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Instructions - C5/C6 Vroshlag Shock Mount Install

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  • Instructions - C5/C6 Vroshlag Shock Mount Install


    While not known as a "Corvette shop" (instead we have developed packages to cover about 20 different chassis), we here at Vorshlag do sell an awful lot of coilover dampers for the C5, C6, and C7 Corvettes. There are several reasons why we are uniquely situated to have better coverage options for the Corvette than other shock resellers.

    As we have seen first hand, NOTHING transforms a C5/6/7 Corvette's performance on track or in autocross situations more than ditching the antiquated leaf springs and factory dampers (yes, even "Magneride") and going to proper adjustable monotube coilover dampers with REAL spring rates. Once we had functional ABS on our 2006 Corvette (above) the factory spring rates REALLY showed their limitations - with massive body roll, brake dive, squat in acceleration and heave/warp in transitions. These cars just flop around like a dying fish on stock springs...

    We have the lap time data and race wins to back this up, of course. Much of this really comes down to the LACK of decent aftermarket leaf spring upgrade options with enough spring rate, as well as some "swaybar effect" that these transverse springs have in practice. The small number of leaf spring offerings has even shrunk further in the last few years, and never could have covered the massive breadth of spring rate and length options in 2.25" dia coilover springs - just like "lowering" springs for other cars, they were all just too soft.

    When going to coilover shocks we can also shorten the dampers to work in a better shock stroke range at a lower ride height. Just lowering a C5/C6/C7 on the stock or OEM replacement dampers will remove all of the lowering amount in bump travel - which is BAD. Proper coilovers, designed correctly, can maximize bump travel while allowing for a decently lowered ride height.

    Unlike many shock resellers we work directly with the damper manufacturers' engineers to create unique damper arrangements and appropriate coilover shock lengths, as well as creating and manufacturing our own shock mounts, perches, and even spring rate packages - developed on our own cars or testers we work with. We even sell these items and spring knowledge to other shock dealers we compete with - because we have the data and the solutions.


    Vorshlag makes a unique front upper spherical shock mount for the steel framed C6 and all C5 Corvette models. This post is written to help explain WHY we make these mounts (and our Corvette shock offerings) this way, and then to show HOW to install these correctly.

    Both our front and rear shock mounts for the C5/C6 are unique to the industry, and we do this to allow for a better coilover shock arrangement - with more total stroke and easier access to the shocks' damping adjusters. Let's look at the front upper mounts first.

    The old ways of attaching coilover dampers to the C5/C6 chassis were crude. The factory lower mount is a "T bar" and can easily be converted from an internal rubber bushing to a lower spherical. The "pin" upper has a threaded pin that goes through a hole in this upper shock mounting pocket that attaches tot he frame.

    Like millions of cars going back into the 1930s, a pair of rubber bushings connect the damper to the chassis. One bushing goes above and one sandwiches below this structure to secure the pin. This allows for some pivoting during suspension travel. This is absolutely NOT the best performance mounting for any damper, and when moving the suspension loads to the shock this is extra bad. We need to move away from rubber mounts to metal spherical mounts - which have no "Squish" but do allow bind-free pivoting.

    Back in 2008 we made our first AST coilover setup for a C5 Corvette. We sold AST dampers from 2006-12, and were the exclusive importers from 2006-09. During that time we tried to develop new shock offerings for as many cars as possible. On this first C5 we only changed dampers - not the springs - so we only had a limited number of variables to juggle. We learned a lot of things then - including what not do to.

    We didn't have a good idea for mounting the front upper mount, so we did what everyone else did at the time (and most still do) - we converted the "pin" upper to an "Eye" upper, then I fabricated this "eye to pin" clevis adapter that bolted into the same upper front shock pocket. This removed the rubber bushings and the spherical upper "eye" mount in these shocks fit into the clevis adapter. Downside: we lost TWO INCHES of front shock stroke doing this - amazingly, many still mount dampers this way on a C5.


    To solve this issue we came up with a new form of mounting the upper shock pin onto a C5/C6 back in 2015, on this C5 below. This new upper shock mount layout gained back the full 2" if stroke without the need to stick a clevis adapter and eye upper shock into that hole, nor did we revert back to the rubber shock mounts.

    Instead of doing another clevis adapter or keep the factory rubber "squish bushings" above and below the factory mounting hole, we made a spherical upper shock mount that pushes the pin into the stock mounting pocket - with one catch. To install these unique Vorshlag upper C5/C6 requires some modification to the factory upper shock mount, but we chose this path for a couple of VERY good reasons.

    This mounting modification allows for TWO INCHES OF MORE SHOCK TRAVEL, as it moves the upper spherical bearing ABOVE the top of the factory shock mounting structure. Second, we bias the new larger hole to move the top of the shock INBOARD, which moves the coilover spring AWAY from the upper control arm. This allows us to spec coilover dampers we sell to work with a spring that doesn't interfere with the factory control arm.

    We include a CNC plasma cut "drilling" fixture with every set of C5 front upper shock mounts. The tricky bit to install these upper mounts is drilling an oversized center hole (1.75") AND two smaller mounting holes (5/16") into the front upper shock mounting structure. The steps below show how to do this correctly.

    The first step is removing the factory shock and lowering the upper control arm out of the way so you can work. Then take our drilling fixture and press it into the identically shaped inner pocket on your C5 or steel framed C6. With that held in place, use a paint pen to mark the two mounting holes for the new shock mount. Ignore the upper shock mounting hole for now.

    With the two 5/16" mounting holes marked, use a center punch then drill these two holes with a 5/16" bit. Once you have one hole drilled you can install one of the included M8 bolts and nuts into the drill fixture (see above right) and more perfectly drill the second hole.

    Now bolt the drill fixture in with both bolts and nuts, then drill the new center hole with an 1/8" pilot hole for the hole saw used in the next step.

    The outer diameter of our C5/C6 front upper shock mount needs a 1.75" diameter hole to move above the plane of the stock shock mounting structure - which we need to clearances to this size. You will need a fresh 1-3/4" hole saw, which you will mount to an arbor that uses a 1/8" pilot drill bit.

    Above left you can see the two mounting holes and the new 1/8" pilot hole drilled in the step above left. Use the hole saw and carefully cut through the upper shock mount steel structure. Move anything out of the way on the top side - like the coolant reservoir or anything else.


    The resulting hole is shown above on our C6 - which is now 1-3/4" in diameter - that allows the new Vorshlag upper shock mount's "bearing tower" to pass through. Lastly we like to clean up and shoot the bare steel from the new holes with some black spray paint to prevent rusting. These two pics above are from a steel framed C6.

    Now the two examples we show here - a 2002 C5 and a 2006 C6 - here have slight differences in the install steps. This is because the C5 and C6 Corvettes are not precision made cars. There can be 1/2" difference in front wheel fitment and tire rub from side to side, with the exact same wheel and tire mounted to both sides. This sounds impossible, but this is a known issue in the Corvette world. So don't fret if your 1/8" hole for the hole saw pilot guide ends up into "air" - it very well can end up within the stock shock hole opening (like it did on this C5 above).

    If that is the case, move the Vorshlag drill fixture to the TOP of the factory shock mount structure, bolting it in place with the same two M8 bolts and nuts. Then the drill fixture becomes the pilot hole for the hole saw, and when you cut the hole with the 1-3/4" hole saw it will cut slightly INTO the fixture. Don't worry, it is made from thick steel and you can cut into this many times before this fixture is ruined (we only need to use it twice!). The "slug" that results will show the larger diameter and offset from the factory shock hole (the two pics above are from a C5).


    The rear upper shock mount is relatively easy to install and hasn't changed much since our first C5 install in 2008. Below left is our first C5 rear upper shock mount (prototype) and below right is our production mount in a C6 - the rear mounts can work on all C6 models, even the aluminum framed cars (C6Z & ZR1)

    We order MCS dampers rotated this way (not inverted) to be able to easily access the shock knobs from the rear trunk area. These mount just like the stock rear mounts but again, have a spherical bearing not a rubber mount. You can even re-use the pair of M8 bolts to secure them into the threaded inserts in the chassis.

    Now to access the upper rebound knobs when we configure the dampers this way - the knobs would be hidden inside of a blind cavity. So, to make these knobs accessible we drill holes through the fiberglass floor, as shown above. Don't worry, this is legal in virtually every competition class we know of.

    The first time we cut the holes for the floor I was nervous - but it isn't structural, just a cosmetic weather barrier. We originally put a 14" long 1/8" drill it up through the shock mount hole from underneath, drilled into the trunk floor, then hole sawed it from above.

    We have realized since that again - this alignment isn't super critical. All we are doing here is allowing access to the top knob, and the shock mount itself seals the opening to the ground. These pictures are of both C5 and C6 cars, which have slightly different rear floor fiberglass floors. The remote reservoir pass-thrus are a whole other matter.

    Pro Tip: If you plan on ordering your dampers this way (knob on top) and elect to cut this access hole for the top knob, just know that this adds some road noise inside the car. If you ever plan to street drive the car, reinstall the factory carpet for the trunk. To access the knob just cut an "L" shaped slit above each knob. Then you can just peel this flap out of the way to make shock adjustments.

    That's all we have to show here. If you are buying these shock mounts from us and have additional questions, call or email us and we can chat. Thanks for reading!
    Last edited by Fair!; 01-13-2023, 04:58 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev