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July 31, 2019

Front Suspension

[Click the pics for a better view]

The front suspension on the GT6 is a pretty typical double wishbone arrangement.  Specifically, it is an SLA (Short-Long Arm) type, where the upper wishbone is shorter than the lower one.  SLA suspensions allow good control of tire contact patch by varying camber angle during cornering.

So this task is to basically to make some sense of this:




The suspension components mount to a pair of subframes, or "turrets" which are bolted to the frame.  The subframes are fairly complex weldments.




Some kind of blasting is about the only DIY way to get at all of the rust.




Then a couple of coats of a good 2-part epoxy primer.




The mounting hardware for the turrets includes these threaded bars that slip into channels in the frame.  I like to re-use original hardware where practical.  It's not just being cheap--most of the original British bolts had distinctive head patterns, and keeping them is a nice touch that some people appreciate.  Much of the zinc or cad plating on the hardware--if it had any in the first place--is pretty much long gone 50 years later, so I typically replate with zinc.




Ready to go back on the frame.  The yellow color on the hardware is a chromate coating that helps the zinc last longer.




Next up was the lower wishbones.  As soon as I forced, pried, or cut them away from all of their attachments, I remembered vividly why the car was put in storage over 30 years ago.  I don't know if this is common for GT6/Spitfire cars, but both A arms had similar damage to the holes that mate to the trunnion.  In fact, I suddenly remembered exactly the place where the trunnion let go and the front wheel went wonky.




This also explains the used, but serviceable lower wishbone I found in the boot as I was preparing to remove the body.  I must have bought it at a bone yard decades ago, planning a repair that never happened.

So my plan became to try to fix the better of the two bad arms.  I hammered a few areas back into place, then welded up the holes on either side.




Then faced the surfaces off smooth...




...and redrilled the holes.




I was pretty happy with how the arm came out, and was fine with using it, paired with the good used arm.  I must have had a surplus of bad karma that day, though.  When I compared the two arms, it slowly dawned on me that they were both for the left side of the car.




After the facepalm, I slipped into damage control mode.  The arms are identical, I reasoned, except for the sway bar bracket.  It looked like I could save the day if I could just move one of the brackets to the other side of the arm.  So that's what I did.  I painted the backside of the bracket and the inside of the arm whare it would be hard to reach after the bracket was in place.




The lower arms attach to these brackets, which in turn attach to the frame.




One of the reasons that cars are often so disagreeable to dismantle is the rusted fasteners.  Some fasteners rust sooner than they might because they have no protective plating.  As far as I can tell, these brackets were not plated.  So as a service to the next restorer, I selectively plated the threaded studs.  The rest of the bracket was powder coated, but powder coat doesn't work well on threads.

 


Lower arms ready for install.  I'm using polyurethane bushes throughout the suspension, but I'm avoiding the heavily-marketed, neon-colored, high-priced ones because I don't like paying for hype.  Poly bushes work fundamentally differently from the stock rubber bushes.  They require lubrication.  I use a tenaciously sticky silicone grease sold specifically for poly bushes.




The upper arms didn't prove to be as interesting as the lower ones.  They powder coated nicely.




Then for the spring/shock assemblies.  I bought this spring compresser, but it turned out to really be for much bigger springs, so I had to modify it pretty heavily to get it to work.




On the TR6, I opted for fairly expensive adjustable Koni front shocks. As suggested by quite a few on-line posters, I initially set them for the softest setting, which I imagine to be more or less equivalent to the damping from a stock type shock.  Well, after driving a couple of hundred miles in the TR, I don't have much inclination to change the shock settings.  So now I'm thinking that the whole Koni thing might have just been me caving to marketing or peer pressure.  As a backlash measure, for this project I bought stock replacement shocks for a fraction of the price of "premium" shocks.  

The springs measured right on spec for free length, so I didn't see any reason to replace them.  I shot them with a nice epoxy.




Using the spring compresser is a bit of a sweaty-palm operation, at least for me.  The spring has to be compressed at least 2-1/2 inches to capture the shock, and at a spring rate of a couple of hundred pounds per inch, there is some pretty good energy stored there.  

That aluminum disc was a mystery for a while.  It goes on top of the spring assembIy, but I found only one of them.  I discovered on one of the forums that since on a GT6, the fuel tank is on the left side of the car, this shim was only installed on the left side of LHD GT6 cars to offset the asymmetrical weight of the fuel and the driver.
 



Next job was to extract a vertical link from this crusty mess.




On inspection I sadly found some significant corrosion damage to the trunnion threads on one of the links.




So I reluctantly ordered a vertical link.  On the right is the bad link, on the left is the good original link, in the middle is the new link.




Since the stub axle on the bad vertical link appeared to be fine, I had planned to remove it and use it in the new link.  The axle had other plans.  The nut galled on the axle and brought most of the axle's threads with it.




So I reluctantly ordered a stub axle.




Powder coated the links, cleaned up the trunnions, which were both a good fit.




The bush assembly for the trunnion looks complicated, but it can really only go together one way.




This job be done.




The GT6 front suspension is really pretty similar to the that of the TR6, so this job went fairly quickly.  I think I have around $350 in this part of the project, and the majority of that was for the vertical link and stub axle.

Now, on to hubs and brakes.

Comments to Ed at elhollin1@yshoo.com

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