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Author Topic:   squaring the suspension
Dirt Freak

Total posts: 338
posted November 05, 2004 05:43 AM  
i have always either used stringing the car or squaring my suspension off the lower grease zerks on the front as a method for squaring my suspension, then this morning (while pondering on the throne)
it occurred to me that maybe thats a bit off the mark and here is my logic.

if the zerk on the lower is the point to use then we already are off the mark because our pos. caster on the front end throws the center line of the spindle to the rear.
which causes an out of square condition when we square our rearend to it.

i just wonder if we should be measuring off the back of the spindle center line for more accuracy .
i have also used the other method from circle track where you drop lines to the floor and square off the centerline of the car but there again we used the grease zerks on the front lowers as a reference point.

any thoughts on this thought provoking ponderance of mine for the day???

Dirt Forum Champ
Total posts: 2007
posted November 05, 2004 06:53 AM  
By using lower grease zerks you also assume that the lower a frame has the holes cut in it right and is not bent or bushing worn etc. Its not uncommon for the lower A's to be off, we built a jig to check ours with so that we can make our spares match and we can change them out with out affecting anything else. Using the inner pivot points like the bolts i think would be better than the lower zerk.

Ego Racing
Dirt Forum Champ
Total posts: 724
posted November 05, 2004 07:22 AM  
For several years we have used system we came up with and it works very well.
On the frame of the car on each side we welded two small 1 inch long tubes. Each front is located behind the front tire and each rear is just in front of the tire. The tubes will alow us to slide in 1/2 inch conduit and it holds snug. We use stands to string the car, then slide the conduit peices into the tubes, the conduit is marked on the end to show STD and a few marks on either side of STD. We move the srting into place to the STD marks on the conduit and then measure to the leading and trailing edge of our rear and front rotors. If everything is good you are done. This will also let you know if your chassis got bent because when lined up on std on both sticks tha rotor measurements will be way off. When we ran on asphault we had plates like bump steer plates we bolted to the hubs, this would give more precise measurements.

Dirt Freak

Total posts: 270
posted November 05, 2004 08:23 AM  
It has always been my belief that the rear end should be squared to the chassis not the front wheels.After bad bushings,bent mounting points and A-frames the grease fittings are not accurate. If your car has a motor plate,it is square to
chassis.Drop plumb bobs off it and measure back.The motor set back rule measures off the back of the engine to the center of the housing so it is to your advantage to do this so you are legal.Then check wheel base to make sure you are legal there.Remember you are pushing the car, the front wheels will go where the chassis goes.I have seen cars squared off the front wheels handle poorly because the front suspension was bent somewhere causing the rear end to be off as much as an inch or more.Good luck!

Dirt Full Roller

Total posts: 33
posted November 05, 2004 11:12 AM  
The motor plate works best most chassis builders have the stubs turned and u can check that off the motor plate also

Dirt Freak

Total posts: 324
posted November 05, 2004 11:56 AM  
ive found a set of holes in the d-w 8 that seem to be as acurate as anything else. they are in the rail behind the upper a-frame mount, close to the center of the rail just before it turns out & down to the outer rail. they are strait across from each other when the stub is "new" or cut from a straight donor, but the engine is in the way when the car is assembled. it seems to be the spot to use, for now anyway. we use the 68-72 chevelle stub, but this one came from an old gutlass in the local u pic, all the same stuff up front,except the a-frame bushings.i think dirt works uses it for a reference point also, because it is plated with a washer on a new car.

Dirt Maniac

Total posts: 180
posted November 06, 2004 12:21 AM  
I understand all the reasons stated above, but here's my 2 cents. The car only "sees" the 4 contact patches at the tires, whether the suspension in the front is bent, moved, relocated or whatever in relation to the rest of the chassis. Is it really correct to have the rearend square to the motor plate, or the front frame stub, or factory frame holes, when it then might Not be square to the front suspension?

The bottom A-frames are static, and the top are adjustable, more-or-less. I would think most any point on the bottom a-frame would work for squaring, but especially the grease zerks, which gets our measurement out closer to the wheels than the pivot bolts do.

Spindle centerline would also work, but the wheels would have to be absolutely straight ahead at the front. If they are not perfectly parallel, it would add another variable to the equation, throwing off our measurement.


Dirt Maniac

Total posts: 170
posted November 06, 2004 01:20 AM  
Using the motor plate you would assume that it is square to the centerline of the chassis ,but you better check with the builder to make sure this is true or you could be chasing your tail.....I have always had good success dropping plumb bobs through one of sevreral factory jig holes to choose from and marking the floor with a sharpie .

Dirt Maniac

Total posts: 190
posted November 08, 2004 07:48 PM  
a 70 cutlass is the same frame and lower control arms as a 70 chevelle?
measuring from the front suspension(zerks) to the rearend will tell you if your wheelbase is equal side to side, but does nothing for telling you if the diff is square in the chassis. even if the diff the same distance from a reference point that is consistant, is it centered side to side in the chassis? dont think your zerks will tell you that. and if it isnt centered and your measurments from you zerks are the same, it obviously isnt square, is it?
i will say it is best to find a reference hole on each side to measure from, even if you have to drill a hole or weld on a tab, as well as one from side to side, and dont worry about "square" worry about what works.

Dirt Maniac

Total posts: 190
posted November 08, 2004 07:49 PM  
i was asking if a cutlass was the same as a chevelle, 68-70. have a friend that wants to give me a couple.

Dirt Forum Champ
Total posts: 1172
posted November 08, 2004 10:35 PM  
all 68-72 gm a bodies share the same lower control arms and geometry. Frames beteen a cutlass chevelle and gran prix are all the same, elcamino and station wagon and convertable were boxed side rails.

Dirt Full Roller

Total posts: 65
posted November 09, 2004 09:24 AM  
We are talking about squaring right? Centering the rear end is very different and very easy. Just get the measurement from the chassis builder from the rear frame rail to the third member and it's adjusted with the p-hard bar. No big deal. Squaring the rear end is much more involved as mentioned above. For the most accurate measurement I would suggest dropping a plumb from both ends of the motor plate to create a straight line (extend the line so that it runs just outside of the width of the car) and then measure straight back from that line to the hubs. Hubs are machined and are more accurate than any part of the cast rear end housing tubes. I've had good luck that way. If you can get the line drawn, you dont even have to jack up the car.

Dirt Freak

Total posts: 324
posted November 09, 2004 03:27 PM  

Dirt Newbie

Total posts: 3
posted November 12, 2004 09:20 PM  
on the harris chassis, the 2x2 that the rear trailing arm brackets are attached to is supposed to be sq. with the chassis. I hang a string off the front side of the rearend on both sides of the housing and measure forward to the 2x2 this should put your rearend sq. with the chassis.

does this sound logical?

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