: Diff Swap 05 STS



Cadzilla8
07-19-13, 10:47 PM
Hey everybody just looking for anybody's thought on this as I'm not 100% certain I should go for it. I have a v8 sts rwd with 2.73 gears and no posi. I want to get the 3.42 diff with posi. Hoping to get some better traction at quick acceleration and faster acceleration. Looking for some thoughts of if I should tinker with this or not and keep why I have.

EChas3
07-20-13, 01:56 PM
I'd try tires, first. You're not still on the OEM Michelins are you?

Subsailor613
07-20-13, 04:26 PM
You'll probably have to swap the whole 3 rd member, as I have
read, that Cadillac, to save on weight, actually welded the ring gear
to the carrier, to eliminate the weight of the bolts.
This should show how much has been done to increase MPG,
as I am sure they went through the engine also !
The 3.42 gears WILL reduce your total MPG some,
Guessing 3 or 4 MPG or more ?
As I have 3.23 w/Posi, and I miss the mileage of my prior 2.7 gears.
(Upgrade from 2005 to 2006 STS)
With 3.23 I get 15 and 25, almost 26
I like the knowledge of having Posi, but dearly miss the MPG.
17 and 27 almost 28.
You ONLY street race, once in a while, but MPG is forever.
Some models DID have larger REAR tires, than the fronts.
Happy Motoring :thumbsup::rockon::usflag:

Cadzilla8
07-20-13, 07:44 PM
Yeah sorta been rethinking it. The 3.42 gears would be more about a speed think and a performance upgrade. The posi would be a safety thing. True that amount of time im seriously going to demand on the car that i would need it is so minute. I do break traction every now and then in the rain or when driving like an A hole and its sorta weird when 1 wheel spins.

----------

As for tires I have Michelin energy lx4 those might be the same as oem ones not sure what the car came with and I know the owner before me always replaced tires with same thing. Plenty of thread left though

EChas3
07-20-13, 11:40 PM
My wife's car came with those tires. They are optimized for mileage and treadlife at the cost of road noise and traction on any pavement that isn't clean. dry & warm. With just 20,000 miles on them, I considered them dangerous.

The car did get 25 MPG at 80 MPH on a tank of regular gas with them.

dkozloski
07-21-13, 12:39 AM
Where the problems come up is getting everything electronic and related to speed to work. Everything interacts from the speedometer to the EMU to the fuel mileage computer, ABS, and stability system. Good luck! The EMU is programmed serially with one long digital word that somebody that knows all the secrets can construct. According to "The Old GM Guru" this process can sometimes cost GM five to six figures.

ddgm
07-21-13, 10:58 AM
I was thinking of going the other way. I used to drive from Ontario, Canada to Fort Myers, Florida for the winter and was looking for a 2.73
hoping to improve MPG. I have the 3.42 with POSI. However I bought another vehicle to leave down there and am going to fly back & forth.
I did see a complete carrier on ebay for $300 with the 2.73. I would be interested to hear the results if you decide to do this, just to satisfy my curiosity.

Doug

Charles Warren
07-21-13, 11:17 PM
How do you know what gears you have?

dkozloski
07-22-13, 02:35 AM
How do you know what gears you have?Look at the tag on the bottom of the spare tire cover in the trunk. One of the RPO codes will denote your final drive ratio.

Charles Warren
07-22-13, 09:14 AM
Look at the tag on the bottom of the spare tire cover in the trunk. One of the RPO codes will denote your final drive ratio. i think i have 3:23 limited slip. and i know cts has open differential

Subsailor613
07-22-13, 02:13 PM
Anybody know the difference between "Limited Slip and Positraction" ?
Thanks

Ludacrisvp
07-22-13, 03:36 PM
This might be a useful video for those that aren't experts in diffs ... the video was made by / for toyota.


http://www.youtube.com/watch?v=gIGvhvOhLHU

From what i've read (not sure how accurate it is) is that positraction is GM's name for limited slip differentials.
So they are the same thing LSD = Posi.
Compared to the 3 open differentials in the AWD models

Charles Warren
07-23-13, 03:16 PM
but our diffs are not lockers if they were they would be louder than what they are thats a question and a guesstimation lol

Charles Warren
07-24-13, 09:07 AM
forgot to add if your in park and your car is in the air/wheels off the ground and you turn 1 wheel one direction and the opposite wheel goes the opposite direction then you dont have a posi. my gtp has a posi diff and ive noticed before we put a posi diff in it it did this but after we put the diff in it made both wheels turn the same direction and locked that direction when the gears clicked

Subsailor613
07-26-13, 06:36 PM
I would LOVE to get a 2.7 rear end with Posi-Traction.
After having a 2.7 and a 3.23, Yes, I would give up
a little performance for gas mileage.
Is there such a setup, and would it fit a 06 ?

Charles Warren
08-31-13, 01:22 PM
just dropped my diff today and tag says i have i=2.73 :( 15793747 but is it limited slip??? because i spin both tires i see 2 marks when i burnout

1BadCadSTS
08-31-13, 01:46 PM
2.73 is standard rear end. I believe g80 is limited slip rpo.

Charles Warren
09-03-13, 12:14 PM
oh ok so I could have 2.73 with lsd. I think I do I'll check rpo tag later. I just put 2 gallons of 112 and car runs so smooth now. And I encourage you all to install poly engine mounts and poly diff bushing. My car has no more shake and gets better mpg and feels like she wants to run away :)

Subsailor613
09-03-13, 05:27 PM
Anyone know if the 2.73 is available with Posi/Limited Slip (LSD)?
The 2.73 I had in my previous STS, did NOT have LSD.
Happy Motoring

dkozloski
09-03-13, 06:28 PM
I can't wait until somebody tries this. Everything about the car that involves a calculation that includes speed is going to be haywire. Speedometer, odometer, gear shifts, mileage, range, OLM, ABS, stability system, ECM, and NAV. I'm betting there will be some more as well because of the tight integration of the computer systems. The relationships between all these factors is determined by one long data word that must be obtained from GM Techline. If somebody somewhere has already put together your partiular combination they might be able to help you. If not it can cost a high five figures for them to develope it for you which they won't do anyhow.
Good Luck with your dream.

EChas3
09-03-13, 09:12 PM
2.73 to 3.42 is a big differential; over 25%. Trust me, I drive both a 2.73 & a 3.23; only an 18% difference.

btlegacy
09-04-13, 10:38 AM
I believe the 2.73 never came with an LSD. I would buy another LSD unit and then swap the ring and pinion from yours to it. You may have to order different shims for it to be set up correctly

Subsailor613
09-04-13, 12:24 PM
From what I have read, the Ring gear is welded on, to save weight.
There are NO bolts.
Swapping the whole third member is the only way.
Did they use different axels on the LSD, as opposed to Non-LSD ?

Can't the dealer re-calibrate the speed input, changeing the speedo,shifts, etc,
Tire size change,or rear end gear change ?
Happy Motoring !

btlegacy
09-04-13, 12:45 PM
I have my old carrier that I took and will split it to examine inside

dkozloski
09-04-13, 02:39 PM
From what I have read, the Ring gear is welded on, to save weight.
There are NO bolts.
Swapping the whole third member is the only way.
Did they use different axels on the LSD, as opposed to Non-LSD ?

Can't the dealer re-calibrate the speed input, changeing the speedo,shifts, etc,
Tire size change,or rear end gear change ?
Happy Motoring !The mathematical relationship between all the elements in the digital data system is determined by one long serially loaded data word that if I remember correctly is called a "V" word and must be calculated and validated separately for every legitimate combination of equipment and variables. GM claims this can cost into the high five figures. If this data word has already been developed for the variation you anticipate you might talk them into letting you use it but it can only be loaded by a dealer. This is not to be confused with the monkeying with shift points, fuel tables, and speed limiters that the tuners do.

btlegacy
09-04-13, 02:55 PM
I believe that the ECM may be able to be modified based on other GM ECM's that I have worked with as this E55 ECM is supported by HP Tuners. We have adjusted gear changes for many other ECMs with HP Tuners and and are evening running a 3.42 CTS rear in our LS1 Miata which we were able to modify the tune for to support that Ratio.

btlegacy
09-07-13, 09:28 AM
I opened up the diff I took off from my 05 STS. It is a Non-LSD 3.42 diff and I do not see anything that is welded. Some pics below:

http://imageshack.us/a/img10/9817/xiq9.jpg
http://imageshack.us/a/img202/3541/qr78.jpg
http://imageshack.us/a/img547/638/pewf.jpg
http://imageshack.us/a/img826/8152/jgff.jpg


From what I have read, the Ring gear is welded on, to save weight.
There are NO bolts.
Swapping the whole third member is the only way.
Did they use different axels on the LSD, as opposed to Non-LSD ?

Can't the dealer re-calibrate the speed input, changeing the speedo,shifts, etc,
Tire size change,or rear end gear change ?
Happy Motoring !

Subsailor613
09-07-13, 01:18 PM
I ONLY read it, I brought this to light, as it "may" be a possibility.
In your case it is bolted, also, does not mean others are not welded.
I question it also, Why would some be welded, and some not ?
Great Pics,Thank You.
Happy Motoring.

dkozloski
09-07-13, 05:40 PM
There is no damn way the ring gear could be welded to the carrier. The gear is highly heated and this would be destroyed by the heat of welding. Welding would warp both the ring gear and carrier making it impossible to set contact pattern and lash.

Subsailor613
09-09-13, 06:27 PM
Great point of information, koz, I did not put any technical knowledge
into saying it, as I only read it. In my younger years,I frequently changed out
whole third member, But NEVER changed out
a ring and pinion, so am NOT familiar with the setup on these.
I wanted to do that, but the technical knowledge I did NOT posses,
AND additional funds,stopped me COLD.
At that time I wanted a 5.38/1 over a 4.11/1 locked, "Those were the days" !
Happy Motoring.

P.S. If I come across the article on welding the Ring Gear,
I will post it here.
Also we probably are NOT talking stick welding here.

Charles Warren
10-06-13, 05:49 PM
I emailed madtuner he said he could change gear ratios too. What would be needed to go with ctsv differential? Or should I go 3.42 and make it posi?

dkozloski
10-06-13, 11:48 PM
Great point of information, koz, I did not put any technical knowledge
into saying it, as I only read it. In my younger years,I frequently changed out
whole third member, But NEVER changed out
a ring and pinion, so am NOT familiar with the setup on these.
I wanted to do that, but the technical knowledge I did NOT posses,
AND additional funds,stopped me COLD.
At that time I wanted a 5.38/1 over a 4.11/1 locked, "Those were the days" !
Happy Motoring.

P.S. If I come across the article on welding the Ring Gear,
I will post it here.
Also we probably are NOT talking stick welding here.I have seen differentials with the spider gears welded to create a redneck positrac but only in stuff like a home made tractor with a truck rear end.

Neutrocuted
10-07-13, 04:53 AM
Does anyone know why they don't put posi in the rear diff on the AWD models? I had LSD on my Ford Bronco that had push button 4WD and the LSD worked great in all modes! I know the traction control on the STS4 will apply the brake of the spinning wheel to send the power to the other wheel but I've had that system over heat and turn off during snowy conditions. Posi would have saved the day I think???!!

Charles Warren
10-07-13, 05:52 PM
Because the engineers are boneheads sometimes

ShDmitry
02-16-14, 04:42 PM
I also think about diff swap, but I don`t know if I need LSD. We have rain a few days a year? My city on the mountain and I need more power on steep hills.
Now I have 3.23 without LSD, I think about 3.73 or 3.90.

btlegacy
02-28-14, 05:40 PM
I have done some research on this as I have swapped diffs on my 05 STS RWD and we have also used this diff type on our LS1 swap Miata. This differential type is used on many GM vehicles and most of them are interchangeable. The ones I have seen and tried out are as follows:
Cadillac CTS 1st Gen
Cadillac CTS-V 1st Gen
Cadillac SRX RWD
Cadillac STS
Cadillac STS-V
Early Saturn Sky/Pontiac Solstice

All of these diffs can interchange with minor difference and the axles will slide in for the most part. I replaced the factory Non-LSD 3.42 rear differential in my STS with an LSD 3.42 rear differential from a 2006 CTS. I research the parts for rebuilding these units and changing ratios but for the most part it is cheaper to get a low mileage complete differential unit out of another car. I paid $163 shipped on ebay for the 06 CTS Diff with 67k miles.

wake
03-02-14, 12:07 AM
I can't wait until somebody tries this. Everything about the car that involves a calculation that includes speed is going to be haywire. Speedometer, odometer, gear shifts, mileage, range, OLM, ABS, stability system, ECM, and NAV. I'm betting there will be some more as well because of the tight integration of the computer systems. The relationships between all these factors is determined by one long data word that must be obtained from GM Techline. If somebody somewhere has already put together your partiular combination they might be able to help you. If not it can cost a high five figures for them to develope it for you which they won't do anyhow.
Good Luck with your dream.

Is it really that complicated?

I have a Tech II but don't have the option to change the gearing on my vehicles probably because the vehicles I own only came with one gear ratio. I can however change tire sizes on the Escalade since it came with different sizes available, but only standard sizes from a list.

I'd call the dealership and ask them about changing the gear ratio in the PCM if the answer is no (sometimes liability is the reason for the no answer) then maybe an option is finding a donor PCM from a salvage car that had the same powertrain that his car has with the gears he wants to install. As long as it's a GM option for that year there should be a calibration for it already in existence. The only issue that I can think that you might have to deal with is the theft deterrent system, I had this issue on an 02 Trailblazer I installed a tuned PCM in and had to do the theft system re-learn.

Also some aftermarket tuners may also be able to modify the gear ratio for you if they tune your type of vehicle.

Maybe I haven't messed with the newer vehicles enough but from what I remember it shouldn't be impossible to change gear ratios. The transmission shifts based on engine load and the transmission gear ratios are the same whether you have 2.73s or 4.10s.

dkozloski
03-02-14, 04:14 AM
Is it really that complicated?

I have a Tech II but don't have the option to change the gearing on my vehicles probably because the vehicles I own only came with one gear ratio. I can however change tire sizes on the Escalade since it came with different sizes available, but only standard sizes from a list.

I'd call the dealership and ask them about changing the gear ratio in the PCM if the answer is no (sometimes liability is the reason for the no answer) then maybe an option is finding a donor PCM from a salvage car that had the same powertrain that his car has with the gears he wants to install. As long as it's a GM option for that year there should be a calibration for it already in existence. The only issue that I can think that you might have to deal with is the theft deterrent system, I had this issue on an 02 Trailblazer I installed a tuned PCM in and had to do the theft system re-learn.

Also some aftermarket tuners may also be able to modify the gear ratio for you if they tune your type of vehicle.

Maybe I haven't messed with the newer vehicles enough but from what I remember it shouldn't be impossible to change gear ratios. The transmission shifts based on engine load and the transmission gear ratios are the same whether you have 2.73s or 4.10s. This was the subject of a long discussion when the current RWD Caddys first came out and included a GM PowerTrain engineer who said that because of the way that the ECM is programmed and performs powertrain calculations it is very complicated to change final drive ratios without upsetting everything related. I think the method of changing the programming is by creating what they call a "V" word which is serially loaded into the ECM in much the same way that an OnStar unit is initialized.

wake
03-02-14, 11:23 AM
This was the subject of a long discussion when the current RWD Caddys first came out and included a GM PowerTrain engineer who said that because of the way that the ECM is programmed and performs powertrain calculations it is very complicated to change final drive ratios without upsetting everything related. I think the method of changing the programming is by creating what they call a "V" word which is serially loaded into the ECM in much the same way that an OnStar unit is initialized.

Ok, then it sounds like maybe a PCM from a donor car equipped (powertrain wise) in the final config the OP is looking for might be the only answer. Everything else as far as option content should be handled by the BCM so it might not be too hard as long as the gear choice is one of the stock GM offerings.

I wonder how aftermarket tuners are handling these issues.

dkozloski
03-02-14, 12:51 PM
According to the engineers, V-words have been created for a host of configurations. If what you are doing has been done at the factory all you have to do is beg GM to release it to you. He said that some of the v-words cost into six figures to engineer to get all the pertinent systems working together.

wake
03-02-14, 03:12 PM
According to the engineers, V-words have been created for a host of configurations. If what you are doing has been done at the factory all you have to do is beg GM to release it to you. He said that some of the v-words cost into six figures to engineer to get all the pertinent systems working together.

The problem comes from liability a lot of times in trying to get a different calibration. Not many people I know could convince a dealer to reprogram it.

For example, in the late 90s when GM still made the Camaro and Trans Am a lot of owners found out they were governed at 110mph, my best friend being one of them with a 95 model. He tried to get the dealership to remove the speed limiter that other Z28s didn't have. He found out that the dealership wouldn't because the car left the factory without Z rated tires that you get on the performance models with the 3.23 (maybe 3.42) gearset (his had either Y or H rated tires from the factory). The tires on the car when it left the factory dictated the speed limiter. My 97 T/A didn't have the speed limiter on it because mine came with the Z rated tires.

My Olds Aurora also has a speed limiter. There was a performance model, I believe called the "Autobahn Series" if I'm remembering correctly. It came with more performance oriented gears and Z rated tires from the factory. Those were drag limited only, no computerized speed limiter from what I read. My 94 Non ETC Eldorado also had a speed limiter at 108mph, my 98 ETC didn't.