85 720 automatic transmission swap

[720 keeper]

Wondering if the 86-88 2.4L hard body automatic transmission with overdrive will swap right in to my 85 720? Other than wiring in the overdrive switch. Has any one else attempted this? Thanks.

[Lockleaf]

It will bolt up. The transmission you speak of is 4n71b. As far a i can tell it's an electronically controlled transmission that had an option for a lock up converter as well. The ecu controls the transmission, so you would have to determine a manner of making that function. I'm also not sure if they are different lengths.

 

And if you have a 4x4 then everything changes. Much bigger job feeling with tcases and driveshafts and mounts.

[datzenmike]

If it's an L4N71B there is only the switch on the shifter handle to turn off the 4th gear. The transmission was changed to ECU controlled with the KA engines.

 

 

Here's my L4N71B from an '84 Maxima...

 

It's about 1" longer than the regular 3N71B in front.

 

Trans mount is differently placed and the middle section is moved to the rear about 5-6" so check tunnel clearance. The bell IS removable and can be swapped between L and Z series, but I suspect not with the 3N71B. The L4N71B has the same interlock switch with the reverse lights plus two wires for the 4th gear lock out.

[Charlie69]

I have gathered the parts to do this but I have not had the time to do the wiring involved to do this.  As Mike said you need the transmission control box under the seat of the hardbody.

 

What I did was pull the entire wiring harness with the the ECU, the transmission box, all relays and switches.

 

My plan is to upgrade at the same time to throttle body injection instead of the carb. 

 

This will involve a lot of wiring. 

 

I have also decided at the same time I swap the transmission I will swap in a VG33 V6.

 

My thought is to just buy the whole truck and do the swap and after I get the swap finished get rid of the donor truck.

 

I am not saying this is the only way to do this swap but I like to have dependable drivable vehicles so this is the approach.

 

If you want to see how involved the wiring is for my 66 520 with the L20B automatic, 720 heater, AC and electric fuel pump then click on the link below in my sighature for my 66 520 build.  I am drawing a complete wiring harness diagram as I go.  This build started with a 1980 720 wiring harness that I am upgrading to fit my 520 needs.

 

Mike is it possible to switch the front case/bellhousing from the later 4 speed automatic trans to the to the earlier non electric 4 speed automatic trans like can be done on the 5 speed manual trans.

 

I am talking about the 4 speed automatics found in the early Maximas.

[720 keeper]

Okay thanks guys for the in put, the truck is a 2wd and I'm currently on the lookout for a running donor truck that has the floor shifter with the od button on it so I can dissect the electronics, and have all the parts I going to need. Thanks again will keep everyone posted as this project goes on. I just hate the fact that at 70mph the poor truck is running at 3500- 3900 rpms.

[datzenmike]

I have gathered the parts to do this but I have not had the time to do the wiring involved to do this.  As Mike said you need the transmission control box under the seat of the hardbody.

 

What I did was pull the entire wiring harness with the the ECU, the transmission box, all relays and switches.

 

My plan is to upgrade at the same time to throttle body injection instead of the carb. 

 

This will involve a lot of wiring. 

 

I have also decided at the same time I swap the transmission I will swap in a VG33 V6.

 

My thought is to just buy the whole truck and do the swap and after I get the swap finished get rid of the donor truck.

 

I am not saying this is the only way to do this swap but I like to have dependable drivable vehicles so this is the approach.

 

If you want to see how involved the wiring is for my 66 520 with the L20B automatic, 720 heater, AC and electric fuel pump then click on the link below in my sighature for my 66 520 build.  I am drawing a complete wiring harness diagram as I go.  This build started with a 1980 720 wiring harness that I am upgrading to fit my 520 needs.

 

Mike is it possible to switch the front case/bellhousing from the later 4 speed automatic trans to the to the earlier non electric 4 speed automatic trans like can be done on the 5 speed manual trans.

 

I am talking about the 4 speed automatics found in the early Maximas.

 

Not sure what auto you mean but.... The early Hardbody to about '89? with the Z24i engine had the L4N71B similar to the picture I posted. AFAIK it only had two wires for disabling the 4th gear... that was it. Again, as far as I know, only the later Hardbody KA engines got the EFI controled automatic and they look nothing like the one I pictured. The electronically controled automatic was for emission controlling.

 

I don't think the later computer controlled automatic has a removable front case. They are totally different looking from the L4N71B.

 

The L4N71B L series front case from the maxima is removable and should fit the early Hardbody Z24i L4N71B. I think there may have been VG L4N71B transmissions too.