The Hollister Road Company

 

Installing an IFS from a 1975 C10 into a stock frame 1958 3100

Dave Chapman 11/18/2004

pic1

GM IFS bolt on for a 1958 - 59 Task Force Chevy pickup.

The idea of this project came from an article I read in American Rodder about a bolting in a Chevy IFS into a Advanced Design Chevy Truck. The article went on to say how you could with little difficulty bolt in a 73 -87 C10 front IFS into a 47 - 55-1st Chevy truck. Like most back yard fabricators I didn’t completely read the information and just went out and bought a bone yard front clip from a 75 C10 to put into my 59 Task Force.

The Advance Design designation is the group of GM trucks from 1947 thru 1955 1st edition. In 1955 they changed body styles in mid year, hence the 55-1st and 55 2nd. The Task Force designation is the group of GM trucks from 1955 2nd thru 1959. The Advanced Design is the more rounded cab and hood with one to three rear windows and the rear fenders were rounded as well. The Task Force has a more squared cab and front fenders with a single rear window either large or small. The rear fender and bed design of the Task Force trucks were carried on until late 60's on the step side pick up trucks.

The Parts:h

When you buy the front clip it can be from any 73 – 87 C10. Buy the entire front frame section. You need the frame rails from the firewall forward to the bumper. You will be using some of the frame sections to mount hardware on the Taskforce frame. It should have then disk brakes and calipers as well as the steering box and linkage. Motor mount brackets are a plus. Try to get it as complete as you can. Clean it as soon as you get it but don’t disassemble it just yet.

The Problem:
Only after I got it home did I realize the front frame width of the Advance Design was 28.5”, the frame width in a Task Force was 34” and the cross member of the C10 was tapered in toward the front from 30.5” to 28.5” over a 10” distance and was 29.5” @ the axle C/L. I needed to taper the front frame rails of my 34 inch wide Task Force to fit the 29.5” C10 cross member and to meet the correct taper angle at the 114” wheel base center line of the front axle.

The Tools:
A Pro Cut 25 plasma cutter. (The answer to most things),
Body Jack,
SP 175 Plus mig welder
A 36” speed level
A speed square
4 - 3 foot 1 ½ square aluminum tubes
A Saws All with metal blades
Angle finder
Hack Saw
Tape measure
Plumb Bob
Sharpie markers
Jack stands
Floor jack
Various clamps and vise grips
Several 3/8”, 7/16” and ½” bolts with a slit in the threaded portion to accept a tape measure lip. You use these to put into the reference holes and slide the tape end into the slot. That way you measure in the same spot in each pilot hole every time with out having 2 people to measure. If you can lay your hands on a tram all the better.
You will need various hand and impact tools.
The 55 – 59 truck assembly manual.
The 55 – 59 service manual
A laser level
A frame caliper – it’s just a sheetrock square with some modifications to make it a very larger venire caliper.

 

The Task: Square the frame and taper it to fit.

 

Squaring the 58 – 59 Task Force Frame
when replacing the front suspension
with a GM IFS front end.

This project requires a skilled welder and some knowledge of
frame fabrication and bracing.

It’s important to write every thing down and measure every thing more than once. Because of the nature of this project it is very important that the cuts, bends and welds be done only once. At the end of the article I will recommend some tricks and tools to make it easier to measure and locate the axles along with frame dimension and locations.

The Task Force frame is considered square if its 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  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.

pic2

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 rear holes in an X pattern as pictured above. 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”. You will make measurements correspond to the pilot holes in the frame rail. It is the index points that all suspension parts will be located from. This will make the front and rear axle C/L parallel. We will use these holes to make sure that the axles are square to the fame 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 of the front axle, make sure the frame was 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 transmission member, record these measurements they will be very useful later on when tapering 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. 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 sheetrock square, a tape measure and a piece of flat stock that will lie across the rails and overhang each side by 2”

pic3

This 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 to measure from by placing the tape measure lip in the slot and measuring to where ever I need to.I 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 sheetrock square at the 0” mark.

pic6 pic7pic5

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 it’s behind the axle and it only a 1/4“, I’m not worried about it at this point. We move to the other side and setup the same way.

pic9

As you can see it glides down the rail highlighting 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.

 

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.

pic11

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.
pic12

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

pic13  pic14

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.

 

Tapering the frame rails for the new cross member.

Now with the frame being straight and square and level within 1/16” checked at the recommended cross points, locate the front axle C/L. It should be 30.50” from the front frame end with the brackets and extensions removed (it will be different on 55 1st – 57). Mark the frame at that point on the top, side and inside bottom. It should end up just about ½”rearward of a ½” pilot hole in the top side of the frame.

pic15

 

The front axle C/L should also be approximately 150.5” from the rear frame rail end with the brackets and extensions removed on all 55-2nd thru 59. Now with that said you may want to move the C/L forward or backward to get the wheels sitting the wells the way you want them. So you may end up with a wheel base slightly shorter or longer that 114”. Mine has a 112” wheel base.

 

Measuring and marking for the front frame taper cuts

Between the rear cab mounts and the cross member that hold the hand brake pivot there are 3/8” pilot holes one on each side. Put in a slotted bolt and tighten the nut, it should be snug in the hole. These are the holes you will line up you r front-end from. Measure and mark at 46” from that bolt forward, it should come to just forward of the front rear spring hanger. Mark 57 inches from the bolt and 65” from the bolt. These are the cut marks you will use to bend the rails to shape. Do this on both sides.

pic16pic17

I found that a speed square is idea for making sure that the top mark is square to the side rail. Because the frame rails in a Task Force truck are straight front to back you can line up off the frame rails with the speed square to mark the top. With a plumb bob transfer the top mark to the lower rail. Use a hack saw and make a notch to rest the plumb bob string in that way you are sure to be exact when marking the bottom. This is a critical point if you mark the bottom even a 1/16” front or back of the top mark the bend will make the frame rail go either high or low at the front frame horn and that will be magnified on the next bend. So take your time and to get it right.

Measure the left side from the rail end to the mark you made just ahead of the rear spring hanger of the front axle. Record that dimension and measure that distance up the right side rail and mark the frame at that point. Transfer the top and bottom rail marks as you did on the left side being careful to accurately line up the top and bottom marks. Cross measure from the slotted bolts to the new marks and make sure you are with in 1/16”, if not re measure to find out why.

You will not cut the frame rail down the side; you will be cutting out small pie shaped pieces from the top and bottom parts of the rail. Save the pie shaped pieces if you can. Re measure the frame to ground at the marked cut locations on each side and record them. If all measurements are within spec your ready to mark the cuts. If you have removed the front cross member tack weld a piece of channel across the front to keep the rails from moving around. If you have not removed the stock front cross member yet drill out, chisel off and punch out all the rivets and remove the front cross member. You will have to trim the flanges that were used in riveting the cross member in.

We are ready to mark the pie cuts.

You now measure and mark ¼” to the front and rear of the top mark you made in the previous step. pic20
From those marks draw a line from the inside rail mark to the center mark toward the out side of the rail making a pie shape pointed to the outside of the rail.

Mark number 2 and 3 does not get a pie cut because it bends in the opposite direction. The first mark is a pie cut the second mark is a straight cut and number three is straight. The first cut will close up when bent in, the second will open into a pie shape when bent out as will the third.

In the next series of pictures the frame piece is not a task force frame. It’s a 75 C10 scrap piece and it is only intended to show you how to mark and cut the frame.

Let me stop here and just say that I see a lot of “Professionals” on TV cutting, tacking and grinding with no gloves, shields and rarely a mask. They do it for speed and Hollywood or just to be cool. What they don’t show is that when those guys and girls are 50 they will be complaining about retinal scaring, skin cancer and nervous disorders from the welding fumes. So cover up and shields on when cutting welding and grinding. And always wear a mask when welding. The Manganese in welding rods and wire can cause severe nerve damage and is very toxic.  And always have a fire extinguisher handy and that’s full.

pic21pic22

pic23pic24

Draw the lines back to the rail.

pic25

Lay a metal speed square or flat stock along the mark so you get a nice clean straight cut.

Make the cut past the rounded part of the rail.

pic2627
The nice thing about plasma cutters is that you can cut out a piece to close tolerance.
And if you made a mistake weld it back in with out much trouble. Top and bottom pies cut out.

2829

I started to bend this piece and you can see on the bottom at the side rail it’s starting to pinch. You may have to run the torch or saw thru that area again. Do it one pass at a time. So you don’t end up with a big gap. I bent this by hand with out much trouble.

3031

Now cut out the piece of pie out. Do the same on the bottom of the rail. Make very sure it is directly in line with the top cut and it must end at the inside rail surface. Then repeat it on the other side. Clean it up with a saw if needed. Do not bend the rails yet. We only want the rails to bend once in the correct direction. Make sure your helper doesn’t wiggle it back and forth to see what happens. Bending back and forth weakens the side rail. You will be surprised at how easily the frame rails bend with the pie cuts removed.

 

Now is the time to get the C10 suspension ready.

 Support the clip so that the top of the frame rails are level. It should have at this point everything still mounted just as if it were in the original truck. If you have wheels to put on it that will help in leveling and rolling it under the truck when you make the bends. The front and rear of the rails will be sloping downward if the clip is level

32

The frame section that the cross member is bolted to should be level. That’s how it sits in the 75 C10 and that’s the way it will sit in the Task Force truck.  So using jack stands and a floor jack get it braced up securely and leveled. We need to measure where the holes go and were the steering gear and idler arm are located. Put an angle finder on the bottom side of the steering gear and measure and record the angle. It will be need to setup the angle on the Task Force frame.
 Remember that the C10 frame is taller than the Task Force frame at the axle. The 58 -59 is approximately 5.25” and the C10 is 6”, so when measuring take this into consideration.

Measure and record:
1. Measure the steering gear angle while it is mounted on the C10 and the top rail is level.
2. Measure the distance the steering gear mounting holes are from the most forward A frame shim bolt.
Remove the steering gear and idler arm from the frame and disconnect the sector shaft arm from the drag link. Leaving the drag link and tie rods in place and connected.
3. Clamp an angle iron on the top of the leveled C10 frame lengthwise with the frame. Make sure it’s long enough that it reaches past the last most forward bolt of the steering gear mounts and measure down to the bolt holes from the angle iron and record. Take into consideration the different height difference of the 2 frames.
4. Do the same for the idler arm.  You also need the angle of the idler arm mounting shaft where it bolts to the frame.
5. 6. Unbolt the cross member from the C10 frame. Save all the bolts, brackets, and hardware. Lift the frame off the member.
7. Slide the cross member under the Taskforce frame rails.
8. Remove the tacked angle iron from the across frame.
9. With the C10 cross member under the task force frame raise the member up to the frame to start bending the rail in and raise it up again so the rails are just inside the member.
10. Find the center line of the cross member which would be the spindle center line, make sure that the steering is centered, and the line measures 150.50”from the rear rail end. Jack it up snug to the frame. Don’t lift the frame rails when jacking it up and don’t force it to fit tight along the length of the cross member pads with the body jack.
11. Make some poster board templates of the mounting holes and locations on the C10 frame clip.
12. Measure those 3 cut spots along the front frame rail to the floor see if the bend has raised or lowered the rail.

Cross measuring at this point may not be accurate because after cutting the rail it may have sprung from stored tension. Measure from the slotted bolts to the forward most alignment shim bolt, it should be approximately 64 ¼”.

The front cross member should be centered to the frame. With a body jack spread the second section until they are against the cross member mounting pads. The front may be slightly away from the rails. With the cross member located in its correct position measure from the forward most alignment shim stud to the slotted bolts. Adjust if needed.

We now need to find out where the cross member is in relation to the frame. We’ll use a laser level and run it down the rail to the front of the truck.
33

With the laser level shoot it straight down the rail. You can see how it just glances off the side of the rail. Put a tape measure just ahead of the most forward mounting bolt to the frame. It should measure approximately 2 ½” from the rail to the laser line. Make sure it’s the same on both sides.

34 35

 

With the rails at 2 ½” from the laser line on both side we know we are centered to the frame rails. This is important for two reasons. First the front end alignment would be off and the drive line would also be off.

This is a good time to check the wheel position in the wheel openings of the fender.
You need to set the front nose clip on the rails. Because you have narrowed the rails the front mounts will no longer work. Lay a 2x4 across the front frame just under the nose mounts. Measure from the hole of the support bracket to the slotted bolts, it should be approximately 84 ¼”. Brace up the nose clip and see where your tires sit in the wells.
Make the necessary adjustment by moving the cross member forward or backward measuring from the slotted bolt so we keep the alignment..

36

Now drill and bolt the rear most top hole on each side of the A frame pads, the hole closest to where the old steering box was located. Just snug up the bolt, do not torque it. Measure to check the rail down to the floor and see if they are within tolerance. If the rail is high you need to make a cut behind the lower cut or in front of the upper cut about a 1/8”. So you’ll be making the pie just a little wider bringing the v point of the cut either forward or backward which ever is needed. You’ll have to hit the new cut with a sledge hammer precisely at the edge of the new cut to bring the rail down and only at the cut and about 3” up the side, not all the way up the side rail. The opposite procedure is used if the rail is low. This is why it’s so critical to take your time and get it right the first time. Before you go slamming it make sure it is secure on the stands the last thing you want to do is knock it off the stands and lose all the measurements and alignments. Push the rails out on the last cut until they are the same width as the rails at the front shim bolt in the A frame pad, measure and adjust. Tack a channel stock across the front of the rails to keep it in line. Cut the original transmission mount out when you are completely finished.

You will need to make some access holes to get to the bolts and tighten the cross member.

3738 

I welded spacers on the motor mounts to raise the engine for better cooling.
After the front end was put in place I made a cross member to stiffen up the front end. It also serves as a place to mount the sway bar and the relocated radiator mounts.

39

As you can see in this picture the end of the rails have been stepped, this was to accommodate the radiator core support. The new frame width in the front is approx 28” so we had to relocate the front core support mounts.

40

You can rebuild the front end as you would any 73 -87 C10, adding air bags and drop spindles. I tried using dropped lower A frames but they were to low and even at ride height they were way to close to the ground. So I settled for 2 ½” drop spindles and air bags with stock A frames.

As you can see it gets fairly low to the ground.

41

Expect to have this front end off and on several times before you get all the holes lined up, drilled and bolted. The poster board templates help a lot. For the bottom holes in the A frame pads I used a center punch thru the nut under the upper A frame shaft. Once you have those in you can bolt in the inside brackets and use them as a template for the frame bolt holes.

42

 

You may also have to relocate the steering shaft.

43

Next cut out the steering box mounting pad on the C10 frame. Cut it so you have about 1 inch to trim off when fitting it to the task force frame. Next clamp the angle iron back on the frame and use the measurements you took from that location on the C10 frame and transfer them to the Task Force frame remembering the frame height difference. When you have it lined up trim it to fit the new frame size. Trace the trimmed piece onto the task force frame and cut out that piece. Weld in the new steering box mounting plate. When you’re done weld on a 1-1/2” X 3/16” X 24” long plate on the top of the rail as picture below. This will give it added strength to support any stress. Do the same on the bottom inside .

44

You may have to do the same thing for the front A frame pivot pocket on the frame. If so cut out and weld in the piece of the old frame like you did for the steering box. The other option is using offset upper bushing shafts. Moog makes them.

45

There will be a few dozen other minor issues to deal with that will become evident and easy to over come. But you got passed all the hard stuff. The following are some random pictures that may help you out. Good Luck.

46

I raised the engine a little with these spacers welded to the stock mount support bracket.
47

48

You use headers from a 73 – 87 C10 as well as all the suspension parts and motor mounts.
The front frame horns are longer on the 58 -59 3100 than a 55 -57 by about 2.75”, measured from the center of the front spring hanger mount on the frame to the front frame end. On the 58 -59 it is approximately 9 on the 55-1/2 – 57 it’s approximately 6.25”
The task force frame is 55 ½ thru 57 is 178” and the 58 -59 is 180.5” overall
The front axle locates 150.50” inches from the rear frame end.
Front Axle C/L is approximately 27.50”on a 55 ½ - 57 and 30.50” on the 58 - 59 from the front frame end.
The front axle C/L is 29.50” from the front cab mount.
The radiator mount brackets should be 47.50” from the front cab mount and 30” wide.
The frame and boxing plates should be 0 .150” thick.
The crank shaft C/L should be 3 degrees down toward the back. Or the manifold carburetor mounting surface leveled.
The stock ride height, frame to ground is 25.6” in the rear.
Fender to fender in the front is 74.32” on the outside
Fender to fender on the rear is 76” on the outside
The frame is 34” wide front to back and the front rails slope downward after the front engine cross member.
114” wheel base.
The rear end locates 36.5 inches from the rear frame end with all extensions and brackets removed.
39.25” from the back of the cab to the C/L of the rear axle.
Front dash (firewall) is 98.25” from the C/L of the rear axle
Curb weight stock 3410 lbs.

info@thoroco.com