T400 - 700R4 swap

[sobregonso]

Hello all. I own a '87 Sliverado, and it has the T400 tranny in her. Obviously a great transmission, but I'm curious about a swap to a 700R4.. Too bad the original owner didn't already request that option from the factory new, but he didn't, lol. Anyways, I'm thinking I'd like to do the swap for mainly the overdrive gear in it, for a lot better mileage, that would be great considering the 'daily driver' status of the truck. I know the 350TBI w/ a 700R4 could pull down mid-high teens in mpg easily. So the question is to everybody; is it worth it? How easy would the swap be? Price on the swap, or at least price on a transmission? Would it matter much to buy a new 700, or buy an old one and have it rebuilt? Thanks for the help, any input would be greatly appreciated!

[Layne]

Definitely worth it. It has taller first and second gears for more grunt, and you'll have that awesome OD. I scored a 700 for free and had a guy build it with my own purchased parts for 1300 including removal of my three on the tree and install. A new one will prolly be more expensive than a used one that you can have built just as good for cheap. stay away from the older ones, though. I think 86 and newer is good; the early ones had some weakness issues.

[Captkaos]

88-92 has most all the major upgrades.

[Da67goatman]

Agreed, the 700r4 will give you much better performance and mileage.  Its true pre-88 have issues so stick to the newer ones, beware that after 92, they went electronic and will need the computer that controls lockup on the torque converter, at that point they became 4L60E.  If you look in classifieds and on craigslist, they can be found for $200-600 depending on mileage.  Another thing you should know is that newer 700r4s had electronic speedometers compared to mechanical cable ones.

As for the swap, I pulled a tbi 454 th400 combo out in favor of a tbi 350 700r4 combo and all i had to do was move the crossmember back a couple holes, 2 i think.  My 2 piece driveshaft gave me enough play i didn't need it shortened, but if your running a single shaft you should measure to be sure.

I'm here if you have more questions, and good luck to you.

P.S. I was getting 18mpg average, for 250k miles until the motor died.

[sobregonso]

I really appreciate the help, looks like I'll be looking for a 88-92 R4. Will I need to convert to a floor mount shifter as well, or could I still use it up on the column? Thanks again.

[Captkaos]

You can still use the column shift.  Probably won't be able to access L1 though.

[sobregonso]

Well I will probabably find me a used one then, and I'll get it rebuilt. What all will I need to make sure to get w/ it when I take it off of a 88-92?

[Da67goatman]

When you go to get one, i would recommend getting the TV cable, torque converter and depending on price even the driveshaft, But its really up to you.  A new TV cable can be had for $23+(link Included) torque converters vary by application, but new one can be had for $120-expensive (I'm currently looking for one out of a diesel for the low stall speed 1200rpm).  I mention the driveshaft because it could save you a good portion of time(shortening and re-balancing yours) if it happens to be the perfect length.  These are just my suggestions so feel free to question them, I wont be offended.

TV cable 700r4:
http://cgi.ebay.com/ebaymotors/700R4-700-2004R-TRANSMISSION-TV-CABLE-KICKDOWN-DETENT_W0QQcmdZViewItemQQhashZitem11105e888QQitemZ4580567176QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

P.S. L1 will be usable if the shifter linkage is adjusted properly.

[HAULIN IT]

Is this a 2wd or 4x4 truck? Spline count on the output shaft is different
from the TH400 & 700R4. Lorne

[MarkS]

This might be a bit off topic but what were the issues with the pre-88 700r4's? just curious as I have a 87 with a factory 700r4 and a 67 swapped for a 700r4.

[Layne]

Weak planetary gears and other stuff I think

[77 Beater]

How would you wire the 4 pin connector? I'm thinking about doing a similar swap but don't know if the 4 pin connector for the 700-r4 is on non-overdrive equipt trucks or not. 

[Captkaos]

read this for how to lock up the converter.
http://www.73-87.com/7387garage/drivetrain/lockup.htm

[77 Beater]

Thanks. This will be very helpful. The part about swapping the 4-pin connector for a single-pin sounds a bit odd but I'll look into that more.