Shackle Flip Stability

[Blazer_Boy]

How does a shackle flip behave in harder corners. I know that the center of gravity is different because of the lift but does get it even more tippy around town. How would behave under a heavy load in a K20? Thanks

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[outlaw612]

Mine has been done for about a month now with no problems.

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[Blue85]

As for stability, it will be identical to any other lift of the same height. For load carrying, the type of shackle flip that you do may make a difference. Using the ORD or rear spring front hanger, the load capacity should be unaffected. If that little shackle can carry the weight, the bracket is not really an issue. For the cutout shackle flip, strength could be an issue unless the stock bracket is gussetted after cutting. But again, if you look at how thin the shackle itself is, you don't fear the bracket as much. I don't think that anyone on here has ever reported failure of any shackle bracket following the flip.

<font color=green>There's nothing like the smell of a rich V-8 in the morning...</font color=green>

[CaptCrunch]

Well the flip will add some flex to your rig, but if you plan to tow a heavy load you might want to think about trying to stiffen up the rear for that load. Personally I would just do rear springs if you plan to tow. You could possibly look into an air bad type setup or go the cheapie route and put some Rancho 9000's back there and stiffen them way up when you tow. I've never tried it, but was thinking about trying it on mine. Other then that the flips I have seen done and have ridden in seem fine around town (once you get the whole vibe issue taken care of )

-Mikey
1987 Chevy K5 Blazer- 350 TBI
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[Grim-Reaper]

I'm sorting out the towing issue. I just about flipped my truck yesterday towing 3k. Still trying to get the taste of seat cover out of my mouth.
At about 70 mph we were going down hill into a slight curve and a wave in the pavement at a bridge pitched the trailer and got it bouncing. At one point the trailer got airborn came down so hard on one wheel the cargo slamed into the side wall and bent it out at a 40 deg angle about ripping the trailer apart. The tounge came down with so much force 3 times it bottomed out the rear supension of the truck and dragged the trailer spare that was bolted to the tounge.The rear supension of the truck then rebounded unloaded and the trailer started to drive the truck sideways when the supension unloaded.
I don't know how I got it back under control. The first thing through my mind was that I had lost a wheel or the U-bolts broke on the rear axle. We figured out what happen by looking at the 1/4 mile of skid marks left before I got it back under control. At different points both the truck and trailer were sideways. The trailer spare hit the pavement at least 2 times ( to understand how violent that is the bottom of the spare is about 10 inches off the ground. I have never felt it drag before). This was BEFORE I got on the brakes. I have trailered enough that I know when the trailer starts fish tailing you either floor it or ease off the gas. Slamming on the brakes unloads the rear tires and often that will jack knife you. I fought the erge to do so. That I remember. It kept running through my mind...NO BRAKES...do not hit the brakes. I floored it trying to get the truck to pull the trailer back into line. It wasn't working.
All hell was breaking loose and I was at the point I was just trying to loose speed before we rolled and got on the binders. I just knew we were done. nothing I did with the steering was pulling it out. Just wanted to get rid of the speed. I figured the slower it was going when it rolled the better chances we had at surviving. Old girl pulled it out somehow. I think that the trailer spare hit the pavement the third time about the time I was braking hard. That indicates that if had a lot of weight on the tounge so it would have loaded down the rear tires keeping them intouch with the pavement preventing it from jack knifing. That was right at the end of the skid marks you could clearly see a black mark in the center where that spare was dragging.
The side of one of the trailer tires clearly shows when it had been riding on the pavement sideways. looking at the skids left confirm the trailer was on one wheel sideways trying to pass the truck.
Trailer was ballanced right (about 200lb on the tounge). I had several things working against me. My soft rear springs (stock 86's with flip). trailer at about max weight and not enough drop in the draw bar for the trailer to sit level with a load. Not that far out of whack but the trailer was full and the CG was high (trailer is 5 ft from floor to ceiling) I think that with the soft spring, not enough shock valving on the truck and no shocks on the trailer was all contributing factors. 9000's are something I will be looking at. I think I will also be adding an extra leaf to the spring packs. Hate the loss of flex but I do need to bring the rear up about an inch and stiffen up the springs for towing.
Yes I fully agree at this point to be very cautious if you tow a lot. I'm not sure the flip was a factor in this but I think the suspension flex was. The trailer was jerking so violently on the truck it was getting full compression and extension. I think that it is a negative when towing after yesterdays fun. 9000's on max would have helped. I think a stiffer spring rate would have also been a help.
Just becareful when towing. I'm not sure that much would have been different if I had been in The wifes stock 79 other than stiff 70's springs and lower CG on the tow rig. I think it would have still happend. The trailer at it's weigh just took that off camber lip wrong and got out of line. I am going to move the axle back on the trailer. I think that will make it less prone to tounge hight.
I think the towing issue is more a hight/CG, Tire size and suspension stiffness issue than a Issue with the flip. I think any flexy lift no matter how it's done is going to net the same end results as to towing manners. The flip takes blocks out of the mix lessening axle wrap and side to side leverage. I see that as a plus not a negative.

Women dig dents and flat paint!
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75 Jimmy, Dollar
Grim-Reaper

[marv_springer]

Wow!! ... That's scary stuff!... so, nobody got hurt?!?? It's not clear to me... it did go over?!?

I agree that the towing issue is a serious one... Many times I have people ask me how to get "long travel" but still be able to tow and haul. I tell them you gotta make a choice..... you can't have both.

In fact I've come to recommend that my suspension NOT be used for ANY towing...

Get those 9000 shocks - they will help!

Marv

<P ID="edit"><FONT class="small">Edited by marv_springer on 10/22/01 10:22 AM.</FONT></P>

[Leadfoot]

Another question concerning the shackle flip. If essentially the shackle is reversed (down instead of up), it is no longer than the original, and both the shackle and bracket are stronger, I would assume the shackle flip would be more stable, than say a regular shackle with a 4" lift block. Also less axle wrap. Does this logic make sense or is there something inherently wrong with the shackle pointing down instead of up (the whole compression shackle vs. whatever you want to call the other style)? I just figured the shackle flip would be more stable than a 4" lift block (I still think 4" springs are more stable, but they do limit articulation), plus less axle wrap, but I have never compared the two so I don't know. Anyone else go from a 4" block to a shackle flip (without the block) or vice versa, and how was it?

See my rig at <a target="_blank" href=http://coloradok5.com/gallery/Leadfoot>http://coloradok5.com/gallery/Leadfoot</a>

[tRustyK5]

I agree...but I think when a flip is done there are usually other things done to increase flex in the rear. Namely inboard mounted shocks, removing the overload spring, etc. etc. This can lead to a flexy rig, but as in Grimmy's experience not a very good towing platform. The Springer set-up is not just a simple shackle flip so again it could be less stable when towing.

I would imagine that a straight shackle flip with no spring alterations, stock shock location, and regular shocks would still be stable enough for towing. I still have rear blocks () but when I moved my shocks inboard I also removed the Receiver hitch...I still have a bumper hitch for smaller lighter stuff but will no longer tow anything of consequence with my Jimmy. I made my choice and chose flexy over towing.

BTW the stock orientation is referred to as a tension shackle, after flip is compression shackle.

Rene

<font color=green>Dyslexics of the world...UNTIE!</font color=green>
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[BadDog]

Man, that sounds terrible. I've had a long heavy trailer fishtail badly (6 or so oscillations) behind a short bed lifted truck and nearly lost it (the trailer and my mind). Scared the stew outa' me. I can just imagine how that experience (much, MUCH worse than mine) would feel. My hat is off to you. Way to keep it together!

About the flip. Stephen said something a few days ago that I have never considered before and it got me thinking. I'm going to paraphrase what Stephan said in his post and extrapolate with my own thoughts.

The manufacturers of trucks (that are actually meant to be trucks rather than Yuppie toys) almost always use a tension type hanger for the rear wheels. Why? Well picture the setup in your mind. As the arched spring compresses, the front is stationary, and the rear of the spring must move back since the spring is de-arching. So, a positive arched spring (bowed down) that is forced flat will be several inches (depending on initial length and amount of arch) longer from eye to eye. Also, (those of you who were here then) remember the discussions between Twizter, Donnovan and myself (and others) last spring? We had a long discussion about spring geometry and how it affects suspension flex. Anyway, the length and angle of the shackle work like a lever to either act against or help the springs ability to move the eyes apart (flex) depending on their relationships to each other. We were talking about front springs primarily, and compression shackles specifically, but similar things are at work here. For those of you who didn't see it, I'll hit the high points in the next 2 sections.

Now consider a tension shackle. At rest the shackle is generally going to be pretty close to vertical. As the axle moves up (a load is added) the eye moves back off vertical in an arc described by the length of the shackle (arc radius is length from bolt to bolt). Further more, when the shackle reaches some point behind vertical, but before horizontal, the shackle is going to line up with the force (vector) from the spring which was previously causing the shackle to move. At this point the spring becomes (more-or-less) a rigid arch. One of the strongest and most stable architectural designs used to make strong bridges and structures for 1000s of years. This is the "infinity point". Mathematically you would say that the spring rate, beginning with some value at rest, can be described by a curve which goes to infinity (infinite rate, therefore rigid) as the spring compresses (load is applied). End result, the first part of spring travel has a relatively soft rate, but, as it compresses, the effective rate gets higher and higher as the spring approaches the point where it becomes, effectively a rigid arch. This increasing rate is due to the spring having ever greater difficulty moving the rear eye back so that it can flatten out. It gives a relatively good ride unloaded (softer rate) and also allows extremely heavy loads to be carried without crushing the suspension. Even under heavy load the ride is not bad, maybe even better, as the spring rate "automatically" adjusts to the load. This is a simplification and the shape of that curve are affected by may things including the length of the spring.

Now, look at what happens with a compression shackle (stock front or rear with a flip). The earlier thread with Twizter and Donnovan involved a similar behavior with compression shackles (in the front) when the spring eye (at rest) is forward of the shackle frame mount (common with many aftermarket lift kits). With the spring eye forward of the frame mount, it causes a sort of arch like behavior due to the shackle being more in line with the spring arch (further along the curve on it's way to infinity) resulting in a very stiff initial movement that gets softer as the shackle moves past vertical. Basically, the force vector applied by the spring to that mounting point is almost in line with the shackle bolts (which would describe an rigid arch). In that case, for a more flexy suspension that starts compressing relatively easy (and takes less additional pressure to get the same amount of as it goes further) you want a longer shackle that starts out with the spring eye *slightly behind* the frame mount of the shackle. This effectively starts you out with a given spring rate which actually *drops* as load is applied (spring is de-arched). Anyway, the same thing is happening to the rear springs with a flip. Here, if you look at the forces on the shackle and spring, you can see what is happening. When you add a load, there is a force pressing the frame closer to the axle. Again, this causes the spring to de-arch, which, in turn, causes the rear eye to move back. Now, with the shackle arranged as a compression shackle, the spring eye moving back is causing the shackle to start to act as a lever which actually makes it easier for the spring to flatten out. The over-all affect of this *reduces* the spring rate as more compression occurs. I know I repeated my points a bit but hopefully the rewording helps in getting across the points.

Summary, shackle flip is not an ideal situation if you want to tow or haul stuff.

I hope this makes sense...


Bad Dog

85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.

[pcorssmit]

Grim, first of all, that sucks. A few questions, though:

1. Did the trailer tires have the correct, equal pressure, and are they rated for the load?

2. Single Axle trailer?

3. Does the trailer have brakes?

Coming back from Moab this year w/the Blazer on the trailer (about 8000 lbs), I had a rear trailer tire that was losing air (unknown to me). Combined with wind gusts and not enough tongue weight (the primary contributor to my problem, I think), I would occasionally get the trailer swaying. As you mentioned, it isn't always possible to accelerate out of the sway. However, all I had to do was apply the trailer brakes and the sway went right away.

Also, you may want to look into the factory overloads. I still have them on mine, and can't complain about the flex. At normal ride height they don't touch the spring pack, but will bring up the rear 1/2".

Pete

'83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
'97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd