Avocado Mist ???
S Idaho

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J7M46sn
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Re: Rear leaf springs, 4" lift, too short?

Post by J7M46sn »

OldFarmTruck22: Thanks for the 'block of wood' info, I had heard of that trick, but couldn't visualize how that may work... I ordered JP40RS springs for the rear of the truck.

kjandb: Thanks for the video, I see how the block of wood trick works. I'm not sure if that will work for me until I try it. I think on that Wagoneer in the video, it has 'post' suspension mounting points, and I think their shackle remains in a vertical position between spring and post. On the J-truck, the shackle mounting point is a like a welded box, and the shackle sits inside of it. The block of wood may still work, I'll just have to try it and see.

Thanks fellerz!
Mike
1977 Jeep J20, 360, T18, D20, D44, D60, 4:10s

OldFarmTruck22
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Re: Rear leaf springs, 4" lift, too short?

Post by OldFarmTruck22 »

J7M46sn wrote: Mon Feb 06, 2023 1:45 pm OldFarmTruck22: Thanks for the 'block of wood' info, I had heard of that trick, but couldn't visualize how that may work... I ordered JP40RS springs for the rear of the truck.

kjandb: Thanks for the video, I see how the block of wood trick works. I'm not sure if that will work for me until I try it. I think on that Wagoneer in the video, it has 'post' suspension mounting points, and I think their shackle remains in a vertical position between spring and post. On the J-truck, the shackle mounting point is a like a welded box, and the shackle sits inside of it. The block of wood may still work, I'll just have to try it and see.

Thanks fellerz!
If the frame end is 'boxed', you still need to stretch the spring to lengthen it. May just be a matter of moving the block further towards the center of the spring and increasing the size to a 6x6. Also you might find it's easier to connect the rear end of the spring first and stretch the front end into place. Depends on your block location on the frame.
78 FSJ AMC 360 Quadratrac

OldFarmTruck22
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Re: Rear leaf springs, 4" lift, too short?

Post by OldFarmTruck22 »

Looking forward to hearing how those springs ride. I been looking at them for my 2 Door.

Let us know.
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Stuka
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Re: Rear leaf springs, 4" lift, too short?

Post by Stuka »

Yeah, Brad's wagoneer is post mount. But its the same thing for the 76+ FSJs. The springs need to be pre-compressed, and then bolt up the shackle.

Also, in Brads video they did it the hard way. They should have had the shackle bolted to the post, and then compressed the spring and rotated the shackle to bolt it up. Having the shackle bolted to the spring, and then trying to push it onto the post is kind of dangerous.
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Re: Rear leaf springs, 4" lift, too short?

Post by rocklaurence »

That's the big performance issue with Hi-arched springs. The fronts are only 47" long and adding 4" of arch creates a half-circle spring which is very stiff and often exceeds the travel of an OEM shackle. Im running Rancho 2.5" front springs with an FSSR and its Crazy how stiff the front is. The rear springs are longer and the issues isnt as extreme but it still exists.
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Yeller
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Re: Rear leaf springs, 4" lift, too short?

Post by Yeller »

There’s a fix for that stiff front 😉😃🤐
The bus I ride is so short it is a yellow Smart Car full of squirrels, monkeys and clowns.

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https://www.fsjnetwork.com/forum/viewt ... 12&t=21395

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Topic author
J7M46sn
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Re: Rear leaf springs, 4" lift, too short?

Post by J7M46sn »

I got it figured out... When I installed the right rear leaf spring, I inserted the front spring eye bolt through the frame mount first (spring pivot point). At the rear of the spring, I already had the shackle loosely bolted to the spring eye, and laid the other end of the shackle in the boxed mount on the frame. I used a 2x4x24, laid flat underneath the bed, and on top of the spring eye. The 2x4 was inserted such that there was about six inches past the spring eye, towards the rear bumper. Then I used a floor jack positioned under the middle of the spring, and started jacking up, which flattens (compresses) the spring and increases the horizontal distance between spring eyes. While the spring is being flattened out, the rear spring eye slides along the 2x4, and the shackle hole gets closer and closer to the hole in the box mount on the frame. I was still able to wiggle the loosely bolted shackle, which helped get everything to line up.
RRear002.jpg
RRear001.jpg
My pictures are sideways, but hopefully they help. I hope my little description helps as well. I heard and read posts that say 'use a block of wood', but none ever explained how to do that. I lifted my 1974 Chevy truck about 25 years ago (still have the truck!), and vaguely remember doing something like this. I had a '54 Willys CJ3B that I installed a spring lift on too, but I don't recall having any problems doing that one.

I'll let you know how the truck rides in the spring. I live in Ohio, the roads are covered in salt and brine. The truck is an Arizona truck, and only has light surface rust underneath. Thanks for the help fellerz!
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Mike
1977 Jeep J20, 360, T18, D20, D44, D60, 4:10s

Srdayflyer
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Re: Rear leaf springs, 4" lift, too short?

Post by Srdayflyer »

i ran into the same issue, but i used a come along to compress the springs to get the bolt hole to line up

9.3x62
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Re: Rear leaf springs, 4" lift, too short?

Post by 9.3x62 »

Thanks, OP, I just followed your method this evening and it worked a charm! Between this part and breaking the rear shackle bolts (wah!), I figure it's down hill from here.

OldFarmTruck22
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Re: Rear leaf springs, 4" lift, too short?

Post by OldFarmTruck22 »

How the new springs feel going down the road?
Thinking about putting same ones on my 2 door.
78 FSJ AMC 360 Quadratrac

sierrablue
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Re: Rear leaf springs, 4" lift, too short?

Post by sierrablue »

Yeller wrote: Wed Feb 08, 2023 5:56 pm There’s a fix for that stiff front 😉😃🤐
Throw a diesel over it!!!! 😝

Oh wait you're a 4-link guy...
(not that I'm opposed to 4-links)
'71 Wagoneer (DD)
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There are 2 major differences between new Wranglers and FSJs. FSJs are meant to be both utilitarian and capable, not just capable. FSJs are also rarely initially recognized as Jeeps by the average American.
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