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I need to replace my transmission in my 2003 5.7l 2wd Ram. I was under the impression that all 5.7l 5-45rfe's were the physically same but there are different part numbers given for 03 vs 04/05 transmissions. Can I swap in a 2005 transmission on my 2003 ram?
 

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There are three important differences between the 2003 and 2005 transmissions:

1) Cooler line fittings changed (for 2005 MY) to a quick-connect fitting. Threads in the case are the same - just the connection to the line changed. So you will need to pull the fittings off your old trans and swap them onto the new one.

2) The extension mounting screws (underneath the extension, that attach the extension to the rear mount) changed (for 2005 MY) from English (7/16-14 × 1.25) to metric threads (M10 × 1.50 × 28 mm). So you will need to get new screws to go with the new trans. From Mopar they are P/N 06503699.

3) The apply orifices for the Reverse clutch and 2C clutch were reduced (in size) for 2005 MY. These orifices are in the steel separator plate in the main valve body assy. The trans calibration in your (2003) truck is set up for the larger orifices, so you will need to remove the oil pans, remove the valve bodies, split them apart, and swap the separator plates (install your old plate into the new VB). Or, you could just swap your entire old VB assy into the new trans.

While you have the VBs out, I would recommend that you check the size of the solenoid switch valve (SSV) bore (which is inside the main valve body casting, not inside the solenoid module). It is very common for this bore to become worn (oversize) at high mileage (90K+), and if it is worn you will get pressure leakage into or out of the OD clutch passage (not a good thing). On top of the valve body is a sliding code plate (that moves when you run the shift lever back and forth). Inside the center "chunk" of the valve body, underneath this sliding plate, are two valves - the manual valve (which has a pin that engages the slot in the code plate - this is the valve that moves when you move the shift lever) and the SSV. The SSV is retained by a rectangular plastic retainer, and it has three (3) barrel-shaped plugs at the outer end of its bore. You want to check the size of the four (4) outer lands in this bore (where the plugs slide). The diameter should be 11.544 mm (0.454 inch) max. If both of your VBs (old and new) have any of these lands worn oversize, replace the entire VB assy with a new Mopar VB. The P/N for your 2003 truck is 05080732AD, but apparently those are all out of stock. So you can buy a VB assy for a 2010 truck (RL166834AD) and then swap your old separator plate into that brand new assy. The new Mopar VBs are all anodized to resist the SSV wear, so your new VB should last much longer than the original one. All 2010 MY (and later) RFE transmissions already have an anodized VB. Note that Mopar uses a "reman" part number for the valve bodies. This is so we can get the old VB back for core. But the service VBs are all new (anodized) units now.
 

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If his '03 solenoid pack has a black connector (early built '03) and the '05 has the white connector, isn't an adapter required to lock the connector down. I know using an '03 and down transmission needs this to work in a newer truck, but I'm not sure the other way around.
 

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If his '03 solenoid pack has a black connector (early built '03) and the '05 has the white connector, isn't an adapter required to lock the connector down. I know using an '03 and down transmission needs this to work in a newer truck, but I'm not sure the other way around.
No, the solenoid connectors may have different colors, but they are the same shape and are interchangeable functionally. The black connector was the original one. The white connector denotes the "NVH" solenoid module, which was introduced in 2004 MY Jeeps and went across the board in 2005 MY. That solenoid module contains individual solenoids that are designed to be quieter than the original design (no more "solenoid buzz" when coming to a stop or shifting into gear from Park/Neutral). That solenoid module can be used in place of the earlier one; the electrical pinout and connector configuration are the same.
 
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