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Stock 700r4/4L60 behind mild 350

813 Views 11 Replies 5 Participants Last post by  ReuahcsKire
I'm looking at swapping a mild 350 (bored .060 over, 268 Comp Cam) into my 89 S10 4x4 w/ a 4.3L, and I was wondering how well the 700r4/4L60 will hold up. I've read everything from it being the same as the V8 700r4/4L60 to it won't last a second. Is this true? How much HP will it handle?

If it won't hold up, what about it is different to a v8 700r4? Thanks
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A 700R4 is capable of handling the power you are talking about. Or while you have it out you could get it built to be even stronger. Don't need to go hog wild, but there are a few things that could use improvement. By 89 the 700R4 was getting pretty tuff. I ran one behind a 454 in a RWD S10.
2 things will kill a 700R4 quickly. Proper adjustment of the TV (throttle valve) cable. It's not just a kick down like back in the day. It controls the transmission's internal pressure and one good WOT pass, with it way out of adjustment, can fry the trans.
The 2nd is the size of your right foot. Beat on it hard enough and long enough will kill any transmission. Most of the complaints about 700R4's are from guys who beat them and have no idea if the TV is adjusted or not.
That's what I was figuring. I just kept reading that the 700r4 used in the 4.3L trucks were different, and wouldn't hold up. Thank you
@oldeerslayer is correct.
All 700R4's & 4L60E's use the same gear-train/internals. As the transmissions evolved they did make refinements to parts.
For example:
The input housing for instance changed to allow for thicker steel plates in attempts to reduce heat related clutch distress. They improved torrington bearing sizes for longer longer life, but the basic design remained the same. Reverse input drum feed orifices changed and pistons were made larger for garage shift feel and low mileage clutch distress. As electronics came out a lot changed, but the gear-train stayed the same style. I use a 4L60E input drum in almost all my 700R4 builds. Again refinements to a basic design were made.
Originally the basic difference between a 4.3L V-6 & a 5.7L V-8 700R4 unit fell on the pressure system & 3-4 clutch capacity, 2nd servo size, governor & valve body.
1)The 700R4 for a 4.3L(first year 1985) in the beginning had a .420 boost valve & the 5.7L had a .470 boost valve, along about 87 the 4.3L ended up with the .470 boost valve too.
2) the 3-4 clutch in the 4.3L had 5 frictions & the 5.7L had 6 frictions. this was done by simply replacing a friction with a steel plate
3) the V-6 units got a 554 servo that was larger than the 553 V-8 servo. This change had to do with shift feel and the fact that a V-6 engine produces less torque than the V-8
4) the governor weights were lighter on the V-6 over the V-8, this allowed the V-6 to have slightly later shift points across the ranges.
5) the valve-body had different shift valve sizes and spring rates between them to allow for the differences in shift timing the engineers wanted for overall drive ability.

As the 4L60E was introduced the internal differences became smaller because, hey it was electronically controlled. the shift feel and schedule was all done in the PCM programming. Electrically is a whole other Oprah show.
So the changes between the V-6 & V-8 became the pressure regulator boost valve, the 2nd servo size and an accumulator valve. All of these are for overall shift feel.

So the real bottom line is, don't put a V-6 unit behind a V-8 if you want it to last. You can put a V-8 unit behind a V-6 and other than slightly firmer shifts, you'll probably never know.
Any 700R4 can be built to handle the Torque/HP you require...
Alright, this makes sense. I'm fairly young, and this is my first project, both with rebuilding an engine, and restoring a project all together, so please forgive me for my ignorance, but I figure I'd ask. Are these something that would be simple to replace or upgrade for it to be able to handle being behind a 350, or would that require a complete rebuild and overhaul? And if its the latter, I'm assuming it would make more sense just to find a good 4x4 700r4 out of a truck with an SBC instead of just rebuilding it.
The transmission has to be torn down to replace any internal gear-train component. My feeling is if you are that far in you may as well build it to match your needs... That way you know what you have. A good USED transmission is exactly that USED! You have no history with it. You were not the one driving it. You can't see inside, so you don't know how worn the 3-4 clutch or the reaction shell is. Over 50% of my work is from guy's that bought a used transmission...
Now you may experience trouble with a rebuilt unit, but my CB/No Go % is less than 5%. More times than not it is a broken rotor from being installed incorrectly...
Alright, thank you very much
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