Posted 13 December 2012 - 10:36 PM
Terrific news tonight.
With every bolt torqued to its maximum and countless re-torquing to ensure proper installation, further diagnosis with a set of chassis ears confirmed the BMR/Shelby Adjustable UCA to indeed be the culprit responsible for the clunking, something we already knew after reinstalling the OE assembly eliminated the clunk entirely.
Proving again why he’s worth his weight in gold, my tech wasn’t satisfied with punting on what should have been a perfectly functional upgrade, especially given the tubular UCA’s extra robustness and ability to support a more aggressive pinion angle. In addition to other suspension attachment points he was able to eliminate, he mic’d both ends of the UCA and was able to identify two discrete and distinct clunks, one at the bolt that attaches the UCA to its mount and the other at the bolt that connects the opposite end of the UCA to the differential.
He proceeded to dissect the component and began measuring tolerances. He discovered a .016 diameter gap between the upper bolt and the metal bushing collar through which the bolt passes. A similar .010 gap also existed at the other end. He proceeded to have machined a pair of appropriately-sized cylindrical shims that he press fit into the bushing collar and around the bolt at the opposite end to take up the slack.
The rear end is now as clunk-free with the complete suite of tubular and billet rear suspension components, including the WhiteLine Watt’s linkage, as it came from the factory. Absolutely no metal-on-metal impact exists despite being set to support a negative 1.5 degrees of pinion angle. Even with the supercharger loving the huge chunks of cold late-autumn air and conditions being cold for even the UHP A/S tires currently on the car, the rear is rock stable with phenomenal forward bite and finally functioning EXACTLY as I hoped.
The only other additional modification made was removing the Shelby Adjustable Sway Bar link ends. The 5490-B Sway Bar includes selectable attachments points of its own, making the adjustable ends superfluous while also introducing a metal-on-metal rattle that can't otherwise be dialed-out by virtue of their design and construction.
Lastly, I had Dynamat added to the rear seating and forward portion of the trunk compartment to compensate for the inherently less NVH dampening the rear-seat delete yields. I had the chassis double-layered directly opposite suspension attachment points to further dampen out any additional resonance the firmer parts and their lesser amounts of deflection transmit.
Even without adding an additional layer of Dynaliner on-top, the cabin is now much more quiet today than with the OE components that bend and flex and whose relatively soft bushings go a long way toward dampening NVH on their own. I now have the best of all worlds, with suspension that’s razor sharp but not at-all uncomfortable for everyday street driving with a cabin that’s quiet enough to converse at normal conversational levels without deadening the car's exhaust note or the enhanced supercharger whine by virtue of the resonator delete added to gain sufficient clearance for the front strut tower brace.
The final step of the suspension upgrade will be to incorporate the Shelby rear strut tower brace in the trunk once I’ve swapped-put the OE Shaker Sub for the Shelby Kicker unit whose form factor allows the brace to pass cleanly beneath and behind it.
I remain frustrated that Shelby wasn’t able to guide me toward shimming the UCA rather than trying to refute the clunk the item description clearly references and attributes to needing an upgraded mount in conjunction. Ultimately, the tolerance between the supplied bolts and collar were so wide that it simply wasn’t well-fitted and incorporated enough slop into the configuration to not only introduce the undesirable clunk, but potentially become a point of failure after repeated metal-on-metal impact.
Presuming all such components don't have similar gaps or customers are able to correct and compensate for them, I'm very satisfied with my choices. I’m now absolutely thrilled with the car after achieving precisely what I had hoped in terms of improving its handling, rear-end stability and lowering its CoG without needing to endure any downside in the form of introducing any negative NVH characteristics. Fortunately for me, I’m lucky enough to have a tech whose fastidiousness and desire to have the car perform as it should exceeds even my own.
I'd heartily recommend this particular upgrade path for anybody who's seeking to achieve a similar goals.
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