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Hello world,

I have a 2005 Chrysler 300c that I just bought. I'm not planning to get a programmer and change the electronics unless I actually have too. But I am about to slam in the wrong gear set. Call me crazy but I'm about to see how long a gear set from a v6 rear end will absorb the 5.7L torque. That's another reason I don't want to tune it and stress it even more. So anyone have any experience swapping in a v6 rear end? Also this isn't a hotrod, just more of a beater car, and the v6 rear is a whole lot cheaper, and I'm told will bolt up to the same connections and all as the v8 rear. But ultimately will I have to recalibrate the speedometer to make it run right, or will it only throw off the speedo. I can live with a bad speedo in the short term as long as it will still shift gears correctly. The spewed input/ouput sensor is in the trans, so I'm assuming by changing the final ratio the shift points should be measured before that change and should just change speed wise, proportionally to the new final ratio and still be smooth and all. But I hear some modern cars will crap themselves and not know how to run if you change gear ratios like that.
 

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I'm not going to offer an opinion on the rear end swap, but I'd suggest that you pick up a used tuner to correct the gear ratio in the BCM. Tuners for the first-gen cars are cheap on the secondary market, I think I paid $125 for mine.
 

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I'm not going to offer an opinion on the rear end swap, but I'd suggest that you pick up a used tuner to correct the gear ratio in the BCM. Tuners for the first-gen cars are cheap on the secondary market, I think I paid $125 for mine.
Thanks. The rear end is a 250 dollar gamble, with free shipping. Wish me luck, and not lots of fragments, lol.
 

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Thanks. The rear end is a 250 dollar gamble, with free shipping. Wish me luck, and not lots of fragments, lol.
Best of luck with the swap. I don't think you're likely to grenade the carrier, but you'll have some work to do, swapping the flanges and so on. And if they send you a 198mm 3.90 rear out of a 2.7, the result ought to be interesting.
 

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Best of luck with the swap. I don't think you're likely to grenade the carrier, but you'll have some work to do, swapping the flanges and so on. And if they send you a 198mm 3.90 rear out of a 2.7, the result ought to be interesting.
This is what I bought. Mopar Replacement 52114594AF
A Chrysler dealer told me it would probably bolt up, and summit told me that it will bolt up to the 2005 300c platform. Fingers crossed they're right. It's the same spline count and everything supposedly.
 

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Looks like a 3.90. Like I said, ought to be interesting.
Sorry to keep bugging you, but what are you talking about with swapping the flanges? I've not done much with rear ends before, and nothing this modern?
 

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I don't want to come off sounding like I've done this swap, because I haven't. But there's a good possibility that the carrier you get will have a different driveshaft flange than what you have currently, either three-bolt or four-bolt, unless you checked that in advance with whoever sold it to you.
 

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I don't want to come off sounding like I've done this swap, because I haven't. But there's a good possibility that the carrier you get will have a different driveshaft flange than what you have currently, either three-bolt or four-bolt, unless you checked that in advance with whoever sold it to you.
Okay, thank you. I will be on the look out for that. According to summit it should be a direct swap, same input and output connections. I've got my fingers crossed.
 

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FWIW, I'll give you my 2 cents worth on this, both from some experience and also a little forum here say. First, the V-6 one should bolt up, but I don't remember if the axles/hubs are different or not for them I know they are when going from your stock 5.7 setup to a 6.1/6.4 setup, as I've done this. The drive shaft hook up may also be different. My guess is that, once you get it figured out, if you drive it "sanely" you won't have too much problem with it withstanding the additional power. Just so it's not overdone. IMO, good luck with that, as it'll feel a whole lot better than the stock 2.82 setup did.

Now to your real problem once you get it installed. As said above, you definitely need a tuner with the capability to change the rear axle ratio and/or tire diameters.....if you change tire sizes somewhere along the way. The NAG1 transmission TCM uses the speed sensors in the axles, along with the transmission output shaft RPM and amount of expected slip to calculate what gear you're in.....or should be in. Your lower gear ratio will immediately throw P07XX codes unless you correctly program the differential ratio and tire diameter......been there, done that. Your shift schedules will also be all wrong. If you're using the stock diameter tires (within a small percentage) you'll only need to do the diff. gear ratio adjustment. All of the early name brand tuners have the capability to change gear ratios. I have two early Hemi LX's, an 05 RT and an 06 SRT and I have both Superchips and Diablosport Tuners as well as an HP Tuner for both, and they'll all allow these changes.

Good luck and have fun.
 

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FWIW, I'll give you my 2 cents worth on this, both from some experience and also a little forum here say. First, the V-6 one should bolt up, but I don't remember if the axles/hubs are different or not for them I know they are when going from your stock 5.7 setup to a 6.1/6.4 setup, as I've done this. The drive shaft hook up may also be different. My guess is that, once you get it figured out, if you drive it "sanely" you won't have too much problem with it withstanding the additional power. Just so it's not overdone. IMO, good luck with that, as it'll feel a whole lot better than the stock 2.82 setup did.

Now to your real problem once you get it installed. As said above, you definitely need a tuner with the capability to change the rear axle ratio and/or tire diameters.....if you change tire sizes somewhere along the way. The NAG1 transmission TCM uses the speed sensors in the axles, along with the transmission output shaft RPM and amount of expected slip to calculate what gear you're in.....or should be in. Your lower gear ratio will immediately throw P07XX codes unless you correctly program the differential ratio and tire diameter......been there, done that. Your shift schedules will also be all wrong. If you're using the stock diameter tires (within a small percentage) you'll only need to do the diff. gear ratio adjustment. All of the early name brand tuners have the capability to change gear ratios. I have two early Hemi LX's, an 05 RT and an 06 SRT and I have both Superchips and Diablosport Tuners as well as an HP Tuner for both, and they'll all allow these changes.

Good luck and have fun.
Which tuner would you recommend, considering I only really need the ability to correct the speed sensors? Also I know the axels for the v6 and v8 are a couple millimeters different in length and the CV joints are a couple mm different in diameter, depending on whose charts you look at. Some parts distributers claim they are identical, but the nut is the same size and thread and everything, and the splines are identical. No matter whos you look at, drive shaft connections too. I'm hoping it's a simple plug and play, both the guys I called seemed to agree. What I don't know is if it's the 198 or the 210. I'm assuming 198, but even the Chrysler guy couldn't see it in his parts system for some reason. But I don't drag race, neutral drop it, power break it, I don't even use the sport stick mode. So I'm hoping it won't break right away. I do like to romp it now and then to pass people, or just enjoy the acceleration, but I shy away from abusive behavior.
 

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For the LX vehicles, I prefer the Diablosport (DS) for the LX's, but the ones I have are circa 2006. The newer ones may or may not have all the features you're after, so definitely check to make sure all the items you're interested in (now and perhaps later) are included. Unlike the HP Tuner, both the SC and DS tuners are easy to use handhelds and, with the DS, you can have custom tunes made for your specific application. I don't believe you can do that with the SC though, even though both are now made by the same company.

On mine, when going from the stock setup to the Getrag LSD setup (off a late model 392), the axles were more heavy duty and the spline counts were different, hence the need for the hubs. Driveshaft on mine was a plug and play.

If you stomp it from a roll it's not as bad as from a standing start. Like I said earlier, you'll love the lower gears around town but on the highway you're RPM will be between 2500-3000 RPM at 65-70 mph. On mine, I went from about 1800 RPM at 65 mph (2.82 stock gear) to about 2200 RPM at 65 mph (3.06 LSD gear), so it really wasn't that bad and it put the engine RPM up a little closer to the power curve which really starts coming on slightly above 2500 RPM with the cam I have in it..
 

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Discussion Starter #14
My part came in the mail. It looks like it will bolt straight up, same flange and everything. I'm in the process of acquiring a tuner before I do the job. I'll let y'all know how it turns out, and eventually if the rear end lasts.
 
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