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Discussion Starter · #1 ·
I have the frame welded to the frame table and the c-4 rear end and suspension sitting in place but am wondering about the pinion angle. At the monemt I have the third member set up level from side to side and front to back and then started to think about pinion angle. The output of the transmission and the input of the third menber are the same didtance from the ground and centered in the frame but do the u joints wear out faster if there is no pinion angle. Also for a 2 dr post 56 do I want to set it up with the half shafts level or sligntly angled down , I'm going to try the stock corvetter spring first before I go to coil overs if necessary.
 

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The pinion should be parallel to the transmission output shaft. So if the engine is down 4 degrees in back, the pinion should be up 4 degrees in front.

The halfshafts should be level at ride height, but don't have to be perfectly level to work correctly. There is a forward offset to the halfshafts to ensure the u-joints rotate as the halfshafts turn. In other words, the inboard u-joint is forward of the outboard one by about 3/4".
 

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I set up my C4 rear suspensions so the toe adjuster is level at ride height. That way any bump steer will be minimized in the travel of the suspension.

Andy
 

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Discussion Starter · #5 ·
I have the rear end mounted and the pinion angle taken care of but now it looks like the toe in adjustment bars are going to hit the lower part of the frame on any bump over 2 inches. Is the best thing to do, cut out a half circle section and fill it in with tubing and then add some plate to the outside of the frame rail or is there an easier solition like replacing the rod end with a heim joint?
 

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We have helper parts! check out our "rear steer assembly" about 2/3 down the page.

http://www.newmancarcreations.com/products/

it relocates the center pivot point down and has all the bushings so that you can install the tie rod on the bottom side of the knuckle mount taking care of your issue.
 

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That Newman toe adjuster is a nice piece. A couple of my customers bought them and had them sent here for me to install. They lower the center and ends of the toe rods. Here's a pic of one installed and some more attached.



I'm pretty sure you can also buy them from The Street Shop, but you'd have to call Tray Walden and ask him. He builds some nice stuff.

http://www.streetshopinc.com




I have also built them myself from threaded rods and heims, and a center spacer to use under the heim ends. It's pretty easy to do, except for dealing with the taper in the knuckle. I bought some tapered bushings that a machine shop made from Stainless steel that look a lot like the Newman parts. They cost me $20 each. There are probably other ways to eliminate the taper. See pics attached.

I wouldn't recommend c-notching the frame...it's already pretty weak back there and could cause the rear of the body to move a lot more.
 

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I bought some tapered bushings that a machine shop made from Stainless steel that look a lot like the Newman parts. They cost me $20 each. There are probably other ways to eliminate the taper. QUOTE]

From Speedway Motors.

 

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Nick, unfortunately, those are upside-down. The taper is larger on top, and you need to put the heim below it. So if the short threaded end was a lot longer, and the taper was correct, that would work perfectly.
 

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Those Speedway parts would work if you recut the taper from the bottom side with a tapered drill made for that purpose. Unfortunatley though, they are too small in diameter as well.

I have used the technique of "C" notching the frame above the toe adjusters with no problems as long as you don't get carried away. About 1" of clearance is all you will gain though. There is no suspension load rear of the batwing mounts so you will not weaken the frame in a critical area. Another approach is to cut the taper from the bottom of the rear hub with the correct tool, and install the stock ends from the bottom side. You will then have to fabricate a plate to move the center piviot down exactly the same amount. If you don't move the center mount you will get toe out on the outside tire on turns and that is not good (roll oversteer).

Using heim joints on the street should be avoided if possible due to bearing contamination and subsequent wear issues.

Andy
 

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Discussion Starter · #11 ·
I ended up cutting a "c" from the frame rail bottom and filled it in with some heavy wall tubing. I then added a 1/4 inch plate on the outside of the frame rail to give it more strength. The only stress on the rear portion of the frame should be coming from the anti sway bar, the question is will this stress be less or the same as the stress put on the rear frame rail by the original suspension and the spring hanger. The body should also be considered a frame (strength) member and there is a little stress from the rear bumper bouncing up and down. My goal in doing it this way was to keep the toe in rods a level as possible as they are in a different arc than the half shafts.

Another queation though is do you really need the torgue bar or can you attach the pinion support to a crossmember just above the pinion support holes, the same crossmember that the shocks will attach to? And the lower shock post is at the wrong angle can you just heat it up and bend it or do you have to make a different kind of mount?
 

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You can indeed mount the pinion as you have described and it will work well. I have built mounts that utilized urethane bushings for the pinion. I have even done some mounts with a urethane bushed rod end so the pinion angle can be adjusted.

I haven't had the need to bend the shock mounts to get them in the right postition, you should be able to make them work in the stock configuration. I typically install the shocks on custom mounts welded to a horizontal gusset plate in the corner between the new crosmember for the pinion support and the inside edge of the frame rail.

Your frame should be fine the way you describe it... The stress will be different than when the original suspension was installed. There will be less leverage on the rail at the notch point with the anti-roll bar bolted up close to the rear axle (and your notch) as opposed to the stress from the leaf spring pushing up from way back toward the end of the frame rail.

Andy
 

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I have used the technique of "C" notching the frame above the toe adjusters with no problems as long as you don't get carried away. About 1" of clearance is all you will gain though. There is no suspension load rear of the batwing mounts so you will not weaken the frame in a critical area. Andy
I have to disagree here.

There is BODY load rear of the batwing.

With the stock leaf springs the weight of the rear of the car is carried on each end of the spring, so the load is distributed at 4 points. The rear of the leaf springs push up on the frame near the bumper, at the shackles. This helps to keep the frame supported to carry the load of the rear of the body. There is no body mount from the front of the frame hump to the rear crossmember, which is about 4 feet.

When you install the C4 rear you have concentrated the entire load near the top of the frame hump, either at the batwing ends if you're using the stock C4 spring, or at the coilover upper mounts if you use coilover shocks.

So now you have the frame unsupported from the batwing back to the bumper. And I assure you that the frame WILL flex. Cutting a c-notch only makes that flexing worse. And the body will flex with the frame. That's why I recommend the use of a dropped toe adjuster.

As for eliminating or reversing the taper, it's not easy to do by drilling or reaming. The large end of the taper (top of knuckle) is about 7/8" in diameter, and the small end about 1/2". You would have to weld up the hole and re-taper it, or install some sort of a sleeve. That sleeve can be a tapered sleeve like I, Newman, and Street Shop use, or one could bore out the hole to 7/8" all the way through and install a cylindrical sleeve. Then you could use a heim with a regular bolt.
 

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Another queation though is do you really need the torgue bar or can you attach the pinion support to a crossmember just above the pinion support holes, the same crossmember that the shocks will attach to? And the lower shock post is at the wrong angle can you just heat it up and bend it or do you have to make a different kind of mount?
Take a look at the pics I posted. On my conversions I use a pinion support with urethane bushings. The Dana 44 and Dana 36 holes are in a different location, so if you ever change your rearend you will have to deal with that.

On my own car I built a torque arm, partly for cosmetic reasons. I like the looks of the arm myself, but it's a lot of work to build. The C4 arm won't work without a lot of modification.

Here's a couple pics of my torque arm...



 

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I am with Chevynut, the relocation of the tow is the proper thing to do rather than cope the frame. You will have frame flex and it will be noticeable.

We have very nice cast aluminum torque arms and cross members for sale that do exactly what you are looking for. The cross members are drilled and tapped for the torque arm mount to bolt on and we supply the tabs to weld to the frame so that the cross members bolt in and out. I would not bolt the front of the diff to a cross member that is positioned directly above the front of the diff. If you are planning on having any HP you will have problems with wheel hop and could possibly break the diff housing. The best way is to spread out the pick up points as far as possible. This gives you a "lever arm" that handles the forces much better. You have to remember that all the forces working at the wheels to drive the car forward, are also working on the diff trying to wrap it in the opposite direction. when you attach the front of the diff to a cross member that is right on top of the pinon your lever arm is about a foot long. That tube will flex and bend! Spread that lever arm out and you will have a much better chance of keeping the diff stationary.
GM used a torque arm that connected to the trans, making it as long as possible. They spent lots of money making that suspension system work to the best of its ability. I would recommend following their lead.

some pictures of our Torque arm and cross members.





 

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Kyle what is the cost of the torque arm?
 

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I would not bolt the front of the diff to a cross member that is positioned directly above the front of the diff. If you are planning on having any HP you will have problems with wheel hop and could possibly break the diff housing.
Kyle, most everyone besides you guys use a pinion support above the differential on a C4 rearend installation. The C3 vettes used a similar setup, but they had a bracket connected to the nose of the differential. None of my customers that have cars that are driving have ever had any wheelhop problems or any other problems. I have asked them specifically about this. Have you heard of anyone having problems with this setup, or is it just an unproven concern? There isn't much, if any, movement in a urethane bushing with a 3/4" steel sleeve. Also, my crossmembers are 3/16" wall 2x2 steel. They aren't going anywhere. ;)

Sure, a toque arm carries the load further forward, and reduces the load, but it adds cost and takes up space. You also MUST have a crossmember of some kind to connect it to which also adds cost.

You guys have some nice pieces, but I don't like the cast crossmembers for a couple of reasons. You can't get very good exhaust clearance with them, and the exhaust WILL hang down below the frame. They also do little or nothing to stiffen up the frame. The AME-type crossmember allows for full exhaust clearance and does a great job of stiffening the frame torsionally.

Can you tell me what your pinion angle is set at for that torque arm?
 

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Yes we have heard of people experiencing wheel hop!
It is apparent that any suspension upgrade to these cars helps them. We have shot for the highest level of driving performance that we could. We feel that we have proven our chassis and it is good that there are options out there.

Sawdawg, here is an option for you to consider, if you have any questions on any of our products please don't hesitate to contact us.
 
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