OD transmission conversion

[sht2kll]

Howdy all: My 86' M1008 has a th400 tranny and a np208 T-case. I would like this truck to be a little move road worthy (cruise at highway speeds). I already have bigger tires (315-75-16) on it. I would like to get an overdrive transmission. I thought about getting a Gear Vender overdrive, but for the price it might be just as easy to put a newer OD tranny in it. A couple of questions, Does anyone know what Trans mission my work best with the equipment I have, or am I looking at new T-case? Would a 4L-60 tranny bolt up to my 6.2? Any insight you folks might have would be greatly appreciated. Thanks. Tom

[DmaxMaverick]

The 4L60E (light duty, not recommended for any but the lightest Diesel application) or 4L80E trannies will "bolt up" to the engine. That's not a problem. Either of the "E" trannies will require electronic control (aftermarket stand-alone controllers are available). You'll need to adapt the tranny output spline to mate with the NP208, or upgrade the TC at the same time (which presents another fitment issue, the front shafts on the later TC's are on the opposite side). Add to that, no matter how you do it, front and rear driveshaft lengths and transmission mounts will have to be adjusted.

In the end, a GV upgrade may be the best option. It will require much less adaptation, and no electronic controllers.

[wpdozer]

I have a M1031 with a 700R4 conversion that installed by the privious owner and with the help of some members here resolved the last issue i've had with this swap. I would strongly sugest keeping your TH400 and installing a Gear Vendors overdrive unit behind it. If you go with the 700R4 it must be from a 4x4 and it must be from a diesel as the valvebody's are different from a gasser. A bone stock trans cannot be used as your 6.2- 4.56 gears and heavy tire combination will kill it. A heavy duty rebuild is strongly recomended with a 1600 stall diesel torque converter. You will have to get an adapter to mate the trans to transfer case. You will also have to count the splines on the output shaft on the trans and make sure they match the splines on the 208 transfer case. A torque converter lockup controller must also be used along with the PROPER TV cable. You will not have modify the drive shafts as the 400 and 700 are within a 1/4 in in lenth. How do I know all this? I went through all of the above. At the end of the day, either the 700R4 or the Gear Vendors overdrive conversion will cost you about the same. The overdrive setup is a simple bolt on upgrade with some equally simple wiring involved. Choose wisely, That TH400 is bullet proof so don't throw it away, you may need it again. Wayne.