74 rear post mount lift

[Firegoose]

I am in the process of lifting my 74 J20 in the rear to match the front SOA (7"). I have re-engineered a spring hanger bracket from a ford to do away with the front post mount on the rear. I have a set of J-10 rear springs that I was wanting to use and the reason I was wanting to use them is because they are the same length and center as my old post mount springs.

My problem is this I marked the center of the axle on the frame before I removed the post mount and original springs, once I flipped the rear shackle(@90 degrees) and temporarily installed the front spring holder the center of the axle is 1.063" toward the rear.

My question is this. Do I need new springs to do this "shackle" flip? I sort of remember someting about chevy 52" springs ...I think. If I do need a new set of springs does anyone know the dimensions? I have a local spring shop here that can do almost anyting.

Also my Jeep is only a bare frame at the moment and I was curious as to the degree my rear shackle should be at? Due to there being basicly no weight on the Jeep. Would 90 degrees be acceptable ?

[Stuka]

You dont need new spring, but when you change the shackle, the spring geometry changes. The front mount should have been moved straight down to its new location, and the rear mount should have been moved about 1.75" forward.

EDIT: Oh yeah, the 52" springs are for 75 and older wags, cheros, and short bed j-trucks. Long beds like you have use a longer spring, closer to 57" as I recall.

[ March 05, 2006, 03:09 PM: Message edited by: Stuka ]

[Elliott]

There are two reasons you don't want the rear shackle at a 90* angle, it will give a harsher ride and it could possibly flip forward on articulation and cause the spring to bind.

[Stuka]

I have never seen/had a spring flip forward because the shackle is facing straight down. But it will make for a slightly harsher ride.

[Firegoose]

Originally posted by Stuka:
You dont need new spring, but when you change the shackle, the spring geometry changes. The front mount should have been moved straight down to its new location, and the rear mount should have been moved about 1.75" forward.

I had planned on moving the front hanger straight down but I didnt think about the rear hanger.... So moving the rear hanger 1.75" forward will do the job. What will the shackle angle be once I move the rear hanger forward ? Or what should it be (bare frame only)?

Another question, would it be simpler to just move the spring or a new spring underneath the frame ? I think Crazy has his that way.

[Firegoose]

Pics for whatever reason...





After all the fab is done it does get POR-15

[ March 05, 2006, 04:52 PM: Message edited by: Firegoose ]

[Elliott]

My hangers are partially under the frame:

[Elliott]

With your shackle hanging like that and no weight on it it should be fine under load I would think.

BTW, what is the GVWR on that J20?

[ March 05, 2006, 05:25 PM: Message edited by: Elliott ]

[Firegoose]

6500#



Elliott, when you moved your spring hangers did you have to relocate your axle perches ?

[Tad]

Jason,
I am sure Elliot had to move his rear perches for that.
Or his axle is not stock (I do not remember).

[Elliott]

Yeah, the perches had to be moved anyway, I have a 14 bolt in there and needed a lil more room for the spring mount plate to clear the drum backing plates so I'm inboarded 3/4".

[ March 05, 2006, 06:04 PM: Message edited by: Elliott ]