64" rear swap

[owenst7]

This is on my 76 K5. When the floors were changed (early 80s?), the body mounts behind the front seats were moved outboard of the frame. This would interfere with your forward spring hanger if you were to copy me. I'm sure it can be done though with some retrofitting and/or just making an integrated body mount/hanger.

Being that 64"s are a foot longer than the stock 52"s, they have many advantages such as reduced wrap and more travel. Not to mention, they are still in use today, and can be had in junkyards in better condition than used 73-88 springs.

I got mine off a '95 Heavy half ton pickup. Mine have four leaves plus the overload. This is about the ideal spring rate for me. I can very easily flatten them but I have no noticeable wrap so far.

I removed the forward hangers and the rivets in the body mount crossmember. Conveniently, the crossmember uses the same hole spacing that the hanger used. I simply moved the hanger forward to share the holes with the crossmember. This moved the hanger forward 5.5". Since 64"s are centered just as my 52"s, but 12" longer, then hanger needed to move forward 6" to maintain the stock axle location. As I mentioned, I only moved it forward 5.5". This results in placing the axle .5" rearward of stock. This really wasn't noticed at all, other than my stock length driveshaft was definitely not going to work longterm now(although it didn't seperate the few times I wheeled it). I suppose you could even do this without the shackle flip and the driveshaft would probably be fine...however I have no idea why you'd want to do that.

The rust and holes show where this (hanger) used to be. I am holding it about in the location that it ended up.

The frame stripped...again, you can sort of see where things sat for 33 years.

Here's how things bolted up. As I said before, I just moved the hanger forward into existing holes. I didn't like the idea of putting more holes in the already weak horizontal plane of the frame, and there was no need to anyway. You can see the remains of two rivets that were holding the hanger. After doing about 48 rivets with limited tools, I could care less if they sit there as an eye sore.

Another shot that shows the stock location and the new location. a few of the rivets were a huge pain because the body supports were in the way, along with my exhaust on the other side. If you can get a grinder in there to girnd the heads off, and remove the rivets on the other side of the hanger, you can beat a prybar in there and pull the hanger off the last few rivets. There really isn't a "good" way to do them...Each one holds the frame together differently and there's about a thousand different ways to fight them out of there. Key word is "fight". Rivets really suck, but I guess they do their job well. You can also see where the vertical face of the frame (what we're looking at now) needed holes drilled. A few of these were really tricky to drill. I think I ended up using a cardboard pattern and drilling a couple from inside the frame. I actually used my dinky little 12V cordless a few times here because there was such little clearance to work.

 

[owenst7]

So now that the front hangers are in, it's time to do the rears. Being a mechanical engineer, I had fun doing the trig to figure out the location of the rear hangers in relation to my shackle angle. You might get away with leaving them in the stock location depending how stiff of springs you use and a few other variables...but in my opinion it's going to reduce your ride quality and risk inverting your shackle on the trail. To each their own.

With a 6" shackle, moving the rear hanger back about 1.9" is going to give you somewhere around a 41-43* shackle angle when the spring is longest (dead flat). I didn't go all the way to 45* because bushings can deflect, my measurements aren't perfect, springs stretch, etc. A longer shackle will reduce the angle, so you would not need to move the hanger as far. However, after doing the math, I chose a 6" shackle because it would not limit the travel of the springs with the given weight of my axle/tire setup by being too short. We're already sacrificing departure angle to an extent with the longer springs, so it was in my best interest to run as short of a shackle as possible without sacrificing droop.

Hanger back 1.9" from stock.

Full droop is obviously further with this due to the weight of the axle and tires.

The shackle angle was at 40* here I believe, which is just a hair from completely flattening the spring. I was pretty stoked my math worked out correctly.

Weight of the truck on the springs. I think it ended up with a shackle angle around 35.7* at ride height.

Just some more shots of how things ended up.

I threw the stock 52"s from the rear under the front of the truck. The perches on the 14b are a bit shorter than the stock cast ones, and dana 60 perches are taller than dana 44 perches. With all that taken into consideration, the truck ended up pretty much level using stock 52"s and stock 64"s (HD 1/2 or LD 3/4 ton pack, 4x4). I feel that it sat maybe half an inch low in the rear, but I carry a decent amount of tools and gear, and my fenders are a bit cobbled up...so It's kind of hard to tell. I would say that I would not have felt it was sitting low if I had used the stock cast perches on the 14 bolt, thats how close it was. Either way, I wanted to move the axle further back to increase wheelbase and departure angle, so I used a zero rate to move it back another 1.5". I had zero clearance issues with the 35"s this way, and I have not trimmed the rear at all yet. I now have 40"s (got my money back out of the 35"s I bought two years ago, w00t!), and I will see how they fit. The rears look pretty close, but I have big plans for re-arranging stuff back there anyways once I get time.

Right now the wheelbase is about 108.5" with the front in stock location. I will move the front forward more as soon as I can afford a new front shaft and some stock suburban rears. The front shackle angle is not perfect, and I would prefer to run the longer 56" anyway for other reasons. I am also building this truck to keep up in the rocks with coilovered buggies around here, so I'm demanding more travel from this suspension than most guys.

 

[owenst7]

Here are a few pictures of the truck in action after the spring swaps. I was previously running 4" lift 46"s in the front with no swaybar and stock 52"s in the back with a homemade flip and two leaves taken out. It actually flexed very good before (much better than most GMs I've worked with), but it is a whole new rig now. It drives better on the highway and it's almost difficult to get a tire off the ground. I can really feel the rear axle being moved back 2". It greatly reduced a lot of the bounce you get from going over bumps on the highway because the mass of the truck (mostly the damn np203) is better located in relation to the rear suspension. It's hard to describe, but the longer springs and stretched rear make it feel much more stable like a car rather than the tall SUV that it is. Some of that may also be attributed to the heavier axles, as adding weight under the suspension greatly lowers the moment (center of gravity) of the truck, but I'd say the suspension is a lot more significant factor here.

Maiden voyage on 'tons, new suspension, and new steering.

e-brake lines are limiting droop here (I hear them ALL the time). I am putting discs on it next year so I'm just ignoring this for now.

DL clearance with 52"s

 

[owenst7]

One thing that does suck about this:
With the old rears with two leaves removed, it sat pretty much the same height. My 48" hilift could easily get the back tires off the ground. I have since bought a 60", and even in the driveway, it will only get the tires a few inches off the ground before maxing out. I now have to use a chain to keep the axle from drooping if I need to pick it up on the trail. Pretty small price to pay for all that droop though .

 

[Hogback Fabrication]

Being that 64"s are a foot longer than the stock 52"s, they have many advantages such as reduced wrap and more travel.

Longer springs actually wrap a lot more because the lever arm is longer. Most people who run 64's end up running an anti-wrap bar.

 

[owenst7]

Longer springs actually wrap a lot more because the lever arm is longer. Most people who run 64's end up running an anti-wrap bar.

Wrap resistance increases exponentially per unit length of the spring. Most people run anti-wraps on 64"s because they don't run enough support leaves, they remove the overload, or they are running blocks. The main leaf of a 64" is designed for a pickup which has way less weight on the rear suspension most of the time than a K5. Toy guys run too few leaves for the amount of torque they produce and require to move big tires, and K5s and Subs need to run more along the lines of a 3/4 ton pack because of all the extra rear weight.

Why do you think pickups run such long rears? It allows them to have a soft main leaf for comfy riding around town, but there is wrap resistance when they are towing or loaded down due to the long spring. With the increase in torque from motors in the past couple decades, along with higher ride quality and payload/towing standards, rear spring length has greatly increased. I think Ford Super Duties are running a 70"+ rear now.

 

[ryoken]

I agree with Chris.... there's no way 64" s are better for axle wrap.. you can't just blame it on someone disecting the leaf's or having blocks... it's inherent in the geometry.... plenty of people in here have done it, and developed axle wrap when none was had with a shorter spring...

 

[owenst7]

I agree with Chris.... there's no way 64" s are better for axle wrap.. you can't just blame it on someone disecting the leaf's or having blocks... it's inherent in the geometry.... plenty of people in here have done it, and developed axle wrap when none was had with a shorter spring...

I'm not about to graduate with a degree in this stuff just cuz it looks good on a diploma. Physics is my thing.
http://www.youtube.com/watch?v=VGvwlI4YMQs&feature=player_embedded#

The main leaf of 64"s is not the same spring rate as 52"s or 56"s. You can't just swap them and say they are the same thing, and if wrap results blame the length of the spring. You are comparing apples and oranges. Increased wrap from 64"s is not related to trigonometry, it's related to dynamics of the material used. The main leaf of a 64" is not ideal for this application, but using a heavier spring pack gives us the ability to make up for a lot of that. My springs ride somewhat stiffer than my '96 1/2 ton, but because I can compress them fully without transferring much force to the front suspension, increasing wrap isn't worth the trade off of running a lighter duty pack.

I have less apparent wrap than I did with the stock springs in the back. I also am running very close to the stock spring rate on the rear. I'm still able to max out the compression travel easily, and the droop is a lot more than the 52"s allowed. The ride "stiffness" is about the same, but there is increased travel and reduced wrap, which is what I wanted.

 

[ryoken]

I guess my 30+ yrs of building vehicles don't mean jack then...

 

[owenst7]

I guess my 30+ yrs of building vehicles don't mean jack then...

Nor does the knowledge of the "ford chassis systems engineering supervisor" mean anything then. With all due respect, I don't think a major truck manufacturer like Ford is developing "theories" that aren't based on the scientific method.

Nor does my 15+ years of building and wheeling vehicles mean anything either.

 

[Hogback Fabrication]

Wrap resistance increases exponentially per unit length of the spring.

I still believe that to be backwards.

All of your other comments seem to be aimed at the complimentary leaves involved. So, if a set of 52's and a set of 64's each were sitting flat on their overloads, you think the 64's would wrap less?

The center of the torque applied is 32" away from either spring eye with 64's while it's only 26" away on from either spring eye with 52's. Simple dynamics would tell you that the 64's will be almost 25% less effective at controlling axle wrap, all other things being equal.

That's how I see it, feel free to correct any of us

 

[owenst7]

I still believe that to be backwards.

All of your other comments seem to be aimed at the complimentary leaves involved. So, if a set of 52's and a set of 64's each were sitting flat on their overloads, you think the 64's would wrap less?

The center of the torque applied is 32" away from either spring eye with 64's while it's only 26" away on from either spring eye with 52's. Simple dynamics would tell you that the 64's will be almost 25% less effective at controlling axle wrap, all other things being equal.

That's how I see it, feel free to correct any of us

Your math is correct but your dynamics are not. The moment is not around the eye of the spring, and you are neglecting cross sectional area of the material resisting torque. Did you watch the video? I didn't just pull this out of my ass.

If you were able to set up this test:
A long strip of spring steel.
Cut a 64" strip and a 52" strip from the SAME material
apply a given torque to each
The 64" strip will deform less.

Elastic strain (deformation) is related to the stress applied to a material by a linear function until it reaches its yield point (plastic deformation begins). Stress is the quotient of force and the area it is applied to. To lower the value of stress, the denominator (area) must be increased, or the numerator (force) must be decreased. Since force is fixed for our purposes, we can reduce stain two ways. We can increase area or we can increase the modulus of elasticity (the slope of the function). Increasing the moduli would be increasing the spring rate, which we don't want to do. In that case, we must increase the area resisting the force.

 

[crawdaddy]

I am also going to be running 64" springs. A custom spring pack not a stock unit that I pulled support leaves out of. When I ordered my springs I was informed by the manufacturer that they WOULD wrap more than the stock springs and that it should be addressed with a traction bar of sorts.

 

[owenst7]

I am also going to be running 64" springs. A custom spring pack not a stock unit that I pulled support leaves out of. When I ordered my springs I was informed by the manufacturer that they WOULD wrap more than the stock springs and that it should be addressed with a traction bar of sorts.

Custom springs are going to be lower spring rate which is why wrap would increase. They will probably ride very well. I couldn't afford custom leaves and didn't want a really soft spring rate because I deal with lots of sidehills and I don't want the truck to feel like a slinky.

 

[rdn2blazer]

This is on my 76 K5. When the floors were changed (early 80s?), the body mounts behind the front seats were moved outboard of the frame. This would interfere with your forward spring hanger if you were to copy me. I'm sure it can be done though with some retrofitting and/or just making an integrated body mount/hanger.

Being that 64"s are a foot longer than the stock 52"s, they have many advantages such as reduced wrap and more travel. Not to mention, they are still in use today, and can be had in junkyards in better condition than used 73-88 springs.

I got mine off a '95 Heavy half ton pickup. Mine have four leaves plus the overload. This is about the ideal spring rate for me. I can very easily flatten them but I have no noticeable wrap so far.

I removed the forward hangers and the rivets in the body mount crossmember. Conveniently, the crossmember uses the same hole spacing that the hanger used. I simply moved the hanger forward to share the holes with the crossmember. This moved the hanger forward 5.5". Since 64"s are centered just as my 52"s, but 12" longer, then hanger needed to move forward 6" to maintain the stock axle location. As I mentioned, I only moved it forward 5.5". This results in placing the axle .5" rearward of stock. This really wasn't noticed at all, other than my stock length driveshaft was definitely not going to work longterm now(although it didn't seperate the few times I wheeled it). I suppose you could even do this without the shackle flip and the driveshaft would probably be fine...however I have no idea why you'd want to do that.

The rust and holes show where this (hanger) used to be. I am holding it about in the location that it ended up.

The frame stripped...again, you can sort of see where things sat for 33 years.

Here's how things bolted up. As I said before, I just moved the hanger forward into existing holes. I didn't like the idea of putting more holes in the already weak horizontal plane of the frame, and there was no need to anyway. You can see the remains of two rivets that were holding the hanger. After doing about 48 rivets with limited tools, I could care less if they sit there as an eye sore.

Another shot that shows the stock location and the new location. a few of the rivets were a huge pain because the body supports were in the way, along with my exhaust on the other side. If you can get a grinder in there to girnd the heads off, and remove the rivets on the other side of the hanger, you can beat a prybar in there and pull the hanger off the last few rivets. There really isn't a "good" way to do them...Each one holds the frame together differently and there's about a thousand different ways to fight them out of there. Key word is "fight". Rivets really suck, but I guess they do their job well. You can also see where the vertical face of the frame (what we're looking at now) needed holes drilled. A few of these were really tricky to drill. I think I ended up using a cardboard pattern and drilling a couple from inside the frame. I actually used my dinky little 12V cordless a few times here because there was such little clearance to work.

Been there done that. Nice how the holes basically line right up. I shapped a piece of I think 3/16 thick steel and capped my shackle bucket, added a good amount of strength to the bucket I think, the outer tab atleast. Drilled an aditional hole in the center of the bucket and frame for an extra bolt. Also welded a plate inside to seal off the inside so it can't fill with dirt/mud. Bolt head is still completely accessable though. I also welded gussets into the crossmember support to help stiffin that assembly up. Also the arc in the bottom frame support that bolts to the shackle bucket and frame, you can't put a socket extension and socket on the bolt head and have it stick straight out. the radius at the top is too low. I used a 1" drum sander in a die grinder to raise it so I could have the extension be straight, that just bugged me. You should have tried not to scar the bucket so bad, would have looked cleaner. I know it's a PITA though. Not hijacking, just sharing mine too, and some things you might not have thought of. Good job man.

 

[owenst7]

Been there done that. Nice how the holes basically line right up. I shapped a piece of I think 3/16 thick steel and capped my shackle bucket, added a good amount of strength to the bucket I think, the outer tab atleast. Drilled an aditional hole in the center of the bucket and frame for an extra bolt. Also welded a plate inside to seal off the inside so it can't fill with dirt/mud. Bolt head is still completely accessable though. I also welded gussets into the crossmember support to help stiffin that assembly up. Also the arc in the bottom frame support that bolts to the shackle bucket and frame, you can't put a socket extension and socket on the bolt head and have it stick straight out. the radius at the top is too low. I used a 1" drum sander in a die grinder to raise it so I could have the extension be straight, that just bugged me. You should have tried not to scar the bucket so bad, would have looked cleaner. I know it's a PITA though. Not hijacking, just sharing mine too, and some things you might not have thought of. Good job man.

the truck is deinitely not for aesthetics, just function, lol. My tools suck and I couldn't take the body off to get a better angle. The bolt lineup thing is really annoying. Had I not been in such a hurry I probably would have just made a whole new hanger.

I like the idea of reworking the crossmember. It's on my todo list for when I have more time. One of my next projects will be to make the frame a lot stronger. The pictures of yours are good to add. I know a lot of guys have done this, but when I was planning mine, I noticed a lack of info and it was spread all over. I figure for the next guy (assuming they know how to search!), this thread could be of great reference.

 

[crawdaddy]

rdn2blazer what did you use to paint the frame and brackets? Looks really good!

Sorry for the hijack

 

[Hogback Fabrication]

If you were able to set up this test:
A long strip of spring steel.
Cut a 64" strip and a 52" strip from the SAME material
apply a given torque to each
The 64" strip will deform less.

Here's a really crude drawing of a long spring and a short spring, both with a force acting up on them the the front of a spring perch.

I'm sure this isn't breaking news to anyone but its easier to visualize.

The longer spring will wrap more because there is a longer distance between the spring eye and the center pin. Longer distance means a longer moment which means the spring will deflect further.

For the same reason that longer spring flex more (leverage), they wrap more.

Elastic strain (deformation) is related to the stress applied to a material by a linear function until it reaches its yield point (plastic deformation begins). Stress is the quotient of force and the area it is applied to. To lower the value of stress, the denominator (area) must be increased, or the numerator (force) must be decreased. Since force is fixed for our purposes, we can reduce stain two ways. We can increase area or we can increase the modulus of elasticity (the slope of the function). Increasing the moduli would be increasing the spring rate, which we don't want to do. In that case, we must increase the area resisting the force.

This is not related to what we're talking about. That definition is just stress/strain, it has nothing to do with moments. Moments involve distance (leverage).

 

[owenst7]

This is not related to what we're talking about.

I'm sorry if this is offensive but this statement clearly shows your lack of understanding on the factors here. Strain is the deformation of an object under a given stress. We absolutely are discussing strain here. That is pretty much solely what spring wrap is. If my explanation of spring length in relation to deformation is confusing, I'm sorry, I am studying engineering not teaching. I understand I'm not explaining this the best, but if you are actually interested in the truth and not opinion, i suggest you pick up a book on strengths of materials. This is 100 level materials stuff and a good book on it will have diagrams and such that will help you understand.

The drawings you posted only show that a longer spring will potenially put more load on the bushing at the eye of the spring. They are only addressing basic physics and fail to address the property of the material or the springs architecture.

And if you're still too stubborn to listen to me, watch the darn video I posted. It's like the first statement he makes. If you don't believe a major diesel truck manufacturer, well then explaining this is a lost cause.

 

[Hogback Fabrication]

I'm sorry if this is offensive but this statement clearly shows your lack of understanding on the factors here. Strain is the deformation of an object under a given stress. We absolutely are discussing strain here. That is pretty much solely what spring wrap is. If my explanation of spring length in relation to deformation is confusing, I'm sorry, I am studying engineering not teaching. I understand I'm not explaining this the best, but if you are actually interested in the truth and not opinion, i suggest you pick up a book on strengths of materials. This is 100 level materials stuff and a good book on it will have diagrams and such that will help you understand.

I have a bachelor's in Mechanical Engineering from one of the best engineering schools in the country, I promise you're not talking over my head I may even know a thing or two about trucks too. That doesn't inherently mean I'm right or anything.

I did watch the video. Stress/strain are related to how a material deforms under a load. That would be related to, say, the spring actually breaking. When we're talking about axle wrap, we're talking about moments, or how torque is involved in this.

If I come across as being a dick or something I promise it's unintentional, just trying to discuss this