So I am thinking it might be somewhat useful to full time 4wd ability in my 97 4R.
So far I have read some theory about how it could be done: transfer case, ecu, wiring, etc. I haven't seen any part numbers or names for the different transfer cases, which would be useful to know. I have also been looking at the ADD system. I am still pretty new to truck arena but I have lots of experience as a mechanic and in the import sport compact world.

So my question is how different are the transfer cases different between multimode and non multimode? If you were able to disable the ADD system would that just turn the 4wd into something close to a full time 4wd system?
How would I make this happen?

P.s. I have an auto trans

I'm not a mechanic and can't speak to the compatibility between the two t-cases (although right off the top of my head it seems to me you'd also have to swap the ECM out as well.) However, simply removing or disabling the ADD will NOT give you "AWD" or anything close to it.

In order to use 4wd on the street (AWD or Full Time 4wd - pretty much interchangeable terms) you must have a center differential. The center diff allows the front and rear axles to turn at different speeds. Without a Center diff, driving on the street in 4wd will make your drivetrain bind up until you eventually experience some kind of failure in the system.

All the ADD does is disconnect the front wheels from the drive mechanism of the front axles (same thing that locking hubs used to do.) Without an ADD all it means is that when you are driving around in 2wd, you are making a lot of metal move that doesn't have to. But it won't hurt anything.

Keep in mind that even "conventional" 4wd Toyotas have shift-on-the-fly up to 60mph with the ADD. So that means if you're cruising down the road and you start to come across some ice or snow, you can reach down and pull the lever into 4wd (or push the button if you have a limited.) Once you are past the snow you can shift it back to 2wd. I do this all the time in mine.

Honestly if you want Full time 4wd on your 97, here's the best way to acheive that:

1. Clean the 97 up real nice.

2. Sell it on Craigslist

3. Use the money to buy a 99-00 Limited or an 01-02 SR5.

There also might be a sensor you'd need at each wheel also. IMO this is a big undertaking and might be worth just simply buying a '99-'00 Limited or an '01-'02 SR5/Limited.

lol thanks for the advice, I feel silly asking this stuff since I worked in the field but its been a long time since school and I worked at Honda dealerships so real 4wd vehicles just never were around. I personally have had a civic, two turbo awd talons, and currently have a '77 280z I am restoring in the garage.

I'll look into the part numbers and builds and see what would be involved. I thought the speed was 50mph for the ADD vehicles to switch into 4wd. Also I know everyone says not to go above 55mph in 4wd but I have not seen one warning on the car or in the owners manual. In fact the only thing I found said the car was capable of 120+ in 4th gear in 4wd. I really doubt that is possible...

What wrong with using the 4wd you have on the street? Its fine, just dont daily drive it in 4wd. I dont understand why you would even want a full time 4wd mode.

When you dont need it in 4wd why have it engaged?

And i have done 70 in 4wd in my 97 no problem

Well like I said I have always heard not to go above 55 or so in 4wd. I really think that if it was a concern to go above 55 in 4wd then Toyota would have put big postings about it somewhere. The awd would be nice when there are icy patches and I am going 75 or 80 around a bend on the interstate. Just push the button and forget about it unless I start seeing deep snow.

The part time 4wd mode is not the same as being in 4hi and is more like AWD in say a Subaru and there's nothing wrong with using it all the time (the 4th gen V8s and 5th gen Limiteds have full time 4wd) as it isn't going to do any damage and it's great to use on rain slicked roads. My mom has a '99 Limited and she uses the AWD mode when the roads are wet even in the summer.

AWD is a nice feature. However, like jmoney said and like I used to do in my Tacoma you can go on the freeway no problem. As long as you aren't doing figure 8s in a parking lot with regular 4wd you aren't going to hurt anything.

AWD is a nice option if it's available in your vehicle of choice and the margin of error is quite large over a 2wd system but speed is not a limiting factor in regular 4hi and no damage will occur just make sure you engage it at a more sedate 50mph and I usually let off the gas when I engage it at any speed.