79 series rear leaf springs into 75 series

[sprung over GQ ute]

G'day not sure if this question has been asked before but I was wondering if anyone has attempted to fit a set of 79 series ute rear leaf springs into the back of a 75 series ute.

I am currently in the process of attempting this but am starting to wonder if I may be wasting my time.

Stats on 79 series springs (out of vehicle)
1420mm straight line from centre of eye to centre of eye (170mm longer than 75 series)
245mm from bottom of straight edge (placed across from eye to eye) measured to top leaf (adjacent to locating pin)
660mm from centre of front eye to locating pin (straight line) (same measurement for 75 series = 570mm therefore in theory the rear diff will be moved back 90mm - I will elaborate on this later)
780mm from centre of rear eye to locating pin (straight line)

Stats on 75 series springs (out of vehicle)
1250mm straight line from centre of eye to centre of eye (170mm shorter than 75 series)
234mm from bottom of straight edge (placed across from eye to eye) measured to top leaf (adjacent to locating pin) therefore 75 series springs in theory are a flatter spring
570mm from centre of front eye to locating pin (straight line) (same measurement for 79 series = 660mm therefore in theory the rear diff will be moved back 90mm - I will elaborate on this later)
680mm from centre of rear eye to locating pin (straight line)

I also have extended shackles which measure 160mm from pin to pin

I initially attempted to fit the standard 79 series springs directly into the rear of my ute however quickly learnt that this was not going to work due to the spring length being too long. With my extended shackles I was able to fit the springs however the shackles were on a servre angle up against the chassis and also the spring would not drop as required so that the shackle angle straighted out.

My next thought was to bring both of the eyes of the standard 79 series springs closer together. This I thought in theory should retain the over all length of the spring along the arch allowing for more up and down travel and I will be able to fit the spring so that the shackle angle is not hard up against the chassis at rest on level ground. I therefore had the springs reset so that they are 1300mm from eye to eye (down from 1420mm). This is 50mm longer than the 75 series which I thought would push the rear shackle back improving ride quality and allowing extra flex as the shackle when fitted to the standard 75 series springs was nearly at 90 degrees (Alloy tray on rear). By resetting the springs to a distance from eye to eye of 1300mm a significant lift was to be expected. This has resulted in an additional 110mm of lift calculated by measuring from the bottom of straight edge (placed across from eye to eye) measured to the top leaf (adjacent to locating pin). As the vehicle was once sprung over this lift is still relatively mild (thanks to two defect notices it is back to spring under). Bringing both springs eyes closer together has also resulted in the distance from the centre of front eye to locating pin (straight line) being reduced over the standard 79 measurement. This will require me to relocate the rear guard and the possible need for a tail shaft spacer. (I have a custom tail shaft with extra long splines)

I have since refitted the reset 79 series springs which fitted up well and with no load on them (i.e vehicle on axle stands and diff not bolted up) had a nice rear shackle angle. With a jack under the springs I am able to take them through their full range of motion resulting in the shackle scrubbing out on the chassis under full up travel and shackle nearly straightening to 90 degrees at full drop. Things were looking very promising at this stage as an excellent travel had been achieved. However the weight of the vehicle was still not on the newly reset springs

I then proceeded to bolt up the diff. Once this was down I was able to jack the vehicle up from under the diff so that the springs took on the weight of the vehicle. This is where things have gone wrong. It appears that the newly reset springs are unable to support the weight of the unladden vehicle (with only an alloy tray). The result is that the springs flatten out so that the shackles again are hard up against the chassis at rest on flat ground.

I am not sure why this has occurred? I have either been stiched up buy the suspension shop who reset the springs. I am aware that you can either get a hot reset or cold reset. I was advised that he would only need a cold reset if I had an alloy tray and no loads were regularly being carried. Apparently hot resets are done to prevent springs from sagging over time due to constant heavy loads.

The other scenario is that the springs are still too long and what appears to be happening is that it is actually the shackle which is moving back when load is applied and the spring is not completely flattening out before the shackle scrubs out on the chassis. ( Not sure if this makes sense?) This appears to be particularly occurring as the weight of the vehicle is progressively applied down on the spring i.e. as I start to jack the diff up the spring starts to flatten out and elongate however a point is reached where the spring does not flatten any further however the extra weight of the vehicle as applied results in the rear shackle only pivoting until it is maxed out on the chassis.

What seemed very practical in theory as not resulted in the desired outcome to date. If the spring reset has been done correctly (and I have strong doubts that it has as at rest and unladden everything sits and moves through its range of motion perfectly however once the load of the vehicle is applied the springs seem to just give way to their original shape. I would have thought that 6 leaves should be able to support the back of a Toyota ute fitted with an Alloy Tray?) or the leaves are just too long. If they are I don't envisage alot of options other than to possibly get the top and wrap leaves shortened or a custom set added to the existing spring packs. The other option which is not ideal either is to further extend my rear shackles. At the moment they are 160mm from pin to pin does anyone know when you start pushing the limits with extended shackles? The other option which I sure everyone is thinking of will be to move one of the hanger points on the chassis. Doing this is out of my league and is something I want to avoid especially if some toss pot wants to hand out another defect notice.

If anyone one has attempted this before or has any recommendations on how I can make it work please let us know. Once I have this sorted the next challenge will be to fit the standard leftover 75 series rear leaf packs into the front - maybe I'm a gluten for punishment?

[hillbilliywheelchair]

havent done it but been talking about it and from what i've read on ih8mud you need a minimum of a 250mm eye to eye shackles
but let us know what you come up with

[sprung over GQ ute]

Thanks for the info. One of my next steps was to go and get 4 bits of flat plate approx 3-4mm thick, 75mm wide and 300mm long and start drilling some holes in it say every 50mm as a trail and error exercise to see if I can use this as a shackle template. If it is discovered that I need the pins 250mm apart to achieve the desired shackle angle then I will go and purchase some 7-8mm plate and drill the pin holes at the required distance apart. Just wondering if a 250mm shackle measured pin to pin is going to be too long? I can gusset each shackle together for added support.

Cheers for the help. If anyone else has any thoughts please let us know

Thanks

[Dannyboy]

Have you thought about relocating your shakle hangers on the chassis by cutting them off and welding them back on furthur back. When doing this you can set you shakle angle to 45 degrees with the load on.

[sprung over GQ ute]

Yes I have considered this as a potential option but as mentioned in the inital thread I really want to avoid relocating the spring hanger mounts as I do not have skills, equipment or ability to undertake such a task and I also do not want to making permanent mods to the chassis which might have to be reversed if I end up with another defect notice (already have had to deal with two of these). Any other solutions where I avoid cutting and relocating the spring hangers would be much appreciated

Cheers

[bj on roids]

Yes I have considered this as a potential option but as mentioned in the inital thread I really want to avoid relocating the spring hanger mounts as I do not have skills, equipment or ability to undertake such a task and I also do not want to making permanent mods to the chassis which might have to be reversed if I end up with another defect notice (already have had to deal with two of these). Any other solutions where I avoid cutting and relocating the spring hangers would be much appreciated

Cheers

Yet your sig line states that a welder and a grinder will fixz anything!

[sprung over GQ ute]

Yes if you own one suitable to do the job and know how to use it. This is not my login or call.

Any thoughts or ideas if you beleive I have been stiched up by the spring resetter would be appreciated ?

Thanks

[GO79]

Maybe if you can find tools get some spring hangers of a wrecked 79 series and weld them behind your irginal one so you can have a choice and don't have to grind/ unpicking the original ones

[sprung over GQ ute]

Thanks for the suggestion.

I was wondering if anyone can explain why the load carrying capacity of the spring would be reduced by resetting the springs so that they have increased camber / hook. I would have thought that the type and grade of steel which is used to make up each leaf would influence its load carrying capacity and not the shape of the spring. It appears that leaf spring packs must be progressive in their ability to carry load i.e. the more a leaf pack flattens out the greater its ability to support load and I don't mean because the load bearing springs come into play. Can anyone explain the physics behind why a leaf pack can not support the same weight when reset to a greater camber?