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Improving the 2004/2004 CTS-V Rear Differentials

Boom Goes The Dynamite: Using parts from BMR Suspension and GForce Engineering to increase the longevity of the notoriously weak ’04/’05 CTS-V rear differentials

Kevin DiOssi Dec 12, 2012

You would be hard pressed to find a single GM guy who doesn’t crack a smile at the thought of owning a CTS-V. Back in 2004, GM was firing on all cylinders in spite of slaying the brands’ two muscle cars, the Camaro and Firebird. This period of time saw the emergence of the new GTO, the best Z06 in the C5 body style, and a total image rebranding for Cadillac. These LS-powered machines were some of the best muscle GM had produced in years, but there’s always room for improvement.

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Top Gear host Jeremy Clarkson once joked that the CTS was designed by a man with only a ruler – a poke at its straight angled surfaces. Well, it’s possible that the team responsible for the drivetrain upgrades were given the same tools of trade. Ask any V owner and they will all tell you that the most notable problem with any CTS-V from 2004 thru 2005 are the rear differentials.

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01. Here is the area of great attention where we find the trailing arm, toe rod, cradle bushings, and axles. All four of these items will be replaced to rectify our wheelhop issues.

In a nutshell, GM slacked off a bit on the V by allowing it to hit the streets with a severely underwhelming rear differential behind the LS6 power. The consequence of this problem was made clear rather quickly when CTS-V owners began to break their diffs shortly after owning the car. The solution? Well, if you ask GM, the solution was to warranty the problem and hope people went away. Not really a solution as many V owners would return to their dealership for second, third, and fourth replacement rear ends.

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Enter BMR Suspension. Why were these cars breaking differentials so easily? If you ask the head of product development, Brett Rockey, he’ll tell you it has a lot to do with wheelhop. “As a CTS-V owner who was always afraid to really push the car, I was excited to try and address the problem with a solution that would, at the very minimum, increase the longevity of the rear differential and help prevent it from grenading.” He set out to address the leading causes of excessive wheelhop and bushing deflection.


03. One of the coolest attributes to suspension upgrades is that most of them are true bolt-in parts. Meaning, you can get this kind of job done very easily in your driveway in a very reasonable day’s work. Kyle Briese kicks things off by swapping out the easiest part – the trailing arms. Held in by two bolts, the trailing arms are easily removed without load on the suspension. The trailing arms are responsible for distributing the load of the rear wheels into the chassis.

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13. The final part to install is the chassis brace from the AWK001, which ties the left and right sides of the cradle together. It’s a nice “icing on the cake” piece, but it isn’t compatible with all aftermarket exhaust systems without modification. On this ’05 V with a Magnaflow system, Kyle had to loosen some pipes and tweak them around a little for a clearance-free fit.

14. While the parts we have added will certainly address many of the leading causes for wheelhop, there is still more that can be done. For that final piece, I give you the GForce Engineering Anti-Wheel Hop axle kit. Constructed out of a proprietary blend of steel that is claimed to have higher torsional twisting strength than traditional 300M. You’ll first notice that they’re both a different size. This actually is done to alter the harmonic differences that cause wheelhop. Next, you’ll notice that it’s just the axle and you’ll need to build them. Before you moan and groan, this comes at no expense to strength, however, it keeps costs low. How does $540 for lifetime warranty axles that reduce wheelhop sound?

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The first part that Brett came up with was the AWK001 ($300), the Anti-Wheel Hop Kit. This bar transforms the floating differential into a fixed mount with machined polyurethane spacers to reinforce the cradle at the trailing arms’ mount. BMR claims this kit alone will reduce wheelhop by as much as 75-percent! Next was the Pinion Support Brace PSB001 ($150). “The differential is mounted to the rear cradle by soft rubber bushings,” he explains. “There are two bushings in the rear and only one in the front, which is responsible for maintaining pinion angle – critical for U-joint life, launch consistency, and overall driveline efficiency.”

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In its own testing, BMR measured as much as 4-degrees of pinion deflection under heavy launching using the OEM bushing. The pinion support brace simply reinforces this crucial area with a low defection polyurethane bushing. As a result, the “spongy” feel is greatly reduced off idle, deflection is virtually eliminated, and the “thunk” heard when the OEM bushing bottoms out is gone. Both parts have a minimal impact on ride quality and road noise. These parts work in conjunction with toe rods (PN TR001, $280), trailing arms (PN TCA018, $230), and the Shock Tower Brace (PN STB008, $340).

It’s hard to argue that the two parts work well, as the difference felt could be called “night and day” by someone who drove them before and after. But, for the sake of this article, we set out to attack another crucial area of wheelhop – harmonics. Not all differential failures are a result of punishing wheelhop, some of it is caused by drivetrain harmonics. The diminutive rear axles on the V aren’t up to the task of transferring all the power to the wheels without contributing to the problem on their own. That’s where GForce Engineering comes in with its anti-wheelhop axles. This affordable solution can support big power, comes with a lifetime warranty, and can be installed fairly easily in an afternoon.

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To demonstrate the installation of these wheelhop solutions, BMR’s CTS-V tech, Kyle Briese, performed the work on his own V in the BMR facility. It took approximately eight hours from beginning to end. Had we known the procedure for the stubborn axle clips going in, we probably could have shaved off another hour of cussing and fussing. Now his daily driver has addressed the weaknesses of an otherwise stellar car. How about yours?

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20. With the axles apart, it’s always a good idea to test fit the clips to make sure you’re working with the right parts before moving forward. Ours checked out, so we began to reverse the process and put them back together using the new parts.

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27. Behold the final product: a two-fold strategy by BMR and GForce to eliminate wheelhop and make the first-gen V capable of withstanding burnouts and donuts until your heart’s content.

Sources

BMR Suspension
Thonotosassa, FL 33592
813-986-9302
http://www.bmrsuspension.com
GForce Engineering
www.shop.gforce1320.com

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