4L60E or TH400

[70K10Hunter]

figured I'd throw this out in the mix see what kind of response, I bought a complete donor vehicle for my build (70 K10) the donor vehicle is a 97 2Dr Tahoe 4x4, it's got a good running vortec 5.7 but the trans is shot it doesn't move an inch either direction. my 70 truck came with a working TH400, so I either have to rebuild the 4L60E or go through the 400 to make sure it is solid.There are so many different upgrade components for the 4l60 that I could potentially spend well over a grand just in parts,this truck isn't going to be my daily driver, so other than the final gear ratio and an another gear on the top end what are the pros and cons of both ? which is more durable/reliable?
I am already going to use the vortec just dont know that I want a computer controled trans.

[SunSoaked]

my $.02

If it's not a daily driver, I would run the 400. That 4L60E is a good trans but your going to sink some $ into it to make it work. In addition to any internal work and dealing with the computer control, you probably need a 4wd tailhousing. I'm not sure what the output shaft is, but I doubt its a 32 spline that would mate with your current T-case. I assume its a 32 spline np205?

I would find a good gear ratio for the axle based on you engine/trans combo and the on/off road ratio and enjoy it.

I was in a similar situation a month ago. I had a built 700r4 (2wd) and comtemplated doing the same thing. I knew I wanted the best of both worlds and forced myself to sell it and not settle for anything less than the NV4500.

A week later I found one. No regrets. However, mine is a DD and I already had 4:56 gears, so it made more sense in my case.

[99-LS1-SS]

IF I'm not mistaken the 4L60E is based off of the TH350 and the 4L80E is based off of the TH400. If strength is a consideration I would go with a TH400 if mileage is the consideration then the 4L60E.
This is just MY personal opinion so take it for what it is worth. I have never been impressed with the strength or durability of the 4L60E. If it was up to me I would go with the 4L80E. It will handle more power and abuse and it should last longer.

[bk2life]

Originally Posted by 70K10Hunter

my truck came with a working TH400.

that and not a daily, think you answered your question!

[martindc1]

What gear ratios do you have? IMO 3.08's don't work too well with overdrive. The problem would be compounded by bigger tires. With half ton axles, if it were me, I'd just stick with the TH400 unless your gear ratios are numerically higher than 3.73.

[70K10Hunter]

my front axle is 3.07s I can only assume the rear is the same or 3.08s. The truck has 31s on it now I am wondering what kind of pulling power and bottom end the PO had with this setup, I will be putting 35s on. its not an issue to do the gears for me, Im thinking 3.73s or 4.10s with the TH400. What do you guys think?

[blasher]

Is there a difference between 3.07 and 3.08 gears? I always figured it was a difference in rounding the numbers. I have a 40 ring and 13 pinion so I round the 3.0769 up to 3.08.

Here's my experience: My K10 has the 3.08's with 31" tires, and a 3 OTT shifting a SM330 HD trans. I really like the ratios for a three speed. It's a good set-up if you are running highway speeds frequently. I don't tow or haul heavy loads though, and first gear with this set-up might be a bit tall for that. Gas mileage is very good. With a 305 V8 and Q-jet I get 16.5 on the highway (GPS verified). Just my 2 cents. I hope it helps with your decision.

[70K10Hunter]

Heres my preliminary setup, 97 5.7L Vortec coupled to a TH400 probably 3.73s and BFG 35s with a 6" lift.

[argonaut]

35" tires, powered by a small block, I'd go for at least 4.11 gears.
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[Redcap]

Originally Posted by argonaut

35" tires, powered by a small block, I'd go for at least 4.11 gears.
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Yup. A big block can get away with 3.73 gears and 35s...not so great for a smallblock.

[70K10Hunter]

sounds like 4.11s
Thanks

[76k10]

I run 3.31s with 35"s. Works great for me. Drop it in low for the trails and run 75 down the interstate.

[andrewmp6]

Yeah if you don't care about gas mileage the 400 is the better trans.

[Ackattack]

One thing to think about is that the 4L60E has a lower first gear.

If you're going to use the fuel injection on the engine I would go ahead and use the 4L60E since the computer won't be a problem.

I had 3.73s in my tahoe with 33s and it drove fine. Since this isn't a daily driver, I think I'd go with 4.11s

[argonaut]

You can kind of get away with the larger tires and the smaller gears with the auto trans because the torque converter takes up the slack. However it is harder on your torque converter and your transmission fluid. I suppose the stall speed of the torque converter is also a factor.
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[84 400]

I run 3:08 and 35's and it sucks. No power even with a healthy 350 and sm465. I just got a set of 373's only because I am swapping to a turbo diesel very soon. I would go 373 if you do alot of highway and run the th400. If you don't run highway alot go 4:10 at the least.. If you run the 4l60e I would go 4:10 or 4:56. As mentioned think of a 4l60e as a th350 with OD or an improved electronic 700r4. The 4l80e is like a th400 with OD.

[SunSoaked]

Sell em both and stick the 4500 in her I have a guy selling a brand new rebuilt one for $800.