I am trying to verify zero preload on my 36 in. S&W ladderbars.
On the scales I have equal weight on the slicks(840 lbs. each).

With the car on a level surface if I separately remove the front attaching bolts on either side the bars each RAISE UP evenly about 1/8 inch .
From what I understand this means there is little or no preload on either tire. CORRECT??? This would agree with my scales.
To get the bolt back in I have to put a little pressure on the top of the bar to realign the hole. I am in the MIDDLE hole of the front bracket.
Also the drivers side hole alignment is slightly offset towards the rear of the car and the passengers side is slightly offset towards the front of the car. I am able to realign them with a screwdriver.
Is this normal or should I adjust something to get these even and how would I do that?
Thanks Mike

Little or no preload means there is no bind or tension on the suspension links that would influence the corner weights. If you can slide the bolts in an out that easily, and/or if the adjuster is loose enough to wiggle by hand (no load on it), that's pretty close. Corner weights are a separate issue and are influenced by where the weight (fuel tank, batteries, driver, etc.) is distributed in the car, and spring loads. Neutral preload and equal weight on the rear corners is great. Should be easy to get it to go straight and square.

As far as having to pull the bars fore or aft to get the bolts in, the rear should be perpendicular to the centerline of the car. This is adjusted by running the front links in or out of the bar. If the rear is square, don't fool with them.

CM the bolts do not just fall out when trying to remove them. As said when I do get them out the bars raise approx. 1/8 in UP. If I pull down on the bar I can get the hole to reasonably line up but I also have to realign(pull on bars) back and forth to put the bolt back in.
Is his reasonably close? Every year I have a good alignment shop go over the car and they say the the rear is in the car square. Should I verify this also with measurements?
Thanks Mike

I'm surprised either bar goes the same direction. If there is any preload one bar will go up, the other will go down. No preload the bar shouldn't move. Do you have it in park with the front wheels chocked? If there is any tire rotation the bars could move slightly. Most door slammers are right side heavy and will require some right side preload to get the rear weights equal.
A couple of points;
#1 I'm assuming driver weight and fuel are in the car.
#2 If the car still has torsion bars start by raising the rear off the
ground (jacking in the center). Equalize the front ride height side to
side. Unequal left to front height will influence rear corner weights. That
all goes out the window when it pulls the front wheels off the ground.
#3 Make sure to check the side to side location of the rear housing once
you set your desired starting preload and pinion angle. A big move will
pull the housing off center and require readjustment.
#4 Take at easy on the first few hits. It may need a tweek to go straight.
It doesn't take much to make it leave right or left. Add right preload if
the car veers right, remove preload if it goes left.
Doug

The fact that you need to apply equal work to either side when installing the bolts shows that the ladder bars aren't preloaded. You have to pull down, probably because the coil overs are mounted in the rear and the axle is becoming the pivot point due to the weight on the car, causing the front of the ladder bar to rise. I think it's fine. I would have your shop do a four wheel alignment and find out if the rear axle is squared to the front (thrust line) and get it to less than .5 degree. This should be done before adjusting your front end toe.

I agree.

I have weight in drivers seat equal to driver. Front torsion bars are adjusted to have equal height on front end. I have the car currently on my scales and adjusted to equal weight on rear tires. rr 842 lr 838.
rf 923 lf 944.
I just installed new Double adjustable QA-1 coilovers and new springs.
I have my local guy do 4 wheel alignment before going to the track.
I just wanted to verify that I do not have preload on either tire. the car seems to like it that way.
I was also concerned that I might have some binding of the bars since I have to move the bars around some to get the bolts back in. They don't just slide back in easily as is often described.
Thanks Mike

1/8" movement isn't much. Both bars going the same direction is also an indication. "Easily" means you can pull it the 1/8" with one hand, a few pounds of force, and not work up a sweat. Pre-loading ladder bars will sometimes get into floor jacks and pry bars to get them back together. I wouldn't want the bolts to fall in or out of the holes. A little wiggling is normal.

If your alignment shop does a 4-wheel and says it's square, that's better than rolling around on the floor with tape measures and plum bobs.

What kind of 60's? I don't know your combination, but looking at those corner weights, I'd take the thing to the track and let the car tell you if anything needs to be tweaked. I would expect it to be real close unless it's really quick.

CM, With great track prep we will go 1.29. Car seems to like being set up with equal weight on rears.
Thanks Mike

Well, preloading, or lack of it, is mainly concerned with going straight and square, not so much going quicker. Although smooth, straight and square is the quickest method. Going into the 1.20s with a ladder car, I would expect to need to run those shocks fairly tight.

CM, it has only gone 1.29 a few times last year on Big event nights when the track is GREAT. .Most of the time with good prep it is in the low 1.30's. I'm hoping to make that happen more often with the new Double adjustables I just installed. That and trying out stiff sidewall slicks that hopefully will last longer.
Mike

I think if the car is launching straight and consistant, with out preload is good. My buddies car had to have at least 50 lbs. more on the rr to leave straight.

My weghts are with-in 30lbs right to left with no preload. The car needs 5 flats. With that it goes dead straight. My 10.20 car never cared. This car (9.0) it's a huge difference.
Doug

On my car(4 link) I had 12# of preload and it
drove straight as a arrow.. that wasnt even 1
flat.. I just turned it by hand.. was very
EDIT
On my Rampage(ladder bar car) I have less than
a flat in it also

Preload is the intentional binding and loading of the suspension links. Some is fine, but I prefer to use as little preload as I can in order to avoid that and allow the suspension to work as freely as possible. If it goes beyond what I can do without a wrench to turn the links - usually a couple of flats - I will use other methods to get the weights close to where they need to be and use the bars to dial in the last few pounds. If we have some load in it and need some taken out once we get to the track, it's easy to just tweak a bar some.

One other thing that OFTEN gets overlooked when putting a car on scales is tire pressure. Make sure the tires aired up to where they will be on track. A few pounds can make a big difference. Also preload will be different on every car to get it to go straight. Generally the more power the car makes the more preload it will require, that's a universal statement but holds true more often than not.

FWIW the Vette is a ladder bar car, very short ladder bars at that. We have been 1.13 60' and we know there is more let. We don't make a ton of power as its just a SB but it works well and could not be in a worse car in terms of platform for a racecar.

If it only moves an 1/8" one way or the other. It's close, Just standing...

Just remember that any pre-load you add will
be the opposite when you let off the pedal on
the big end.. so try to add as little as possible
to keep things happy but make it go straight

There is no universal number as far as what each corner should weigh. As power goes up weight generally needs to be moved. Big power can require the car to be neutral or weight being moved to the left rear. Scaling allows you to establish a baseline. The car will tell you what it wants from there.

If you have a car you're familiar with or a personal car, scaling the car after it's been sorted, just as it sets with no driver, and recording the information, will save time. It will allow you to put the car right back after having something apart or replacing parts without having to load ballast in the drivers seat. Typically I record with and without numbers. Unless the usual driver gains or loses a bunch of weight, it works out fine.