Automatic tranny upgrade questions

[Pjackb]

After much debate I’ve decided to keep my 510 project automatic to please my other half. We have plenty of manual cars which se enjoys but she asked me to make this one automatic and build a relaxed cruiser. The car is a 70 with a BW35 column shift early transmission.

Since a larger engine is going in consisting of Z22 block with cammed and ported U67 head the BW35 transmission obviously won’t cut it .

I’ve done quite a bit of research and have settled on a L4N71B from a 83-84 Maxima , It already has the right bolt pattern since it’s on a Lseries engine and I like that it has a short 1st gear that will match well with the Subaru 3.54 LSD I’m putting in and provide close to an ideal 10:1 ratio for quick launch and will cruise around 2500 rpm @70mph.

I think this will work well and still be a fun driver even with the slush box but I do have a few questions that I couldn’t find answers to and that I’d like help in clarifying; (looking at you Datzenmike since you seems to be the expert)

1. How wide is the L4N71B compared to the BW35 and 3N71? does it fit or are there tunnel mods required?
2. The transmission is 6” longer (32.5” long to the 26.3 of the BW35) do I need to fabricate new mounts for it or is the length in the tail shaft and I can reuse the mounts?
3. Because of the length will there be issues with shifter placement? I plan to use the shifter from the Maxima .
4. Which flex plate should I be looking at as a good match to the engine and tranny ?
5. Any other mods needed ?

Thanks for your help

[datzenmike]

L4N71B top and a regular 3N71B that is 31.5" long. I think they were within an inch but more like 5.5 compared to the 510's 26" length.

If running a 6 bolt Z22 crankshaft the 4N71B 6 bolt flex plate will fit right on using the torque converter pilot.

This thing...



The 4N71B uses a much larger locking torque converter so the flex plate is dished for clearance...





The over drive 4th gear can be locked out with an electric switch on the shifter.


1/ It will be a snug fit, better if the car was originally an automatic.

2/ Mount is unlikely to just line up so expect to modify it.

3/ Put the shifter where you like. It's a rod and can be shortened to suit.

4/ Use the Maxima flex plate and torque converter.

[Pjackb]

Awesome thank you

1/ It will be a snug fit, better if the car was originally an automatic.

Yup my car has a BW35 in it right now

If running a 6 bolt Z22 crankshaft the 4N71B 6 bolt flex plate will fit right on using the torque converter pilot.

This thing...


4/ Use the Maxima flex plate and torque converter.

It doesn't look like I can get any of these parts new or rebuilt so I will be getting a transmission from used part lot I imagine all these parts should be there correct ?

[datzenmike]

A wrecking yard transmission will include the torque converter. With luck perhaps it isn't out yet and you can grab the flex plate.

[Pjackb]

Thank you

[datzenmike]

The Maxima L4N71B flex plate is unique to the '83-'84 Maxima. The '86-'89 D21 Hardbody Z24i also uses the L4N71B and the flex plate should be the same but... part numbers say no.

[Pjackb]

good to know thanks