4L80e and NP241c Upgrade

4L80e Upgrade
Here is my 4L80e experience

Started with a 1988 24,000-mile M998 that had been updated with the 6.5L NA, still had the TH400 and NP218.
The TH400 became a 4L80 and the NP218 was replaced NP241c, to allow the 2wd operation. Time will tell how the 2wd works, but lots of modern HD pickups(my 2500 Ram only disconnects at the T-Case) have the same operation and really reduces the wear & tire of the front end and allows better drive-ability.
Transfer Case:
I had a local guy with a transmission, so I ended up looking for a T-Case first and found a deal. Bought if for $45 off FB. It was unknown history but felt very tight. I still went ahead and ordered gaskets, seals and chain kit. $45 +168.53+12.99 ($226.52)

Transmission:
The local guy never came through with the parts, so I decided to go with a civilian model and make it work. Found a Transmission with T-case on FB ($300). Found a like brand new low stall torque converter on FB($100). The final main part need was a standalone controller. After much research, I decided to go with the US Shift, Quick 4. One main difference was the need for a 2[SUP]nd[/SUP] control table because the transmission does not have the output speed tone ring, I am taking the OSS from a tone ring on the transfer case output. Main parts for the swap $1,152. This transmission is a total wildcard and I am hoping for a year before needing to rebuild. Lots of the smaller parts will be covered in the install section.

Pre-Job Worries:
I read every post I could find on doing this swap, but there are still so many questions that really don’t get covered. Augi’s write up was awesome and a must read for anyone attempting this upgrade, but I tracked my job to hopefully give so more input.
Here is my 4L80e experience and thoughts.
Price: how much is this really going to cost. Numbers get thrown all over the place. Transmission/ Transfer/ Controller are the 3 biggest cost drivers. For me, driveshaft/ modifications were high.
Shifter: $500+, read my mod thread on how I did this for Cheap
Transmission to Transfer case adapter: I was not using the military set up, so this was a big worry. The transmission I bought had this stock adapter and it worked perfectly with my transfer case.
TPS & Tach: I found the proper TPS for my 6.5L GEP and Quick 4 doesn’t require tach, but was a concern before starting.
Overall, I knew I didn’t have all the parts needed before starting, but my plan was for 4 weeks and I could source what I needed as I went.

Transmission & Transfer Removal:
· Disconnect Battery, Install tire blocks
· Remove transmission ATF (I used vacuum syphon), kept oil in X-Fer
· Remove Rear Drive shaft (4- 15mm heads rear, 5/16 head front)
· Remove exhaust cross pipe (9 bolts- 9/16 heads, both sides)
· Remove Front Drive shaft (Mark both sections alignment if separating) (5/16 head strap bolts)
· Remove Tranny Inspection cover (6- 15mm heads)
· Unbolt torque converter (6- 9/16” head bolts)
· Remove Transfer case shift linkage (2 cotter pins)
· Remove transmission shift linkage (2 cotter pins)
· Remove transmission cooling lines (2 rubber hoses with clamps)
· Remove exhaust clamp on X-fer case
· Remove dipstick (Bolt on Head & push fit) (I didn’t do this and made it more difficult later)
· Remove TH400 Kickdown cable (removed in engine valley)
· Remove Electric connector on Tranny (simple push on fitting)
· Remove Speed cable at back of X-Fer case (large knurled nut)
· Remove vacuum lines (I really waited until the tranny was ½ lowered)
· Support rear of engine with jack (I used scissor jack on 6x6 blocks)
· Loosen tranny cross member (13/16” bolt head & 7/8” bottom nut)
· Loosen (break only) bell housing bolts (6- 9/16” head)
· Place transmission jack (going back, I would have supported transfer case and remove crossmember the place jack in a better balance spot)
· Remove Bell housing bolts
· Remove crossmember
· Slow back and lower transmission and transfer case


Installation of Transmission & Transfer:
· Transmission on Tranny Jack
· Insert Torque converter- ensure proper depth (measure Engine to Flywheel too)
· Jack up Transmission in to alignment pins on block and push forward in to place
· Install 6 Bell housing bolts- Don’t use bolts to pull up gap (finger tight at this point; 9/16”)
· Fabricate Rear cross member (or buy A2 one)
· Transmission support block might need to be changed/ fabricated. (I used the civilian model but had to modify to fit the holes in the A2 cross member I bought)
· Bolt up transmission rear support block (15mm at transmission: 9/16” @ crossmember)
· Install cross member (hand tighten bolts at this point 13/16” top: 7/8” bottom)
· Ensure bell house fit and torque bolts (9/16” to 32 Ft-lbs)
· Install transfer case (I used studs in Transfer case)
· Install Loctite & Torque 6 tranny to transmission extensions nuts (15mm
· Install dipstick
· Transmission Cooler line install. Used existing hard lines via existing rubber connectors
· For me, transmission Pan removal and filter/ fluid change (Dex VI)
· For me, fill transfer case (Dex III)
· Transmission Shift Linkage Installation (see other section for my modifications to 3 Speed shifter)
· Transfer Case Shift Linkage Installation
· Install inspection cover (modified stamped steel LS block one from E-bay junk yard seller $45)
· Install rear drive shaft
· Install front Drive shaft (I had to move Carrier Bearing ½” for shifter clearance. TBD long term!)
· Install Exhaust cross over piece
· NOTE: Exhaust support at transfer didn’t work from NP218 for me. TBD long term if need custom one)

Installation of Quick Shift 4:
· Plug in 3 transmission plugs (I used electric connection on transfer output)
· Route transmission harnesses (Tranny main plug & 2 Speed pick-ups) to cabin
· Find location for Controller (I did it where fording valve would be) used a simple metal bracket
· Locate Keyed Power (I hardwired in to Wire 29A off key switch)
· Wire 24V-12V Transformer and wire 12V out to Quick 4 Vehicle harness
· Install TPS (6.5L remove Fan Cut out Switch & replace W/ TPS) (2-3/8” head bolts)
· Wire TPS to Vehicle harness
Power up Quick 4 and Set up TPS, then configure for HMMWV
·

My Actual issues:
TPS: What a huge pain in the ass! The back bolt that held the fan cut out switch in place was so ****ed hard to do. Just had to keep at it, re-install was a joyous PITA too! I ended up super gluing the washer to the head to allow hand turning the bolt
Dip stick: I bought a flexible 36” one from E-bay. What a waste of money. Can’t get a funnel small enough to fit in, and its not long enough to mount any place convenient.
Quick 4- I used the laptop to set the TPS, it must be done via controller or it screws up. I also had tach input checked and this caused an error message. Tech support was Fantastic, both issues easily fixed.
Fan cut out switch: I looked at the bracket to move and I am not really sure about that. I think I am going to run without it, I rarely use full throttle and if the fan is on, I am not going full throttle, unless I need to out run a tornado…
Civilian vs military transmission support. I bought the A2 crossmember, but I had to custom modify the civy rubber support.
Drive shafts: I bought an A2 rear and had to have that shortened, not a bid deal, but my front shaft was a total disaster. The government had the 2 shafts out of phase & each shaft out of phase. I needed a new larger u-joint to match the NP241 flanged output, carrier bearing replaced, and the shaft shortened. Overall, the rear mods were and expected $74, but the front was $289- 3x my planned costs
Un-related, but I spent days diagnosing a bad started solenoid as I tried to crank it up the first time after I was ready to do initial testing.

Good work Joe. It will be worth all the hard work.

Woof! Plenty of work and troubleshooting, but I don't mean to disparage. Great job and thank for sharing the writeup for all interested.

This helps me NOT want to go this way, owing to the amount of work and my meager setup/tools. Valuable, but not like I'd hoped, but very valuable.

You're really hitting the truck hard with maintenance and improvements, glad to see a rig getting so much attention.

BDGR

This is one of the best writeups ever! There should be an award for this!

This is a great write-up.

Just a quick question... Was this 1988 vehicle rebuilt with an A2 wiring system or is it A1, and was the fuel cell the old or the newer version, and was the E-brake the old or the newer version?

This was an '88 that had a GEP 6.5L & the new parking brake done by the Government at some point. I am not sure which fuel tank I have, I can't tell by looking at it underneath which style it is. I am also unsure which wire harness I have, but the engine harness was P/N 12339350 (I had a bad connector and changed it out a few months ago)

TOBASH said:

This is a great write-up.

Just a quick question... Was this 1988 vehicle rebuilt with an A2 wiring system or is it A1, and was the fuel cell the old or the newer version, and was the E-brake the old or the newer version?

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looking good Joe.

GasTurbineTech said:

My Actual issues:
TPS: What a huge pain in the ass! The back bolt that held the fan cut out switch in place was so ****ed hard to do. Just had to keep at it, re-install was a joyous PITA too! I ended up super gluing the washer to the head to allow hand turning the bolt
Dip stick: I bought a flexible 36” one from E-bay. What a waste of money. Can’t get a funnel small enough to fit in, and its not long enough to mount any place convenient.
Quick 4- I used the laptop to set the TPS, it must be done via controller or it screws up. I also had tach input checked and this caused an error message. Tech support was Fantastic, both issues easily fixed.
Fan cut out switch: I looked at the bracket to move and I am not really sure about that. I think I am going to run without it, I rarely use full throttle and if the fan is on, I am not going full throttle, unless I need to out run a tornado…
Civilian vs military transmission support. I bought the A2 crossmember, but I had to custom modify the civy rubber support.
Drive shafts: I bought an A2 rear and had to have that shortened, not a bid deal, but my front shaft was a total disaster. The government had the 2 shafts out of phase & each shaft out of phase. I needed a new larger u-joint to match the NP241 flanged output, carrier bearing replaced, and the shaft shortened. Overall, the rear mods were and expected $74, but the front was $289- 3x my planned costs
Un-related, but I spent days diagnosing a bad started solenoid as I tried to crank it up the first time after I was ready to do initial testing.

Transmission	$300.00	FB Market Place
Torque Converter	$100.00	FB Market Place
Controller (Quick 4)	$752.00	US Shift
TPS	$43.78	Rock Auto
Support Cross member	$25	Military truck show (TNJ Murray)
12V Power supply	$19.92	https://www.amazon.com
Dip Stick	$63.99	Ebay
Filter/ Fluid	$75.97	Auto Zone
Shifter	$20.00	Misc Steel/ hardware
Drive Shaft- Rear	$241.00	Bought A2 ($165) local machine shop shortened ($74)
Drive Shaft- Front	$289.20	Stock had to be reworked extensively, new flange mount type ($289)
Transfer Case	$45.00	FB Market Place
Transfer Rebuild	$168.53	All State Gear
Misc Hardware	$20.00	Tru Value
Transmission	$1,930.86
Transfer Case	$233.53
Sold TH400 w/ NP218 & NP246	-300 & -165
Total	$1,674.39

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Hey,
Extremely useful writeup!!!!
I am doing a similar setup as yours, with the US Shift. Wanted to aske where you pull the Engine RPM Signal Input from ? did you use the speed sensor off of the oil pump?

Thanks!
Gal.

hummer-h1 said:

Hey,
Extremely useful writeup!!!!
I am doing a similar setup as yours, with the US Shift. Wanted to aske where you pull the Engine RPM Signal Input from ? did you use the speed sensor off of the oil pump?

Thanks!
Gal.

Click to expand...

Gal,
I didn’t hook up an rpm signal input. It is not a required for the US Shift installation. You don’t get the learning capability of the controller. I planned to go back and figure out a signal (my 6.5l has an oil pump sensor) but 18 months later and it drives just fine, so never got around to doing it.
Joe

GasTurbineTech said:

Gal,
I didn’t hook up an rpm signal input. It is not a required for the US Shift installation. You don’t get the learning capability of the controller. I planned to go back and figure out a signal (my 6.5l has an oil pump sensor) but 18 months later and it drives just fine, so never got around to doing it.
Joe

Click to expand...

Thanks so much Joe,
Looks like I will give it a shot without, see how it goes. I will let you know


Gal.