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v1 to v2 rear cradle swap

38215 Views 155 Replies 56 Participants Last post by  AAIIIC
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.
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Seems to me that a complete changeover to an '09 rear cradle assembly is not only very expensive, but also of little interest to CTS-V owners. The CTS-V production numbers are a fraction of Corvette, which in itself is consider quite small. Then, the numbers of those who seriously modify their CTS-Vs is much smaller yet. I suspect that all of them are active members of this forum. All this means is that it is unlikely any vendor is going to spend a lot of R&D money to produce and market this kind of modification.
What does seem more practical and doable is to adopt some of the changes made to the '09 cradle assembly - specifically the half shaft diameter changes. The differences in the '09 half shaft diameters is very important, I think. To really do the job right without a lot of engineering math, one would create two new half shafts using the same material and shaft diameters as the '09s. A less expensive change might be to just change a single half shaft on a V1, but this is more along the line of "Brute Force Engineering." Such a modification would be more reasonably priced, and much more marketable, provided it works.
At the end of the day, I do not think this mod wouild be a complete and total cure to the V1's wheel hop, but no doubt it will help somewhat.
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Rey, That "less expensive change" has been discussed by many here (it's actually the reason I have a spare set of axles). However my concern is less about wheel hop (I can control that 100% with my right foot), and more about longevity of the diff. I know that my biggest concern with this car is what to do when the diff blows, I am out of warranty, and therefore will have to fork out $$$ for a new diff (V1 style). I don't believe a company will come out with a retrofit kit, rather a few of us will come up with the instructions to do it ourselves.
Just like DoubleMint gum, you're both right.

Rey did hit upon one interesting point, and that is it would reasonably inexpensive do one halfshaft on a V1. Which one would be an issue (if it even really mattered), and the question wuld be how much would there be to gain ... a 2% reduction in WH (and associated improvement in the longevity of the diff) or would there be an 80% reduction. If it showed minimal improvement, then we'd know and focus elsewhere. If there was a dramatic improvement, then I'd think the market might be a couple dozen or maybe more (depending on price, of course). The experiment assessing the proposed "fix" would have to be controlled: same vehicle, same tires/pressures, same shocks, same pavement, same temps, same, same, same ... just different halfshaft.
As the prospect of any major mod like this is fast approaching over 20% of the value of the car (like a maggie), the market is shrinking.

I wish mods were tax deductible........:sneaky:
Instead of a whole cradle swap, just do the 09 axles, driveshaft or any one piece for that matter, and diff. If you can shove a Dana 60, 9" ford or 8.8" cobra diff in there than a V2 diff could be made to fit. Add the different size half shafts and you have helped to reduce the wheel hop and have a diff that can take the abuse if it did. Its already been said for a V2 cradle swap fabrication needs to be done so there will never be a bolt in solution. This way you dont need to buy the gas tank, rear cradle, and all that jazz. All you would need is the diff, a couple axles, and a drive shaft and a good fab shop. Everything you would need for the whole cradle swap but this leaves fewer parts to be purchased and maybe a tad bit more fabrication.

Here is another question. If you do swap tanks, will the existing sending unit be compatible with the new tank? Will we have to use the V2 sending unit and will it be compatible with the our car? Is the fuel filler in the same location? Are the straps in the same location? Are the fuel lines the same size? All this stuff would have to be figured out to do the V2 cradle swap. I say just modify the V1 cradle to accept the V2 diff and call it a day.
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Heavy
Actually, I CAN get a tax credit for doing research and development on my V! My company owns it and any money and time I spend developing anything with the possibility of future sales is fair game. I usually use this to try to develop new ways to do things in my molding business, but it would apply here as well.
As I see it, there are a number of different solutions. Number one in my mind is the offset front bushing location. Every time the car accelerates the whole housing will twist. Designing a second mount for the front would probably help a lot. Second, a girdle around the housing to prevent or minimize distortion due to gears pushing the case out of dimension. Both these fixes, designed correctly will probably make the dif live longer even with wheel hop. These are what I plan to work on since they should be minimal cost for max benefit.
So I will see if I can develop anything that actually will work and I can get an SR&ED tax credit while doing it. So a bit of win win!
Just like DoubleMint gum, you're both right.

Rey did hit upon one interesting point, and that is it would reasonably inexpensive do one halfshaft on a V1. Which one would be an issue (if it even really mattered), and the question wuld be how much would there be to gain ... a 2% reduction in WH (and associated improvement in the longevity of the diff) or would there be an 80% reduction. If it showed minimal improvement, then we'd know and focus elsewhere. If there was a dramatic improvement, then I'd think the market might be a couple dozen or maybe more (depending on price, of course). The experiment assessing the proposed "fix" would have to be controlled: same vehicle, same tires/pressures, same shocks, same pavement, same temps, same, same, same ... just different halfshaft.
I agree that changing to 09 "spec" axles would be a step in the right direction, as to which axle to change, it would seem that should be in keeping with which one is the largest diameter on the 09 - specifically, endeavor to maintain the same ratio of differance between diameters as the 09 has. However, this axle would still not address the reported difference in splines between the 09 diff and the 04-07 V hubs, if the changes were "staged" at a different time. As to trying to adapt the 09 dif to the earlier subframe, I think there is a real advantage to using what the engineers have designed for 09(as well as being an OEM part) to mount and assure the diff is properly aligned and secured - that is the foundation on which the whole project should be based (remember, you may want to go 150+mph in this project,so peace of mind is also relatively important:lildevil:) - using as many OEM parts as possible is GOOD, (while also making the conversion relatively reversable, if ever it need be. As has been pointed out before, we are really looking at two problems that happen to be related/interrelated. The axles supposedly address WH, while the diff addresses longevity.That's my two cents worth!:D

That being said, being as how I have had a maggie in the box, along with other goodies, (kinky, no!:D) for almost two years waiting for a diff/launch solution (and my warranty to expire), so as I said, I am ready to move forward to try to solve the problem that keep our V's from being enjoyed the way they should be. Unfortunatley, my fab shop source of 30 yrs, passed away last year, so I would offer my 05 as a mule, and fund the parts (asking Luke to be gentle!!;)) if we can find someone in the group that has fabrication facilities/capabilities they could donate (or at least also be gentle:D), preferable in the Southeast/East.
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The cradle does have its short falls but is not necessarily the whole problem. Its how its mounted to the car that is causing the biggest problems. Granted, I think it would be better to have a V2 cradle in the car and if it was a reasonable solution I would be all for it. I was just looking for a cheaper yet equally effective solution.

@ Albertan,

I suggested the second pinion brace when nutz started building his steel diff and of course it got shot to shit by him because he was trying to sell his idea and of course everybody was on his side. Now look at his all mighty diff. It may not break but nobody can afford it nor are they willing to spend that kind of cash on something that does nothing for the hop. Which may I remind everybody is what I said when he was building it and people yet again shit on what I said like I was trying to be a prick and bash his idea.

I still think that if you can get rid of some of the torsional stress on the case produced by the off set bushing that would do wonders for diff longevity. I still cant figure out why he spent so much building a diff yet never even looked at addressing the wheel hop that causes 99% of diff failures. Hmm I wonder if it was because he was trying to make a buck? Nutz also stated that wheel hop is all in the axles. Which its not. Yeah some of it may be due to equal torsional strength in the axles but 95% of the problem lies in how the cradle is designed and how it was attached to the car.

The cradle is not best design. With the trailing arms being mounted in front of the forward mounting points on the cradle, it really loads up the bushings in the cradle itself. Stiffen the mounting points and you can over come the short falls of the cradle design. This is why the kars kit works. It stiffens the front of the cradle and keeps it from wrapping up. The kars kit mounts to the trailing arm mount and is then attached to the body of the car. If the cradle mounts were in front of the trailing arm mounts, I dont believe we would be having this conversation as wheel hop would not be as prevalent and much more controllable.

This is the hot rod magazine solstice that originally sparked the idea for a pinion support for the V

http://www.hotrod.com/projectbuild/hdrp_0605_pontiac_solstice_project_v8_engine_build/photo_19.html
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It is of little or no use to stroll down memory lane as to what was said or recommended in regards to NUTZ's endeavor (which is to be applauded) IMHO

The elimination of a lot of wheel hop can be achieved by getting rid of every rubber suspension part. Cradle bushings ect...

My "holy Grail" for this week is a cradle that will accommodate a Holden 12 bolt.
Okay my rants over. I promise.
The guy spent a lot of money. Woopdy freakin do! Its not that hard to take a piece of metal, measure all of its dimensions, and make the same thing only out of better material. It just takes a lot of money but no great skill to accomplish. It takes absolutely no engineering to do that. Engineer a fix for the wheel hop and then you have my applaud.
And your contribution to helping with this has been exactly what? :histeric:
My rants over but let me try and explain why our cars hop so bad. It is simple mechanical leverage. With the trailing arm mounts in front of the forward cradle mounts, the forward cradle mounts now become the fulcrum and the trailing arm is the leverage. It acts like a teeter-totter. You push on one end the other end move the opposite direction. When it get to its limit it loads up and springs forward. With the engine putting constant pressure on the trailing arms they push back causing it to oscillate. Once its starts it will only end when one end stops pushing back, ie you loose a lot of traction and the wheel isn't giving the proper resistance to sustain the hop, or you remove the pressure by lifting off the throttle.

Again, this is why the kars kit works. It doesn't completely get rid of the hop because there are simply to many variable like tires, surface of the road, etc. but it does help. The reason it helps is because you have effectively moved the forward cradle mounts father forward removing some of the leverage of the trailing arms. Granted there is a lot of force and the kars support still gives and the mounts are still engineered wrong so you will still see hop under the right circumstances. If you could get the mounts out farther were the trailing arms were pushing in the middle of the cradle instead of one end, the oscillation could not start because there would be no leverage. This is not to say that now the control arms them selves wont start to hop, but this is were good shocks with proper dampening and rebound finally come into affect.
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The cause for wheel hop can be many things as that article stated. My statement was not a general statement to all cars like the article. I was pointing out the main flaw in the design of the CTS-V cradle that causes 99% of the wheel hop and why it is so prone to wheel hop. It can be fixed and without spending thousands upon thousands of dollars. People say the shocks are the problem. People say the drive shaft is the problem. People say the diff mounting is the problem. People say all that is the problem. The main problem is the cradle and the way it mounts to the car. I have yet to see a person acknowledge this and until you do, you will have wheel hop that no shock, no diff, and no drive shaft will fix because none of that is currently the cause of the hop.

Wheel hop is not unique to the V as many if not all IRS cars experience wheel hop at some point in there life. However, the CAUSE for wheel hop in the V is unique because of the way the cradle is designed and mounted. There is no guessing what the problem is. I just laid it out in front of you.
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Because some people here drive the car harder then you do, a "fix" for wheel hop and exploding rear ends is being researched.

Obviously this thread is of no use to you, so you should probably quit posting in it.
Hey, ctsv154, any chance you can put those ideas of yours into a step-wise series of schematic drawings for an old brain like mine? In particular, can you make it such that even I (not having the cradle and the associated links committed to memory) can visualize the wind up of torque before the tires break loose and the torsional force/stress buildup around the various suspension components and their attachment points?

I really like that very concise article of heavy's ... well explained, IMHO. Taking that and applying it visually to the V would greatly assist us aging engineers comprehend things without the need to crawl back under the car. :cool:
Really, you don't need a schematic. If you get a quick look at a picture of the cradle assembly (there should be some floating around here somewhere), you'll see it right away.

The trailing arm's mounts/attachment points to the cradle are actually forward of the cradle's mounts/attachment points to the unibody/frame - you get a whole lotta leverage. It introduces a huge amount of instability to the cradle. Really pretty assinine. Ranks right up there with the single offset front cradle mount.
All this talk of "trailing arms" better refer to the rear two mounts on the differential itself because the trailing arms that go to the shock locations by the wheels see no twisting moment at all. They do see a whole lot of compressive forces when the wheels start to move foreward and the car wants to stand still though. In a solid axle coil spring design the upper and lower trailing arms do have to stop the axle from twisting, but in our cars it is solely the job of the three rubber mounted attachment points on the differential.
The more I look at it the more I wonder. The rest of the rear seems to be really heavy duty and then there is the weak looking aluminum differential, what weren't they thinking.
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