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Squaring a Task Force Frame

Using a laser level and common measuring tools to check a Task Force Chevy truck frame for alignment

 

 

I realized when preparing to modify my 1958 Chevy Truck (Task Force series) truck that to install the modern suspension I wanted that I should first make sure the frame was not damaged or bent. It makes little sense to spend a lot of time and money if in the end the frame is distorted. All that work will never be right and – worse – the new work would just reinforce the damage. Sure, I could have dragged the frame to a frame shop and spent a lot of money to set up and check the frame and more money to repair it, but I was certain I could get the job done with a little thought and careful measuring. I'm not one to throw money away or have others do my work for me. So I set the frame up where I could work on it and removed the bed and cab. When you are doing things as basic and complex as a new suspension, removing a few more bolts mean nothing and getting the sheet metal out of the way makes the whole job a lot easier.

The Task Force frame is considered square if the cross measurements are within 3/16". Ideally it should be 1/16" or less. Depending on how far out it is dictates how you square it up. If it's more that 3/16" you may need to get it professionally squared up. Along the frame are several reference pilot holes 3/8", 7/16" and ½" in diameter that were either used for other accessories on different models or used on the assembly line as guide holes. We use the 7/16" and ½" reference point to square the frame rails. You will need to locate the front end from these reference points as well as other points that you will measure and record as we go forward. The rear most reference pilot holes are located approximately 1" or so from the rear frame end. Locate the holes that are approximately 72" forward of the rear bed bolt holes. They would be just behind the cab. Place one slotted bolt in each hole. Finger tighten the nuts so it they don't fall out or tilt. Measure back to the front left hole to the right rear hole. Compare the measurements. This will give you the out of square measurement. Make several cross measurement at the reference point holes up the length of the frame.

Once you have determined that you are square to the reference points measure the length from the reference holes behind the cab to the end rail is straight down the rail not cross measured. The dimension to the end rail should be 73" +/- 1/16". This way you know that the frame horns have not been modified. You will make measurements correspond to the pilot holes in the frame rail. These are the index points that all suspension parts will be located from and it will make it easier to get the front and rear axle C/L parallel so it doesn't dog walk down the road. We will cover this in a different section. With everything stripped off the Task Force front end except the cross members, the transmission cross member and the rear spring hangers on the front axle, make sure the frame is leveled front to back, side to side and began measuring. And cross measuring again. Take a measurement from the frame to the floor every 12" from the front frame horn to the rear frame horn, record these measurements they will be very useful later on when modifying the frame. If they are very different from side to side the frame may not be straight or the floor is not level. You must determine this before proceeding and take corrective action if needed. If your floor isn't level you will need to subtract that dimension from the measurements high side. So if your frame is level but the frame to floor dimension on the right side is ½" more than the left put a level on the floor and see if its off level by a half inch. If it is just subtract that ½" from the right side floor to frame measurements. If its level find out what's wrong.

To check the rails for straightness we are going to use a laser level that you can buy at any home repair store. We will also check the drive line for alignment in the frame and make sure that the rear end is in the proper position side to side. You will need a laser level, a sheet rock square, a tape measure and a piece of flat stock that will lie across the rails and overhang each side by 2 inches.

 


Figure 1: This Laser line level is more than sufficient to do the job. You can also see that I have cut a slot in the bolt pictured next to the level. I use these bolts to measure from by placing the tape measure lip in the slot and measuring to where ever I need to.Its great for cross measuring when no one is around to help.


Figure 2: I have placed the level at the rear of the frame rail and shot it down the rail toward the front. In this picture you can see that the laser is hitting the blue level at 34" mark and at the sheet rock square at the 0" mark.

Figure 3: In the left picture it hits the side of the C notch and axle and goes all the way to the squares 0" mark. This tells us we have a straight rail from the rear axle to the front cab mount. In the right picture you see that the half circle at the rear of the level is slightly to the left of the frame rail. This indicates that we have a taper toward the center of the frame of ¼" after the axle. Because its behind the axle and it only a ¼", I'm not worried about it at this point. We move to the other side and setup the same way.


Figure 4: As you can see it glides down the rail high lighting the various high spots and hitting the square at the 0" mark. It doesn't get any straighter than this. We do have the same problem after the axle as we had on the right side it tapers in ¼" to the center. I suspect this is caused by welding in the C notches with out proper bracing, but it can be fixed with little trouble and we'll worry about it later.

Figure 5: On to checking the center line of the frame. What we are doing now is to check if the engine, transmission rear end and new cross members are centered. First we setup the laser level in the center just above the transmission.

Figure 6: Notice that the red laser line goes down the rib on the transmission to the center of the yoke. This is the engine alignment point so we can determine if it is set in the frame correctly. It is exactly like sighting a gun. If it pointed left or right of the first cross member marks we would have to adjust it now. Because that would mean that the engine center line was not parallel to the frame.

 

Figure 7: The laser goes down the rib crosses the center of the yoke and intersects the mark on the cross member and square. We now take the square off the frame and look down the other marks.


Figure 8: Here you can see the laser go down the trans rib past the center of the yoke intersecting the center marks on the three cross members and hitting the pinion shaft in the center. This tells us we are aligned front to back on the drive line as well as centered in the frame.

We hit the pinion shaft on this one because it is what is called a pinion centered rear end. Not all rears will be pinion centered so the laser may not hit the pinion shaft at all. This GM 12 bolt was originally carrier centered, meaning the carrier housing is centered in the frame and the pinion shaft is offset. We made it pinion centered when it was narrowed to eliminate the drive shaft compound angle that a carrier centered rear has.


If you are wondering why all this drive line stuff is so precise, its because very often people slap in a drive line and later wonder why they have a vibration at 55 or 60 mph that they can't find. It's much easier to fix a misalignment now than later.
Now that you know your frame is straight and square you can proceed with confidence that your hard work and new parts won't be wasted. If it turns out to be sprung or bent get it to a frame shop and have them line it up for you. You can also try finding a used frame but you have the task of squaring all over again with no promise of a better out come.

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