limit strap tech

Chuckman

Chuckman

Well-Known Member
Joined
Oct 9, 2005
Location
Huntersville
vehicle in question: lengthened CJ7

front- a 5" coil springs from early bronco with 26" radius arm style links. springs drop out of buckets a good 4" but are retained by a centering post, YJ sway bar.

rear - long chevy springs with spring over, no torque arm

both axles are 60's. tires 37 /24bolts. big motor, 5 speed. standard shocks all around, nothing fancy.

heavily road driven, plan on towing a large trailer. wheeled some but not nearly as much as I want, but when I do, I really push it hard. the front lifts sky high under acceleration ,and of course it flexes like mad (however Im sure that the shocks are holding the axle at full droop= not good), and Id like more on road control. for the front do I run limiters at the shocks or one in the center, or both. if in the center, how/where do I mount it, and what length do I need to run over stock position. for the rear, same question. It has worked great as-is for a looooong time, but I'd think theres a lot of room for improvement. the auto hid alot of the bobbing, but the long throw of the nv4500 really enhances the dang nose lifting/diving.
what say yes wheelers of the web?
 
I do not know what will keep the nose from lifting and diving in the road, but I do know limit straps are not the answer.
 
I'm guessing that the rear squats when the nose rises? You likely need different rear springs, and stiffer shocks. Same for the front most likely. If you have a center of gravity that's high and toward the front of the vehicle (maybe that big engine), the rearward weight transfer can be pretty severe under acceleration, especially if the rear springs are soft and/or the rear shocks can't properly damp the springs. That causes the rear to lift. The bobbing in the front is because the front springs are likely too soft for the amount of front weight, and the shocks are can't control the front springs. Heavy motor, tall Jeep, soft springs, shitty shocks, bad front end lift.

And yes, poor geometry will make all of those things worse.

A sway bar will only work around turns, and won't do anything for the nose lifting/diving. Sway bars only work in single wheel bump or in roll, not when both wheels move in the same direction.
 
^ front springs are looooong and correct for the front weight as they are for an EB
 
Front springs too long, rear too soft, maybe set the stance a little lower in the front than the back
 
Fabrik8 said:
I'm guessing that the rear squats when the nose rises? You likely need different rear springs, and stiffer shocks. Same for the front most likely. If you have a center of gravity that's high and toward the front of the vehicle (maybe that big engine), the rearward weight transfer can be pretty severe under acceleration, especially if the rear springs are soft and/or the rear shocks can't properly damp the springs. That causes the rear to lift. The bobbing in the front is because the front springs are likely too soft for the amount of front weight, and the shocks are can't control the front springs. Heavy motor, tall Jeep, soft springs, shitty shocks, bad front end lift.

And yes, poor geometry will make all of those things worse.

A sway bar will only work around turns, and won't do anything for the nose lifting/diving. Sway bars only work in single wheel bump or in roll, not when both wheels move in the same direction.
Click to expand...

I would mostly agree with this... I would not goto a stiffer spring as it will hurt offroad performance. The issue is likely the rear suspension having very little anti-squat. Could be axle wrap mixed in also. Not a usual issue with leafs, but if the WB is short enough it could be. I believe that properly valved shocks would solve most of it, or atleast slow the movement down enough to make it less noticeable.

A traction bar in the rear will increase the anti-squat for sure, but might not be the best solution.

Pics and more measurements would help for certain.
 
paradisePWoffrd said:
I would mostly agree with this... I would not goto a stiffer spring as it will hurt offroad performance. The issue is likely the rear suspension having very little anti-squat. Could be axle wrap mixed in also. Not a usual issue with leafs, but if the WB is short enough it could be. I believe that properly valved shocks would solve most of it, or atleast slow the movement down enough to make it less noticeable.

A traction bar in the rear will increase the anti-squat for sure, but might not be the best solution.

Pics and more measurements would help for certain.
Click to expand...

Changing shackle lengths to change the relative angle of the leaf spring is about the only adjustment ability you have for anti-squat, yeah.. Leaf springs aren't an easy thing to adjust, that's for sure.
 
:nopics:
 
it works great offroad and that's really what mattered at the time- and I built this loooooong before all the suspension calculations were available to the common man and way prior to NC4x4 or Pirate4x4 came to be. so I did the best I could at the time. I'll see if I can find some ramp pics.
 
these were before I put in the chevys in the rear, but you get the idea. this was taken right after I drove from charlotte to URE at street pressures, just drove on up and posed this pic. she'll walk way up further with tires squatted. but the springs droop out of the buckets pretty good at this point. quite a bit of negative arch on the rear right spring at this point.
 

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Nice Jeep.

I have no constructive input to solve your problem though. The idea of some good shocks with adjustable valving to dial it in sounds good.
 
Limit strap the shocks and you limit the downward droop of the shock, thus limiting flex and you will limit total droop. Mount one in the center and it will only protect the driveshaft from over flexing!!

While I like the use of the long EB springs, that is probably what is causing the nose to rise. The spring are reasonably soft and probably have a lot of preload in them. So when you accelerate, the rear is lifting the weight off the front and those preloaded springs readily unload for ya! The leaf spring rear is creating a lot of anti squat as they wrap up. Possibly as much as 100-110% depending on how much the pinion is rising. Thats a lot! Bet this thing hooks good in a straight line!

(Note, traction bars will reduce antisquat. Not raise it)
 
Do you know who made the front springs? Most of them made now are variable rate and very soft. An old pair of Skyjackers or Superlift would be better for street manners.

A beefy set of coils for a F150 would be another choice.
 
Limit straps are to prevent top out damage to the shocks.

We made clamps for the top and bottom of the coils on my dads truck to keep the coil in place.

A traction bar in the rear could raise antisquat depending on location.

You probably have pro lift front geometry when in 2wd.

You could increase some rear antisquat to keep rear from squatting as bad, but the front will still lift, and the vehicle will still pitch.

More than way to skin this cat.

Increasing rebound in the front shocks, and increasing compression valving in the rear could reduce pitching under forward acceleration, but most likely make the ride quality worse.

Maybe you should rig up a light sway bar, mounted parallel to frame to act as an anti-pitch bar. Just saying for the sake of arguement.

If it were me, I would do this:

Get a traction bar in the rear to prevent wheel hop and axle wrap, but locate it to increase antisquat as well. Just guessing here, but I would say make it look like typical upper links of a 4 link, using the leafs as the "lower" links.

In the front I would clamp both top and bottom of coils so the axle won't droop and farther than the coils will physically allow,

and limit strap the shocks to prevent top out damage to shocks, if necessary.

You would have to completely re design the front suspension to get rid of any pro lift geometry in 2wd, that could be anti lift in 4wd...

I will say this is all a guess based on theory, and Without some good side view images of suspensions and plotting link angles and locations, I couldn't say for sure.
 
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meh, guess Im just gonna continue to beat on it like a hooker that owes me money
 
Mac5005 said:
...A traction bar in the rear could raise antisquat depending on location...
You could increase some rear antisquat to keep rear from squatting as bad, but the front will still lift, and the vehicle will still pitch.
Click to expand...

You and Ben are referring to this backwards. As the instant center rises, antisquat increases. If you limit the instant center from rising, (such as a traction bar), that decreases antisquat.
 
ol'Jeeps said:
You and Ben are referring to this backwards. As the instant center rises, antisquat increases. If you limit the instant center from rising, (such as a traction bar), that decreases antisquat.
Click to expand...

Torque based antisquat is directly related to the control arm merge angle.

Substitute the leaf spring location in for your lower links and add a traction bar to the top of the housing, and substitute that's as the upper links.



Disclaimer: I know this is not the best method for calculating leaf spring A/S, but it to me is the fastest for comparison purposes.

There are tons of variables that contribute to the actual A/S value and that's why I am only talking about theory.

IMO, A traction bar built like a radius arm will have high torgue AS.

IMO, leaf springs have no torque antisquat.

Radius arms bring the suck in the rear as the antisquat is too high, leading to the axle walking under the rig on climbs , and too high A/S can lead to wheel hop.

Can we agree that any changes in the rear will not affect how the front lifts?

But changes in the rear will only affect how fast the rear squats.

The front is still going to lift on acceleration is 2wd, regardless of rear geometry.

Radius arm style setups have high A/S, in the front this becomes anti dive under break torque. Under throttle in 4wd, this force reverses to become pro dive or (anti lift).

But in 2wd, the horizontal road force pushing against front of tire, reverses the torque to make the front suspension pro lift.
 
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Still not right. Move point up = more anti squat. Move point down = less anti squat. Term is confusing, yes.

The instant center is a theoretical point. It can be directly measured with rigid bars, such as 4 links. But it cannot be accurately measured with leaf springs, because under acceleration, the anti squat rises with axle /spring wrap up. The mounting points only matter when the lifting bars are rigid. If you completely stop the spring wrap, you can then measure the instant center. And you will find you have lowered the instant center, thus reducing the amount of anti squat.

No, Front lift is a direct result on the lifting forces due to the reaction to the forward bite of the rear tires transmitted through the rear end geometry. Only difference between a 2 wheel drive and a 4 wheel drive, is the the front is still trying to pull you forward. It can't mechanically transfer any appreciable amount of weight, other than it's own weight. (okay, they are probably doing some high anti squat shit on the front of front wheel drag cars, but if the rear was lifting the front end, as it naturally should with rear wheel drive, what ever the front geometry was doing would be substantially negated)

An extreme illustration would be...

...lower the anti squat enuff and the tire just spins, (or wheel hops). It can not impart any lifting force what so ever to the chassis.

...raise the anti squat enuff, and the rear tires plant and and try to drive under the chassis. At this extreme, I guess there would be no front lift cuz it would only be raising the rear of the chassis!

The ideal amount of anti squat will transfer the maximum amount of weight to the rear tires, Depending on several factors, this will be a combination of front lift and rear squat.

Good llustrations...

watch the best pro truck pullers. Front wheels 1-2 feet in the air, a little squat in the rear. (mostly from tire squat as there isnt much, if any, rear suspension!)

watch a pro stock drag car on launch. Slight front lift, limited by the wheelie bars, a lot of rear squat. That why 4 links were created. They have to actually dial some bite, (that reads lower the anti squat), out of these because if the full potential of the tire/chassis "bite" was realized, they would do mind blowing wheel stands!

watch a dirt car. Their "bite" is so tenuous, that they try to lift the entire car onto the right rear tire! SO much anti squat that the entire chassis rises!

Only way to tune the front end in respect to limiting lift is...Remove the preload on the front springs, raise the rebound rate of the front shocks, tie the front end down to the axle. In other words, front tuning can only limit front lift by making the front end "heavier" than the given amount of weight tranfer can overcome. Either dynamically or physically

Anti dive is only a factor in braking.
 
Anti forces are different front to rear.

Vehicle pitch is a factor of both.

Even if you have 100% rear anti squat, the front will still lift.

If you have 100% front anti dive, the rear will still lift under braking.

Re-read my last post.

Anti-dive in breaking is anti lift under throttle in 4wd.

In 2wd there is no torque based anti lift geometry as there is no torque input to pinion.

There is still horizontal ground force pushing against tire under 2wd acceleration.

The principles and dynamics are the same no matter the application.

you can change the front geometry to change front lift characteristics. But this is dependent on many factors that can reverse in 2wd vs 4wd.

Either way the weight transfer is dependent on cog height, wheelbase, and acceleration rate.

Geometry changes dictate whether this weight transfer is applied to the springs or onto the links.


Take a 4" lift yj spring, spring under.

Built an upper link from
Center of frame to top or truss or top of diff.

This setup will create rear lift under acceleration, proving over 100% antisquat.

I'm not arguing that the instant center location in reference to COG height and wheelbase locates the antisquat percentage,

I'm just arguing that depending on suspension design, leaf pack location and design, traction bar design etc, that setup could be pro squat or anti squat or anywhere in between.

You can't say X traction bar setup will always create pro squat. It is dependent on far too many variable to have a blanket statement like that.

Plot the points, show some numbers.


Less spring preload, more rebound valving, or higher spring rate and more compression valving is a recipe for poor ride quality.

Heavy unsprung weight (big axles and heavy tire and wheel) with relatively light sprung weights(jeep) needs light spring rates with good preload, and fairly light rebound valving to have a halfway decent ride quality.

Changing the shock valving as a band aid on suspension geometry is a recipe for the next thread:

My jeep rides terrible, but vehicle pitch and roll is improved. Pissing blood after a weekend at Uwharie on the uber tall water bars.

It would be far easier to lower cog height, or slow the acceleration rate to minimize the vehicle pitch but neither of those are practical or fun.
 
Mac5005 said:
Either way the weight transfer is dependent on cog height, wheelbase, and acceleration rate.
Click to expand...

Don't forget the important part: Weight. COG is just a location, you also need a force acting about that location. ;)

Again, a short wheelbase Jeep with a heavy engine (front weight bias) and a high COG is going to have a lot of weight transfer no matter what, unless you have (like you said) unreasonably stiff springs or an unreasonable amount of anti.
 
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Mac5005 said:
Anti forces are different front to rear.

Vehicle pitch is a factor of both.

Even if you have 100% rear anti squat, the front will still lift.

If you have 100% front anti dive, the rear will still lift under braking.

Re-read my last post.

Anti-dive in breaking is anti lift under throttle in 4wd.

In 2wd there is no torque based anti lift geometry as there is no torque input to pinion.

There is still horizontal ground force pushing against tire under 2wd acceleration.

The principles and dynamics are the same no matter the application.

you can change the front geometry to change front lift characteristics. But this is dependent on many factors that can reverse in 2wd vs 4wd.

Either way the weight transfer is dependent on cog height, wheelbase, and acceleration rate.

Geometry changes dictate whether this weight transfer is applied to the springs or onto the links.


Take a 4" lift yj spring, spring under.

Built an upper link from
Center of frame to top or truss or top of diff.

This setup will create rear lift under acceleration, proving over 100% antisquat.

I'm not arguing that the instant center location in reference to COG height and wheelbase locates the antisquat percentage,

I'm just arguing that depending on suspension design, leaf pack location and design, traction bar design etc, that setup could be pro squat or anti squat or anywhere in between.

You can't say X traction bar setup will always create pro squat. It is dependent on far too many variable to have a blanket statement like that.

Plot the points, show some numbers.


Less spring preload, more rebound valving, or higher spring rate and more compression valving is a recipe for poor ride quality.

Heavy unsprung weight (big axles and heavy tire and wheel) with relatively light sprung weights(jeep) needs light spring rates with good preload, and fairly light rebound valving to have a halfway decent ride quality.

Changing the shock valving as a band aid on suspension geometry is a recipe for the next thread:

My jeep rides terrible, but vehicle pitch and roll is improved. Pissing blood after a weekend at Uwharie on the uber tall water bars.

It would be far easier to lower cog height, or slow the acceleration rate to minimize the vehicle pitch but neither of those are practical or fun.
Click to expand...
X2. What I am guessing....

Most ppl install radius arm style traction bars, and try to package them under the vehicle and up out of the way. As mentioned before radius arms generally don't lead to the best geometry.

If he is running long chevy leafs on a fairly stock wb jeep, his rear AS likely isn't very high. Installing a traction bar will likely raise it. Even though the rear might not squat as much or any, the front suspension will still likely lift under acceleration.
 
I agree @Fabrik8

But,

Which is more practical?

Changing entire drivetrain to cut weight to reduce sprung mass?

Or

Lower the drivetrain to reduce the cog height?

My point is that it's almost as practical as saying only use half throttle, or unplug two plug wires all To reduce the accel rate.

Sounds like the perfect suggestions for the OP to fix his front lift and rear squat.

Hijack/off

:he said jag off:
 
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