Switching to auto.

[CG]

I had a spare 4x4 1/2 ton chassis with both differentials and automatic trans.. I was going to transfer this all over to my 71 4x4 with 4spd. Rear was shot in my driver and I wanted automatic. All I ever transfered over was the rear.

I don't know much about gear ratios, but I do know, that rear end, matched to my 4spd didnt work too well going up hills with any kind of grade. I had to shift down to third all the time. It has a pretty healthy 350 in it too.

Ive since given that truck to one of my sons (for the third time...don't ask) its his problem now. I'm keeping the auto trans set up though (the one I never got around to switching over).

Well now I'm the proud owner of a 71 4x4 3/4 ton with a 4spd. If I swap the auto trans set up into this truck am I going to have any drive ratio problems?
I really don't care for shifting, and since this truck will see nearly all street use I think the auto trans is a good choice.

Thanks for any insights.

Mark

[DieselEater]

I like manuals, but thats cool to have an auto. Just measure the input and output shafts on the auto and make sure everything is the same. Shortening the drive shafts isn't hard either. The reason you didn't have much power on the hills in 4th gear is due to the large gap between 3rd gear and 4ths 1 : 1. You should gear your vehicle for this 3rd to 4th situation, and just have really low 1st and 2nd.

[earl87gta]

I believe the 350 trans and the 4 speed have the same final ratio. here is a web site I like to use when changing gears and tire sizes it will give you an Idea of what you will have. http://www.grimmjeeper.com/gears.html
I like the auto Idea to and thought hard a bought using one then I ended up going with an NV4500 but my wife would still rather have the auto so I may change to a 700r4 before its over with.

[1969k10stepside]

No driveline mods,no issues.No lengthening,shortening driveshafts,etc.You just need the auto tranny,the correct th350 style np205 and adapter,tranny linkages,flexplate,etc and you have to drill holes in the frame for the tranny linkage brackets.PM me if you have any questions,or post here,I just done the same thing to my 71..

[brianthelion02]

I hated the rockwell t-case in my 69 so i yanked the sm-465 and rockwell and used a 700r4 with the 241 t-case out of a 92 blazer!I love this combo,really low gears and with the od i can easily go with the 75 mph speed limit,and my mpg went from 8 to 14 mpg!!!!!!!! I dont use mine for extreme 4x stuff,just mainly use it for towing!!!!!!!!

[CG]

I have all the correct OEM stuff to change it over, but Brians post has me thinking...I wonder how much that would set me back to do that conversion?

[1969k10stepside]

Dont know but the 700r4 is longer so you would probably have to lengthen and shorten driveshafts doing that.It sounds like the right way to go though..If you really care that much about the mpg gain,go for it.If not make the swap with parts you already have and save some money and probably get some more from the removed 4spd/205 combo.If I was using a 700r4,I would use a np205 behind it,but that's just me...

[brianthelion02]

I had to shorten the rear driveshaft and i used the late model front shaft,was a bolt in!!!!!!!!

[brianthelion02]

Someday ill run across a 205 t-case for it,for now the 241 works great!!!!!!!!!