Moving rear axle 1-2" back?

[74 Bronco Billy]

I have seen it mentioned that the rear axle is moved back 1-2", some times more. What are the benefits, the negatives, and lastly the hassles? How is this accomplished?
I just cut off my spring perches as they were collapsing, so I am tentatively just assembled. New perches are bigger, but not welded in yet. Advice welcomed at this point. The leaf spring bolt is tight going into the the spring perch hole.
Thanks,
Forrest

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[bknbronco]

you move the axle back to center in up in the wheel well opening if need be. This is typically 1" and only possible by welding on new perches and using new top plates, both with a extra hole drilled behind center.

 

[bronconut73]

You can simply drill the axle pad and the u-bolt plate an inch or so from the stock hole. Then re-assemble. That's what I did,
It is better to weld on new longer axle leaf spring pads with the extra holes in it already. The longer ones help with axle wrap too.
Probably the best way is to move your spring hangers back on the frame.

I only went back about an inch and a half. Beyond that it looked like my axle would hit the gas tank feed lines.

It actually rides better now.
No big increase in axle wrap, but I was worried about that,

 

[1971BroncoSport]

Axle offset plates

I used these

http://offroaddesign.com/catalog/Axle Offset Plates.html

 

[DirtDonk]

If those are WH springs then the center bolt has a larger than stock head, so that could explain why it's tight going into the new one.

The usual practice is to drill out the hole to the size that fits the larger head. Just over 9/16" if I remember.
If your new perches only have the one center hole, then you'll need to drill a new one forward of the existing one the amount you want to change. Just make sure it's the larger diameter to fit the pin.

Paul

 

[DirtDonk]

By the same token, you could always grind a little off the head to make it fit the existing hole if that was easier.
But since it sounds like you're interested in moving things, you have to drill a new hole anyway so larger is better.

If you're not really interested in moving the axle back and were just asking for the reasoning, then enlarging the existing hole, or grinding some material off the head, would still do the trick.

Paul

 

[migs]

Simplest way is to just drill new holes forward of the originals. I moved my axle back 3/4" to gain a little clearance away from the front of the lower rear wheel well opening. The further you go back it starts heading up the rear arch of the spring which can affect the pinion angle.
Looks like the new perches you have are the longer antiwrap type, if that's the case and especially if you move the axle back you might want to consider ditching the tiny bottom leaf. I did, I noticed it's almost smaller than the perch and when the axle is moved back its no longer fully sitting on it.
One other thing, your spring shackles are on backwards if you wish to obtain maximum axle droop. They will work in that position but as the spring pulls them forward the edges on the open side facing forward like that will hit the hangers limiting axle droop.

 

[74 Bronco Billy]

You can simply drill the axle pad and the u-bolt plate an inch or so from the stock hole. Then re-assemble. That's what I did,
It is better to weld on new longer axle leaf spring pads with the extra holes in it already. The longer ones help with axle wrap too.
Probably the best way is to move your spring hangers back on the frame.

I only went back about an inch and a half. Beyond that it looked like my axle would hit the gas tank feed lines.

It actually rides better now.
No big increase in axle wrap, but I was worried about that,

Good to know that it rides better, and the new perches are huge and do have 3 holes in them

I used these

http://offroaddesign.com/catalog/Axle Offset Plates.html

Those look interesting, but I think I can use my perches to get the 1" that is suggested

If those are WH springs then the center bolt has a larger than stock head, so that could explain why it's tight going into the new one.

Good eye. I destroyed the old bolts when I took the springs apart and had them powder coated. They kept rusting. I used the larger bolts that came with the 6 degree wedge kit. I don't need the wedges if I rotate the axle to ideal pinion angle, right? And if I ever need more angle, I have the wedges...

The usual practice is to drill out the hole to the size that fits the larger head. Just over 9/16" if I remember.

I will be trying this, though the head did fit the bolt before I put the weight on it...

If your new perches only have the one center hole, then you'll need to drill a new one forward of the existing one the amount you want to change. Just make sure it's the larger diameter to fit the pin.

Paul

By the same token, you could always grind a little off the head to make it fit the existing hole if that was easier.
But since it sounds like you're interested in moving things, you have to drill a new hole anyway so larger is better.

If you're not really interested in moving the axle back and were just asking for the reasoning, then enlarging the existing hole, or grinding some material off the head, would still do the trick.

Paul

Simplest way is to just drill new holes forward of the originals. I moved my axle back 3/4" to gain a little clearance away from the front of the lower rear wheel well opening. The further you go back it starts heading up the rear arch of the spring which can affect the pinion angle.
Looks like the new perches you have are the longer antiwrap type, if that's the case and especially if you move the axle back you might want to consider ditching the tiny bottom leaf. I did, I noticed it's almost smaller than the perch and when the axle is moved back its no longer fully sitting on it.
One other thing, your spring shackles are on backwards if you wish to obtain maximum axle droop. They will work in that position but as the spring pulls them forward the edges on the open side facing forward like that will hit the hangers limiting axle droop.

Migs, thanks for the reply and good eye. Those are the extra wide spring perches for anti-wrap, with 3 holes. I kept staring at that damn shackle, trying to figure out if I have it on backwards or not. Ugh. And I had the bolt on backwards the 1st time I put it together. Changes it for the picture.
So, you're recommending the removal of the smallest leaf, does that affect the ride height? Is it doing much for the whole pack?

Thanks for all the replies, really appreciate it.

 

[DirtDonk]

...I kept staring at that damn shackle, trying to figure out if I have it on backwards or not. Ugh.

Yeah, you're not alone. The "intuitive" direction is with the open face towards the spring. And that's actually how most aftermarket (including Migs' I think?) are oriented. So you were half-correct!
But Ford designed them with the open face to the rear. And the stock ones definitely work better that way.

I don't need the wedges if I rotate the axle to ideal pinion angle, right? And if I ever need more angle, I have the wedges...

Correct on both counts.
You're at the perfect stage to set your own correct pinion angle once the vehicle is at ride height.
If you're not at that point, but still want to fully weld them, you can compress your suspension with ratchet straps or something along those lines, get the distance between the frame and the axle to the expected height (stock, plus whatever lift you have) and then set the angle.
Assuming you know already (hey, you got this far, right?) but just for other's reference, assuming you're still running a double-cardan shaft you'd set that angle to put the pinion about 1 to 2 degrees down-bubble from the centerline of the driveshaft.

So, you're recommending the removal of the smallest leaf, does that affect the ride height? Is it doing much for the whole pack?

You can leave it if the leaf turns out to be longer than the perch. But usually it's at, or just shorter than the long perches. In which case it's advantageous to remove it.
And being that the perch is slightly taller than the stock one too anyway I think, it's not a bad thing to remove that one leaf if only to compensate.
The amount of lift you lose with the lower leaf is really just the thickness of the leaf itself. So you're down about 1/4" or so by doing so. They're virtually "filler" leaves when it comes right down to it.

Paul

 

[DirtDonk]

Oh, and on a side note, and since you were talking about flipping bolts around, I'd flip the main front spring eye bolt too.
It's more factory "correct" and I think it looks cleaner too when just the head is showing on the outside and the nut and exposed threads are more protected in the pocket on the inside of the hanger.

I believe I have seen some original Broncos with the bolt outward like you have. But by far most of the ones I've seen over the years had just the hex head showing.

Paul

 

[migs]

Like Paul said, those perches are taller so that should more than compensate for the missing bottom leaf. I have wild horses 3-1/2" rear lift springs and similar perches to those and think the fit and work better together without that tiny leaf. My Bronco sits perfect to my eyes and rides great.

As for the shackle, I have a thread here with pictures showing the swing and travel of the shackles in the stock hangers.

 

[nvrstuk]

There's benefits to moving the axle back 5-10 or more inches but not unless you're a hard core wheeler... otherwise just move the axle back enough to center it in the fender opening...

 

[74 Bronco Billy]

Once again, sage advice from all. Thanks a lot. F

 

[bobtail]

as a dumbass I have to ask what the benefit is when moveing the axle back. aside from centering the axle in the wheel well

 

[DirtDonk]

For most EB owners it's due to clearance for larger tires with uncut rear fenders.
When you start getting towards the 33" diameter tires, many EB's (but not all) will start to rub on the leading edge of the rear wheel well opening.
Even on cut fenders with flares, you often see a nice half-moon shape ground down into the leading edge of the flare.

Then there's the school of thought that a longer wheelbase is more stable and offers some traction benefits off road. Which it does...

Most are going for tire clearance though I think.

Paul

 

[74 Bronco Billy]

Next step is drill out a little bit of the forward hole on the perch, then reinstall, allowing axle to move rearward. Do I keep the top portion of the bolt in the center hole or do I place it offset too? Orientation with extra hole forward or rearward? Do I use center hole or offset? And is the 4 hole U bolt plate correct in orientation? I.e. angled edges down?
Thanks,
F

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[migs]

Yes, the hole in the top clamp should be moved from center the same distance as the one in the perch. And you are correct, those angled edges face down toward the spring to allow a little better flexing without a sharp edge digging in.

 

[74 Bronco Billy]

Yes, the hole in the top clamp should be moved from center the same distance as the one in the perch. And you are correct, those angled edges face down toward the spring to allow a little better flexing without a sharp edge digging in.

Now this makes a lot more sense. Guess I gotta get out the calipers and measure the holes on the top clamp with the perches to see if they are the same distance...I don't think they are. I really am not looking forward to drilling holes in the top clamp plate if the holes are not close. Yikes! Let's see, that's drill the perches a little bit, measure, reassemble per directions below. And take out the smallest leaf on the bottom....

Brian, thanks for the advice on how to tighten the leaf spring clamps down. I'm posting it here for others to know it too. Per Migs: "when tightening done those U bolts sometimes it helps to have some weight on the springs to help compress them down. you might notice when you go to tighten it up the ends of the top clamp touch the spring arch leaving a gap underneath the middle of it. I've even used a jack strapped to the frame to push the axle up to help close that up rather than trying to make the nuts on the U bolts suck it together."

Thanks again Brian.