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14K views 111 replies 16 participants last post by  The Tony Show 
#1 ·
So, at what point do you think AWD will be a MUST in order to harness the power from the engine? And do you think AWD would be a good thing, or a bad thing on a "V" car?
 
#101 ·
Rich,
So you're saying that if there's more parts, there's a more chances for failure? Okay, that's a possibility I guess, but what about the idea that your differentials failed simply because there's too much power for them? In that case, adding AWD to the mix will reduce the load on the rear diff. And I'm not totally following your logic on how a cast iron housing is going to make the rear "bullet-proof". Were there actual housing failures on the Gen. 1 cars? Were there failures that are directly resulting from some structural problem with the old housing? And finally, forgive my ignorance on this one, what was the Gen. 1 housing made of? Not busting you here, I'm being serious. I guess I always assumed the housing was cast iron. Guess not. Was it aluminum?
 
#102 ·
First gen CTS-V differentials were sand cast aluminum. Most of the replacements were due to whining/binding on turns, but there were a few cracked or shattered cases from wheelhop or sudden hooks.

The biggest problem (as I see it) was the soft bushings used to mount the differential, combined with the design of the attachment points securing it to the rear subframe. They were all on the same plane (all the mounting bolts ran front to back), and there was enough pinion deflection under hard throttle that you ended up with excessive internal wear if driven hard, and a broken case if driven real hard. In theory, an aluminum case would be plenty durable in this application as long as the pinion angle issues were addressed, but I give the engineers credit for over-engineering this one in an attempt to be certain that it holds up to the power.

The new CTS-V not only uses a cast iron housing, but the diff is secured on two planes (both front to back AND top to bottom), which will correct the pinion angle changes under load. I don't know for certain yet, but I would assume that they're using a higher durometer bushing as well after tracking how many tore or compressed in the first gen.

Lessons learned from the 04-07 are going to make this car pretty awesome.
 
#103 ·
As was aptly described, the Gen 1 differential housings were cast aluminum. The point I was attempting to make is that the new differential housing will be made of a much denser and heavier material (cast iron has a specific gravity of about 2.5 times that of aluminum) which of course adds more mass. Whether that's a significant weight addition overall is less important than the fact that the original needed to be beefed up structurally as well as the need for some design changes to internal bearing and/or gear components.

I suppose that if you could assure yourself that the power was always equally distributed between the front and rear drive train components you could take credit for this and reduce the design loadings for each. However, that still doesn't negate the fact that you have a lot more moving parts. My experience is that the drive trains on 4WD vehicles - be they trucks or SUVs - have a tendency to develop problems before anything else. So why compound the problem with the V since this has been its Achilles heel in the past?
 
#104 ·
If one were to design an AWD V with mass production and logic (ha!) in mind, it would use the same rear axle assembly as a RWD V.

Take a 450 rwhp '09 V, now dump the power 60/40 through AWD and it's 270 hp sent to the rear and 180 hp sent to the front. With AWD, wheelhop and its nasty shock loading will be a non-issue. The rear differential should live forever. A nice built in weak link like a driveshaft or clutch would be a good thing.

The key is to ensure the transfer case and new front axle parts are worthy of the power. 180 hp in the front differential doesn't require a Dana 44. It would suprise me not that the CTS4 front setup is over designed to handle the V application. Plug and play one blown 6.2L engine and go.

Owned countless 4x4s and AWD vehicles over the years, some new, some with 200k+ miles on them - zero problems with the drive system.

For the next gen V, AWD, 2-door, hand brake and a bunch of other things are on my four year old wish list in the V forum. I'll live with the pop-tart nav system if we get a handbrake!

P.S. Move the V emblem to the fender where it belongs! The door? Are you kidding me? Kick that person off the V team and put them on something like the next gen Aveo. Cars no one cares about - sort of like Toyotas. :D
 
#105 ·
I think we've managed to cover a decent variety of concerns here but let pose one more. I guess a "food for thought" statement more than anything.
It's been my experience that over the years, quite often, people (usually people with more money than brains) produce a car that simply has more power than can be adequately used. Most of the time, these are tuner cars, or special-interest customs but, sometimes, they are actually production cars. The ability to actually utilize the engines power (put the power to the pavement as it were) has often been the ultimate determining factor of what would be considered the maximum power for a given vehicle. Go beyond that point and you have wasted power and/or a dangerous vehicle. But technology has provided an answer that at least to a point, allows the maximum power of a given vehicle to be greatly increased. It's called AWD folks.
Now GM certainly has enormous experience with 4WD (light, medium and even heavy-duty trucks) and to a lesser degree, AWD (mostly brought on by the SUV craze) but, they do not have a whole lot of experience with AWD in cars. And folks those are two totally different beasts IMO. So the question is, can GM produce an AWD drivetrain that will be effective in a performance car?
 
#110 ·
All that's required for an AWD drive train is available off the shelf from Borg-Warner, Getrag, and other suppliers just like everybody else uses. There's no need to reinvent the wheel. Current STS transfer cases are Borg-Warner. The diffs are Getrag. A quick check of their websites shows that some pretty skookum stuff is available.
 
#107 ·
Product Development (R&D is some circles) is a wonderful, but time consuming, endeavor. Anything can be accomplished given the time and effort. The question is whether it's worth it. We all know that the V has been tested time and again on the Nurburgring and other courses. When the last gen 1 car had been through countless tests and GM thought it was ready for production there was still a lot of work to be done. We have yet to see whether the changes they made on gen 2 have addressed the major problems and whether we have raised the benchmark for all other manufacturers. If an AWD is in the making, GM will need to spend a lot of time and money developing it on this car. Even if it's their decision to go forward with it I wouldn't count on it until gen 3 at the earliest.
 
#108 ·
Thanks, guys for the welcome (Rich) and the explanation of the 1G V's rear diff, I am taking a crash course on the 1G V's issues from this board and so far I'm impressed with the technical knowledge of folks here, and hoping for the best with the new V. I guess I didn't appreciate the issues with that diff and the reason it might be difficult to make an AWD V for this gen. I'm sure it can be done, though. If it can be done, it might be a worthwhile upgrade.
 
#112 ·
Anybody with common sense can figure out what happened with the 1st gen V's rear diff - bean counters. Getrag's specs on their web site clearly show the diff as rated to handle 260 ft/lbs of torque, which was fine for the base CTS (too close for comfort in my opinion, but technically up to the job). When the V was built, I'm sure someone along the way suggested an upgrade, but it obviously didn't happen, most likely because an accountant came up with a risk/reward scenario (ex: replacing 500 under warranty will cost less than contracting a complete redesign).

I think GM has learned the hard way over the last 3 decades that this sort of thinking is what allowed the imports to steal so much market share, and it would seem that they are making fewer major choices today based solely on the bottom line. Bottom line is crucial to maintain the business, but so is product image and customer enthusiasm. It seems like they're figuring that out, even if it is taking a maddeningly long time.
 
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