4L80E in my 84 Sub, please help ASAP.

[coxfmly]

Hello again,
I have an 1984 3/4t sub with a 6.2 turbo and a TM400 trans. Last week in the junk yard I found a 1991 3/4t Sub with a 6.2 and 4L80E trans. I pulled the trans, torque converter,drive shaft and cross member for $200 bucks. Trans has a factory rebuilt sticker on it.

I want to upgrade to a 4L80E but I'm not sure what else I needed to pull off of that truck. I'm under a time crunch since 91 will be crushed soon if it hasn't already. I have read every post for the last year I didn't see a list of parts needed for this swap. I have looked into a controler but they are big $$$.

Also, will a mid 90's 3/4t rear end fit in my rig w/o any major issues? My truck's rear end makes a clunking sound once it's warm every time I pull away from a light. Shop said it's about to go. I could get the rear end for under $100 bucks....

Any help and advice would be greatly appreciated, Paul

[daustin]

I think you'll need the ECM and wiring to/from it. Also the temp switch/sensor (one on the thermo xover, other in the head), and the TPS. The earlier 4L80E use those to control the shift points. The gm diesels went to electronic IP's in '94. The '92-93 6.5TD's work like above, as i found out with my '93 3500 6.5TD/4L80E.
Don

[EWC]

Doing the same swap in my 85 dually . Get the wiring harness , both under the dash and the engine compartment . They changed the firewall connectors in 87 ? and added a few more . Just enough to make it interesting . The shift linkage from the steering column to the trans is a little different , I'd get all the parts . If not you could probably make do with a 700R4 linkage . The speedo cluster is also electronic and with the harness it should work . The harness should have the VSSB or DRAC that will run the speedo and in the circuit for trans input . Pay attention to the v belt drive as this may be different , it may have a vac pump setup or the vac pump at the rear of the engine may have a sensor for engine RPM to the TCM ( Transmission Control Module ) . The TCMs do come up on fleabay so they are not that rare . Just watch which one you get as the 91 - 93 was different than the 94 and up . TCM mounts under the dash ? I spot welded a set in from another truck . TPS switch from the side of the injection pump as your TH400 shouldn't have that . I'm a little picky when it comes to some of this stuff as I want it to look like GM put it there . If you look at the wiring books , the circuit for the ignition switch in a 91 is different than the earlier models . It plugs in the same , just wired differently internally . You can make that call .That's a start !

[coxfmly]

Daustin and EWC,
Thanks for the data. I will go back to the yard and see if it is still there. You have noted quite a few items with acronyms. Could you possible tell my where I might find these items and what they might look like? A few items I will be looking for are the ECM, VSS, TPS, TCM, PWM etc.... I will try to get the entire wire harness subject to the link I have already cut out. I had taken the loom which ran down to the trans. Unfortunately the dash was already trashed. In my area it seems the fun thing to do is to break instrument clusters or completely take them apart and leave them on the seat :(

Will I need to use the 91 IP. ?

Any thoughts on the rear end interchangeability?

Thanks again, Paul

[Robyn]

There are some companies that make a stand alone computer and the needed wiring and such to run the 4L80E

This is probably the easiest and best way to get the setup working properly with the least amount of headache.

The complete harness will be provided to connect all the stuff you will need to connect.
Tell the sales staff what rig you have and what the complete package is so they can fit you up with the right stuff.

Best
Robyn

[coxfmly]

Robyn,
Thanks for the advice. It sounds like it would cost a bit more but in the long run might be easier.

Would you by chance know if a mid 90's 3/4t rear end fit in my rig w/o any major issues? My truck's rear end makes a clunking sound once it's warm every time I pull away from a light. Shop said it's about to go. I could get the rear end for under $100 bucks....

Thanks, Paul

[DA BIG ONE]

The 4L80e is easy to convert to manual shift which eliminates controller issues, Trans Go manual shift kit comes complete for this application.

[EWC]

Transgo has a listing for running a vacuum line into the trans and making it shift . I don't know if this would work or not . ECM : Electronic Control module , TCM : Transmission Control Module , TPS : Throttle Position Sensor , VSS : Vehicle Speed Sensor , VSSB : Vehicle Speed Sensor Buffer , PWM : Pulse Width Modulation . The ECM is a computer that operates the engine and the transmission . The TCM is a computer that operates the transmission only . For your truck , or the Suburban , with the 4L80E , diesel , a 3/4 or 1 ton and a 91 you should have a TCM . The stand alone ECM might be a better way to go but that only gets the trans running . You still have to figure out a way to run the speedo . If the truck is a 4WD , you may be able to use the older transfer case with the cable speedo . Swapping to an electronic speedo ( 89 - 91) would not be necessary . There are some modified tailshaft housings that do accept the speedo cable , one was on fleabay a couple weeks back for $250 and new units run up to $400 .

[daustin]

Another option for the speedo is JTR, they have little boxes that convert the VSS to cable operation. JTR - Jaguar's That Run. Also BowTie Overdrives has a lot of stuff for the electronic Gm transmissions. They are oriented toward retro-fit into '60's GM musclecars, but that conversion faces much of the same items as yours would. (Cable speede, tranny controller..etc) Good luck with that, it should be neat when it's done.
Don