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Discussion Starter #1
I don't know if anyone else gets that droning sound from their 3rd member or not at around 55-60 mph. I also had that noise in my 2004 CTS and had heard that it was a problem with these rear ends on certain model years. But, I doubt if it's going to catastrophically fail because it's been doing it since about 90k and I now have 160k (but that doesn't mean it won't). But I'm considering replacing it with a G80 LSD from an '08 RWD.

Understanding how TC uses engine management and individual wheel braking to provide traction to the other wheels I'm wondering if a G80 will interfere with the TC systems... or if it's just a bad idea in general.

Has anyone done that before?

Thanks guys!
 

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'11 CTS-V Coupe M6, '05 1SG STS4 V8
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I feel like in theory it should work, as long as you already have 3.23 gears, but who knows really. It's probably not like swapping a solid rear end in a classic car. Lol.
 

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Yes it will "work"

The only issue I can think of is if 3 wheels hook and 1 doesn't you may have some nice tq steer to fight with and that's a BIG if...

I have a variloc rear axle (similar to an LSD) in the rear of my Jeep and an open in the front with really no ill effects.

Just make SURE you get a 3.23... the LSD rears came with 3.23 and 3.42 for the STS and 3.73 for the V6 SRX if memory serves me right.
 

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Not to steal this thread but since we're on the same topic- can I swap to a taller gear set in my v6 awd STS? I have 3.23 gears currently (GU5 rpo code). Would be nice for better mpg. Or will this affect the transfer case/transmission?
 

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You mean 2.73 gear which is in the 1SE V8? Theres a reason that rear end wasn't available in the V6, its a dog. Throw that in the V6 especially in the non DI V6 and it would be pathetic. Not to mention your speedo and shift point would be off unless you had the ECM tuned with a 2.73 V6 cal (which doesn't exist) so special tuning would be required. Enter Madtuner or HPTuners.
 

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Discussion Starter #6
Yes it will "work"

The only issue I can think of is if 3 wheels hook and 1 doesn't you may have some nice tq steer to fight with and that's a BIG if...

I have a variloc rear axle (similar to an LSD) in the rear of my Jeep and an open in the front with really no ill effects.

Just make SURE you get a 3.23... the LSD rears came with 3.23 and 3.42 for the STS and 3.73 for the V6 SRX if memory serves me right.
But isn't the center diff open? And would the 60-40 split kindda negate the tq steer?

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The reason I am bringing this up is because my CTS RWD w/LSD does so good in the snow. The TC behaves really good and keeps the azz end in line. Very little fish tailing with it on. I haven't been able to try it without the TC because the OG has been with me every time I want to drive it in the snow... and the Lord knows how I hate to get her wound up! "STOP THAT!!! YOU'RE GONNA CRASH MY CAR!" And on, and on, and on! LOL

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Not to steal this thread but since we're on the same topic- can I swap to a taller gear set in my v6 awd STS? I have 3.23 gears currently (GU5 rpo code). Would be nice for better mpg. Or will this affect the transfer case/transmission?
I don't think there are other ratios available for the STS4, could someone confirm that? If so you would have mis-matched ratios between the front and the rear which is serious bad news.
 

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'11 CTS-V Coupe M6, '05 1SG STS4 V8
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Gotcha. I suppose it would. Just curious, thanks man. Bump for the OP.
 

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2006 STS4 V8 1SG & 2007 STS V8 1SE
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I've read here that all AWD STS have the 3.23 gear. I consider it just right for the V8 5-speed AWD. Open differentials or not, mixed front & rear ratios would be trouble.

If you found the rear end with the right gearing & LSD, I'd expect engaging stability control or traction control to wear the rear pads much faster than normal. You might be OK by simply monitoring the pads more often.
 

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Discussion Starter #9
But then look at the other side of that same coin, with more traction available at the rear maybe there would be less need for TC intervention than with an open end... Maybe. But I'd agree that when it does break loose it would have to hit both rears instead of just 1.

But it seems to me that the throttle management kicks in so fast (too fast for my liking) to reduce torque that what's the difference anyway. I think that I might prefer to have the additional wheel providing added traction and then turn off the TC and go with the seat of my pants like the old days b4 ECD (electronic control dictatorship). Now I'm not saying to turn off the SC 'cause we all know how much trouble you can get into without SC at the same time you turn off the TC because stability control has saved my toches more than a few times. I almost never turn it off.

Just thinking out loud and looking for some input.
 

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Discussion Starter #11
I'm not sure about that. I believe the carrier is the same as the STS and CTS, but I'm not sure. I've actually found one I'd like to purchase and it's out of an '09 STS. I'm mainly hoping for a quieter ride and thought that I'd investigate the G80 since I'm doing the swap.
 

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SRX does use the same drivetrain but you lose LSD (G80) for both of them when going from RWD to AWD.
 

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It must be a different program. The STS AWD traction control applies braking to the free-spinning wheel(s) so often resulting from the three open differentials. That equalizes the delivery of power to all four wheels and is actually a very efficient system, much the same as traction control in F1 cars. Only when wheel slip continues does the system reduce the power delivered.

I'd expect little or no braking for Traction Control on STS models equipped with a limited-slip differential. Selective baking on those models should be a Stability Control System or Anti-lock Braking System action.

If an AWD vehicle were equipped with an axle using an LSD, the Traction Control System should only activate the brakes on that axle in tandem (together) when it was spinning faster than the other axle.
 

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Discussion Starter #18
I hear ya! That is what's going to happen. But just a little history. I had a 1993 full size Ford Bronco XLT that I broke the rear end on shortly after it was out of warranty. I got talked into putting in an Auburn LSD which I later found out was a cone type LSD. It drove me crazy because whenever I'd turn a corner it would click like crazy. On the occasional trips up the slippery boat ramps pulling out a 23' Sea Ray it worked great, but for everyday driving it sucked.

That's why I was trying to "stick my toe in the water" here to get some opinions. I don't want to buy it, install it, then want to rip it out because it's steering crazy or acting weird or something like that.

I can imagine what they would have to say at the dealer because the car didn't come with it, and I know they shouldn't recommend anything but OEM, so their opinion I'd have to take with a grain of salt. But if a GM engineer was to explain why it wasn't offered, I'd surely listen.
 

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The companies with the most production car experience with AWD are Audi and Subaru; the latter building no other drive trains for more than a decade. I'm not as familiar with Audi's history (even if I do recall it's a long and storied one), but I do know Subaru and aftermarketeers have both worked hard to get a lot of power from those flat opposed engines to the ground.

I recall from studies of various correction systems using negative feedback, multiple feedback loops tend to introduce oscillations into a system. The control circuits work against each other and then double-up. I think an automotive engineer would explain that having both an LSD & electronic anti-slip would cause over-corrections, so one has to be eliminated. Since the electronic variety is perfect for steerable wheels on the front, it wins the battle for the rear as well.
 

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Discussion Starter #20
That's the kind of feedback I was hoping for. But, my CTS has LSD and electronic TC but I don't know if the RWD CTS uses braking for TC or not. It doesn't make sense to use braking. Does anyone know if it uses only throttle management or both?
 
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