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datzenmike

Datsun L series auto trans pix

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Here's a transmission that hardly ever gets a mention. Probably because they rarely screw up, they just keep on working and working...

 

The Nissan 3N71B automatic. Three piece all aluminum case with removable/interchangeable front bell housing to fit any RWD Nissan motor.

 

3N71Bs were made in two lengths 26" and 31.5" depending on vehicle. Here's a shorty bolted to a 1200 motor, note the stubby tail stock:

 

3N71BDat1200.jpg

 

Here is a longer 3N71B from a 620 truck, note the longer tail stock:

 

trans74620L18auto-1.jpg

 

 

 

Nissan Motor Company, and its spinoff, Jatco, have produced a large number of automatic transmissions for many auto makers. The Jatco 3N71B transmission was the first 3-speed automatic transmission from Nissan Motor Company. It was an introduced in '72 as a conventional alternative to the then-ubiquitous and popular Borg-Warner Type 35. It was designed for use with rear wheel drive vehicles with longitudinal engines. Beginning in 1982, it gained a locking torque converter (L3N71B) for greater efficiency, and gained an overdrive 4th gear in 1983 (L4N71B), culminating with preliminary electronic sensors and control functions being added in 1985 (E4N71b).

 

Some sources claim the L means (L)ight duty and E is for medium duty.

 

IMG_0148.jpg

 

The above transmission is an L4N71B. The fourth gear is a 0.686 over drive, to make use of the L24 inline six that powered the '84 Maxima wagon that it came out of. This would reduce an engine RPM of 3,000 to just over 2,000! That's over 30%!! The O/D can be turned on or off with an electric switch on the shift handle. This transmission and flex plate should bolt to any 6 bolt L series four cylinder. As you can see the main body of the transmission has been moved to the rear to make room for the O/D gear just behind the bell, and has a shorter rear housing than the 3N71B

 

 

Top L4N71B with 3N71B just below it.

transautotopL4N71B84Maximagoonand3N.jpg

 

 

The L4N71B is 82cm long the 3N71B is 79.3cm almost exactly 1" different. The torque converters are similar on the outside only and have different input spline types.

 

 

 

3N71B bottom pan:

 

IMG_0170.jpg

 

 

L4N71B bottom pan:

 

IMG_0168.jpg

 

 

The L4N71B (above) appears deeper and you can see some of the hydraulic controls for the O/D between it and the bell.

 

This would be great in any vehicle with tall gears (high numerically) and some power and would keep cruising revs down.

Edited by datzenmike
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This is very cool!! My 72 is an auto and I have thought of keeping it. What is the value of the overdrive used but in working order? Is it just a bolt in with 12V to the OD switch? I have my eye on a L20 complete with trans (4 speed I think) or I can take an auto of 74 or so vintage from a truck. price is $250.00. I was looking at side draft style Fuel Injection to go it. I also found a nice A/C unit brand new from vintage air that will fit inside the car. I just have to figure a way to mount the sanden compressor.

 

Joe

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Auto with overdrive and a low geared rearend is cool. :)

 

Too bad those things can't handle much power. If you turn up the boost much in a 280ZX turbo with auto the transmission starts slipping a lot.

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A 510, would have a short tail auto (I believe) so the drive shaft would have to be shortened with either of these two transmissions. The '74 auto you mention may be the same length as yours. As mentioned in the text, some were locking torq converter (L3N71B) and some were O/D (L4N71B).

 

Also, if the locking torque converter wasn't available 'till '82 or later, the only L series motor made then was the L24 Maxima and maybe the L28 280zx, in order to have the L bolt pattern. Bleach would be the guy to ask about the Z car automatics. It is can be turned on/off manually by a two wire console switch.

 

The value of the L4N71B O/D transmission? Near me it's rare as rocking horse shit and I don't want to part with it, but everyone has a price, right?. I would some day like to try it out, but I'm switching to a Z series motor and the bell housing bolt pattern is wrong. The bells on the suto do unbolt but it appears that they are different lengths front to back... Maybe why the L4 is one inch longer?? If I put a L3 bell from a Z series on it the L4 torque converter may stick out too far. Or maybe the auto flywheel is recessed differently, I'll have to research this.

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The overdrive is what you have a switch for in the 1983/84 Maxima.

 

As for the locking 3-speed, I've never heard of them. Maybe nobody cared so much to look into it. Most people have done 5-speed swaps on Z's with an auto. But the 280ZX never had a switch for anything in the auto. The 280ZX also did not have the 4-speed auto available even in 1983. (last year of the L28 in the Z)

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510s had both the B/W and the JATCO 3N71 autos- the B/W was a column-shift auto and shorter, the JATCO was floor shift. Original ones also had a different tail badge (one said BW Automatic, the other said Nissan Automatic). The BW was pretty much before '71 and the JATCO after, though I don't really know the cutoff.

 

An L4N71B with the right bell pattern for the NAPS-Z might be found in a KA 240SX or a Hardbody / Pathfinder with the Z24i.

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My 72 510 Auto is console shifted. I am told the auto trans in it is almost indestructible. I don't think the L16 put much stress on it so it may last for many many miles. This has got me thinking low rear gears and OD auto trans!! could be fun since mine will be more of a highway cruiser.

 

Joe

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The "Jatco" in my 72 brown 4 door let go in my at 142000 miles, RIP. It immediately got replaced with a 5 speed :D!

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The 3N71B in my '81 510 Wagon is still holding up- and I stuck a Z24 in it, so it's recieveing a bit more torque than it did the first 197,000 miles...

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My 72 510 Auto is console shifted. I am told the auto trans in it is almost indestructible. I don't think the L16 put much stress on it so it may last for many many miles. This has got me thinking low rear gears and OD auto trans!! could be fun since mine will be more of a highway cruiser.

 

Joe

 

Well the L series with O/D appears to only have been available on the '83 and '84 Maximas. All you need is the bell off of it if it isn't working and a O/D transmission from a KA motor 240, or maybe a pathfinder. I need to go the other way and find a bell that will fit the Z series motor and the O/D automatic.

 

Thanks Bleach and Datsunahollic.

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I have the J-series in my 521 right now, but I need to swap over to the L-series for the auto transmission... I know I could go with a different engine, but the L16 appeals to me... however, I do a lot of highway driving, and I'd like to keep my final gears (4.88?) to save on cost and to add a bit of kick at the low end... At the same time, I'd rather not have electronic controls...

 

So, the '83/'84 Maximas had a 4(?) speed automatic with overdrive, and will bolt to an L-series motor? Or, the bell housing for an '83/'84 Maxima and an O/D transmission (again, 4 speed?) from a KA 240? Is the overdrive included in the number of gears, or is it additional (4 speed w/ O/D = 4 speed, or 4 speed w/ O/D = 5 speed)? Also, are both the Maxima and the KA transmissions hydraulically operated, or electrical?

 

Datzen... feel like selling the transmission to me? ^_^

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The L4N71B is a regular 3 speed with a 4th, separate gear for O/D. This is not a locking torque converter. The 4th gear can be locked out with a switch.

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L4N71B was the '83+ auto, the same one used in the maximas?

 

I don't really know much about transmissions... or about engines for that matter, but I can figure most of it out. I'm assuming what you mean by "locking out" 4th gear is that the transmission won't shift into it, correct? Does the OD affect all the gears, or is it sort of an additional gear? For example, if I don't "lock out" the OD, will it affect everything from first to third, or will it just "kick in" after the engine/wheels reach a certain speed in third gear?

 

Sorry for the n00b questions... but as far as I know not all "O/D's" work the same... my DD has a three speed w/ O/D, but it kicks in "after" third gear, providing the engine rpm's are correct and I'm travelling at the right speed... However, I've driven a Camry with O/D, and it's a sort of on/off deal... you turn it on at highway speeds or for extended driving to reduce engine rpm, but when it's on it seems to affect all gears...

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If I could find a good, inexpensive engine/transmission combo that would fit without too much work, I'd love to go with a semi-auto or a tiptronic... but, that's a little out of my reach ATM, so I need to go with an automatic...

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L4N71B was the '83+ auto, the same one used in the maximas?

 

 

Sorry for the n00b questions... but as far as I know not all "O/D's" work the same... my DD has a three speed w/ O/D, but it kicks in "after" third gear, providing the engine rpm's are correct and I'm travelling at the right speed... However, I've driven a Camry with O/D, and it's a sort of on/off deal... you turn it on at highway speeds or for extended driving to reduce engine rpm, but when it's on it seems to affect all gears...

 

The only L4N71B with an L series bolt pattern came on the '84 and '84 Maximas. In '85 the VG motors were used with FWD.

 

It's my understanding it would work like your Camry, it engages only in third at proper RPMs and can be turnd on/off.

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Sorry, I should have clarified... My DD is an Explorer, and it has the O/D that engages only after 3rd gear, but no on/off switch... The Camry's O/D seems to affect all gears more or less equally, but it has the on/off switch...

 

Thanks for the information though. I didn't know that most of the earlier L-series autos were only a three speed. I'll make sure to keep a lookout for one of the later ones.

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Sounds like the on/off switch you're talking about might be a torque converter lockup button. My old Geo Storm has a button like that, and it affected all gears while driving like you said, but it was pretty much worthless unless you were on the highway. But I also had the option to shift out of OD into 3rd manually, without locking the converter.

 

Sounds like your button may lock the converter, and turn OD off, or something like that?

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Could be... That seems to be the most likely possibility. What is the actual definition of an overdrive? Is it a gear ratio that's lower than 1:1? It seems to me that most transmissions end in a 1:1 ratio...

 

And while I'm on the topic of gear ratios... I was considering buying an ex-military vehicle at one point, and the thing had a "cross-country" gear... it was stupidly low, something like 7.35:1... The thing was pretty light and had a really low center of gravity, and apparently could climb some stupidly steep hills...

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Overdrive is anything lower that 0.999:1. Nissan overdrives vary, from around 0.7:1 to 0.88:1, depending on the application. Overdrive is anytime the gear ratio allows the engine speed to be less than the transmission output RPM (output RPM is "Over" the engine speed). Useful only for highway use.

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The only L4N71B with an L series bolt pattern came on the '84 and '84 Maximas. In '85 the VG motors were used with FWD.

 

Correction, the above should read "came on the '83 and '84 Maximas"

 

The '82 had the L3N71B with the new locking torque converter.

 

Sounds like the on/off switch you're talking about might be a torque converter lockup button. My old Geo Storm has a button like that, and it affected all gears while driving like you said, but it was pretty much worthless unless you were on the highway. But I also had the option to shift out of OD into 3rd manually, without locking the converter.

 

Sounds like your button may lock the converter, and turn OD off, or something like that?

 

No, this a a true separate 4th gear, an O/D ratio. At highway speeds an electric servo pulls it in, I imagine, so the switch just disables it.

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Alright... I'm picking a lot here, and I know what overdrive specifies, but can anyone tell me what locking the torque convertor actually does?

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Think of the torque converter as two electric fans facing each other. You turn one on, and it directs a flow of air at the second one, and it begins to turn by itself. Now imagine your L series motor turning a fan, but instead of air, a liquid is used. The liquid pushes past a second fan and turns it. The second fan is connected to the rest of the transmission and drives the rear wheels. Obviously there is a certain amount of slip and the input speed is higher than the output speed, but this is good at low speeds as it allows you to stop in gear with the motor running. As RPMs rise the torque converter's efficiency rises too and the slippage becomes less. This is VERY simplified explanation of fluid coupling.

 

In the lock up position the second fan can be directly coupled to the first. This can only happen when in third gear with response to a minimum speed set by the governor, and also depends on throttle position. This removes ANY slippage and results in a dropping of 200 to 400 RPMs.

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Thanks Mike, that makes a lot of sense... I have a few older ('70's, '80's) auto books, so I look through them sometimes for clarification, so I remember reading a bit about fluid couplings and all... fortunately they still apply to the Datsun...

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Overdrive is anything lower that 0.999:1. Nissan overdrives vary, from around 0.7:1 to 0.88:1, depending on the application. Overdrive is anytime the gear ratio allows the engine speed to be less than the transmission output RPM (output RPM is "Over" the engine speed). Useful only for highway use.

 

 

Automatic..1st....2nd...3rd.. 4th....rev

L4N71B ... 2.458 1.458 1.00 0.686 2.182

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