[Mangoman]

That sounds unusual since the diff is vented, any expansion due to heat should just vent out and no pressure should ever build. Maybe checking the vent function should be done. I've always topped til it dribbled out and never an issue and thought the below the fill hole recommendation was a fuel economy thing.

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No idea about the vent, it's there and I swapped over the little hose with the vent cap check valve and it was working just fine. Dodge was going to refund me for the seal but it was under $3.00 so I wasn't too worried about the cost. All I know is I replaced the seal, drained the diff, re-filled it and left out some and it's ok now. I was told by one of the Dodge techs it should be under the fill plug by an 1/8 to 1/4 or it'll blow a seal. I said the same thing about the vent and he just shrugged and said he didn't know what to tell me but I'm not the first one to have that happen from over filling it.

 

[snobrdrdan]

That will be over filled. It's supposed to be either 1/8 or 1/4 below the fill plug. Trust me when I tell you do not over fill it or you will blow out a seal. I filled mine as you started till it just ran out and the car was sitting in my driveway which turns out isn't level where it was parked. I blew the passenger side axle seal and had to replace it. Almost blew the pinion seal too but thank God the axle seal went first! The driveshaft tunnel under the car above the pinion seal was coated in what resembled a white lithium grease that was pushed out due to my over filling. I opted to pull the passenger side axle to replace the seal rather then drop the diff again. Brand new rear and my dumbass blew out a seal! God I was pissed at myself! After the first qt it's only a couple more oz that it needs, I HIGHLY recommend measuring it out and avoiding fill till it drips out method at all costs.

Alrighty then....thanks for the tip!

So when you replaced the new seal, what'd you use to install/push/press it in?

 

[snobrdrdan]

Do you guys recommend new OEM driveshaft bolts, or just reuse the OEM ones with some blue loc-tite?

 

[Mangoman]

Gently taped it in till flush then used the inner card board tube part of a roll of masking tape and taped it in the rest of the way.

 

[91DakBuilder]

I use the factory pink bolts with blue loctite. So far so good. Just put my factory driveshaft back in for a road trip. I’ll do the same method of blue loctite on the DSS shaft when I put it back in as well


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[snobrdrdan]

I use the factory pink bolts with blue loctite. So far so good. Just put my factory driveshaft back in for a road trip. I'll do the same method of blue loctite on the DSS shaft when I put it back in as well

I think the "pink bolts" are for the older style cars though....the newer ones use a T50 torx bolt

 

[91DakBuilder]

I think the "pink bolts" are for the older style cars though....the newer ones use a T50 torx bolt

You're right I didn't catch that I've got a 13 R/T. Not a 15+. That is terrible you have to deal with the Torx trash.

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[snobrdrdan]

Big thank you to ronan978 for the DIY write up. You made it sound/look simple and convinced me to DIY it.
I did it by myself, and I gotta say it was a little tricky trying to manhandle the diff and getting everything to line up while on my back (with the car on ramps).

It's done but, again, it wasn't fun

Here's another good write-up, btw, if you want to add it to the first post:
https://static1.squarespace.com/static/58eed750d1758e9c1359a528/t/58f69446579fb3776b327ec7/1492554943722/TECH+ARTICLE+DIFFERENTIAL+REPLACEMENT+15+AND+UP.pdfAnd my driveshaft bolts were T50 torx heads

 

[ronan978]

Great write up Ronan978 .. I've read your posts on results of your 3.70 swap and am not surprised at the lack of improvement.. you stated you believe the 3.70 is too much gear for the A8 and I submit it's not too much but the wrong gear for a stock or in your case a mildly modified 6.4 and here's why .. I used an online gear calculator over a year ago when deciding on a gear change for my A8 Scat. assuming an average trap speed of a stock 6.4 is around 113 mph . below are the rpm's crossing the stripe at the end of the 1/4 using different gear ratios.

3.09 @ 113 mph in 5th gear = 5273 rpm
3.70 @ 113 mph in 5th gear = 6315 rpm ( too high )
3.70 @ 113 mph in 6th gear = 4895 rpm ( too low )
3.90 @ 113 mph in 5th gear = 6656 rpm ( way too high )
3.90 @ 113 mph in 6th gear = 5159 rpm

too high or too low rpm and you lose acceleration.
the 3.70 with close to stock hp is the wrong choice for the drag strip in 5th or 6th gear .(it could be a good choice for a high hp N/A or low hp F/I )
also, look how close the finish line rpm is between the stock 3.09 in 5th gear is to the 3.90 is in 6th ...almost the same except the 3.90 accelerates faster . I gained .2 with my 3.90 swap.
an N/A 6.4 with 3.90 and a cam that would go to 7k would be an interesting experiment.
I'm trying to shine some light on why things turned out the way they did . not Sh*T on what you've done. hopefully I accomplished that...

also have you looked into the Per4mance Development rear differential brace to fix your wheelhop ? I have one on my 700 whp Scat and it really tightens up the rear.. no hop period..

Just wanted to touch on this a bit more :
This weekend I decided to put the 3.70 back in the car. Now with ported heads , custom cam , and a 426 along with fbo. Any how , another thing relative to this gear is going to be tire size. I'm now running the 3.70 with a 305/40/18MT SS(27.6") about an inch smaller than oem. With the stroker , cam , gear and tire , the car feels incredible and is almost always in its powerband. I haven't run any numbers or tests yet , but damn it feels good.

Back to the original post quoted: I feel the 3.70 could be an optimal choice depending on the tire size chosen. We can deviate all the way down to a 27" tire to bring it closer to the 3.90's rpm at the line in 6th gear, or we can run a larger 29-30" and find what would probably be the happiest middle ground crossing at 6k in 5th. [for a stock/mild 392] My numbers will be different, but I'll get back when I get a chance to do some runs.

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[18Hemi300]

Will the challenger differential work as well? I'm looking at getting the 3.09 LSD for my 2018 300.

 

[ronan978]

Will the challenger differential work as well? I'm looking at getting the 3.09 LSD for my 2018 300.

Yessir

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[18Hemi300]

Cool. Thanks for the info Ronan!! Got in a huge debate on the 300 Facebook page because guys said the 300s are different. Luckily it's already been done by one guy. The axle shafts are smaller, but the spline that goes in the housing are the same size.

 

[ronan978]

Cool. Thanks for the info Ronan!! Got in a huge debate on the 300 Facebook page because guys said the 300s are different. Luckily it's already been done by one guy. The axle shafts are smaller, but the spline that goes in the housing are the same size.

No worries! My 3.70 came out of a hellcat challenger. But we've swapped a 3.09 ,3.70 , and a 3.90 into my buddy's 5.7 multiple times with said axles.

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[BDL]

Ok this is a lot of good information. So I currently have the 3:09 and want to change to the 3:70 would you recommend this change with the 6.4 running a ProCharger??? Currently running a 315 drag radial.

 

[ronan978]

Ok this is a lot of good information. So I currently have the 3:09 and want to change to the 3:70 would you recommend this change with the 6.4 running a ProCharger??? Currently running a 315 drag radial.

At the moment , I have every intention on doing just that. Right now with the na stroker it is fantastic!! Always in the powerband. I would imagine it being a good combination with a centri blower too as it'll keep you in the higher power band at wot , but still have nice torque at part throttle when the blower is in less use(if that makes any sense ). Especially since you can play with the tire size a bit. I'm not going to lie , traction can be tough in first , but the following gears fall in line sooo much better. Also , with the 3.09 , I was NEVER using eighth gear.

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[BDL]

At the moment , I have every intention on doing just that. Right now with the na stroker it is fantastic!! Always in the powerband. I would imagine it being a good combination with a centri blower too as it'll keep you in the higher power band at wot , but still have nice torque at part throttle when the blower is in less use(if that makes any sense ). Especially since you can play with the tire size a bit. I'm not going to lie , traction can be tough in first , but the following gears fall in line sooo much better. Also , with the 3.09 , I was NEVER using eighth gear.

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Thanks!!! I will put in the 3:70 gears once the 6.1 intake is finished just waiting for everything to return from powder coating.

 

[ronan978]

Thanks!!! I will put in the 3:70 gears once the 6.1 intake is finished just waiting for everything to return from powder coating.

Which intake are you swapping ?

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[BDL]

I’m putting on the 6.1 intake and hope to be done in a month then to the dyno we go and see what it does.

 

[BDL]

Swapping the 6.4 for the 6.1 sorry.

 

[ronan978]

Swapping the 6.4 for the 6.1 sorry.

Just did the exact same , I cleaned up all the cast flash , opened to throat up to ~86mm and gasket matched the ports. Picked up 28whp but sacrificed 4rtq(on a 426). A fair trade imo. Also now the acceleration is much more linear, pulls hard all the way thought the rpm's, no more falling flat after 5k And it's ready for a centri when the time comes

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