2004 Cummins 4BT Swap - 5-Speed Tremec 4050 - NP 205


TJ Enthusiast
Original poster
Nov 4, 2020
South Texas
Ok I been working on a 4 BT Swap under my 2004 Jeep TJ Thread and decided that a 4 BT thread would be much easier to follow for anyone else contemplating the same swap
If you go to this link it will bring you up to date and will end where this thread starts
Last edited:
Ok ordered the Tremec 4050 from quickdraw


If you want to go this route budget about 5300.00 Finding an old NV 4500 sourcing all the parts and rebuilding the unit will be a little cheaper but not by very much ( if you had an old donor vehicle that you picked up on the cheap or had out in the back 40 then it might save you some coin.
Last edited:
Some notes and costs for those interested
1. The Cummins 4 BT CPL 1839 (This is the P-Pump Engine and can really be turned up to make some crazy HP/TQ) remember more HP/TQ equals shorter serviceable life you can plan on 3k if your find a deal and up to and probably more like 8-10K
2. Motor Mounts do your research I went with Farmstrong, Inc., Jeff Daniels Jeeps and I Believe Quickdraw also Make Motor Mounts you can Plan on about 350 to maybe 450 dollars
3. Transmissions and Transfer cases, your Jeep 5spd and 231 / 241 T-Case can be used also the NV 4500 and the Tremec 4050 see above for the Tremec complete kit about 5300, plus an Advanced Adapters T-Case Adapter about 550.00 for my Tremec 4050 / NP205 combo
4. The Engine Flywheel Housing Adapter there are 2 Part Numbers an Old Cummins Part No. and a new Cummins Part No.
Engine to Tran Adapter plate Cummins Part No. Old 3923045 Ebay 450.00 and Engine to Tran Adapter plate Cummins Part No. New 3990139 From Cummins 2000.00
5. Engine Test Stand about a 1000.00 I built this big enough to for the Complete Drive Train better to resolve problems here than in the or under the Jeep
6. Turbo Holset Super HX 30 about 800-1000
7. FluiddampnerFluidampr Performance Damper (960311) for 89-98 6BT & 4BT Cummins 630.00
8. MEAN GREEN GEAR REDUCTION STARTER 94-02 DODGE 5.9L CUMMINS - For my motor mounts I need this starter because it is smaller and the stock starter interferes with Motor Mounts about 420.00
9. The Bosch P7100 Pump rebuild. My personal build is everything new or rebuilt I do not want to have to do this twice buy once cry once. Area Diesel Full pump Rebuild about 1500
10. Misc stuff I will post up prices and Sources for when I come to them
a. High Mount AC Bracket and compressor
b. AC Hoses
c. Hydro Boost Brakes
d. Vacuum Pump
e. Radiator and Intercooler
f. Gauges and senders
g. Cummins Overhaul Kit
h. Machine Shop Work
i. Sandblast, Paint and Powder Coat
j. Suspension Lift/ springs /shocks Body lift ect the 4 Bt Cummins is a Tall heavy bitch and I am sure the Suspension will have to be upgraded also I am sensing this may be a good time for GenRight or Savvy Suspension System and some coil overs
k. The Tire Diameter 33/35s and the best Gear ratio for the Cummins Torque Curve ( I am thinking 3:73 or 3:50s
l. Dana 44 Heavy Duty High Pinon for the front
m. NP 205 Shop Manual 43.00 and NP 205 Master Rebuild Kit 150.00

I have probably missed some items but will post em up when cross those bridges
Last edited:
Been making some tweaks on the struts for the engine stand rod ends at both of the ends won't work the engine wants to lay over in the engine stand one end will have to be welded rigid. I will post some pics when it is complete

Also purchased the following
KBS 1 quart Motor Coat Kit Cummins beige108.00
4 cans of brake clean for cleaning the engine 30.00 +/- ( probably could use 2 more )

I Jug of Purple Power degreaser 20.00 +/-
The Brand New Second Hand Cummins Engine Adapter arrived today cleaned it up with Purple power and a brush in a Home Depot Tote and bolted it on the 4BT

Cummins Part No. Old 3923045 Ebay 450.00
NOTE: This is going to relocate the starter to the drivers side mine was originally on the Passenger side of the engine also this part will come back off for paint
  • Like
Reactions: lBasket
Picked up the NP 205 Transfer case yesterday, my KBS coatings Cummins Beige Paint has arrived and ordered the Mean green 94-02 Cummins Starter, I will probably tear down the NP 205, hot tank the case and rebuild it, still need to finish the struts on the engine stand and still waiting for the Tremec 4050 to show up, I am hoping that the overall length of the Cummins 4BT / Tremec 4050/ and NP 205 drivetrain will be shorter or no longer the original 4.0 / 5spd NV 231 drive train. When I get the drivetrain bolted together I will measure both drivetrains and post up the measurements.
  • Like
Reactions: lBasket and Wildman
Good news starter came in today and fits like a glove, I can 100% confirm that the Farmstrong, Inc Motor mounts and the Mean Green starter are compatible. The OEM Cummins Starter was to long and would not clear the MM

Last edited:
  • Like
Reactions: lBasket and Wildman
NP 205 Shop Manual 43.00 from Torque King
NP 205 Master Rebuild Kit 150.00 from Transparts Warehouse Part# BK205FDM (for Ford Married T-Case)

Got the NP 205 unloaded and on the work bench ready for teardown, complete overhaul and twin stick upgrade
Ok so if anyone is interested the Ford NP 205 T-case with the Advanced adapters Adapter - from the Transmission Mounting surface on the adapter to the the middle of the U-joint Socket on the output shaft (Overall Transfer case and adapter length) is right at about 14 inches, also the Advanced adapter is not clockable it only fits one way and it appears to be machined from a casting and not a billet
Last edited:
  • Like
Reactions: lBasket