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3.45 Differentials Installed: Initial Thoughts

8592 Views 89 Replies 6 Participants Last post by  zwade
Picked up my 2016 Durango R/T AWD today after having the 3.45 front and rear differentials installed. Here is some information and my initial thoughts.

I got my differentials off of ebay. I paid $365 for the front differential and I paid $215 for the rear differential. That’s shipped. They were both used. The front one had 36k miles. The rear one had 50k miles. All they needed was fluid, seals and everything were in great shape.

I got them on ebay from terryvilleautoparts and okautopartsms respectively. Both came with 6 month warranty.

Part numbers for mine (there are many numbers for the same differentials. Just cross reference online):
Front: 68263986AA
Rear: 68060039AF

Be sure that they are 3.45 differentials and that the rear says 230mm 9.06 somewhere because it has to be 230mm and a 9.06 to fit the r/t Durango.

Highway Driving:
60MPH rpm increased by about 200rpm in 8th gear
80mph rpm increased by about 100rpm in 8th gear

this won’t kill your gas mileage.

0-60 Improvement: .05 second improvement (went from a 5.55 to a 5.50)
1/4 Mile Improvement: .13 second improvement (went from a 13.94 to a 13.81)
60ft improvement: .02 second improvement (went from a 2.08 to a 2.06)


First thoughts video:
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When you hit 5th at 90 mph it was struggling. Mine right now shifts to 5th at 113 mph lol

Can't wait to see what she'll do when you open her airways! I'm thinking you'll be at the low 13s easy without a cam.
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When you hit 5th at 90 mph it was struggling. Mine right now shifts to 5th at 113 mph lol

Can't wait to see what she'll do when you open her airways! I'm thinking you'll be at the low 13s easy without a cam.
oh wow so they definitely make a difference. Maybe because mine is basically stock besides the tune they don’t work as well as if I was fbo?
When you hit 5th at 90 mph it was struggling. Mine right now shifts to 5th at 113 mph lol
i watched it a few more times and didn’t even notice the mph it shifted to 5th but it sounded super early. I watched a video before the gears and 5th gear shift was 103mph. I know the gears will make a difference but it almost sounded premature because the car just fell on its face after that
I’m going to strap a gopro to the steering wheel and film the tach and speedo tomorrow to see when its shifting because i dont look when I’m driving lol
oh wow so they definitely make a difference. Maybe because mine is basically stock besides the tune they don’t work as well as if I was fbo?
Well a bigger cam can offer you a longer power band. Keeps the curve up all the way through whatever rpm the cam and valve train can handle. That is of course all your other mods free the air flow enough.

So yeah your kind of starving the engine on the mid to high end. The stock intake sucks. But pretty impressed at where it got you.

I think your low end times will be better tomorrow. The low end doesn't suffer as bad from the lack of air flow. Just keep your launch consistent.
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I’m going to strap a gopro to the steering wheel and film the tach and speedo tomorrow to see when its shifting because i dont look when I’m driving lol
You can here it in the video. Sounds like the stock 5500 rpms or so.

Just a quick vid after I first put the cam in getting the afr dialed in. Was 90 something out side. That's a 6400 shift. The 6000 shift from before the cam sounds different than stock too.
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You’ll want a new tcm tune to take advantage of them. With the driveshafts spinning faster, the transmission is seeing its targeted shaft speed sooner and shifting sooner.
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You’ll want a new tcm tune to take advantage of them. With the driveshafts spinning faster, the transmission is seeing its targeted shaft speed sooner and shifting sooner.
you think so? I talked to mags before I got them and he said nothing would be needed. I did email him yesterday to ask some questions but ill check on today’s runs when its shifting and if its shifting early. I didn’t think anything was needed in terms of tuning
It’ll run fine. A tune isn’t needed to make it run. But to take full advantage of the upgrade, it is. Lock up, shift points, all things that are affected by rpm//shaft speed and a myriad of other things. It made a noticeable different in my scat pack when I went from stock 3.08 to 3.73 and then had the trans tune updated for the gears.
It’ll run fine. A tune isn’t needed to make it run. But to take full advantage of the upgrade, it is. Lock up, shift points, all things that are affected by rpm//shaft speed and a myriad of other things. It made a noticeable different in my scat pack when I went from stock 3.08 to 3.73 and then had the trans tune updated for the gears.
I should hear back from MAGs monday hopefully and see what he says and see what, if anything, needs to be done. I'll get it figured out! These gears should have more improvement than what I'm getting
You’ll want a new tcm tune to take advantage of them. With the driveshafts spinning faster, the transmission is seeing its targeted shaft speed sooner and shifting sooner.
It sounds like it's shifting at or pretty near the same point in his other videos. I listened pretty close. He already has a transmission tune. I think it will benefit more from a higher shift point once he gets the high end opened up. Right now power will probably drop off really quick past the stock power band high point, 5400-5500 rpms, with no engine mods.

When he does his next run like he did his last ones I think his 60 ft might get below the 2s. If so all the other engine upgrades, plus a red line shift point, are going to free up his high end and his times will be smoking.
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I just went and filmed the speedo and tach for my 1/4 mile run and I think I figured out why my 1/4 mile didn't improve much with these.

It's shifting into 5th gear at 94mph before it hits the 1/4 mile at 99mph where as before the gears it would finish the 1/4 mile in 4th gear and not have that extra shift.

Here are shift points:

1st to 2nd: 5500rpm at 34mph
2nd to 3rd: 6000rpm at 54mph
3rd to 4th: 6100rpm at 77mph
4th to 5th: 5800rpm at 94mph

If I can get the tuner to make the 1st to 2nd shift point a higher rpm and the 4th to 5th a higher rpm I think I can shave time off. Especially if it doesn't shift into 5th gear before crossing the 1/4 mile.

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It sounds like it's shifting at or pretty near the same point in his other videos. I listened pretty close. He already has a transmission tune. I think it will benefit more from a higher shift point once he gets the high end opened up. Right now power will probably drop off really quick past the stock power band high point, 5400-5500 rpms, with no engine mods.

When he does his next run like he did his last ones I think his 60 ft might get below the 2s. If so all the other engine upgrades, plus a red line shift point, are going to free up his high end and his times will be smoking.
Just posted shift points, 4th to 5th is super early in rpm band and it does it right before I cross the 1/4 mile whereas before i crossed the 1/4 mile in 4th. I think thats hurting my time
Just posted shift points, 4th to 5th is super early in rpm band and it does it right before I cross the 1/4 mile whereas before i crossed the 1/4 mile in 4th. I think thats hurting my time
Yeah it is.

Mine before the cam shifted at 36 and then 57, then 81, then 100. Seems like the higher each shift is, the higher the next shift will be.
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Yeah it is.

Mine before the cam shifted at 36 and then 57, then 81, then 100. Seems like the higher each shift is, the higher the next shift will be.
you think its odd mine shifts at a different rpm every gear?
you think its odd mine shifts at a different rpm every gear?
I'd say so
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Okay so I got a PCM and TCM tune revision installed. Basically I had to do some pulls to make the new tune pressures and shift points which are now all set at 6100rpm.

It's shifting properly now at 6100rpm in every gear except from 1st to 2nd. When in 1st and I do a WOT pull it gets to 6000rpm and then there's a big clunk like it shifts but then the car goes into limp mode and I can't shift or put it in park or anything. It stays in some unknown high gear and I have to stop the car, turn it off and then back on to fix it. It threw a code after that PCM:0101: Lost Communication with TCM.

Anyone ever have that issue before? Almost like at 6k rpm it goes into some kind of safety mode??
Looks like it hit the rev limiter but mine never went into limp mode. Happened when I first got the DD and was paying around with the paddle shifters. Otherwise that's a new one for me. Haven't seen it on the web.

Most hand held tuners have a way to raise the rev limit. I'd put it as high as you can go. I'd be careful
though till you contact the MAGs guys again.
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Pull a log and send it off. My charger would occasionally whack 7000 during the 1-2 shift and never went into limp mode.
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