The final word on retrofitting the '09 differential

[Cadillac Tony]

There have been a lot of questions regrading the potential for retrofitting the improved 2009 CTS-V rear setup into our cars. I've spent the last few weeks researching the issue with a lot of help from some folks at GM (who shall remain nameless unless they say otherwise), and here's the final word- the following will be easier to understand if you have a working knowledge of the terminology of what's under your car:

Yes, it's possible.

No, it's not easy.

The biggest question (or so I thought) was whether the rear subframe cradle that everything attaches to would fit. It turns out that it will bolt right up, as the GMX322 chassis has the same cradle attachment points as our 320 chassis. This new cradle has all the correct provisions for holding the new rear diff in place, as it attaches to the cradle in a completely different way than our current one.

It turns out though, that this is the easy part. According the chassis engineers, our fuel tank will cause interference with the cradle, so we'd need to swap fuel tanks. Then the upper spring seats will not be in the correct location on our chassis, which means they would have to be moved. The unequal axle shafts from the 09 use a different spline configuration than our current ones, which means they won't mount to our 6 lug wheel hubs, so the hubs and rotors would also need to be changed to '09 pieces (as well as the wheels). There's also a new driveshaft in the 09 (Dana vs. GKN), so a new driveshaft is necesssary also.

So, to recap, it looks like you'd need the following:

-Rear cradle
-Fuel tank
-Differential
-Axles
-Hubs/rotors
-Wheels
-Driveshaft
-Modify upper spring seats

I suppose if one had a connection for cheap parts through GM, it could be done for about the same or less than the KARS cradle kit, and other than the spring seats, it would be a "bolt-on" modification (albeit a severe one). This would add not only the stronger rear diff, but cure the wheel hop as well, so I'm sure there's someone out there willing to try it next year when these parts become available to order.

Hopefully that answers the questions we've all had about doing this, and if there's anything I missed please feel free to shoot me a PM.

[LUVMY04V]

Originally Posted by Cadillac Tony

There have been a lot of questions regrading the potential for retrofitting the improved 2009 CTS-V rear setup into our cars. I've spent the last few weeks researching the issue with a lot of help from some folks at GM (who shall remain nameless unless they say otherwise), and here's the final word- the following will be easier to understand if you have a working knowledge of the terminology of what's under your car:

Yes, it's possible.

No, it's not easy.

The biggest question (or so I thought) was whether the rear subframe cradle that everything attaches to would fit. It turns out that it will bolt right up, as the GMX322 chassis has the same cradle attachment points as our 320 chassis. This new cradle has all the correct provisions for holding the new rear diff in place, as it attaches to the cradle in a completely different way than our current one.

It turns out though, that this is the easy part. According the chassis engineers, our fuel tank will cause interference with the cradle, so we'd need to swap fuel tanks. Then the upper spring seats will not be in the correct location on our chassis, which means they would have to be moved. The unequal axle shafts from the 09 use a different spline configuration than our current ones, which means they won't mount to our 6 lug wheel hubs, so the hubs and rotors would also need to be changed to '09 pieces (as well as the wheels). There's also a new driveshaft in the 09 (Dana vs. GKN), so a new driveshaft is necesssary also.

So, to recap, it looks like you'd need the following:

-Rear cradle
-Fuel tank
-Differential
-Axles
-Hubs/rotors
-Wheels
-Driveshaft
-Modify upper spring seats

I suppose if one had a connection for cheap parts through GM, it could be done for about the same or less than the KARS cradle kit, and other than the spring seats, it would be a "bolt-on" modification (albeit a severe one). This would add not only the stronger rear diff, but cure the wheel hop as well, so I'm sure there's someone out there willing to try it next year when these parts become available to order.

Hopefully that answers the questions we've all had about doing this, and if there's anything I missed please feel free to shoot me a PM.

so about 10000 dollars worth of work haha

Im in

[Cadillac Tony]

I'd say closer to half that if you do the wrench work yourself.

[BowenCT]

Wow, well done, Tony. Thanks for the due diligence. Who's gonna be the first?

[rand49er]

Yeah, like Bowen said, good work, Tony!

A couple of ques:

Are the splines out of the tranny the same so the driveshaft change would be just a plug and play?

Seems to me the most difficult thing here is remounting the spring perch, or am I minimizing the gas tank swap, etc.?

At around $5k, this becomes doable. I'd sell both sets of wheels (stockers and the MMs) to help pay for it, and that would open up a whole bunch of cool options for new five luggers. Probably could sell other stuff, too, like my good diff. Hmm-m ... gettin' closer to $4k now and wouldn't have to worry about a couple of post-warranty diff hits to the wallet in the future.

Again, thanks for looking into this Tony!

[LUVMY04V]

Originally Posted by rand49er

Yeah, like Bowen said, good work, Tony!

A couple of ques:

Are the splines out of the tranny the same so the driveshaft change would be just a plug and play?

Seems to me the most difficult thing here is remounting the spring perch, or am I minimizing the gas tank swap, etc.?

At around $5k, this becomes doable. I'd sell both sets of wheels (stockers and the MMs) to help pay for it, and that would open up a whole bunch of cool options for new five luggers. Probably could sell other stuff, too, like my good diff. Hmm-m ... gettin' closer to $4k now and wouldn't have to worry about a couple of post-warranty diff hits to the wallet in the future.

Again, thanks for looking into this Tony!

good point!! and yeah i forgot to say good work too tony

[UnsafeAtAnySpd]

Wow, this sounds really promising. Thanks for REALLY looking into this.

[lawfive]

Nice.

[heavymetals]

KUDOS.

[Cadillac Tony]

Originally Posted by rand49er

Yeah, like Bowen said, good work, Tony!

A couple of ques:

Are the splines out of the tranny the same so the driveshaft change would be just a plug and play?

Seems to me the most difficult thing here is remounting the spring perch, or am I minimizing the gas tank swap, etc.?

You're welcome, everyone- I started researching for my personal car, and wanted to share what I've learned.

Randy, I'll send an email inquiring about the driveshaft splines on the new piece and see if it will bolt up to our T-56. If not, I think a good driveline shop could adapt it (and for that matter, adapt your current driveshaft instead of buying a whole new one).

The gas tank is a cake walk once the rear cradle is out.

[dieselp]

Could the national highway traffic safety administration that is looking in to the diff failures force GM to recall and fit our cars with the new (safer) rear!!! It sounds like it would be a good fix for us and not crazy hard for gm. its better than gm getting sued for some one getting in an accident besause rear diff failure.

[heavymetals]

Don't hold your breath.

Don't expect GM to do anything and you probably won't be disappointed.

Our cars are obsolete.

Get used to it.

[rand49er]

Originally Posted by Cadillac Tony

... Randy, I'll send an email inquiring about the driveshaft splines on the new piece and see if it will bolt up to our T-56. If not, I think a good driveline shop could adapt it (and for that matter, adapt your current driveshaft instead of buying a whole new one).

The gas tank is a cake walk once the rear cradle is out.

Tony, how hard/difficult would it be to alter the spring perch ... I can't recall what that looks like off hand ... are we talkin' a lot of cutting with a torch and then fitting and welding under there? ... UGH!

[lunarx]

Originally Posted by rand49er

Tony, how hard/difficult would it be to alter the spring perch ... I can't recall what that looks like off hand ... are we talkin' a lot of cutting with a torch and then fitting and welding under there? ... UGH!

Does having a Ground Control, (or other) coil-over spring perch make it easier to retrofit?

[heavymetals]

Hey Tony,

Can the 09 shocks be adapted (ie. bolt on?)

Gonna need a computer just to talk to um.

Never mind.....