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7084
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Wed June 16, 2010
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Description:
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if you race a C5, especially drag racing, you probably have experienced the C5's problem with powertrain shake during hard launches at the drag strip or when accelerating hard out of turns in lower gears in autocrosses.
Many people misidentify this as "wheel hop" or "axle tramp" and take traditional measures in solving a problem like that such as: tire changes or suspension modifcations. Sometimes, such changes work by mitigating or masking the problem, but the potential for powertrain shake still exists.
Having experienced powertrain shake once in a while from my 2004 Z06 and hating it with a passion, I searched the web and Zip Product's catalog and found a possible solution, the Pfadt Race Engineering C5 Transmission Brace, so I ordered one from Zip.
The installation is reasonably easy. I was even able to do it without loosening and lowering the rear suspension cradle as its instructions suggest, however, there were a couple of problems during the work.
First, the center-to-center distance of the studs on Pfadt's lower mounting bracket are off by about .020-Inch. You either have to elongate the holes in the rear cradle with a rat-tail file or pull the studs through the holes with the bolts. GM's quality control in drilling of these holes is quite precise, so I think Pfadt needs to more accurately locate the centerlines of the studs it installs in that bracket.
Second, the urethane pads which go on either end of the mount are slipped over rather than bonded to bolts which serve as their mounting studs. When you try to tighten the self-locking nuts, the bolt turns inside the pads. To tighten the nuts properly, you need to hold the pads very tightly with a pair of large slip-joint ("water pump" or "Channel-Loc) pliers. Pfadt needs to bond those bolts to the urethane to prevent this problem and make the installation easier.
Once the mount was in place and all the fasteners torqued properly, we took the car out for an aggressive test drive.
Wow! What a difference! Not only did the car launch harder with no powertrain shake, the car seemed more responsive at quick shifts and the powertrain "rubber banding" one sometimes feels after downshifts or on-off throttle transitions was eliminated.
Executive summary: the Pfadt trans mount from Zip, works very well at addressing the C5 powertrain shake problem.
With any modification which stiffens powertrain mounting, you run the risk of increased noise and vibration. The Pfadt trans mount greatly reduces powertrain shake by replacing the stock rear trans mount–designed to allow the powertrain to rotate around its axis in reaction to drive torque with only modest damping–with a different type of mount which greatly limits that rotation. The Pfadt mount consists of an aluminum brace which bolts to the back of the rear axle housing. The brace is tipped with urethane pads which are lightly compressed against the rear suspension cradle. In the center of the brace is a urethane bushing. A bracket bolted to the rear suspension cradle holds the brace with a big bolt going through that bushing. This mount can pivot like the stock unit, but the urethane pads at the ends of the brace greatly limit and aggressively damp that pivoting.
This part makes a significant reduction in powertrain movement which is responsible for an increase in launch performance and quicker gear shifts, however, with the powertrain now "tied" to the rear cradle with urethane pads; noise and vibration gets transmitted to the car's structure. The noise increase is significant between 2200 rpm and 3800 rpm with noticeable vibration peaks at 2700 and 3700 rpm.
if your C5 is a race car, either drag racing or road racing, and you don't already have one of these Pfadt trans mounts; get on Zip's web site and buy one. You will be amazed at the improvement.
If your C5 is both a street car and a track car, but your racing duty is the more important and you don't drive it on the street for long trips, again, the Pfadt Transmission Brace will eliminate powertrain shake problems and, the racer that you are; you'll learn to live with the noise and vibes.
If you don't often race your C5, it's mostly a street car and you drive it on long road trips; I'd consider this modification very carefully. If you install it, you may find the noise and vibration will be quite annoying.
Bottom line: this product works well at its advertised purpose–solving the powertrain shake problem, but it comes with a noise and vibes compromise.
For more information, visit www.zip-corvette.com
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Keywords:
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C5,trans mount,powertrain shake,racing
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Technical Writer for Internet & Print Media
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Registered: January 2001
Location: Southern California