4L80E/NP205 swap

[bilfman]

Hi peeps,

I just completed a 4L80E/NP205 swap and am going to go through the build here in the forums. I looked on the net many times and couldn't find a 'real life' start to finish of a project like this. I replaced the TH400/NP203 in my 1979 crew dually.

The basics of my dually are it is a 454 with hooker headers, edelbrock performer, edelbrock 750cfm carb. Diffies are dana 60 up front and dana 70 in the rear. The 60 has a eaton tru-trac locker and the 70 has a detroit locker and I am running 3.73 gears. I was running about 2600 rpm at 60 mph.

In 1991 GM released a 4L80E/NP205 combo this was only available in the crew cabs, which were still square bodies in 1991. These are very hard to find, but I was able to locate one for a steal of $600.

I have done many resto in the past 30 years but the electronic transmission had me a little worried. For those of you who feel as I do, I can tell you now it is a piece of cake. As you follow the build you will see how simple it really is.

The trans and tcase looked rough under 21 years of grime, but to me it was a diamond ready to be worked. Here are some pics of the beast when it arrived.

[bilfman]

This is my little gem that will recieve the 4th gear gift....

[bilfman]

What initiated this whole deal was the NP203. These cases were designed to be full time 4wd. When converted to part time, as mine was, they had to be engaged to be oiled properly, this had to be done every 100 miles or so. Another fix to eliminate this is to extend the filler bung with an elbow and a 2" nipple, basically lets you fill the case with another 2" of oil. So my mind was thinking 205 the whole time and once I heard there was an NP205/4L80E combo the hunt was on........

[bilfman]

Break out the rags, sandblaster, chisels, hammer and a lot of 'pita' work and I have the trans and tcase cleaned up enough for putting in the truck. I resealed all covers and changed all the oil seals. Here are some shots of the process.

[bilfman]

The crossmember mount was siezed solid and the studs had to be ground off to be removed. I rebuilt it with a piece of 1/8 plate and a couple of new studs and it was good as new. It was a little tricky welding so as not to damage the rubber mount!

[bilfman]

Now that stuff was cleaned up and workable it was time to REALLY commit. I go from a truck that works just fine to putting in a trans and tcase the I'm not positive work and also enter the electronic transmission realm that is fully foreign to me.

Cleaning the parts up took over 10 hours of work, chip chip chip. The rust on the tcase and adapter had to be slowly chipped off with a small chisel and hammer.

[asphaltburner]

How cool, bilfman!
You've gone the step I probably should have when I went with the TH400/NP205 build in my truck (from TH400/NP203)! The truck is used frequently for heavy chores, but the electronics and overdrive would be nice, especially since my front and rear gears are 4.11:1.
As little as it hits the highway, I guess re-building what I had was a good way to go.
It sure turned out to be an outstanding truck with amazing capabilities!
Good luck with yours!
Todd.

[DirtyLarry]

That is cool! You will love that combo over a TH400/203 every day from here on out. Overdrive is always a good thing. Love the truck too!

Okay, the question begs to be answered….what is so special about a 1991 4L80E/205 vs. a 1985 or later 205 that would have been behind a TH400 mounted to a later 4L80E? The early 90's 4L80E’s had a horrible reputation for reliably but I doubt that 4L80E is the original 1991 piece anyway being most failed before they ever saw 100,000 miles. Is the 4L80E/205 adapter unique to 1991? Seems people have been hanging 205s on the back of 4L80E’s quite easily for years without searching for a rare 1991 specimen but I haven't followed exactly how they did it being I am not much of an automatic fan.

[bilfman]

After a little research I learned this........

The trans/tcase came with the factory computer and harness, I was going to utilize these to save some $$ and not but an aftermarket controller.

For all you cheapies out there like me, forget the former, drop the dime and buy an aftermarket controller. I spent the $600 and was glad I did, much better the trying to work the factory unit.

Also I found out that I had to replace the internal wiring harness of the transmission any tranny before 1993 needs an updated harness to work with the controllers on the market today. These can be very pricy, the best deal I found was from a local tranny shop and I got one for $100. The also suggested replacing the internal solenoid that the harness connects to, this was $70. Sorry I didnt take pics of this but the swap was easy, remove the pan and the harness is right there, just unplug 1 at a time and route the harness just as the one that is already there. The solenoid was 1 screw on a retainer it just pulls straight out. It needed a pretty tough tug to get it out. This whole proceedure took 5 minutes after the pan was off. Here is a pic of the harness ond solenoid...

[bilfman]

The 1991 is a factory mated combo thats all. I know there are adapters out there but it was the hunt and seek that peeked my interest

[bilfman]

Getting late here, more to follow tomorrow.

[bilfman]

A thing I like to do is paint all sealed surface a light color, in this case orange. That way if you get a little leak or seepage you can see it right away.

[bilfman]

So the old 600 pound beast is starting to come out, you can now say " I'M COMMITTED!" Here is the old grimy released from its 33 year old prison.

[bilfman]

The flex plate that came with the 4L80E was a 6 bolter to the converter. This plate did not fit over the old big block crank so I had to use the flex plate from the TH400, the bolt pattern worked but could only use 3 bolts as in the prior combo. I thought that would be fine as it had run the past 33 years on 3 bolts.

[bilfman]

The next step was to get the 4L80E bolted up. There were no clearance issues and it basically bolted up pretty smooth. It fit just as well at the TH400 so no real issues with the implant.

I just left it jacked in place while I worked on the crossmember and tcase. The tcase went on next and it bolted up like clock work with some nifty, yes I used the word nifty, use of another floor jack.

So after bolting the tcase to the tranny I was left with 2 jacks holding the pieces in place. Oh, before I go any further I should mention that I had the truck up pretty high on 4- 12 ton jackstands, major overkill, it was sitting about 24 inches off the ground.

So with 2 jacks holding stuff in place I cut a 30" piece of 2x4 and manhandled it under the tcase, while leaving me enough room to access the rear mount. I then removed the jacks and worked on mounting the crossmember.

The drivers side was easy as I had good access to the frame rail but the passenger side was a bear. Exhaust and heat shield made it impossible to hold, set or wrench nuts in the proper position. I had to weld the nuts to 2-2" wide washers and then cut a side off the washer so it wouldn't turn inside the frame. These were a b**ch to get in place, had to drill some holes in the frame and position then with a long magnet.

[bilfman]

So far it had been a 1 man operation, I'm stubborn like that. But.....I had to recruit some help for, well you would think something HEAVY, but no. I could not for the life of me get the trans dipstick tube in by myself. Clearance was tight. It needed pull and lining up from the bottom and some turning and holding up top. I recruited my neighbour for some help.

No pics for this stuff but here are some of the details. The NP205 did not have yolk on the rear output shaft. Luck would have it that the NP203 yolk was a direct fit. So I ended up using both front and rear yolks from the NP203 on the 205.

Both driveshafts needed modding the rear was lengthened 3 3/4 inches and the front was shortened 2".

I had some trouble with fit, I felt that the rear of the tcase was sitting too low and it affected the driveshaft angle into the steady bearing. I removed the spacers you can see in the previous pictures and all was sitting pretty.

Onto the cooler lines, I needed some extra length on the cooler lines to reach the 4L80 i was able to rebend the existing enough to get the originals to fit.

The shifter linkage to the 4L80E was the same basic set up as the TH400. Only thing was it sits about 2 inches back from the TH400 set up. I was able to unbolt and move the frame bracket back and also welded 2 inches of 3/8 bar to the existing shifter bar to get length needed for the factory shifter to work. It works perfect for PRNOD3 but doesn't hit 2 or 1. I wasn't to worried about this as I rarely use 1 and 2 and if pulling is tough on the highway I can atleast drop to 3rd. Also the TCI controller has a manual shift mode via push buttons if I really want to hit 1 and 2.

The tcase shifter fit right through the stock hole but could not hit 4hi. I had to cut about an inch out towards the front seat to be able to pull the shifter down far enough. This enabled 4hi but the shifter knob was touching the seat. Looked semi pro. So I took it off and heated it up and bent it abour 1 1/2 inches forward and it look like stock positioning now. I used the NP203 boot, worked perfectly, just needed to be moved back toward the seat about an inch as well.

The truss rod to the transmission had to be shortened about an inch to accomodate the NP205. It was a cut, sleeve, tack and full weld proceedure.

[bilfman]

Here is the shifter after the heated bend. Prior to the bend it touched the seat in 4hi.

[bilfman]

Now onto the electronics.......virgin turf and really had me outside the box. But actually was a TOTAL simple proceedure with the aftermarket controller. I researched several and ended up going with the TCI EZ-TCU. I chose this due to price, ease of installation and the programable handheld unit included with the kit.

Let me tell you, the TCI kit was amazing. Very good instructions and the wiring harness was one of the most straightforward I have ever seen. Excellent labelling and each wire is both color coded and ink labeled as well. I got the kit for $615 and can say with 100% conviction it was absolutely money well spent. DON"T EVEN BOTHER WITH THE FACTORY CPU.

The EZ-TCU needs 3 inputs to operate the tranny. I will got through each and the process I did to get each up and running.

1. Speed sensor. This is the rear most sensor on the transmission, or in my case the tcase. It is a 2 wire connection and it appears the GM used 2 sizes of connectors. The TCI harness comes with the smaller one that is used on more current 4L80's. But also has another loose in the kit for older 4L's. I had the older one. I just cut off the one on the harness and assembled the larger supplied connector. There were no instructions for this and it took a few minutes to sort out the parts, as there are several loose pieces in the kit. Bingo 1 of 3 complete.

2. Throttle position sensor(TPS) I searched online for a tps kit for a carb and found one called an acculink. It was about $120. It is pretty simple and the online instructions are great. I had to cut some of my stock rear throttle linkage mount out for it to fit properly but it mounts quite easily. You could use an old one off any salvage TBI unit, its pretty simple to fab yourself too. I had a tps error and was WTF'ing a bit. This turned out to be an easy fix. You need to use a multi meter and check the tps voltages at zero throttle and at full throttle. On the TCI unit it is the white with pink wire that you check the voltage on. Adjust the tps to show 0.2v at zero throttle and make sure it is under 5v at full throttle. This will make sure the tps is in working parameters for the EZ-TCU. The instructions were not really clear on this. But it did kinda mention it in a round about way. BAM 2 of 3 complete!

3. RPM source. The EZ-TCU needs an rpm source. A coil or the HEI tach lead is not a clean enough signal for the kit. BUT!! The kit comes with an easily installed "rpm module" Hook the white wire to the HEI "tach" terminal, black wire to ground and the yellow wire to the EZ-TCU tach labeled wire on the harness and BOOM done! Step 3 of 3 is complete.

After that just plug the harness into the transmission and also plug into the EZ-TCU computer and the electronic side is done. There is a bit of a rat nest of wires left over for other more advanced installs, I just bough a black electronic kit box and stuffed the unused ones in there to clean up the look of the install. Some of the extra wires are for paddle shifting, manual torque converter locking, performance mode, manual mode.

I also ran the handheld unit wire through my firewall.

From there it is just following the instructions in the kit via the handheld unit to program the TCU. It is pretty basic and simple. Just follow the prompts. It is absolutely forgiving if you do make a mistake, just reset it and roll again. Basically it is pretty much impossible to screw up.

I went with basically its stock settings. The only thing I changed was the torque converter setting. On the maiden voyage the converter was going in and out of lock with light movement on the throttle. You can set the % of throttle needed before the converter unlocks, stock setting was 40%. For my truck 75% worked perfect, lets enough throttle to get up a decent hill without unlocking, but if you gas it you unlock and get that get up and go.

[bilfman]

Here is an under hood look of the install. Firewall has the cpu, the bigger black box houses the extra unused wires and extra length of the harness and the other black box is a Cable-X electronic to mechanical speedo converter. I'll get to that later. The other pic is the Acculink TPS mounted to the carb.

[bilfman]

This is the supplied rpm module. Snap to install. White to HEI tach terminal, Blacks to ground and Yellow to the kits harness.

[DirtyLarry]

Tough work! You are also doing great on time….You would make a great flat rate tech! Those 203’s are some heavy dogs aren’t they?? I wish you lived closer as I wouldn’t mind having the range box off the 203.

Curious as to why you have the spacers between the frame and xmember? Those spacers are intended to be on the top side of the frame for use a longer bolt to achieve a higher torque value and increase clamp load of the xmember mated flat to the frame (Same reason those spacers are used by the steering gear box as well…..think of a bolt as spring). The spacers located between the xmember and frame as you have now will cause the xmember to walk around like it is on stilts and will eventually cause frame cracking. Imagine those spacers working like a paper punch. I’ve seen people move those spacers from the correct location to the bottom like you have on lifted trucks to help correct driveline angles only to end up with bigger vibrations and cracked frames. You might want to reconsider that set up.

When I did my NV4500 swap the xmember had to be dropped slightly maintain the 3 degree engine tilt. To do that we made a flat spacer with the tube spacers above the frame as GM designed it to maintain the original high torque clamp load design.


You’re going to love overdrive!

[bilfman]

Onto the speedo. The 4L80E is only setup to control an electronic speedo. OH NOES!!! What do I do???? Onto the internet again. There is a unit called Cable-X ($300) that converts the electronic signal from the trans, to a motor, that then turns the old speedos. The TCI kit makes this install a breeze, it has a supplied plug just for this. I made a wee mistake in my newbness and sourced the TPS, TCU and Speedo control all seperately. I found out after I recieved all the parts the TCI could have supplied the TPS and Speedo control unit. Oh well it all worked out. Anyhow, I think the speedo control TCI supplies is a relabeled Cable-X, just missing the mated connector supplied with the EZ-TCU. I just cut off the harness connector and hooked up the wires as per instruction. Set the dip switches inside the cable-x unit as per the TCI instructions and WHAM, works like a charm. The mechanical reads about 2mph slow at 60, but that is close enough for this cowboy.

[bilfman]

Ah, good to know!! I just had them there because thats how it was on the 203 when I got the truck. Anyhow they are out now.

Originally Posted by DirtyLarry

Tough work! You are also doing great on time….You would make a great flat rate tech! Those 203’s are some heavy dogs aren’t they?? I wish you lived closer as I wouldn’t mind having the range box off the 203.

Curious as to why you have the spacers between the frame and xmember? Those spacers are intended to be on the top side of the frame for use a longer bolt to achieve a higher torque value and increase clamp load of the xmember mated flat to the frame (Same reason those spacers are used by the steering gear box as well…..think of a bolt as spring). The spacers located between the xmember and frame as you have now will cause the xmember to walk around like it is on stilts and will eventually cause frame cracking. Imagine those spacers working like a paper punch. I’ve seen people move those spacers from the correct location to the bottom like you have on lifted trucks to help correct driveline angles only to end up with bigger vibrations and cracked frames. You might want to reconsider that set up.

When I did my NV4500 swap the xmember had to be dropped slightly maintain the 3 degree engine tilt. To do that we made a flat spacer with the tube spacers above the frame as GM designed it to maintain the original high torque clamp load design.


You’re going to love overdrive!

[bilfman]

Here is where I store my handheld wire.

Stats wise on an initial flight I'm looking at about 15mpg. I was at 10 prior to the overdrive and the performer intake. 50% increase, well worth the effort.

I am sitting at 1850 at 60mph.

I was messing around with shift agressiveness and points and the controller makes the stock 4L shift like my old modified nitrous powered muscle car. Hard and fast enough to chirp the duallys. I put it all back to my initial setting, but just so you know it can go there.

Feel free to ask any questions if I missed anything.

Peace

[bilfman]

Yeah thanx Dirty. I noticed something didnt look right with angles and such. I took the spacers out and flat mounted the crossmember earlier today. It is perfect now. I didnt use the spacers but after your explanation I think I will put them back in. Hopefully I can get them in the passenger side, the nuts were hard enough.

Originally Posted by DirtyLarry

Tough work! You are also doing great on time….You would make a great flat rate tech! Those 203’s are some heavy dogs aren’t they?? I wish you lived closer as I wouldn’t mind having the range box off the 203.

Curious as to why you have the spacers between the frame and xmember? Those spacers are intended to be on the top side of the frame for use a longer bolt to achieve a higher torque value and increase clamp load of the xmember mated flat to the frame (Same reason those spacers are used by the steering gear box as well…..think of a bolt as spring). The spacers located between the xmember and frame as you have now will cause the xmember to walk around like it is on stilts and will eventually cause frame cracking. Imagine those spacers working like a paper punch. I’ve seen people move those spacers from the correct location to the bottom like you have on lifted trucks to help correct driveline angles only to end up with bigger vibrations and cracked frames. You might want to reconsider that set up.

When I did my NV4500 swap the xmember had to be dropped slightly maintain the 3 degree engine tilt. To do that we made a flat spacer with the tube spacers above the frame as GM designed it to maintain the original high torque clamp load design.


You’re going to love overdrive!