th400 vs 700r4

[Mikeandwendy74]

Anyone done the swap? how much better on the highway would the 700 be vs the 400?? If I were to keep the gear ratio i have, its either 4.10 or one step lower, what kind of rpm drop do ya think I'd see?

[wthif]

Night and day difference. The TH700r4 has a 70% overdrive. I can cruise at 90MPH with out the engine sounding wound up with stock (31"?) tires and 4.10 gears.

Robyn has mentioned a few times in other threads what should be done to a 700r4 to make it bullet proof and there has also been a couple of articles done on the 700r4.

[DA BIG ONE]

The deeper 1st gear (3.08) and overdrive w/lockup converter is a good choice. It can be made to handle high hp/tq too w/o lots of $$$. Has to be a 87 or newer case........

[Mikeandwendy74]

What kind of modifications do I have to do to fit the 700 in there? move the tranny mount? different flexplate? Does it run on vacuum? Is the 700 electronically controlled? my truck is an 88 not sure if i need something else to run this behind the 6.2. thanks and is it larger? I know a guy who will give me a 700r4 in good shape( I'll rebuild it) for 75 bucks .

[Robyn]

Read the top (Sticky) post in the Chassis and drive train forum

The 700 can be upgraded to hold some big power and work real well.
The cost to do it yourself (parts alone is about $600) if you shop around.
A "K" case 700 is an absolute. 87 to 91 model years.

An older box is not worth your time. Too many issues

If you try to use a 700 in stock trim it will fail its just when !!
Another good option is a 400 with a gear vendors on the back.
400 is a better box IMHO even though I have done the tricks to the 700's

The 400 is just far more robust as far as parts go. Shafts are bigger as well as all the clutches.
The input shaft on the 700 is like swiss cheese with all its passages and oil feed holes.

Even the best updated 700 is still a little shy of where I like to be.

And if you ever decide to do some towing, the 700 is just not the best option.
The 400 with an overdrive can be subjected to some Gawd aweful torture and come out smiling.

The 700 is a great box for a light duty application and will give good gears for starting and great OD for mileage.

The issue remains though that the 700 has very small internal parts and they will only take just so much.

Bigger is usually better.

A 4L80 that's been built would be cool but it takes a controller to run it. $$$$$$$$$$$$$ more

Robyn

[Mikeandwendy74]

well after hearing that and rebuilding my 400 I would hate to rip it out. I might check into the gear vendor O.D. hope its not too pricey or my wifey's gonna gimme a fat lip :)

[DmaxMaverick]

Check out the Classified Ad Forum (http://www.thedieselpageforums.com/tdpforum/forumdisplay.php?f=25). One of our members just put a US Gear aux OD up for sale. One heckofa deal. Don't pass on it if you're serious.

[moondoggie]

Good Day!

I'd definitely consider the Gear Vendors Aux. OD offered - you can have mine when you pry my cold dead hands off it. :D I think he's a little off on the ratio - my impression was that all GV's were 0.78 ratio, or 22% OD.

A couple things to remember: The main Gear Vendors unit is always the same, adapting the input & output shafts is per application. I'd contact GV & find out what you would need for your application, & see if what's being offered will work. If not, you can price the parts from GV.

Also, the electronics package that runs the GV is also per application - same situation as above.

If you have any questions at all about this GV's condition, GV rebuilds these pretty reasonably, or at least they did when I bought mine. You might want to consider finding out what they charge for a rebuild as part of an informed purchase decision. When I bought my GV, they rebuilt it for I think ~ $650, which included fixing anything & everything not perfect. I considered this an extremely reasonable price.

I bought my GV through a fellow DP member. He asked a ridiculously low price, I had it rebuilt, & had to buy input & output shaft adapters, & the electronics package. I've NEVER regretted this purchase.

Hope this helps.

Blessings!