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Old 01-14-2008, 08:05 PM   #1 (permalink)
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Question measuring leaf length

im going to a 52" leaf on the front and need to build new mounts on the front. now when i measure for the new mounts do i measue them at 52"?

the spring length now is only 50.5" just layin on the ground, so underload do they = 52"?

im just not sure at what length to build the new leaf mounts. any and all help would be useful.

Thank ya.
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Old 01-14-2008, 08:44 PM   #2 (permalink)
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What are you working on? The 52" srping swap on a Chevy is well documented in the chevy section. Try the search button.

If it's on something else, see if this helps: He's talking about how to measure for shackle length/placement, but it might help.
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Originally Posted by rcurrier44 View Post
Your needed shackle length is real easy to figure out.

-First, you know how far the leaf spring can posibly come back...its when the leaf spring is flat... So measure along the main leaf by bending your tape measure or using a piece of wire to get the true length of your spring when flat.

-Then Stretch your tape from the front spring eye back to figure out ware the spring eye will be and mark it...or tack a piece of tube about the same size as your rear spring eye to the frame in this spot.

-Then measure from your shackle pivot to this tacked on tube - add 1/4" or so so it clears your frame and doesn't touch - this is the shackle length needed to clear the frame and give you full range of motion...


You should only have to make shackles once...
I'm swappin a set of 52" Chevy spring on the front of my Scout, I used a plumb bob to help center the axle in the wheel well, remember the axle will move toward the shackle as the spring compresses.
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Old 01-14-2008, 08:49 PM   #3 (permalink)
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im swaping chevy rear leafs to a d250 front. going from 48" to 52", i need to build new mounts past where the current frame is.
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Old 01-15-2008, 01:30 AM   #4 (permalink)
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springs are measured along the arc, or if you could, flatten the spring, then measure spring eye to spring eye center. That is why your 52" springs measure 50.5".

Center the diff and then use the center measurements, in this case, 26". That's where you want your front hanger.

For the rear hanger, a lot depends on you shackle length.

You want to set it up so that when the spring goes flat under compression, you use all the shackle length.

When I set up my 64" rear springs the mount points on the frame measured 61" on center. I used a 6" shackle, so my springs go flat before all of the shackle distance is "taken up".

I'd expect your hard mount centers to be somewhere in the neighborhood of 46 - 48" if your going to use a 6" shackle.

It's easiest if you tack weld the mounts or use clamps to mock it up and see where everythings going to end up.
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Old 01-15-2008, 02:20 AM   #5 (permalink)
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springs are measured along the arc, or if you could, flatten the spring, then measure spring eye to spring eye center. That is why your 52" springs measure 50.5".

ok, that helped. i was misinformed on the correct way to measure leafs.

that beaning said, the correct way i should set these up is to take my shackle and hold it about an inch from the frame (to the rear), then measure 52" straight (or what my springs are eye to eye following the arch) and build my mounts there?

if thats true, that makes so much more sence.

let me know guys.

Thanks again.
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Old 01-15-2008, 05:20 PM   #6 (permalink)
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Quote:
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springs are measured along the arc, or if you could, flatten the spring, then measure spring eye to spring eye center. That is why your 52" springs measure 50.5".

Center the diff and then use the center measurements, in this case, 26". That's where you want your front hanger.

For the rear hanger, a lot depends on you shackle length.

You want to set it up so that when the spring goes flat under compression, you use all the shackle length.

When I set up my 64" rear springs the mount points on the frame measured 61" on center. I used a 6" shackle, so my springs go flat before all of the shackle distance is "taken up".

I'd expect your hard mount centers to be somewhere in the neighborhood of 46 - 48" if your going to use a 6" shackle.

It's easiest if you tack weld the mounts or use clamps to mock it up and see where everythings going to end up.
Good explanation, I was going to go in more detail, but wasn't sure what he was working on.

I would measure like noface suggested, from the center line, the length of the spring from center pin to spring eye, (in your case 26") not where you think the shackle should be. That should get you pretty close. Get the front of the spring mounted, then set the shackle angle, remember the spring will flatten out and lengthen with the weight of the vehicle on it. I've seen some guys use just the main leaf during mock up to fully flex out, then build the rest of the spring pack. When setting the shackle angle you want it tilted 20-30* forward so it will flex properly. If in doubt, a flatter shackle angle "\" is better than a steep "I"

X2 on tack welds to check everything before you burn it in solid.
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Old 01-16-2008, 02:08 AM   #7 (permalink)
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[QUOTE=daithi2;7735432]
that beaning said, the correct way i should set these up is to take my shackle and hold it about an inch from the frame (to the rear), then measure 52" straight (or what my springs are eye to eye following the arch) and build my mounts there?

if thats true, that makes so much more sence.

QUOTE]

that does make sense, but it's not that easy

IF you are using the stock shackles (same length), and you are replacing 48's with 52's, AND don't want anymore lift, AND you are happy with the CURRENT shackle angle, you could simply measure 2" forward for the front mount, and 2" rear for the rear mount, as the 52's are 4" longer than the 48's. Your axle would still be centered.

It gets trickier when you use the longer shackles. For example, with 6" long shackles and the above scenerio, moving the front mount 2" forward, you would also move the rear mount 2" forward. You would then have a shackle angle more like "\"

I find that when you run into situations like this, I draw them to scale on some graph paper first with my measurements, and it get's you real close.

Guido in the post above offered some great advice as well.

Between these couple posts, you should be able to get it in the ballpark.

Just remember to measure twice, and cut/weld once! I actually set my tuck on it's own weight with a bunch of C-clamps and vise grips holding everything in place before making a final decision on where to nail it down. It takes some time, but unless you'r doing something someones already done and documented, you get to be the engineer!
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Old 01-16-2008, 04:05 AM   #8 (permalink)
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its lifted now, with a 1" factory block that getting removed and 2" springs.

and the front axle is moved forward on the leafs about 2". im going to use the same rear shackles. in the same location. that way the front end is moved forward even more with the new leafs.

the front leafs now are flat as a dog with a shitty shackle angle (twards the rear) due to being flat, the springs i got are 6" lift rear springs that i took the overloads off. im hoping for 4" of lift out of them.
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Old 01-17-2008, 07:05 AM   #9 (permalink)
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So in this pic everything is correct??. I asked "77oneton" who I stole this pic from (hope he dont mind) and he said it allowed full stuff and maximum droop.
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Old 01-17-2008, 08:16 PM   #10 (permalink)
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So in this pic everything is correct??. I asked "77oneton" who I stole this pic from (hope he dont mind) and he said it allowed full stuff and maximum droop.

IMO the shackle angle is the wrong way. you want a vertical or inside angle giving the spring room to compress, thereby pushing the shackle out.

correct me if im wrong here guys.
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Old 02-08-2008, 11:22 PM   #11 (permalink)
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btt for answer to previous post
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Old 02-09-2008, 09:54 AM   #12 (permalink)
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Quote:
Originally Posted by daithi2 View Post
IMO the shackle angle is the wrong way. you want a vertical or inside angle giving the spring room to compress, thereby pushing the shackle out.

correct me if im wrong here guys.
yea... you are very wrong. you dont want it to be the other way or else you run the risk of having the shackle flipping forward and locking to the frame. you could bend the spring that way. Also that shackle angle is a little steep. i think 30-45 degrees is about perfect.
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Old 03-17-2008, 11:23 AM   #13 (permalink)
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yea... you are very wrong. you dont want it to be the other way or else you run the risk of having the shackle flipping forward and locking to the frame. you could bend the spring that way. Also that shackle angle is a little steep. i think 30-45 degrees is about perfect.
Are you talking about at ride height or all the way compressed?? I have read the 45* thing alot but depending on where and what they reffer to it being at full compression or stuff. I know this is old but I got my shit mocked up and the shackle angle on my 57 fords is at about 40-45 at ride height with a 6.5 shackle. the springs are almost flat though, geuss ill add another leaf.
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