4-link preload

My new car is pulling left pretty hard at launch. The 4-link & antiroll bar are all
neutral with no preload anywhere. I tried jacking up the left rear coilover a few
turns but it had no effect. So I'd like to try preloading the upper pass 4-link bar
a little. If the car is pulling left should I shorten or lengthen the bar?

Thanks
Rich

Unless youre making alot of power (1200+ HP), the car should always want to pull to the right. The left rear tire is usually loaded more at static ride height, and becomes even more loaded during the process of the launch, making the left tire want to run around the right tire. If you are making 1200+ HP, you'll want to lengthen the upper passenger bar, which will "raise" the passenger side of the housing, putting more weight on the left rear tire.
If you're under 1200HP, Id be triple checking that the rearend is in the car square...check it to more than one common point also to verify its all okay. Also, wheelie bars can easily steer a car as well...are you using wheelie bars?

It should be mentioned that not everyone has the exact same idea of what a "neutral" or "zero" preload setting is, or what it takes to get there......which can sometimes create some confusion when the subject is discussed. Also a "neutral" setting and a "zero" setting aren't necessarily the exact same thing to everyone out there. And that what some call "neutral/zero" for use with an anti-roll isn't necessarily exactly the same "neutral/zero" used without an anti-roll. And it should also be mentioned that when some speak of a "neutral/zero" setting, some are talking about the 4-link as a complete assembly. And some are only referring to just the top passenger 4-link bar, or just the top driver 4-link bar when talking about "zero/neutral" (the method used to setup everything plays a part).

In the past on big tire cars with 4-link/anti-roll combos, I have used both of the 2 most popular (most popular in my opinion anyway) methods for finding an initial preload setting. And (for me anyway) both methods have shown over time to be very close to being the same at finding a good (and surprisingly similar) starting point. And sometimes when both methods are used on the same car, they both sometimes do find the exact same starting point (sometimes it happens, sometimes it doesn't).



2 aftermarket "race type" 4-link + anti-roll initial setup methods I have used in the past ..........


Method A, the "hanging" method.

(1) All the front strut/rear shock spring seat adjusters, and top/bottom mounts, are all adjusted to the same side-to-side heights (no height stagger used anywhere).

(2) Then the top driver/left 4-link bar is unhooked, & anti-roll is unhooked.

(3) Then the rear housing is adjusted straight/square with the car's nose-tail centerline using the bottom 4-link bars (no rear wheelbase stagger is used).

(4) Then the pinion angle (U-joint operating angle) is set using the top passenger/right 4-link bar while the car's full race weight (fuel, oil, gas, driver, etc weight) is setting on the ground & compressing the suspension to ride height. The front & rear of the car should be "bounced" a few times while on the ground first before setting the pinion angle (to help make sure the car's weight is fully settled on the springs/suspension as much as possible).

(5) Then the rear of the car is put in the air with jack stands under the 4-link crossmember, and the housing hangs down loose/free from the fully extended rear shocks.

(6) Then with the housing hanging down, the top driver/left 4-link bar is reconnected & adjusted so it's loose & rattles on it's rod-ends. Note that this should technically be called "zero" preload", (and not "neutral") because only said 4-link bar has 100% no/zero load on it at this time.

(7) Then the car is again put back on the ground (again at full race weight) and the anti-roll is reconnected so that both A/R links have no load on them (so all A/R rod-ends are loose & rattle freely). Note that the A/R at this point should technically be called "neutral" preload (and not "zero") because all of the A/R assembly as a whole has no load on either side/link.

(8 ) Then wheelie bar heights are set even side-to-side, no wheel height stagger is used at first (but might be used later if necessary).


It should be noted that for this method to work best the car really does need everything in the chassis/suspension to be as straight & square as possible. Something simple being a little "off' somewhere, (like say if the top rear shock mounts weren't welded in the same place/height on the chassis side-to-side) can have an effect because it can change the distance the housing hangs down side vs side.





Method B, the "sitting on the ground" method, and/or "sitting on setup blocks/stands" method (if you have them).


(1) All the front strut/rear shock spring seat adjusters, and top/bottom mounts, are all adjusted to the same side-to-side heights (no height stagger used anywhere).

(2) Then the top passenger/right 4-link bar is unhooked, & anti-roll is unhooked.

(3) Then the rear housing is adjusted straight/square with the car's nose-tail centerline using the bottom 4-link bars (no rear wheelbase stagger is used).

(4) Then the pinion angle (U-joint operating angle) is set using the top driver/left 4-link bar while the car's full race weight (fuel, oil, gas, driver, etc weight) is setting on the ground (or on setup blocks/stands) & compressing the suspension to ride height. The front & rear of the car should be "bounced" a few times while on the ground first before setting the pinion angle (to help make sure the car's weight is fully settled on the springs/suspension as much as possible).

(5) Then with the car still sitting on the ground (or setup blocks/stands) at full race weight, & the suspension compressed to ride height, the top passenger/right 4-link bar is reconnected & adjusted so it's loose & rattles on it's rod-ends. Note that this should technically be called "zero" preload", (and not "neutral") because only said 4-link bar has 100% no/zero load on it at this time.

(7) Then with the car still sitting on the ground (or on setup blocks/stands) at full race weight, & the suspension compressed to ride height, the anti-roll is reconnected so that both A/R links have no load on them (so all A/R rod-ends are loose & rattle freely). Note that the A/R at this point should technically be called "neutral" preload (and not "zero") because all of the A/R assembly as a whole has no load on either side/link.

(8 ) Then wheelie bar heights are set even side-to-side, no wheel height stagger is used at first (but might be used later if necessary).


It should be noted that this method can sometimes be a little more forgiving (vs the hanging method) if something in the chassis/suspension is a little "off" and not perfectly straight/square. But of course there are limits how much something can be out of wack with any method that might be tried.




Both of these 4-link+A/R setup methods can usually be a good "blind" starting point for side-to-side preload settings on a bunch of cars if you're not sure exactly how much usable power/torque a car has to work with. Under say 900 hp and these methods might initially result in either a straight launch, or it could launch to the right a given amount. Over the 1200 hp range and initially it might launch straight, but it's possible it might also launch to the left a given amount. Only track testing will tell for sure which direction a car will launch with any given setup because every car is different. But most any method used can be pretty much be useless as a starting point & create a bunch headaches if the housing is sitting in the car crooked and you don't know it.

I installed the 4-link following procedure "B". The WB is perfect side-side,
coilovers are exact same height, settings are the same, pinion angle is
perfect, passenger top bar and antiroll bar are loose (no preload). No
wheelie bars. Engine dyno'd just under 1000 on HP alone. Havent tried
the NOS yet because its pulling left.

Car picks up the front wheels a little and pulls LEFT. YES LEFT!
After I get it back in the groove it drives and stops straight.

Sorry this isnt very close or clear but its the only recent video I have
right now.....
https://www.youtube.com/watch?v=SxPEm1BXeD8&feature=plcp

If I lengthen the upper bar on the pass side wont that push the tire
down and put MORE weight on the right rear?

HELP!

Have any videos by chance? Its weird that its going left. Adding negative preload to move weight to the left tire will probably fix it, but I would be worried it was simply covering up a different problem. The upper bar goes down hill towards the chassis side of the bar...making this longer will push this side of the housing "up" removing weight from that tire. Make sense?
Oh, and do all your changes with the suspension hanging...the chassis acts as a jig/fixture that holds everything in place, so dont let anyone give you any crap about it.

>> The upper bar goes down hill towards the chassis side of the bar...
>> making this longer will push this side of the housing "up" removing
>> weight from that tire. Make sense?

Ahhh, gotcha!

Added link to video in previous post.

Will recheck it "hanging". If still good how many flats longer? 2?

2 flats is alot...if you have access to scales, Id start with moving maybe 40-50 lbs that way. There isnt a ratio of flats to how much is weight being moved because each car has different weights in different areas. 40-50 lbs could probably be achieved with less than a flat...no more than one flat though.

Scales are static weight and wont reproduce whats dynamic
with the front wheels off the ground will they?

I just noticed Rt66 posted a couple pics from Fri night.
They are shots from the front.

https://www.facebook.com/photo.php?fbid=10151833854260317&set=a.10151833851375317.864513.237063525316&type=3&theater

https://www.facebook.com/photo.php?fbid=10151833862230317&set=a.10151833851375317.864513.237063525316&type=3&theater

All the weight goes to the rear tires when the front wheels are up...when you force more weight to the left rear with pre-load, it is going to stay there when the front tires are up.
Here's what I use for scaling because they allow you access to everything under the car without the tires in the way...

curleysracecars wrote:Adding negative preload to move weight to the left tire will probably fix it, but I would be worried it was simply covering up a different problem.

That is a good point. Launching left/hard left at or below 1000 hp, even if the top passenger/right bar is "loose & rattles" does point to something possibly being not quite right somewhere else.

Going past "loose & rattles" on the top passenger/right bar (aka adding negative preload) can be tried. But at best it's just a crutch for something possibly being wrong somewhere else. And at worst adding negative preload might straighten the launch Ok, but then possibly screw with how straight the car drives on the top end & under braking.

It does kinda sound like the housing might not be 100% square in the car (or possibly the housing is bent). Or that something somewhere in the suspension might be in a bind at some point during suspension travel.

This is a brand new car I built from the ground up. I personally built
the chassis on a chassis jig and I narrowed the rear end on a housing
jig fixture. When I had the front end aligned on a machine that laser
checks both front & rear axles it was also confirmed. IT IT STRAIGHT
AND SQUARE.

Although the ARB is neutral at ride height I'm wondering if it could it
be the cause during launch with the wheels up?? Maybe I should try
a pass with it disconnected?

SOMEBODY PLEASE HELP THIS GUY ! Mainly cuz mine is doin the same thing - only goin to right - and i'm needing help too. Nowheres close to 1000Hp. Found that position on starting line is critical - them Mustangs are wider than us.

Going to the right is what they usually do...you need to add a small amount of preload to it.

To the OP...have you measured tire rollout on the slicks? If they are off, that could be an issue. Rotate them side to side just to see what happens...we just had this issue recently.

mines not a 4 link but after I put the stiffer housing and ladder bars under it when I sprayed it it would go left..................I ended up w 30#'s more on the LR, this was on a set of scales w me in the seat, car full of fuel etc. I'll also note per Mike Duffy the left heim end is approx 1/16" further back that the right, in other words the yoke is " pointed " towars the ds a tad bit.....................I have no clue but it damn sure works.

Sounds like you have some rear steer in the car...which is a way to help it go straight. Any car with big power has some rear steer in it...cant put enough preload in them to counteract the power without having the suspension bind up.

curleysracecars wrote:Sounds like you have some rear steer in the car...which is a way to help it go straight. Any car with big power has some rear steer in it...cant put enough preload in them to counteract the power without having the suspension bind up.

The rear-steer (aka rear wheelbase stagger) he's talking about can be a very usable tool to help some cars/combos avoid having to crank in/out a bunch of preload. The thing is you don't really need to stagger the housing centerline very far off of dead square to see a usable change. It can also sometimes be helpful on cars with just a single wheel wheelie bar since you can't use wheelie bar height stagger to adjust the launch like you can with a dual wheel bar.

Although I usually don't use any rear-steer/rear stagger on an initial 4-link setup, I will use it if testing shows it becomes necessary. I think the reason some people say that you should never use any housing rear-steer/rear stagger is it is easy to go too far off center with the stagger and cause other headaches.

I know one guy's car I work on with a single wheel wheelie bar the need for a little rear-steer adjusted in depended on if he had his 500" or his 700" engine in the car.

Very true. 1/8" of rear steer is a lot...Ive heard of cars with 9/16" rear steer, and they wonder why the car is a handful to drive...a little goes a long way.

What is the best way to square the rear axle? I am setting up the truck right now. I don't feel good about any of the 4 ways I have been told.

Put the frame on jack stands, let the rear end hang. I usually begin with making the lower 4-link bolts to where there are 2 flats at a vertical position. This gives you something to measure from. So, measure from the front bolt, to the rear bolt, and make them identical on both sides. This should work if the brackets on the housing are clocked on the axle housing correctly. I'll use the lower bolts to begin, then usually find at least 2 more common points on the chassis to measure from. Usually one of the dimensions is from the lower 4-link crossmember to the front edge of the brake rotor. You can move the tape measure while holding the end against the 4-link crossmember, and find the shortest dimension of the rotor since it is a round piece.
Hope this helps...

I fully understand, just worried that maybe the brackets are slightly off. Maybe I'm worrying too much. My friend Chuck Ford, who tuned Mike Ashley to two ProMod championships, said to just get it square the best I can and run it to see what it needs. He said basically, first 100 ft is 4-link, after that, steering controls going straight. Thanks, I will probably be asking a few more questions.

richter69 wrote:mines not a 4 link but after I put the stiffer housing and ladder bars under it when I sprayed it it would go left..................I ended up w 30#'s more on the LR, this was on a set of scales w me in the seat, car full of fuel etc. I'll also note per Mike Duffy the left heim end is approx 1/16" further back that the right, in other words the yoke is " pointed " towars the ds a tad bit.....................I have no clue but it damn sure works.

If the yoke is pointing slightly to the DS, wouldnt that make the car drive left?
And the 30 lb left rear tire preload is counteracting that??

David Willingham wrote:I fully understand, just worried that maybe the brackets are slightly off. Maybe I'm worrying too much. My friend Chuck Ford, who tuned Mike Ashley to two ProMod championships, said to just get it square the best I can and run it to see what it needs. He said basically, first 100 ft is 4-link, after that, steering controls going straight. Thanks, I will probably be asking a few more questions.

I agree completely! I woulnt trust the brackets. When I built my chassis on the jig I used
a center punch to put reference "dots" on the frame rails. Makes it very easy to squeeze
clamp a tape measure on the dots for future measurements.

If the left rear tire is further back, it will want to run a circle around the right rear tire...therefore forcing the car to go right. I like the center punch idea on the tubes...good idea!

In a situation where you might not fully trust the placement of the assorted rear housing/chassis brackets all being as straight/square as possible with everything else, (such as buying a used/abused race car, or a car not built on a jig, or for whatever reason) then squaring the housing going off a nose-to-tail centerline string is probably the next best choice.



I took another look at the posted Comet launch pics, & video in slow-mo, and it is kinda hard to tell in the video (from the angle & distance anyway) exactly how much it might have gone to the left that time. And there was a little initial rear bounce at the hit (either bouncing on the sidewalls, or bouncing on the shocks/springs). In one pic it seemed to really wind-up the sidewall a bunch, so it's possible it might need just a little more air pressure.

Then I looked at this earlier video, and it did go left a decent amount that time. The amount it launched to the left that video wasn't really a super scary amount, but it definitely was enough to get your attention.

https://www.youtube.com/watch?v=dQK7Gb6C7XQ&feature=plcp

One thing I did notice on this earlier video was there looked to be a greater amount of rear bounce at the hit (but that might be because the camera was closer to the car). So it's possible that the static preload setting might not be 100% the only cause of the left launch. The bounce could also be causing some inconstant traction one slick vs the other.