Transmission dilemma 4l80e / th400

[LVJimmy]

Change the THM350 fluid to type F and run it till it dies. You have no idea if a junkyard trans will last any longer then the one you have that is working. When it does die just do the LS swap with a new trans

 

[jlr113]

I have heard of some people using parts from the 700R and the 4L80E combined to make basically a700R 4-speed without any electronics. I haven't researched the "rumor" yet, I'm not ready to change the transmission.

 

[LVJimmy]

My 700r4 has no electronics besides the TC

 

[mpg7_400]

Hello all,

I have pretty much decided to go with a 4L80E swap in my 1977 K20 pickup. It has a sbc 350, np241 and 4.56 gears. Unless there is some new information as to why i need to scream down the freeway at 2900 rpm....im gonna go with a 4L80. I know the th400 is a badass trans but mine is getting old and i have no idea how many miles are on it. I could spend 2000 and just get the 400 rebuild with some awesome speed parts thrown at it but o/d sounds amazing on long trips.

my BIG dilemma is whether or not to go with a junkyard pull out of a 4wd 2002-2006 chevy pickup (about $650 where im from) or whether to buy a remanufactured one (2000 give or take) I dont have a core so i would have to front a core charge on a new one. Anyone have any experience with used trans or with this particular swap? I know it would be best to buy the new one, however, i dont want to blow my budget on this thing. I do have a boss (wife).

I priced out the TCI EZ-TCU with a vss pulse sender for the t-case (i have a mech speedometer) and some other goodies to include a bigger cooling pan, braded hoses, massive external cooler with a fan with oil for under $2000.

i was also thinking when i get the trans and my dana 60 that i could swap gears to like a 5.38 or so. Im running 37 inch tires right now and i dont plan on going over 40 inches ever. I still want to street the rig but be super capable offroad.

thoughts?

if there is another feed for this question (i haven't found one) please refer me to it.

thanks,
-Daniel

I am running a th 400 transmission on my 78 K5, 33 inch tires, 3.73 axles. While the RPM's seem a little high, certainly no overdrive sensation, I feel for me it is a reasonable choice for a couple of reasons. First, it is a low performance low speed vehicle. I never scream down the highway. Handling characteristics are just too poor with the push pull stock steering and the large tires, front leaf's, etc. Also cruising for me is 65, but 60 feels better. I start to feel a little uneasy at 70. Past that it gets scary. If my tires were perfectly balanced, maybe I could do a little better. The small block 400 with it's low compression (8.5 to 1) and poor head design just doesn't perform all that well at speed. So as you say, th400 is a bad-ass trans. The mileage is poor. It is going to be poor no matter what. If I had a heavier vehicle like a K20 I would be even more inclined to choose (or stay with) the th400. Regardless we all do our own thing, have our own opinions, and make our own choices. There is no specific "right answer" here. Just my thoughts.

 

[Thomas Fournier]

I was thinking that too. But from my research the 4l80e is a stronger trans than the th350 and the 700r4. The th400 is bullet proof but i want to drop the gears that are in it to get a good launch/crawl rate AND keep the streetability. The 700r4s are getting harder to find a more money. Once i drop the 4l80e in i can swap out used ones if it breaks...