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Discussion Starter · #1 ·
I finally got the c-4 rear end in and braced to support the c notches I cut out to clear the toe in rods. I hope I didn't cause any problems by asking those questions there seemed to be quite a number of responses. By the way are the rear tires toed in or out.

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The pictures on the website of your cars usually shows that the upper a arm has two different thickness of spacers , a thicker one being in the front and a thinner one in the rear, this puts more caster in the suspension. With mine sitting level and two smaller spacers the caster (kingpin inclination) is 6 degrees. Is this enough or should I put the thicker one in the front?

What thickness of rectangulat tubing should I use for the new frame member and it looks like you just weld the cradle to the side rails rather than bolting them together.

How close can you get the upper a arm to the new frame side rail without it hitting with suspension drop or do you have to cut out some of the rail to allow for this?

Thanks for all your help on the rear portion of the build
 

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I can't answer all your questions but I can address your comments.

The deal about the C notches obviously has different answers from different folks. But that's the beauty of the forum - differing views and other knowledge get posted so that you and anyone else considering that can read all that and then you can decide - or ask more questions. So that's a good thing.

The 6 degrees of caster seems appropriate, certainly it's a good place to start - you or your alignment shop can then use smaller shims to get it equal side to side. Or get it wherever you want close to that.

Note that those same spacers are also the starting point for the camber setting.
 

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What thickness of rectangulat tubing should I use for the new frame member and it looks like you just weld the cradle to the side rails rather than bolting them together.

How close can you get the upper a arm to the new frame side rail without it hitting with suspension drop or do you have to cut out some of the rail to allow for this?

Thanks for all your help on the rear portion of the build
Most people have been using 3"x4" x .120".

Certainly, you don't want the uppper A-Arm to hit the top of the rail at full suspension travel. depending on the shock that you use, which will be a factor in limiting suspension travel, you may want to notch it a bit. I set my rail fully into the K-member cradle, so the possible a-arm contact is not as close at the rear edge section of the a-arm. At full shock extension my a-arm just barely touches the frame rail. Your final suspension alignment is going to play into this issue too (caster).

A small V-notch just enough to give clearance if you have contact before full suspension drop.
 

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By the way are the rear tires toed in or out.
The GM spec for the rear toe is 0 +/- 0.1 degrees.

FRONT END
The pictures on the website of your cars usually shows that the upper a arm has two different thickness of spacers , a thicker one being in the front and a thinner one in the rear, this puts more caster in the suspension. With mine sitting level and two smaller spacers the caster (kingpin inclination) is 6 degrees. Is this enough or should I put the thicker one in the front?
What year is your suspension? The 1984-85 C4s used the same thickness spacers front and rear and had a caster spec of 3.0 degrees and 3.8 degrees, respectively. In 1986 they went with the thicker front spacer and the caster spec was 6.0 degrees through 1996. You don't need the thicker spacer, necessarily, just add more shims if you want the 6 degrees of caster.

it looks like you just weld the cradle to the side rails rather than bolting them together.
I weld them on my conversions because I think it's more rigid and looks better cosmetically. The stock C4 corvettes have diagonal braces from the center of the k-member to the frame in front and behind the k-member. If I bolted one in, I'd probably want those braces....since that's the way GM inended it to be. LOL! ;)

How close can you get the upper a arm to the new frame side rail without it hitting with suspension drop or do you have to cut out some of the rail to allow for this?
The late suspensions place the upper a-arm 3/4" higher than the early suspensions, so it's not much of an issue with them. How much clearance you have depends on how you build the rails. The stock C4 corvette has aluminum plates on the bottom of the k-member that act as up-stops for the suspension. I don't know how far the suspension can travel from ride height before those stops come in contact. You can limit travel with the correct shock length too.
 

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Discussion Starter · #6 ·
The suspension I am using is a 1986 year and there were some of the thicker spacers in the small parts box that came with the front and rear suspensions. I didn't get to take the units out of the car.

I cut off the front crossmember today several inches in front of the body mount and leveled the new corvette cradle with four adjusting screw jacks so that it is level front to back and side to side and centered along the center string line and at ride height. This is the most I've used a plumb bob on any of my cars.

It looks like the corvette cradle is a little narrower than the 56 frame so I will have to transition in, toward the center of the car, a little before going up with the rail that attaches to the corvette cradle. I just wasn't sure what material to use for the rails.

I plan on running some plate on the inside of the existing and new rails and plug weld them as well as welding the seams between each section of new rail would I have to fish plate them again on the outside for strength?

Each time I arrive at the shop in the morning and look at the frame I'm stunned at how few crossmembers the original frame has. One of the secrets of independent suspension has been that the frame had to be much stiffer than stock to allow the suspension to work rather than the frame and body to flex, I'm allready planning a center x member and a driveshaft loop in the future.
 

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:pics-1:

I think reinforcement on the inside or outside would be sufficient. I did mine on the outside because I wasn't as concerned about the cosmetic appearance. I welded the seam at the junction of the old and new rails, and then boxed that weld with plate that was plug welded and welded on the edges. Mine should be plenty strong enough. :)
 

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The suspension I am using is a 1986 year and there were some of the thicker spacers in the small parts box that came with the front and rear suspensions. I didn't get to take the units out of the car.
The thicker spacers make it easier to get the 6 degrees of caster. I would use them if you have them.

How about some pics?

I'm just now finishing up conversion #19 to be shipped the first week of December. ;)
 
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