M1028 Trans switch from TH400 to 4L80E

[K9Unit]

Your right about the transmission, This is Gm's overdrive version of the TH400. It is a completly electronically controlled tranny just like the smaller version the4L60E. Both the E's stand for the electronic version. I would say the 4L60E performance wise is more equivalent to the 700R4. I'm sure you will have plenty of people tell you they are boat anchors and junk. I have rebuilt enough of them and the 4L60E's that I would have to say from the factory they had some serious problems, the majority of it all stems from the lack of lubrication it receives inside due to some of the orfices being to small. Alot of this is solved when you take it to a good reputable shop that knows more than just standard rebuilding. Oversize holes are drilled, different clutches, govenor change ect. This allows the pumps full pressure to be able to get the the clutchs and bands allowing them less slippage upon locking up which reduces heat and saves your tranny. Once your clutches start slipping your tranny life is limited. This is why the original 700R4 when it first came out was fine, there were no problems until they started putting them in trucks and vehicles that were used for work. They can be made into a good tranny not bulletproof by no means. The 4L80E is almost identical to the TH400 besides it having a overdrive and being fully electronic. You can also swap the gear sets from a th400 to the 4L80E or vise versa, there wouldn't be that much difference other than first gear being a little lower. Back to your question the swap is doable with a few modifications. the worst part is the electrical. I have done a few of these swaps. There are a few companies that make the stand alone comp. for it, my own preference is TCI because thats all I use in my trannies. They are a bit pricey, worth it ? thats up to you and much do you plan on using the vehicle, if your going to use it everyday it wont take that long to get your money back just in saving fuel with the O/D. The only other option, I believe someone already mentioned it is caniblize one for the ecm and part of the harness. I always went the other route because it was a neater set up and alot less wiring involved. Good Luck !!

 

[K5NUTT]

I agree that a well built 700R4 with an appropriate GVW external cooler can do a great job. Thyat being said a junkyard bargain 700R4 is not the way to go....its the classic case of you get what you pay for when it comes to the durability of a 700R4.

I got one run out of the 1400 dollar one i had built due to an engine expiring in my 79 K5 that is on its way to being a CUCV - expedition crossover. The front clip swap is a few days away from starting as well as removing the 700 for repairs to be ready for a trailer ride to phx once it cools down. Currently she has a 4 bolt gm crate 350 that came out of the wifes old 90 V2500 burb...tbi....700R4....14B FF rear w/ 4.88's and an ARB locker and disc brakes. The front is the original 10B with 4.88's...ARB...xover steering...chrome moly shafts with ctm joints. And the xfer (205) was replaced with the ORD 203/205 triple stick doubler set up as stephen is a friend of mine and 60 miles away give or take. She is desert tan with the NOS green military artic covers....and the ORD front bumper with a Warn 10K winch.

DW