TH400 to 700r4 Conversion in 89 k3500

[06scooby]

Hi I'm new here. I just picked up a 1989 K3500 Silverado as a project truck. The Tranny is on its way out. Has anybody here done a 400 to 700r4 conversion? I've found some upgraded 700r4's online. Is this a good idea or should I stick with the 400? I would really like to have the 4th gear overdrive if I can to make the truck more driveable. But I do plan to use the truck off-road and occasional hauling since my primary car is an 06 Legacy. Any suggestions?

 

Thanks,

 

dp

[mmmikkke]

The THM400 is an excellent trans, and lots of people say that. Nobody says that about the 700R4. They're more likely to go into the back room and puke after hearing somebody mention it and the THM400 in the same sentence.

 

If I could have gotten a THM400 in my current truck, instead of the 4L80E, I'd have done it, in a second.

[454ss]

the 4l80e is just as stout as the th400, both are head and shoulders above the 700r4. if you really want od, id go with a 4l80e, there are a number of places that sell the computer and wiring harness to install it in anything you want, they use them in street rods a lot behind big blocks. you could also look into a gear venvors od unit to go behind your current th400, ive heard great things about them also.

[95Sierra2500]

With a proper rebuild, a 700R4 can be just as stout, if not more so, than a TH400. I've seen them go a LONG time (180k+ miles) when the reverse sungear is actually welded to the planetary gear sets instead of just spun-welded in place. That's usually where the weak point of the 700R4 is.