Ladder Bar Chassis adjustment

I have a buudy coming up with a Body Shop Tram to check rearend alignment on my car. I don't have a lot of experience with a ladder bar car. Have 2 questions.
for checking wheelbase length/squareness can't I take and measure from the center of the rear axle to the center of the front spindle?
And for the adjustment don't you use the front eyelits on the front most part of the ladder bar arms?

Tks Tore

Tore wrote:I have a buudy coming up with a Body Shop Tram to check rearend alignment on my car. I don't have a lot of experience with a ladder bar car. Have 2 questions.
for checking wheelbase length/squareness can't I take and measure from the center of the rear axle to the center of the front spindle?
And for the adjustment don't you use the front eyelits on the front most part of the ladder bar arms?

Tks Tore

Tore,
I am not the Guru, but I always use the diagonal measurement for square... length is different, as for the bar adjustment there are different ways of doing this too I use the wheelwell opening height side to side, and use one side to adjust up or down (RR for me).

Front wheels may be staggered for roll out purpose. I would determine a point like lower control arm mount or something to go from but if you do determine the front hasn't been staggered measure from rim to rim. I prefer that because a front spindle center will give a false measurement if the steering isn't centered perfect. You can adjust rear with front mounts easy just a half round makes a big difference.

IMO relying on the front spindles, or any OEM-factory body/chassis landmarks isn't a very accurate measurement starting point. Starting at these points can lead to headaches, stomach acid, and pulling your hair out. The spindle placement side-to-side can have some stagger (on purpose, or by mistake), and OEM-factory body/chassis landmarks can be all over the map.


Squaring the rear housing.......

Find the center of various chassis crossmebers (OEM and/or fabricated) from one end of the car to the other (nose-to-tail) and drop a plumb bob off each to the shop floor and mark each. Then drop a plumb bob off the center of the front and rear of the body and mark them on the floor too. Then stretch a "centerline string" end-to-end to determine how "straight" the chassis/body assembly's centerline marks are lining up with the centerline string. If all the assorted C/L marks on the floor line up with the stretched centerline string then the body/chassis assembly's centerline is presumed straight (or damn close).

Next drop a plumb bob off the center of each rear axle flange to the shop floor and mark them both. Then stretch a second centerline string between these two marks, this second C/L string will cross the first nose-to-tail C/L string. Measure the angle at which the two C/L strings cross each other. If they cross each other at a 90* angle then the rear housing C/L is square with the body/chassis nose-to-tail C/L.

You can also use this same plumb bob method to check if the ladder bar (or 4-link) crossmember's C/L is "square" with the chassis's nose-to-tail C/L.  

You can square-up the rear housing a given amount on a ladder bar car using the front rod-ends. You can also use the rear solid rod-ends to square the housing as well (how much you can use the rear rod-ends depends on the ladder bar design). Either way just don't go crazy and leave a lot of rod-end threads showing.    


On a side note front spindle stagger & rear suspension/ladder bar/4-link preload is the biggest reason for not letting an alignment shop do a "4 wheel" alignment on a drag car. Always tell the alignment shop to only reference the car's nose-to-tail C/L when aligning the front end, and never use the rear axle C/L as a front end alignment reference.

cool40 wrote:Front wheels may be staggered for roll out purpose. I would determine a point like lower control arm mount or something to go from but if you do determine the front hasn't been staggered measure from rim to rim. I prefer that because a front spindle center will give a false measurement if the steering isn't centered perfect. You can adjust rear with front mounts easy just a half round makes a big difference.

This car is a 64 Falcon and has a Mustang II rack and pinion and has a custom frame .I am used to leaf spring cars as there isn't much to screw up.
I appreciate the input guys.

Thanks Tore

Determine a centerline from front to rear. Chalk a line. Pull a 3,4,5 ( Pythagorean Theorem ) This is a square line to your center line. Chalk this line. at this point I usually take masking tape on the floor and hard mark the lines with a fine point ink pen in the areas you are going to be measuring to. Drop plumb bobs on all your rear end components, axle left to right, axle front to rear, ladder bar crossmember and bracket holes. Record each dimension to the corresponding chalked line and determine how to adjust your car for square. If your car was built on a jig something is bound to be square, crossmembers, mounting points, etc. If not your going to try to find a happy medium to make it as square as possible. You then can check the front end mounting points and determine front end stagger etc. You just want to make the car efficient and happy.

I assume it goes without saying that the vehicle chassis and the rearend housing both need to b e levelled side to side whilst dropping all these plumb bobs.



dkp

Thanks everybody