Monday, August 27, 2012

4-Link Coilover Suspension Completed!

As if on cue, the trees are just starting to show the slightest hint of fall and accordingly, I have been able to complete the modifications and corrections to the 4-link rear suspension.  The summer has indeed been a busy one on many fronts and this major project has consumed the bulk of the time spent at work on the Boss over the last several months.  Of course, I had not planned on such a major rework of what was supposed to be a good suspension option, but such is the reality of it and here we are.

The condensed version of modifications and corrections includes replacing every single pivot point with spherical rod ends to eliminate MASSIVE roll bind problems in the kit design as well as free up the entire rear suspension throughout the full range of motion.  Secondly, the rear coilover dampers were less than impressive and as such, were replaced with very nice custom Bilstein coilover dampers made just for this application.  And finally, I selected a proper coil spring that would match the proven front coilover combination more exactly.  Sprinkled in there too was a hardware upgrade along with a few minor touches I have documented earlier in this blog.
For this final round of work, I had to reconfigure the upper coilover mount to reduce the mounting bolt size to the requisite ½” the new Bilstein coilovers employed.  This was a rather simple welding and re-drilling operation but of course, I discovered it also would include a pretty major correction of the hole location on the right side as it was a full 1/8” higher than on the left.  Apparently I’m not supposed to bitch about “close enough” so I just welded the S.O.B. up and put the damn things where they belonged within a few thou and decided I was comfortable being “anal-retentive” or something along those lines…….

Next up, I had to cut off all of the gooey rubber bushed ends of the trailing links and thread them with left-handed threads to allow the length of each arm to be fully adjustable without the need to remove the whole arm to adjust.  Loosen a jam nut on each end and turn to adjust the arm then lock down the nuts.  It couldn’t be simpler.
Then came the tedious task of machining spacers to capture each spherical rod end in the center of their respective mounts.  28 of them to be exact (whew!).  While I was there, I made provisions to add seals to each rod end to keep dirt, water and any other evil crap out of them under operating conditions.  These are nifty little devices I used extensively in my former racing life and are made by Seals-It.  I highly recommend them on any application that requires a spherical rod end.  The price is right and they can extend the life of the rod end many times over.

Two of the “spacers” are actually stand-offs for the lower coilover mount.  Since these needed to be longer to accommodate the new lower coilover mount, I decided to spin these up out of stainless for a nice appearance and corrosion resistance.  I am truly delighted with how these worked out.  I finished the lower coilover mounting configuration with a safety washer at the rear to prevent the lower shock eye from pulling off the mount if the spherical bearing were to ever catastrophically fail.  Another old racing rule of thumb that has stuck with me over the years.
And at last, I was finally able to assemble the entire system and work out a few setup details and take some measurements to see where we landed.  I am happy to say the suspension articulates extremely well, the roll bind has been eliminated and the total radial deflection of the rear axle over the full suspension travel as defined by the panhard rod swing arc is a miniscule 0.052”.  Not a bad result and way more desirable for me than the complexity of a Watts-link.

The one area I chose to leave alone is the chassis and axle mount locations for the trailing links.  This leaves the anti-squat geometry a bit of an unknown variable until I get the car sitting on the suspension at proper ride height and full load, but that will be a problem for another day.  Chances are it won’t be enough of an issue to make me want to do much to change it anyway since this is a street car as opposed to a dedicated track car.  Time will tell.
So now I am off to sand blast the housing a prep it for paint and assembly.  Once that is done, I will be heading back to the body for some work in the axle tunnel and trunk area and then back to the front for some major work on front suspension, steering and engine bay upgrades.  And oh yes……..that surprise I have been hinting at is getting very close to show time!
Upper rear coilover mounting points required welding and re-drilling to 1/2" from 5/8".  Turns out, I needed to correct the location of the right side mount hole while I was at it anyway.
I spent several days machining the proper spacers that would properly locate each spherical rod end in the middle of their mounts.  At the same time, I made room to install Seals-It seals on each side of the monoball to keep the crap out of them for longer life and smooth operation.
While not just a simple spacer, the lower coilover standoffs were machined from stainless as a single piece.  Looks pretty nice and works very well.

I upgraded all of the fasteners in the entire system while I was at it.  You can also see the Seals-It sealing washers more clearly in this shot as well.

The top coilover mounts got sealing washers too. 

Here is a simple yet very valuable safety trick.  I installed captive washers at the rear of the lower shock mounts to help ensure the shock would be retained in the event of a catastrophic failure of the monoball.

Looking at the left rear from the back shows how simple things look from the rear.  The springs will ultimately get powder coated black so as to tone them down a bit.

A view of the right side coilover setup from the rear.  Most of this will be hidden by the fuel tank.

Left side view of the completed 4-link coilover suspension.

Right side view of the completed system.


  1. Hey Sven, "Anal-retentive" is a good thing in my book. Once again, you have "wow'ed" me with your fabrication and technical expertise, not to mention safety with that capture washer. Great idea. I'll be looking forward to the surprise yet to come.

  2. Once again, your quality of workmanship and attention to detail have left me in awe. Nice work.