How much flex for 6" BDS springs??

[Brian 89KBlazer]

How much flex for 6\" BDS springs??

I've done the search, read all I could find about shackle angles, and even contact BDS tech support.
However, I'm still not content with the answers. I've built a custom frame for my Blazer,and have the
whole thing pretty much re-assembled. The only things missing is the interior (seats & carpet) and
the roll cage which I have yet to fabricate.

The problem is, I want to mount the rear shackle hanger such that I do not stop the springs from flexing
at all - either in compression or droop. Same with the front springs for that matter. For the front, I have
ORD shackles and in the rear, I have stock 4" long GM shackles.

The question I guess: Is there any position (angle for the shackle) that will allow the springs to go from full
stuff to full droop? Or will a longer shackle be required in the rear? I'm pretty sure the front springs are flat
enough that the shackle can accomodate the amount of flex they have but can the rear stock 4" shackles ?

Second question is for someone with 6" rear springs (preferably BDS). What kind of spring eye to spring eye
distances do you get with the axle at full droop? What about at full stuff? This would really allow me to know/
figure out what length the shackles would have to be in order to not interfere with the springs motions.

BTW, my rear shackle are like the ORD shackle flip and I've read all the discussions that BadDog, Donovan, and
others had about the shackle angles.

Thanks for your help, I hope! /forums/images/graemlins/smile.gif

 

[imiceman44]

Re: How much flex for 6\" BDS springs??

The way I do my fabrication is by measuring what I have and not rely on anyone's input but for ideas.
You have the springs in front of you, so measure the true length of the spring by laying the tape measure on the spring folowing the curve from eye to eye. Then start from the fixed hanger point and go straight to 4" below or above the rear hanger point depending on wether you want the shckle up or down, and mark the location where the hanger has to be to have the shackle perpendicular to the spring when the spring is flat.
I believe that it should work but if you want more for droop then have the rear hanger a little forward to give the shackle an angle when the spring is flat and you should have the shackle straight up or down at rest and still have room to give more droop which shortens the spring a little more.
I hope I did make sense to you. /forums/images/graemlins/thumb.gif

 

[Brian 89KBlazer]

Re: How much flex for 6\" BDS springs??

Thanks iceman but there's a couple issues with that advice. I already know the main leaf length but that won't work because mounting the shackle hanger 4" ahead of the full lenght of the springs
is so far back that the shackle is dead in line with the spring when at rest and very close to kicking back against the frame. However, the dilemma in moving it forward is that if I go too far, I'll lose some of the springs compression travel.
Which brings me back to what I asked earlier; how short (eye-eye) when drooped to how long (eye to eye) on compression will the 6" spring get?
According to BDS, there's no way a full-size Blazer can compress the 6" springs enough to fully flatten them under flex so my question is how flat
have other people been able to get their 6" springs while flexing off-road? And how far drooped have they been?

Thank again for the input

 

[imiceman44]

Re: How much flex for 6\" BDS springs??

Well I think you read it wrong, I said 4" above /forums/images/graemlins/grin.gif
But if you want I can get you the info and you can try figuring it out.
I am guessing you are using 52" springs?
or is it 56"?

 

[imiceman44]

Re: How much flex for 6\" BDS springs??

OK I did the math here in my simulator and for a 6" spring that would also droop an additionnal 8" down and stuff no more than 8" up, you will need a 5" shackle at the minimum mounted at 48" from the front mount. I would go with 6" myself.
If you want to leave more room for droop up to 12 inches, then an 8" shckle would be required.
Remember the longer the shackle the more tendency to move sideways so you will have an unstable suspension.
If you keep the 4" shackle you will be limited to 5-6" of droop even if the spring gives you more and the shackle mount should be at 49.5" from the front hanger. /forums/images/graemlins/thumb.gif

 

[BadDog]

Re: How much flex for 6\" BDS springs??

I’ll leave it to the engineers to work out the specific answers you asked for. Just thought I would throw out an update of what I’ve got in the works.

I've got a standard 4" BDS lift on the front of my K30 truggy right now, using stock shackle and location. Due to the shackle angle problems you mentioned, droop is not what it could be, and compression is limited by interference to about 5” or so. This is going to be true for most any of the “standard” GM front lifts.

I just received a new pair of main leafs from BDS that are roughly 2" longer than the leafs on my 4" lift. Apparently these leafs came from a set of demo/proto 8" lift springs that were lying around in one of their warehouses. Anyway, I'm swapping these into my rig using the 4" lift supporting leafs. Since the 8" main leaf will not be able to support the weight (at +8” ride height) without the rest of the 8" leafs, I'll still get roughly 4" of lift out of it as the new leaf sags onto the rest of the leafs (which really support most of the weight). FWIW, I was surprised at how soft it is. I can almost push it past the “4” lift” height with one hand. Anyway, I'll also be going to a custom 7" shackle when these go on. Only problem I foresee is that the pin is approximately 3/4" further back that on the 4” lift (no surprise with a 2” longer main leaf). To use it, I will have to cut the half-wrap off the front of the #2 spring, or redrill the hole to the correct offset from the front bushing. I want to keep my axle relocation (2” forward) for departure angle so I’m leaning to redrill at the moment (even though I really don’t like redrilling a main leaf).

FWIW, I was originally planning to just keep my 4" BDS leafs and move the upper shackle mount forward about 2" in the frame rail along with a longer shackle (to clear the frame on compression). It wouldn’t be very hard to relocate. If I don't like the hybrid packs, I'll probably go back to this plan...

On the rear springs, I've had mine all over the place, and nothing resembling a stock setup, so I'll leave that one alone...

Best advice is take some measurements, make some sketches, think about it a while, then give it a whirl...

 

[Brian 89KBlazer]

Re: How much flex for 6\" BDS springs??

Thanks Iceman & Russ

Iceman, although I couldn't reproduce the droop numbers you came up with, you certainly gave me some better ideas on
how to approach the situation. I've been using AutoCAD to estimate the flex & droop in relation to the shackle rotation so
all I did was increase the shackle length each time & see how far I could cycle the spring each time.

Russ, thanks so much for joining in! It was your previous discussion that I found in the search & they really helped give me some
ideas on where to start!!!

I guess, using AutoCAD, I can easily figure where to mount the shackle, the length, & the angle to get full compression (as in the
spring flattened out) but I can't really see where the droop limits would be. I guess only "real world flex numbers" are going to tell me that!

Anyway; great discussion; thanks for it! And I wish there were more technical discussions like this on the board.

 

[imiceman44]

Re: How much flex for 6\" BDS springs??

Hey bryan, my simulator is AutoCad by the way /forums/images/graemlins/thumb.gif
Now for the max droop, only real world testing can give you that number but physicaly, Autocad can show you the max depending on shckle length if the flex on the spring was unlimited.