Promise last tranny post or at least I hope.

I have a 700r. I was reading an article that said the 700 R was a medium duty tranny. I always thought they were pretty tough. But the same article showed the 400 to be a heavy duty tranny. What would be better behind my 6.2?

It all depends on what you intend to do with the truck. If you are doing alot of heavy towing with it, a 400 might be better. If you are just driving it the 700r4 might be the better choice. Of course, this also depends on what gears you have, as a 700r4 with 3:08 gears is a bad combo, it eats the tranny for breakfast... Also, a 700r4 can be built to withstand more abuse, problem is finding someone who knows what they are doing to build it for you.

As for use, I driove it back and forth to work mostly, but I also use it once a month to get steel and about 4 times a year to pull my jeep wherever we decide to go.

The 700R4 can be built to take high torque loads, but will never be able to handle the loads equal to that of a properly built THM400. The shaft and clutch size just isn't as heavy on the 700. Like the previous post says, if you have a final drive ratio higher than 3:73 or even 3:43, I would prefer the 400. The load gets too high for the 700 with the taller gears. If you have 4:10's, the 700 performs admirably, if properly modified and not used to pull heavy loads over extended periods.

On modification, stuffing more clutch discs (thinner) into the clutch housing will increase the overall surface area and, hence, the load-carrying capability of the clutch but does not address heat dissapation. A good auxillary cooler is a "must have" item. There are several companies that sell widgets to improve the overall performance and durability of the 700. Finding a reliable rebuilder that understands these mods and what is needed for your application is important. Start with your local 4X4 transmission shop and research it in the hot rod books. The info is out there and you can make an informed decision. Hope this helps, Fred

An interesting thought that I had the other night while pondering this swap for myself, is I know the TH400 is 1" longer than the 700r4. Did GM make the transfercase adapter shorter on the 400 so the driveshaft length was the same? or will that have to be changed to swap from one to the other? I dont have direct access to them at this moment to answer my own question.

Yes the adapter on the 400 is shorter. I have done swaps from a 700r4 to a turbo 400 without any driveline mods. The input shaft for the transfer case is different however. 27 spline for the 700r4 and 32 spline for the 400.;)

If your transfer case is like most of the ones I've opened up, you will not only need to change the input gear to match the 27 spline output shaft of the 700R4, but you will need to check the transfer case parts for normal wear and tear. This is a good time. The last piece out of the case is the input gear! It gives you a chance to look at everything. Check the needle (Torrington) bearings, thrust washers, chain, gears, etc. The input gear bearing has a high failure rate. It slides onto the input gear with thrust washers on each side. It's the very front bearing in the case.

The shift forks are always a high wear point. Check for the plastic inserts that snap into both forks. They usually end up in the bottom of the case, in pieces. They are available from most trans rebuild shops or from Dodge. I replace them even if they are still on the forks. They wear and fall apart when you least expect them to. If you use it after they fail, the shift fork is soon worn from the thrust of the gear and, eventually, the thing shifts itself into neutral and/or pops out of gear while driving. (If you're lucky, you can mess with the range selector lever and get it into low range and make it off the road! Some fun!) Good luck, hope this helps, Fred

Funny you should mention that Fred... I have been there before.... there comes a point too where you are not even able to get it in low range (and stay there). I hope to not have to play that game again.

Ok, but what about non 4wd vehicles will the same crossmember driveshaft work?? Kinda doubt it but worth asking...

Hmmmmm, I think I saw a non 4wd vehicle once, but I have never owned one!:muahaha:

Me either till I bought the Diesel

The 700 was available in two output shaft/extension housing lengths. Don't know how that would work out with the 400 driveshaft. The 700 trans was used in everything, G-vans, pickups, cars, etc. Somewhere between the two different lengths of output shafts for the two wheel drive trans, you might be able to come up with a match for the 400 2WD driveshaft. I've never tried it as all my swaps have been on 4WD's. Let us know how you come out, Fred

Forgot to add: The slip yoke size (depending on what model the trans came out of) between the 700 and the 400 may not be the same. That would mean changing the yoke. If the shaft length is right, the yoke is available aftermarket. Try to find one with a common u-joint size so you don't have to carry a spare, odd-ball u-joint.

:lol: I didnt know thye made them without 4wheel drive!!!

Oh yes, the 700R4 was used in all types of 2WD vehicles. Trucks, cars, vans, etc. The smaller version was used in the S-10, S-15 body styles. It's bell housing was dedicated to the smaller block and won't interchange with the Chev V-8 style bell housing pattern. The lighter duty S-10 style had fewer clutch discs and smaller depth clutch packs.

The 6.2 Diesel version came about in the '82 models. The 1/2 ton, 2WD pickups used it as well as the heavier models in both 2WD and 4WD. Between '82 and '87, there were many modification/improvements made. The bulletin list grew to be so large, the factory issued a special book which contained all the bulletins in a bound version, so we had them all in one place. When we performed any service/repair on a 700, the first step was to identify the trans by Julian date and check bulletins for modifications/factory upgrades. For example, there were seven, thats right, SEVEN different input shafts used during those years in an attempt to gain strength and durability. The diesels were especially suceptible to twisted, fractured, input shafts because of the increased torque. The oiling was another issue that necessitated changes in the oil holes and passages in the shaft.

The 1987 model 700R4 used in the 6.2 Diesel models was the latest and greatest to incorporate all the upgrades. It is the best one to use for a core to rebuild. The '88 and later 700's had the auxillary valve body and require different parts/service techniques when rebuilding. They work great, just require different mods. I like the '87 because it had the hardened parts needed for reliability and were the easiest to rebuild. The Diesel version valve body contained several pressure switches and lots of jumper wiring for the convertor clutch. Somewhat complicated, but necessary for the diesel.

Hope this long, drawn-out post helps, Fred