Transmission Swap

[Mark B]

Have a 2008 1500 short 2wd 3.7 v6 auto
Question: Will any newer automatic transmission with more gears bolt in and hook up electronically?

 

[HemiLonestar]

Have a 2008 1500 short 2wd 3.7 v6 auto
Question: Will any newer automatic transmission with more gears bolt in and hook up electronically?

LOL...you do know it's never that easy, right? Are you looking for a straight bolt in?

 

[Mark B]

That was what I was hoping lol

 

[PCA4208]

Long Answer: Not unless its the same bolt pattern, electronics, mounting location, output type, etc
Short answer: no

 

[HemiLonestar]

That was what I was hoping lol

No. Nothing will just bolt in. Now depending on how much money and skill you have (or are willing to pay for), anything is possible.

 

[finally03gt]

1. Lots of power
2. Reliable
3. Inexpensive

Choose two from above.

 

[HemiLonestar]

1. Lots of power
2. Reliable
3. Inexpensive

Choose two from above.

Considering he has a 3.7 V6...#1 not really an issue LMAO

 

[ST-8]

Considering he has a 3.7 V6...#1 not really an issue LMAO

Really the one benefit of owning a 3.7 or 4.7 for that matter LOL

 

[SithCommando]

I had the same question. Looking for fuel efficiency and was looking to swap my '08 5.7's 545rfe with the '19 5.7's ZF8HP70 or 8HP75. Where could I be pointed to do/get what is needed?

 

[HemiLonestar]

I had the same question. Looking for fuel efficiency and was looking to swap my '08 5.7's 545rfe with the '19 5.7's ZF8HP70 or 8HP75. Where could I be pointed to do/get what is needed?

Call Sound German Automotive. Order the $1000 retrofit harness. Buy an 8HP70 (anywhere from about $800 used to $2000+ lower mileage or new), don't forget the shifter (according to them, it has to the car style shifter, regardless be prepared to lose that column shifter - ZF is all electronic, no cable). If you 2wd prepare to shell out for that custom driveshaft, ZF has no provision for a slip yoke. If you're 4wd, you have to make sure your transfer case will bolt to the ZF trans or you have to find one that will work. Then all of this has to be installed, then the transmission TCM (which is internal by the way) has to be properly programmed (HP tuners) so you don't blow it up.

Here's the fun part, you're looking for fuel efficiency in a hemi Ram; while that idea in and of itself is funny, you need to do a direct comparison of the two transmissions. Most people would do this swap so they could avoid blowing up a trans, the ZF is much stronger than the RFE and the extra ratios help keep it in the powerband better. The RFE is basically a 3sp with 2 OD gears. The ZF is basically a 6sp with two OD gears. Ultimately the final OD gear in both transmissions is the same ratio (.67:1). The newer Rams get better mileage with them because they can put taller gears in them considering the gear ratios in the trans. You don't need 3.92-4.56 for leverage with a 3:1 first gear when you have 4.71:1 first gear; you can throw 3.55's or even something like a 3.23 in a truck and still get amazing towing ability and then your fuel economy empty goes way up because you have a taller gear with a double OD. The cars get phenomenal mileage with them for this reason. Automatic Hellcat Challengers come with a 2.65 rear behind the 8HP90 (similar but much stronger). They're EPA rated for 22mpg highway with 707hp (or more, depending on year)!

545RFE 8HP70
1st - 3.00:1 1st - 4.71:1
2nd - 1.67:1 2nd - 3.14:1
2P - 1.50:1
3rd - 1.00:1 3rd - 2.10:1
4th - 0.75:1 4th - 1.67:1
5th - 0.67:1 5th - 1.29:1
6th - 1.00:1
7th - 0.84:1
8th - 0.67:1

So for you to ultimately realize the fuel economy you're looking for, you'd have to do this swap (expensive, especially if you can't do it all yourself) AND change your rear gear ratio (2WD) or both (4WD) to match it, otherwise 1st gear will be absolutely useless lol. Figured this out awhile ago when I researched doing this after learning someone figured out how to retrofit them.

 

[SithCommando]

Call Sound German Automotive. Order the $1000 retrofit harness. Buy an 8HP70 (anywhere from about $800 used to $2000+ lower mileage or new), don't forget the shifter (according to them, it has to the car style shifter, regardless be prepared to lose that column shifter - ZF is all electronic, no cable). If you 2wd prepare to shell out for that custom driveshaft, ZF has no provision for a slip yoke. If you're 4wd, you have to make sure your transfer case will bolt to the ZF trans or you have to find one that will work. Then all of this has to be installed, then the transmission TCM (which is internal by the way) has to be properly programmed (HP tuners) so you don't blow it up.

Here's the fun part, you're looking for fuel efficiency in a hemi Ram; while that idea in and of itself is funny, you need to do a direct comparison of the two transmissions. Most people would do this swap so they could avoid blowing up a trans, the ZF is much stronger than the RFE and the extra ratios help keep it in the powerband better. The RFE is basically a 3sp with 2 OD gears. The ZF is basically a 6sp with two OD gears. Ultimately the final OD gear in both transmissions is the same ratio (.67:1). The newer Rams get better mileage with them because they can put taller gears in them considering the gear ratios in the trans. You don't need 3.92-4.56 for leverage with a 3:1 first gear when you have 4.71:1 first gear; you can throw 3.55's or even something like a 3.23 in a truck and still get amazing towing ability and then your fuel economy empty goes way up because you have a taller gear with a double OD. The cars get phenomenal mileage with them for this reason. Automatic Hellcat Challengers come with a 2.65 rear behind the 8HP90 (similar but much stronger). They're EPA rated for 22mpg highway with 707hp (or more, depending on year)!

545RFE 8HP70
1st - 3.00:1 1st - 4.71:1
2nd - 1.67:1 2nd - 3.14:1
2P - 1.50:1
3rd - 1.00:1 3rd - 2.10:1
4th - 0.75:1 4th - 1.67:1
5th - 0.67:1 5th - 1.29:1
6th - 1.00:1
7th - 0.84:1
8th - 0.67:1

So for you to ultimately realize the fuel economy you're looking for, you'd have to do this swap (expensive, especially if you can't do it all yourself) AND change your rear gear ratio (2WD) or both (4WD) to match it, otherwise 1st gear will be absolutely useless lol. Figured this out awhile ago when I researched doing this after learning

You're the bomb! I keep forgetting to clarify mine is 2WD. I also plan on either overhauling my current 5.7 or swapping for a 6.4HD or a 7.0

Thank you so much!

 

[HemiLonestar]

You're the bomb! I keep forgetting to clarify mine is 2WD. I also plan on either overhauling my current 5.7 or swapping for a 6.4HD or a 7.0

Thank you so much!

You're welcome, however you can't just drop in an OEM 6.4 HD. That is a VVT engine and your PCM can't run it. On top of that, because it's a different engine family the accessory drive is different as well. You need to use a 5.7 or 6.1 block as a base and go from there. I find it funny you ask about increased fuel economy and then plan to do things that are the exact opposite lol.

 

[SithCommando]

You're welcome, however you can't just drop in an OEM 6.4 HD. That is a VVT engine and your PCM can't run it. On top of that, because it's a different engine family the accessory drive is different as well. You need to use a 5.7 or 6.1 block as a base and go from there. I find it funny you ask about increased fuel economy and then plan to do things that are the exact opposite lol.

Well, I admit the 7.0 is a monster and unnecessary. But I was reading that the 6.4 had at least 4 mpg in savings over the 5.7 under similar load. Of course that was from the same 2500 platform.

 

[HemiLonestar]

Well, I admit the 7.0 is a monster and unnecessary. But I was reading that the 6.4 had at least 4 mpg in savings over the 5.7 under similar load. Of course that was from the same 2500 platform.

Be that as it may in 4th gens, you still can't just plop a VVT engine into your truck without extensive wiring and PCM changes.

 

[BWL]

I had the same question. Looking for fuel efficiency and was looking to swap my '08 5.7's 545rfe with the '19 5.7's ZF8HP70 or 8HP75. Where could I be pointed to do/get what is needed?

My 17 hemi with the zf 8 speed and 3.92 has almost the same fuel economy as my 11 hemi with 545rfe and 3.92. Only difference between them was the 11 was a quad cab and the 17 is a crew. So a pretty costly endeavor that will never pay you back if you're doing it for fuel economy.

 

[ric3xrt]

You're the bomb! I keep forgetting to clarify mine is 2WD. I also plan on either overhauling my current 5.7 or swapping for a 6.4HD or a 7.0

Thank you so much!

IF your goal is a Daily driver with more Power , the 5.7/6.1 is your better bet, but if you are looking to do a weekend warrior, occasionally driving to work , 6.4 based build , is doable, but the Air condition compressor is a no go. I've done it a few times. you have to keep in mind that the 09+ engines use 58 tooth tone wheel, so you have to open up the engine to change the wheel over to the pre09+ 32 tooth wheel. The VVT system is easy to get around.

Over the winter I did a 441CI based 6.4 into a 03 QC 4x2 the truck had the 05 PCM swap. trans is 8sp ZF up and all the tuning was done with Syked Tuning....sound German is the place to go for the controler for the 8sp and the Nag1 , great people to work with....No f--ked up issues with their controller , it's worth the price.

 

[HemiLonestar]

Over the winter I did a 441CI based 6.4 into a 03 QC 4x2 the truck had the 05 PCM swap. trans is 8sp ZF up and all the tuning was done with Syked Tuning....sound German is the place to go for the controler for the 8sp and the Nag1 , great people to work with....No f--ked up issues with their controller , it's worth the price.

Sending you a few questions

 

[Spsully]

Over the winter I did a 441CI based 6.4 into a 03 QC 4x2 the truck had the 05 PCM swap. trans is 8sp ZF up and all the tuning was done with Syked Tuning....

Uhhhhhhhh. Yes please