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Twin_Turbo 12-30-2012 10:41 PM

C4 coil over installation
So my buddy bought a coil over set for his C4, turns out it's nothing more than stock bilsteins with sleeves, springs, top hat & adjuster ring.

The instructions for installing these call for drilling new holes to move the front sway bar and rear shocks forward and also hogging out the frame and cutting an access hole to get nuts on the bolts in the newly drilled spots. I didn't like that one bit and did some measuring and testing and finished the rear shocks. Sure enough they fit fine without having to drill any new holes or butchering the frame with a chewed out hole. The shock does have to be repositioned but it does not interfere with the stock mounting bolt locations. There's plenty of room to get those in without having to resort to funky wrenches and what not. The idea I had was to simply fabricate a new upper shock mount plate and instead of moving the holes in the frame, move the holes in the mounting plate. Very easy to fabricate. This is it: (excuse for crappy cell phone camera died)

Anyone with basic tools can fab this

Next is enlarging the hole in the frame. It's going to be a pita to grind about a 1/2" elongation out and a recipro saw never cuts a clean hole. I figured best to use a hole saw but how do I get it to center? I fabbed a small plate resembling the shock mount but I used the same size hole saw as I was planning to use on the frame and cut a hole. Then I bolted the plate to the frame and used that to guide the hole saw. I made a clean cut in minutes.

bolted to frame and hole cut

Forgot to take a pic of the completed hole but I used a flapper fisc on my die grinder to clean up the burrs and the sides of the now peanut or "8" shaped hole so it's a nice elongated hole. Looks clean and factory and if you didn't know better you wouldn't notice it has been massaged. With a stock shock there you will never see it.

Next was reversing the dog bone bolts so the bolt head is on the inside for more clearance. I allso chamfered the side of the bolt for more clearance. The shock was shimmed inboard a little.


Just clears the ABS connector.

Also a little mockup of my new Work wheels, they will go on the blue 91 (imilar car to this supercharged LT1)

Next time I will do the fronts and see if I can relocate the sway bar without having to drill new holes in the front and cut an access hole... surely this can be done without ff-ing the car up.

BBShark 01-20-2013 12:52 PM

How do you access the top nut?

Twin_Turbo 01-20-2013 06:08 PM

Bolt the plate to the shock then install it

Twin_Turbo 01-20-2013 06:14 PM

Forgot to post a pic of the hole in the rear opened up..

Here's the front... no need to hack up the car there and move the sway bar if you replace the end links with some rod ends. The frame needs to be modified a bit, the upper mount has to be bent out a little for things to clear. Not too bad and hardly noticable

69427 01-20-2013 10:58 PM


Originally Posted by Twin_Turbo (Post 107085)

I'm running a similar setup on the '69. The original rubber bottom shock mount has been working fine, but I'm contemplating swapping it out for something different eventually. I've seen replacement "swivel" bearings for other brands of coilovers, but I don't know yet if they will fit Bilsteins.

JeffP1167 01-21-2013 06:55 AM


Was there much noticable ride/handling differences before and after? I am thinking about coil-overs for my 82 but not sure if a aftermarket frame eliminates the need for clearance issues.

Was this car a FE1? I want to run FE7 sway bars.

When you adjust them how do you get them exactly right so ride height is correct? How do you determine LBS per inch spring rates? Is it based on front ant rear weights?

Weight wise how do they compare to the mono-springs?

Oh and you should check the 3 bolts that secure the trailing arm brackets I found all mine were loose.

Twin_Turbo 01-21-2013 10:42 AM

Yes there was, especially at speed. The car used to have a floating sensation at high speed, an oscillating motion that the dampers did not take out. The car is a mix bag of parts, had FX3 shocks not sure what bars are on it.

The spring rates are determined by vehicle weight and by the spring to wheel ratio. Esp. on the front the coil over arrangement is close to the balljoint so close to the wheel rate. On the rear there's a bit of a lever arm.

I did not select these springs, my buddy simply bought the whole shebang as a set that came with instructions on how to destroy your frame LOL I decided we would do it differently. This is not my car. I have a set of narrow body coil over shocks and narrow springs for on the 91, they will go in without hacking anything up.

Ride height is set by measuring settled height w/ a tape measure. Street car, no need to scale it.

klkordzi 02-24-2013 03:05 PM

Coilover stud
Check out Speedway. They sell a chrome lower shock stud that will space the shock out from the dog bone.

Tinkler 06-16-2017 06:17 AM


Originally Posted by klkoerdzi (Post 108363)
Check out Speedway. They sell a chrome lower shock stud that will space the [Only registered and activated users can see links. Click Here To Register...] out from the dog bone.

So the plate goes on first then the nut right?

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