Front Drive Alignment and Turned Axle (1 Viewer)

[SouthMS40]

I've got a several year project 1975 FJ40 I'm still working on. It's got an SOA lift with factory springs flipped front to rear, shackle reversal, changed to late model knuckles with 12mm studs and high steer kit. I bought the front housing from the old Profitt's Cruisers cut and turned for the SOA.

Problem is, my input is at best a few degrees low of the TC output for the front shaft. If I leave as is the steering will rotate into the springs if only shimming the angle. It seems the best option is to undo the shackle reversal. Am I missing something, or spot on?

If I need to undo the reversal, should I cut off the mounts or just make custom shackles? I have the resources to make custom shackles if need be. If I have to cut and re-weld mounts I'll have to haul it to our weld shop at work. I'd rather not have to haul it.

A few pics:

 

[shawnfj40]

What does it look like with the springs flipped back?

 

[too tall]

What about trying a shorter shackle on the rear end and adding a small say 2" drop to push the front hanger down? what is your caster angle currently?

 

[SouthMS40]

Originally I had 2-1/2" springs with the SOA but it was just too much so I went with factory springs off the 1972 I have also. With the lift springs, short side to the rear, it looks like the angle was better. How much better, I don't know. The pictures I have from then aren't that good and hard to see the angle.

As for flipping these springs back, I don't know. They were never bolted up that way. I also really want to keep the longer wheel base if possible.

 

[pjohnson]

Whose steering arms are you using?

Was the cut n turn designed for your design of shackle reversal?

 

[SouthMS40]

I'm about as low as I can/want to go on the rear shackle. Adding a drop or spacer to the front doesn't exactly turn me on. The input is at 5 degrees now.

 

[SouthMS40]

Marlin Crawler's 25mm high steer kit. When I ordered the axle housing I ordered for my lift springs. I think that's where my problem is. It's been a while since that was done. I'll have to dig through my file for any notes or details on the housing.

 

[pjohnson]

If your springs were flat you wouldn't have the problem. Dropping the front mount a little might be your best bet.

Is it the drag link that is the problem? What does your pitman arm look like?

 

[too tall]

I'm about as low as I can/want to go on the rear shackle. Adding a drop or spacer to the front doesn't exactly turn me on. The input is at 5 degrees now.

I personally always drop the front hanger when doing a shackle reversal. It levels the spring out so you don't get as much nosedive under braking. What is it about dropping the front that you don't like? Also it looks as though you have room to drop the height of the shackle. You can't use a shackle with the brace welded across the center but a regular 40 shackle or anti inversion shackle mounted upside down should work fine. You say the input is at 5 degrees. What is your caster angle?

 

[SouthMS40]

I'm not hot on lowering the front pin I guess because I'm not sure of a good way to do it. I guess I could make some big cheek plates with the shackle tube lowered. The caster angle is 8-9 degrees positive, leaning back. Roughly it looks like my axle needs to rotate 15 degrees to get the shaft inline with the axle input. Seems like a lot. This would give me a 5 degree negative caster angle, leaning forward. At this point it looks like I just need to undo the shackle reversal. Also, there's 3" difference vertically between the front and rear of the spring. Rear being lower.

 

[SouthMS40]

A few more pics.

 

[SouthMS40]

Flattening the springs, both ends on the same horizontal plane, will only give me 5 degrees of rotation. I'm going to unbolt and do some spacing to see what it does this weekend.

 

[71FJnick]

Sorry, can you post a picture of the interference? I may have missed it, but it looks like the springs clear your linkage, are you only worried about interference if you try to rotate the diff with shims? Or is the pitman arm hitting the spring?
I have a soa with shackle reversal and 4x4 labs arms. It's super close to touching and I have to flex it to be sure, but I think it should be ok.

 

[SouthMS40]

I'm not concerned with the steering so much right now. The concern is the angle between the driveshaft and input on the front diff. If I only shim the axle it's going to jam my steering into the springs.

 

[71FJnick]

Ah I see. If it helps, I rotated my pinion up 15deg, and my knuckles back 19deg from stock. That gave me about 4deg caster.

 

[too tall]

Flattening the springs, both ends on the same horizontal plane, will only give me 5 degrees of rotation. I'm going to unbolt and do some spacing to see what it does this weekend.

I would try to space the fronts down with a piece of 2" square tube. It would be best IMOP to keep your caster below 6 degrees if possible. I always aim for 3 degrees. Are you planning on using a cv shaft in the front? I am guessing that is why you are trying to tip the pinion up?

 

[shawnfj40]

I think its going to take a combination of dropping your front spring hanger and flipping your spring. Of course you could just replace the front axle housing with one that hasn't been turned and undo the shackle swap.

 

[SouthMS40]

What's the optimal caster angle? What's the bare minimum caster angle allowable?

 

[cruisedeisel]

0-4 degrees

 

[rusty_tlc]

I'm not hot on lowering the front pin I guess because I'm not sure of a good way to do it. I guess I could make some big cheek plates with the shackle tube lowered. The caster angle is 8-9 degrees positive, leaning back. Roughly it looks like my axle needs to rotate 15 degrees to get the shaft inline with the axle input. Seems like a lot. This would give me a 5 degree negative caster angle, leaning forward. At this point it looks like I just need to undo the shackle reversal. Also, there's 3" difference vertically between the front and rear of the spring. Rear being lower.

Check out ruffstuff spring hangers. I used them on my SOA project and have no regrets.
FJ40 Leaf Spring Hanger