Tranny Swap for '71 SII

[erikgenerik]

So I recently acquired a bad *** half cab '71 sii 4x4 with a 345, 4spd manual (bw t-19 I believe) and d20 tcase. The rig has front/rear d44s with cv shafts and runs 35" bfgs. I also have a TBI conversion on the 345...I'm by no means a master mechanic and will most likely have this all done by a shop here in san antonio. I'm just trying to prep and find needed parts.

I'm interested in swapping my manual tranny for an auto. Of course I have done some searching on multiple sites and came with a few conclusions...and by a few I mean not many...

1) this swap isnt totally impossible
2) tranny mounts are the same for both units...
3) I should get a d20 tcase that was mated to an auto tranny for ease of use...
4) I should most likely get a 727 from a IH Scout specifically, not another vehicle...to forego having to get a $$$-adapter-$$$
5) I should get a cooler for the a/t
6) the a/t needs to have some sort of hookup to the TBI

anybody know of any really bad problems or snags I'll run into?

I need some help...comments...concerns...rants...raves. Anything to help.
I'm wanting to do this because this is a partial gift for my Dad and he has leg/back issues which = trouble shifting all the damn time and trying to hold clutch/brake and step on the go pedal all at the same time.

Thanks in advance!
Erik

 

[Scoutboy74]

Congrats on the purchase. No, this is not mission impossible. Most often, this swap happens in reverse, but your direction is not unheard of. If you're retaining the 345, then yes, you should source a 727 from a sii 4x4. You need a 727 auto bull gear for proper interface with the d20 t-case. It does not matter if the t-case was behind a manual or auto trans, provided the gear pitch angle in the case matches the angle of the bull gear. Early d20's as found in the Scout 800 models have a gear pitch angle that differs from the d20's found in later scouts. Sii tranny mounts can be changed if necessary. You could also swap in a radiator from an sii with auto that is plumbed for the integrated trans cooler, but it is often simpler to just add an external cooler.
By "some sort of hook up to the TBI" I'm assuming you mean a linkage from the TBI throttle to the trans throttle valve. There must be a means of supplying throttle interface to the trans throttle valve for proper shifting and longevity of the unit.
The most common mistake made when installing any auto trans is to not have the torque converter properly seated. This is how pump shafts and trans cases are easily damaged or destroyed. Other than that, the key to your success will hinge on your ability to source all the correct parts for the swap.